@article{velasco_seng_hodges_peters_pankow_schultz_2024, title={Dynamic measurement of ballistic impact using an optical fibre sensor}, volume={33}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665X/ad27fd}, abstractNote={
 An optical fibre-based sensor is developed for measuring the dynamics of the back face deformation of soft body armor. The measurement system consists of embedding an optical fibre into a thin silicone mat to increase survivability. The silicone sensor mat is placed between the soft body armor and the backing material. The optical fibre experiences times of sticking and slipping. The portions of the impact with the optical fibre stuck are reconstructed into slipping-equivalent strain using exponential extrapolation from adjacent slipping portions. The strain on the optical fibre is related to the projectile acceleration when the optical fibre is slipping. The strain is measured with the optical fibre sensor using a fibre Bragg grating. The system is characterized using a gas gun in combination with high-speed imaging. The system is experimentally demonstrated at the Army Test Center in Aberdeen, MD. Of the 23 shots 17 had an error less than 10%.}, number={3}, journal={SMART MATERIALS AND STRUCTURES}, author={Velasco, Ivann and Seng, Frederick and Hodges, Greyson and Peters, Kara and Pankow, Mark and Schultz, Stephen}, year={2024}, month={Mar} }
 @article{kim_aboubakr_peters_2023, title={Extension of Fiber Bragg Grating Ultrasound Sensor Network by Adhesive Couplers}, volume={10}, ISSN={["2304-6732"]}, url={https://www.mdpi.com/2304-6732/10/12/1366}, DOI={10.3390/photonics10121366}, abstractNote={Previous studies demonstrated coupling of acoustic guided waves from one optical fiber to another through a simple adhesive bond coupler. This paper experimentally utilizes such an adhesive bond coupler to easily extend an already existing sensor network. We experimentally demonstrate this concept for detecting simulated cracks growing from circular holes in a thin aluminum plate. A single, remotely bonded FBG sensor is used to detect the original crack growth, followed by the addition of other optical fiber segments using adhesive couplers to detect new crack growth locations on the plate. A laser Doppler vibrometer is also used to measure the guided wave propagation through the plate to verify that the changes in the FBG sensor measurements are due to the growth of the cracks.}, number={12}, journal={PHOTONICS}, author={Kim, Jee-Myung and Aboubakr, Sherif and Peters, Kara}, year={2023}, month={Dec} }
 @article{negi_kim_hua_timofeeva_zhang_zhu_peters_kumah_jiang_liu_2023, title={Ferroelectric Domain Wall Engineering Enables Thermal Modulation in PMN-PT Single Crystals}, volume={4}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202211286}, DOI={10.1002/adma.202211286}, abstractNote={Acting like thermal resistances, ferroelectric domain walls can be manipulated to realize dynamic modulation of thermal conductivity (k), which is essential for developing novel phononic circuits. Despite the interest, little attention has been paid to achieving room‐temperature thermal modulation in bulk materials due to challenges in obtaining a high thermal conductivity switching ratio (khigh/klow), particularly in commercially viable materials. Here, room‐temperature thermal modulation in 2.5 mm‐thick Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) single crystals is demonstrated. With the use of advanced poling conditions, assisted by the systematic study on composition and orientation dependence of PMN–xPT, a range of thermal conductivity switching ratios with a maximum of ≈1.27 is observed. Simultaneous measurements of piezoelectric coefficient (d33) to characterize the poling state, domain wall density using polarized light microscopy (PLM), and birefringence change using quantitative PLM reveal that compared to the unpoled state, the domain wall density at intermediate poling states (0< d33}, journal={ADVANCED MATERIALS}, author={Negi, Ankit and Kim, Hwang Pill and Hua, Zilong and Timofeeva, Anastasia and Zhang, Xuanyi and Zhu, Yong and Peters, Kara and Kumah, Divine and Jiang, Xiaoning and Liu, Jun}, year={2023}, month={Apr} }
 @article{timofeeva_pankow_peters_2023, title={High-speed polarization imaging for failure detection in fiber spinning}, volume={12488}, ISBN={["978-1-5106-6083-0"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2665277}, abstractNote={Current trends in polymer fiber production for nonwoven material applications focus on increasing production rates and decreasing the fiber thicknesses. The quality of the polymer fibers during the fiber spinning process is influenced by the processing parameters, such as the spinning speed, throughput, and the polymer material. Irregularities in the crystallization process during the extrusion of the fibers can lead to stress concentrations and defects in the fibers that could cause failure of fibers and potential failure of the nonwoven material that is manufactured from those fibers. The ability to recognize these irregularities in fibers using a non-destructive measurement method would reduce the downtimes for production lines as well as provide in-situ quantitative data that could be used for optimization of the production process parameters. In this study, we implemented a high-speed polarization imaging technique that is capable of non-destructive measurement of the internal stress fields as well as detection of defects within a post-fabricated fiber. This imaging technique has been combined with a motion tracking algorithm for accurate alignment of the images corresponding to the same segments of the fiber. The results show that the technique is capable of detecting stress concentration regions in fabricated fibers in static and dynamic testing conditions. The sensitivity of the system also allows to track the changes in the distribution of the internal stress fields in static and dynamic loading. Future studies will apply the technique to the fiber spinning process.}, journal={HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XVII}, author={Timofeeva, Anastasia A. and Pankow, Mark R. and Peters, Kara J.}, year={2023} }
 @article{marashi_bradford_peters_2023, title={Laser Doppler vibrometry measurements of acoustic attenuation in optical fiber waveguides}, volume={62}, ISSN={["2155-3165"]}, DOI={10.1364/AO.483827}, abstractNote={Fiber Bragg grating (FBG) sensors have been widely applied for structural health monitoring applications. In some applications, remote bonding of the optical fiber is applied, where ultrasonic waves are coupled from the structure to the optical fiber and propagated along the fiber to the FBG sensor. The distance that this signal can propagate along the optical fiber without decaying below a threshold value can be critical to the area of the structure that can be monitored per sensor. In this paper, we develop a method to measure the acoustic mode attenuation of fiber waveguides based on laser Doppler vibrometry (LDV) that is independent of the fiber type. In order to validate the method, we compare attenuation measurements on single-mode optical fibers using both the LDV and FBG sensor methods. Once the method is validated, experimental measurements of different coated and uncoated optical fibers are performed to quantify the role of the fiber diameter on the attenuation coefficient. As the radius of the waveguide decreases, the signal attenuation increases exponentially.}, number={16}, journal={APPLIED OPTICS}, author={Marashi, Cameron Sepehr and Bradford, Philip and Peters, Kara}, year={2023}, month={Jun}, pages={E119–E124} }
 @article{kim_peters_2023, title={Modeling of Ultrasonic Coupling between Optical Fibers through an Adhesive Bond for Sensing Applications}, volume={12488}, ISBN={["978-1-5106-6083-0"]}, ISSN={["1996-756X"]}, DOI={10.1117/12.2666031}, abstractNote={This paper presents finite element modeling of an adhesively bonded coupler for the transfer of acoustic modes between two optical fibers. Acoustic modes are propagated through optical fibers for Lamb wave detection with remotely bonded Bragg grating sensors. The model output is compared to previous experimental data, varying the relative diameter of the two fibers. Parameter sweeps of the coupler geometry are also performed to understand how they affect the coupling coefficient.}, journal={HEALTH MONITORING OF STRUCTURAL AND BIOLOGICAL SYSTEMS XVII}, author={Kim, Jee Myung and Peters, Kara}, year={2023} }
 @article{cranch_digonnet_dragic_peters_schulzgen_wang_yang_2023, title={Optical Fiber Sensors: introduction to the feature issue}, volume={62}, ISSN={["2155-3165"]}, DOI={10.1364/AO.495373}, abstractNote={This special issue contains a collection of papers on optical fiber sensors that were originally presented and published in a more succinct form in conjunction with the 27th International Conference on Optical Fiber Sensors (OFS) held in Alexandria, Virginia, United States, from 29th August to 2nd September, 2022.}, number={16}, journal={APPLIED OPTICS}, author={Cranch, Geoffrey A. and Digonnet, Michel and Dragic, Peter and Peters, Kara and Schulzgen, Axel and Wang, Anbo and Yang, Lan}, year={2023}, month={Jun}, pages={1–1} }
 @article{biehl_colmon_timofeeva_gracioso martins_dion_peters_freytes_2023, title={Scalable and High-Throughput In Vitro Vibratory Platform for Vocal Fold Tissue Engineering Applications}, volume={10}, ISSN={["2306-5354"]}, url={https://www.mdpi.com/2306-5354/10/5/602}, DOI={10.3390/bioengineering10050602}, abstractNote={The vocal folds (VFs) are constantly exposed to mechanical stimulation leading to changes in biomechanical properties, structure, and composition. The development of long-term strategies for VF treatment depends on the characterization of related cells, biomaterials, or engineered tissues in a controlled mechanical environment. Our aim was to design, develop, and characterize a scalable and high-throughput platform that mimics the mechanical microenvironment of the VFs in vitro. The platform consists of a 24-well plate fitted with a flexible membrane atop a waveguide equipped with piezoelectric speakers which allows for cells to be exposed to various phonatory stimuli. The displacements of the flexible membrane were characterized via Laser Doppler Vibrometry (LDV). Human VF fibroblasts and mesenchymal stem cells were seeded, exposed to various vibratory regimes, and the expression of pro-fibrotic and pro-inflammatory genes was analyzed. Compared to current bioreactor designs, the platform developed in this study can incorporate commercial assay formats ranging from 6- to 96-well plates which represents a significant improvement in scalability. This platform is modular and allows for tunable frequency regimes.}, number={5}, journal={BIOENGINEERING-BASEL}, author={Biehl, Andreea and Colmon, Ramair and Timofeeva, Anastasia and Gracioso Martins, Ana Maria and Dion, Gregory R. and Peters, Kara and Freytes, Donald O.}, year={2023}, month={May} }
 @article{laflamme_peters_ubertini_2023, title={Special feature on measurement-based decision making in structural health monitoring}, volume={34}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/aca3c4}, abstractNote={in measurement science and technology have yielded new capabilities in measuring states that are critical to the engineering decision-making process, including increased accuracy, speed, cost-efficiency, and scalability of data collection. These improved capabilities are particularly useful for the monitoring of advanced composite materials, where measurements could fully empower their field deployments and utilizations through effective condition evaluation followed by engineering decision, termed condition-based decisions}, number={3}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Laflamme, Simon and Peters, Kara and Ubertini, Filippo}, year={2023}, month={Mar} }
 @article{wang_wee_peters_2022, title={Amplification of Lamb-Wave Detection via Fiber Bragg Gratings Using Ultrasonic Horns}, volume={5}, ISSN={["2572-3898"]}, DOI={10.1115/1.4053582}, abstractNote={
 Fiber Bragg Grating (FBG) sensors are often applied as Lamb wave detectors for structural health monitoring systems. Analyzing the measured signal for the identification of structural damage requires a high signal-to-noise ratio because of the low amplitude Lamb waves. This paper applies a two-dimensional ultrasonic horn between the structure and a remotely bonded FBG sensor to increase the amplitudes of the measured signal. Experimentally we test a variety of ultrasonic geometries and demonstrate a 100% increase in the measured ultrasonic signal amplitude using a metallic ultrasonic horn with step-down geometry. A bonding procedure for the combined ultrasonic horn and optical fiber is also developed that produces repeatable signal measurements. For some horn geometries, an additional vibration signal at the Lamb wave excitation frequency is observed in the measurements. Laser Doppler vibrometry measurements and finite element analysis demonstrate that the signal is due to the natural vibration of the horn. The experimental results demonstrate that using an aluminum ultrasonic horn to focus wave is an excellent method to increase the sensitivity of the FBG to the small amplitude Lamb wave, provided the horn vibration characteristics are taken account in the design of the measurement system.}, number={3}, journal={JOURNAL OF NONDESTRUCTIVE EVALUATION, DIAGNOSTICS AND PROGNOSTICS OF ENGINEERING SYSTEMS}, author={Wang, Chia-Fu and Wee, Junghyun and Peters, Kara}, year={2022}, month={Aug} }
 @article{wang_wee_peters_2022, title={Amplifying Lamb Wave Detection for Fiber Bragg Grating with a Phononic Crystal GRIN Lens Waveguide}, volume={22}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/22/21/8426}, DOI={10.3390/s22218426}, abstractNote={This paper demonstrates that a graded-index (GRIN) phononic lens, combined with a channel waveguide, can focus anti-symmetric Lamb waves for extraction by a detector with strong directional sensitivity. Guided ultrasonic wave inspection is commonly applied for structural health monitoring applications; however, obtaining sufficient signal amplitude is a challenge. In addition, fiber Bragg grating (FBG) sensors have strong directional sensitivity. We fabricate the GRIN structure, followed by a channel waveguide starting at the focal point, using a commercial 3D printer and mount it on a thin aluminum plate. We characterize the focusing of the A0 mode Lamb wave in the plate, traveling across the GRIN lens using 3D laser Doppler vibrometry. We also measure the extraction of focused energy using an FBG sensor, examining the optimal sensor bond location and bond length in the channel of the waveguide for maximum signal extraction. The measured amplification of the ultrasound signal is compared to theoretical predictions. The results demonstrate that significant amplification of the waveform is achieved and that selecting the location of the FBG sensor in the channel is critical to optimizing the amplification.}, number={21}, journal={SENSORS}, author={Wang, Chia-Fu and Wee, Junghyun and Peters, Kara}, year={2022}, month={Nov} }
 @article{hodges_noevere_velasco_hackney_seng_schultz_peters_pankow_2022, title={Ballistic loading and survivability of optical fiber sensing layers for soft body armor evaluation}, volume={73}, ISSN={["1095-9912"]}, DOI={10.1016/j.yofte.2022.103043}, abstractNote={• To survive impact the contact radius between the fiber and impactor must be increased. • Silicone was chosen due to its high strain to failure and elastic properties. • In situ silicone sensors have shown to minimally effect back face deformation depth. • Silicone sensing mats are able to protect optical fibers during impact. The authors previously demonstrated the use of FBG sensors in Kevlar mats behind body armor to measure the transient back face deformation (BFD) during ballistic testing. This paper presents a novel sensor system based on a Fiber Bragg Grating embedded in silicone mats to improve the survivability of the body armor in-situ strain sensing layers. Due to the large amount of deformation, a relative slip between the optical fibers and the supporting structure is needed to maintain the performance of the sensors and determine the relationship between the measured strain and deformation shape. Two silicone materials were tested, Smooth-Sil 950 and Sorta-Clear 40, in both 1 mm and 2 mm thicknesses to evaluate their survivability and impact on BFD. To enhance slipping between the fibers and surrounding silicone a thin layer of petroleum jelly was placed on the fibers prior to being cast in the silicone mats. The 1 mm Sorta-Clear 40 mats performed best in silicone survivability, FBG survivability and minimal impact on the BFD. The new system improves on key deficiencies that were found from inserting the fibers directly into the Kevlar with minimal to no impact on the back face deformation.}, journal={OPTICAL FIBER TECHNOLOGY}, author={Hodges, Greyson and Noevere, Alexander and Velasco, Ivann and Hackney, Drew and Seng, Frederick and Schultz, Stephen and Peters, Kara and Pankow, Mark}, year={2022}, month={Oct} }
 @article{wu_pankow_onuma_huang_peters_2022, title={Comparison of High-Speed Polarization Imaging Methods for Biological Tissues}, volume={22}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/22/20/8000}, DOI={10.3390/s22208000}, abstractNote={We applied a polarization filter array and high-speed camera to the imaging of biological tissues during large, dynamic deformations at 7000 frames per second. The results are compared to previous measurements of similar specimens using a rotating polarizer imaging system. The polarization filter eliminates motion blur and temporal bias from the reconstructed collagen fiber alignment angle and retardation images. The polarization imaging configuration dose pose additional challenges due to the need for calibration of the polarization filter array for a given sample in the same lighting conditions as during the measurement.}, number={20}, journal={SENSORS}, author={Wu, Xianyu and Pankow, Mark and Onuma, Taka and Huang, Hsiao-Ying Shadow and Peters, Kara}, year={2022}, month={Oct} }
 @article{kim_wee_peters_2022, title={Demonstration of Coherent Interference between Acoustic Waves Using a Fiber Ring Resonator}, volume={22}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/22/11/4163}, DOI={10.3390/s22114163}, abstractNote={Optical fibers were previously demonstrated to propagate and detect acoustic modes that were converted from Lamb waves for structural health-monitoring applications; typically, a fiber Bragg grating sensor in the optical fiber is used to detect acoustic modes. Acoustic modes can transfer from one fiber to another through a simple adhesive bond coupler, preserving the waveform of the acoustic mode. This paper experimentally investigates the coherence of acoustic waves through the adhesive coupler, using a fiber ring resonator (FRR) configuration. This configuration was chosen because the wave coupled to the second fiber interferes with the original wave after it encircles the fiber ring. We performed this experiment using different geometries of optical fibers in the ring, including a standard single-mode optical fiber, a hollow silica capillary tube, and a large-diameter multi-mode fiber. The results demonstrate that the acoustic wave, when transferring through an adhesive coupler, interferes coherently even when the main and ring fibers are of different types. Finally, we demonstrate that the FRR can be applied for sensing applications by measuring the mode attenuations in the ring due to a changing external environment (water-level sensing) and measuring the optical-path length change in the ring (temperature sensing).}, number={11}, journal={SENSORS}, author={Kim, Jee Myung and Wee, Junghyun and Peters, Kara}, year={2022}, month={Jun} }
 @article{soman_kim_aiton_peters_2022, title={Guided waves based damage localization using acoustically coupled optical fibers and a single fiber Bragg grating sensor}, volume={203}, ISSN={["1873-412X"]}, DOI={10.1016/j.measurement.2022.111985}, abstractNote={Fiber Bragg grating (FBG) sensors have long been thought of as the ideal sensors for structural health monitoring (SHM) due to their small size, light weight, ability to be embedded and ability to be multiplexed. So, FBG sensors have been commonly used for strain based SHM. In recent times, a renewed interest is seen in the use of FBG sensors for GW measurements using the edge filtering approach which increases the sensitivity several fold. The remote bonding configuration has also been proposed to enhance this sensitivity further. But in order to achieve damage localization, a multi-sensor network is needed. The FBG sensors and the equipment for employing them in the edge filtering configuration is expensive. As a result, their use for SHM in large structures is still limited. Recent studies have shown that the acoustic wave in an optical fiber may be transferred from one optical fiber to another through an adhesive based acoustic coupler. In this study, this phenomenon is used to develop an SHM system which is capable of damage localization using a single FBG sensor. The paper presents a proof-of-concept of the use of the acoustically coupled optical fibers and single FBG for damage localization. The paper also highlights the design considerations of an acoustic coupler and discusses them in detail. The proposed approach has a potential to radically reduce the equipment costs (factor of 3) which is one of the limiting factors in the widespread acceptance of SHM systems in structures.}, journal={MEASUREMENT}, author={Soman, Rohan and Kim, Jee Myung and Aiton, Sean and Peters, Kara}, year={2022}, month={Nov} }
 @article{soman_boyer_kim_peters_2022, title={Particle Swarm Optimization Algorithm for Guided Waves Based Damage Localization Using Fiber Bragg Grating Sensors in Remote Configuration}, volume={22}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/22/16/6000}, DOI={10.3390/s22166000}, abstractNote={Structural health monitoring (SHM) systems may allow a reduction in maintenance costs and extend the lifetime of the structure. As a result, they are of interest to the research community. Ideally, the SHM methods should be low cost, while being able to detect and localize small levels of damage reliably and accurately. The fiber Bragg grating (FBG) sensors are light in weight, insensitive to electric and magnetic fields, and can be embedded. The edge filtering configuration for transduction allows the use of FBG for guided wave (GW) sensing. This sensitivity may be further enhanced through their application in the remote bonded configuration. This paper provides a proof-of-concept for the use of remotely bonded FBG for damage localization. In order to improve the computational efficiency, a particle swarm optimization (PSO) based algorithm is developed. The PSO allows a significant improvement in the computation time which makes it better suited for real-time damage localization. The proposed objective function is based on the exponential elliptical approach. First, the suitability of the PSO for damage localization is shown. Then the performance of the chosen objective function is compared with the brute-force algorithm as well as other objective functions found in the literature. The methodology is employed on a simple aluminum plate. The results indicate that indeed the objective function along with the PSO is suitable for damage localization. Also as the objective function is developed taking into consideration the specific challenges with the use of FBG sensors, performs better than the other objective functions as well as the brute force algorithm.}, number={16}, journal={SENSORS}, author={Soman, Rohan and Boyer, Alex and Kim, Jee Myung and Peters, Kara}, year={2022}, month={Aug} }
 @article{navratil_wee_peters_2022, title={Ultrasonic frequency response of fiber Bragg grating under direct and remote adhesive bonding configurations}, volume={33}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/ac2fea}, abstractNote={Ultrasonic inspection based structural health monitoring is a powerful technique for damage detection in a structure. Ultrasonic waves are often excited at different frequencies to detect damages of different sizes, therefore understanding the frequency response of the sensor can be used to optimize the sensor performance. Fiber Bragg gratings (FBGs) are widely used for this ultrasound collection. The sensitivity of FBGs to a particular ultrasonic frequency is a function of the FBG length and the ultrasonic wavelength. Recently the authors demonstrated that its ultrasound sensitivity is improved for some conditions when the FBG is bonded at a distance away from the adhesive bond, referred to as remote bonding. However, the frequency response of this configuration has not been studied. Therefore, in this paper we measure and compare the ultrasonic frequency responses between a conventional directly bonded FBG and remotely bonded FBG. In theory, the FBG sensitivity varies as a function of ultrasound wavelength-to-grating length (λ/L) ratio. Therefore, for this experimental study, we maintain L constant and vary λ by changing the frequency of the input ultrasonic waves. We demonstrate that there is a region, below a cut-off values of λ/L, for which the remotely bonded FBG output has a higher sensitivity to the Lamb wave amplitude than the directly bonded FBG. The exact value of this λ/L cut-off depends on the mechanical properties of the structure, the windowing of the input Lamb wave, and the FBG properties. We also demonstrate that windowing the Lamb wave excitation signal has a similar affect to apodizing the FBG sensor in modifying the sensitivity response curve.}, number={1}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Navratil, Andrew and Wee, Junghyun and Peters, Kara}, year={2022}, month={Jan} }
 @article{kim_marashi_wee_peters_2021, title={Acoustic wave coupling between optical fibers of different geometries}, volume={60}, ISSN={["2155-3165"]}, DOI={10.1364/AO.441494}, abstractNote={In this study, we investigate coupling of acoustic guided waves from different types of input fibers, through a bonded coupler, to an optical fiber. These acoustic waves can then be detected with conventional fiber Bragg gratings (FBGs). The input waves are measured using a high-resolution 3D laser Doppler vibrometer, and the output waves in the optical fiber are measured using an FBG. We demonstrate that the wave coupling between two waveguides varies with the cross-sectional area and the modulus of elasticity of the fibers.}, number={36}, journal={APPLIED OPTICS}, author={Kim, Jee Myung and Marashi, Cameron and Wee, Junghyun and Peters, Kara}, year={2021}, month={Dec}, pages={11042–11049} }
 @article{discetti_peters_yacoot_2021, title={Announcing the 2020 Measurement Science and Technology outstanding paper awards}, volume={32}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/abfc84}, abstractNote={Stefano Discetti, Kara Peters and Andrew Yacoot 1 Aerospace Engineering Research Group, Universidad Carlos III de Madrid, Leganés, Spain 2 North Carolina State University, Raleigh, NC, United States of America 3 National Physical Laboratory, Teddington, United Kingdom Since 1991, Measurement Science and Technology (MST) has awarded Best Paper prizes. The Editorial Board of this journal believe that such prizes are an opportunity to thank authors for submitting their work, and serves as an integral part of the ongoing quality review of the journal. The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented ‘Outstanding Paper Awards’. This year awards were given in the areas of Fluid Mechanics, Optical and Laser-based Techniques, and Precision Measurement. Although the categories broadly mirror subject sections in the journal, the Editorial Board consider articles from all categories during the selection process.}, number={11}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Discetti, Stefano and Peters, Kara and Yacoot, Andrew}, year={2021}, month={Nov} }
 @article{seng_hackney_goode_noevere_hammond_velasco_peters_pankow_schultz_2021, title={Dynamic back face deformation measurement with a single optical fibre}, volume={150}, ISSN={["1879-3509"]}, DOI={10.1016/j.ijimpeng.2020.103800}, abstractNote={A single optical fibre sensor is used to measure the dynamics of an impact. The method consists of sewing the optical fibre onto a woven Kevlar layer and placing it between the shoot pack and backing material. The measurement is accomplished by using the friction between the layer and the optical fibre to relate the optical fibre strain to impact deformation. Tests are done using a backing material of Roma Plastilina No.1 clay, and transparent ballistics gel with independent high-speed imaging. A final calculated BFD average error of 7.75% is presented as well as a timing error of 15.5% between the imaged dynamic BFD and the dynamic BFD determined by the FBG. This method is also tested at the U.S. Army Aberdeen Test Center in Maryland with a final calculated error of 7%.}, journal={INTERNATIONAL JOURNAL OF IMPACT ENGINEERING}, author={Seng, Frederick and Hackney, Drew and Goode, Tyler and Noevere, Alexander and Hammond, Alec and Velasco, Ivann and Peters, Kara and Pankow, Mark and Schultz, Stephen}, year={2021}, month={Apr} }
 @article{navratil_wee_peters_2021, title={Fiber Bragg grating sensor response to ultrasonic Lamb waves with varying frequency}, volume={11591}, ISSN={["1996-756X"]}, DOI={10.1117/12.2584277}, abstractNote={In structural health monitoring (SHM) applications, fiber Bragg grating (FBG) sensors are typically bonded directly to the surface of a structure to detect ultrasonic waves for damage identification. The sensitivity of the bonded FBGs to guided waves varies significantly with input ultrasound wavelength (λ)-to-FBG grating length (L) ratio, i.e., λ/L. Recently, the authors have demonstrated that the detection sensitivity of an FBG can be potentially increased by remotely bonding the optical fiber at a distance away from the FBG, however its response as a function of λ/L has not been studied in detail. In this work, we investigate the ultrasound detection of directly bonded FBG and remotely bonded FBG with varying λ/L. Specifically, we maintain L constant and change λ by varying the ultrasound excitation frequency. Using a 3D laser Doppler vibrometer (LDV) we first characterize input Lamb waves as a function of frequency, which are excited in a thin plate using a broadband transducer. Next, we measure the output response of directly bonded FBG and remotely bonded FBG to the same input Lamb waves. Finally, we examine the output FBG responses normalized with the LDV measurements of input waves, investigating the FBG sensitivity as a function of λ/L ratio. Understanding this sensitivity is important because many guided wave signals, for example generated by acoustic emission, are broadband. Additionally, multiple frequencies are often used for guided wave imaging of structures.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2021}, author={Navratil, Andrew and Wee, Junghyun and Peters, Kara}, year={2021} }
 @article{kim_marashi_wee_peters_2021, title={Investigation on acoustic wave transfer variation between fibers of different diameters and types using acoustic coupler}, volume={11591}, ISSN={["1996-756X"]}, DOI={10.1117/12.2584249}, abstractNote={When using fiber Bragg grating (FBG) sensors in structural health monitoring (SHM) applications, one of the drawbacks is that the sensor location is fixed once it is installed and it is difficult to extend an already existing system. The use of an acoustic coupler to transfer fiber guided traveling waves from one fiber to another could resolve this issue as the system could be modified for extension. In this study, we investigate the coupling of optical fiber guided waves between two different types of fibers through an acoustic coupler. Specifically, input waves are launched into an input fiber and coupled to an output fiber through the acoustic coupler. The input waves are measured using a high-resolution 3D laser Doppler Vibrometer (LDV) and the output waves from the output fiber are measured using an FBG. We demonstrate that the wave coupling between two fibers varies with the cross-sectional area of the input fiber.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2021}, author={Kim, Jee Myung and Marashi, Cameron and Wee, Junghyun and Peters, Kara}, year={2021} }
 @misc{soman_wee_peters_2021, title={Optical Fiber Sensors for Ultrasonic Structural Health Monitoring: A Review}, volume={21}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/21/21/7345}, DOI={10.3390/s21217345}, abstractNote={Guided waves (GW) and acoustic emission (AE) -based structural health monitoring (SHM) have widespread applications in structures, as the monitoring of an entire structure is possible with a limited number of sensors. Optical fiber-based sensors offer several advantages, such as their low weight, small size, ability to be embedded, and immunity to electro-magnetic interference. Therefore, they have long been regarded as an ideal sensing solution for SHM. In this review, the different optical fiber technologies used for ultrasonic sensing are discussed in detail. Special attention has been given to the new developments in the use of FBG sensors for ultrasonic measurements, as they are the most promising and widely used of the sensors. The paper highlights the physics of the wave coupling to the optical fiber and explains the different phenomena such as directional sensitivity and directional coupling of the wave. Applications of the different sensors in real SHM applications have also been discussed. Finally, the review identifies the encouraging trends and future areas where the field is expected to develop.}, number={21}, journal={SENSORS}, author={Soman, Rohan and Wee, Junghyun and Peters, Kara}, year={2021}, month={Nov} }
 @article{wee_alexander_peters_2021, title={Self-referencing ultrasound detection of fiber Bragg grating sensor with two adhesive bonds}, volume={32}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/ac065c}, abstractNote={In practical structural health monitoring applications, the environmental conditions typically vary over time. This variation can potentially affect the ultrasound detection of a sensor for damage detection, because ultrasound propagation as well as its coupling through adhesive bond layer to the sensor can be altered. In this case, a reference signal measured without structural defect under some initial condition may not be valid for comparison with the distorted signal (due to defect) that is measured under a different condition. In order to extract reference and distorted signals under the same condition at the same time, in this work we investigate a self-referencing ultrasound detection of fiber Bragg grating (FBG) by bonding an optical fiber at two different locations away from the FBG. We demonstrate that ultrasounds in a thin structure can couple to optical fiber guided ultrasounds through two adhesive bonds. We examine the ultrasounds trapped within the optical fiber, which are producing signal interference and beating behavior of the output FBG response. Based on understanding the ultrasound coupling mechanism through two adhesive bonds, finally we test the self-referencing ultrasound detection case, investigating the output FBG response that contains a combined signal of distorted and reference signals extracted through each bond.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Wee, Junghyun and Alexander, Kevin and Peters, Kara}, year={2021}, month={Oct} }
 @article{kuznetsov_pankow_peters_huang_2020, title={A structural-based computational model of tendon-bone insertion tissues}, volume={327}, ISSN={["1879-3134"]}, DOI={10.1016/j.mbs.2020.108411}, abstractNote={Tendon-to-bone insertion provides a gradual transition from soft tendon to hard bone tissue, functioning to alleviate stress concentrations at the junction of these tissues. Such macroscopic mechanical properties are achieved due to the internal structure in which collagen fibers and mineralization levels are key ingredients. We develop a structural-based model of tendon-to-bone insertion incorporating such details as fiber preferred orientation, fiber directional dispersion, mineralization level, and their inhomogeneous spatial distribution. A python script is developed to alter the tapered tendon–bone transition zone and to provide spatial grading of material properties, which may be rather complex as experiments suggest. A simple linear interpolation between tendon and bone material properties is first used to describe the graded property within the insertion region. Stress distributions are obtained and compared for spatially graded and various piece-wise materials properties. It is observed that spatial grading results in more smooth stress distributions and significantly reduces maximum stresses. The geometry of the tissue model is optimized by minimizing the peak stress to mimic in-vivo tissue remodeling. The in-silico elastic models constructed in this work are verified and modified by comparing to our in-situ biaxial mechanical testing results, thereby serving as translational tools for accurately predicting the material behavior of the tendon-to-bone insertions. This model will be useful for understanding how tendon-to-bone insertion develops during tissue remodeling, as well as for developing orthopedic implants.}, journal={MATHEMATICAL BIOSCIENCES}, author={Kuznetsov, Sergey and Pankow, Mark and Peters, Kara and Huang, Hsiao-Ying Shadow}, year={2020}, month={Sep} }
 @article{yang_peters_christensen_jakoby_morris_yacoot_iakovidis_2020, title={Announcing the 2019 Measurement Science and Technology Outstanding Paper Awards}, volume={31}, ISBN={1361-6501}, DOI={10.1088/1361-6501/ab7efb}, abstractNote={The selected paper presents a robust method for post-processing of particle image velocimetry (PIV) images tainted by unwanted background reflections based on the concept of anisotropic diffusion. Using a filter that identifies edges of background reflections, this method facilitates the creation of a background image (capturing the unwanted reflections) that can be subtracted from the original PIV images to eliminate these reflections, which severely hamper data yield. The significance of this paper is that the method is extremely robust compared to traditional filtering methods that rely on averaging in time, meaning that transient reflections can be effectively eliminated, thus maximizing data yield. This opens the measurement technique to measurements in unsteady flow conditions where PIV images are analyzed separately. The paper is well-written with a clear explanation of the theoretical formulation and the numerical implementation of the method. The authors perform a careful error assessment of the method on representative PIV images. The method is then applied to PIV images collected during propeller blade vortex interaction experiments, which are chosen due to the sharp and unsteady reflections from the propeller blades. The analysis of the images and signal-to-noise ratio demonstrate the strengths of the method.Wehave selected this paper due to its fundamental contribution to the laser-based PIV measurement technique and its extension of the technique to measurements in highly unsteady flows. obtain quasi-instantaneous measurements of temperature in a plane. In doing so, they have obtained results that are significantly less biased compared with traditional phosphor thermometry. The paper provides a thorough description of the methodology and results, and is expected to have a positive impact on measurement science as it relates to laser thermometry. This paper [4] describes a relatively inexpensive technique for the calibration of microphones in the frequency range 0.1–20 Hz. This is an increasingly important topic with relevance to windfarm transportation atmospheric studies and building construction. The authors show how differential pressure gauges can be used to calibrate both static pressure and slowly varying pressures up to the range of calibrated microphones. This well written paper gives a clear description of experimental work and results that includes a treatment of measurement uncertainties considerably smaller than those associated with other more involved techniques. Based on the results presented in this paper, the authors have established a new measurement method for microphone calibration.}, number={8}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Yang, Wuqiang and Peters, Kara and Christensen, Kenneth and Jakoby, Bernhard and Morris, Scott and Yacoot, Andrew and Iakovidis, Dimitris}, year={2020}, month={Aug} }
 @article{stewart_weisler_anderson_bryant_peters_2020, title={Dynamic Modeling of Passively Draining Structures for Aerial-Aquatic Unmanned Vehicles}, volume={45}, ISSN={["1558-1691"]}, DOI={10.1109/JOE.2019.2898069}, abstractNote={In the design of hybrid unmanned aerial and underwater vehicles, buoyancy management and weight are two major factors. Large wing volumes used by unmanned air vehicles to fly efficiently drive vehicle buoyancy up, preventing them from submerging. Heavy active buoyancy control systems can overcome this, but cost weight, energy, and time to transition between underwater operation and flight. An alternative design, consisting of a passively flooding and draining wing, is presented in this paper. Relevant dynamic parameters for a full vehicle dynamic model are identified. A dynamic model of a draining structure is developed and verified experimentally on both a simple cylinder and a full wing structure. With proper tuning, the model captures the salient dynamic behavior of passive draining during vehicle egress. A prototype unmanned aerial and underwater vehicle was built, flown, and used to collect flight test data. The model is used to accurately predict the takeoff performance of the vehicle. As given, the model can be incorporated into a full vehicle dynamic model to aid in the design, simulation, and control of hybrid unmanned aerial and underwater vehicles with passively draining components.}, number={3}, journal={IEEE JOURNAL OF OCEANIC ENGINEERING}, author={Stewart, William and Weisler, Warren and Anderson, Mark and Bryant, Matthew and Peters, Kara}, year={2020}, month={Jul}, pages={840–850} }
 @article{wee_peters_2020, title={Laser Doppler Vibrometry Measurements of Conversion of Surface Guided Waves to Optical Fiber Modes}, volume={32}, url={http://dx.doi.org/10.1109/lpt.2020.2973539}, DOI={10.1109/lpt.2020.2973539}, abstractNote={Previous studies demonstrated the coupling of Lamb waves to guided traveling waves in an optical fiber through an adhesive bond. However, the mode conversion at the specific coupling location has not been experimentally verified. This work measures the mode conversion of ultrasonic waves through an adhesive bond, implementing a high-resolution 3-dimensional laser Doppler vibrometer. Specifically, the propagation of surface guided S0 and A0 modes in a thin plate and their conversion into L01 and F11 modes in an optical fiber are successfully verified. In addition, the conversion of a shear-horizontal mode in the plate into an orthogonal F11 mode is also identified.}, number={6}, journal={IEEE Photonics Technology Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wee, Junghyun and Peters, Kara}, year={2020}, month={Mar}, pages={349–352} }
 @article{soman_wee_peters_ostachowicz_2020, title={Optimization of sensor placement for guided waves based SHM using fiber Bragg grating sensors}, volume={11379}, ISSN={["1996-756X"]}, DOI={10.1117/12.2558393}, abstractNote={Guided waves (GW) allow fast inspection of a large area and hence have received great interest from the structural health monitoring (SHM) community. Fiber Bragg grating (FBG) sensors offer several advantage but their use has been limited for the GW sensing due to their limited sensitivity. But the use of the edge-filtering approach in the remote bonded configuration has enhanced their sensitivity and allows use of these sensors for GW measurement. Although these sensors are light in weight and need no additional wiring there is still significant motivation to reduce the number of sensors while maintaining the quality and reliability of the assessment due to their high cost. In addition, for the safety and reliability of the structures it is of utmost importance that the entire structure can be investigated. Hence it is necessary to optimize the locations of the sensors in order to maximize the coverage while limiting the number of sensors used. The problem posed for the optimization of the FBG sensors for GW is different from any other work in this area due to the directional sensitivity shown by these sensors. Hence a novel optimization problem is developed for the application of FBG sensors for the GW based SHM. This paper develops a genetic algorithm based optimization methodology to incorporate the directional sensitivity. The methodology is shown analytically, using inputs from experimental investigations.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2020}, author={Soman, Rohan and Wee, Junghyun and Peters, Kara and Ostachowicz, Wieslaw}, year={2020} }
 @article{wee_alexander_peters_2020, title={Self-referencing ultrasound detection of fiber Bragg grating sensor remotely bonded at two locations}, volume={11379}, ISSN={["1996-756X"]}, DOI={10.1117/12.2559252}, abstractNote={Ultrasound measurement for damage detection in practical structural health monitoring (SHM) applications is often affected by varying environmental condition. In this case, a baseline reference signal measured under initial conditions may not be valid for comparison with the distorted signal (due to structural damage) that is measured under different conditions. In this study, we investigate a self-referencing ultrasound detection of fiber Bragg grating (FBG) by bonding an optical fiber at two different locations away from the FBG. We first investigate the extraction of ultrasonic waves from two different adhesive bond locations, which are measured with a single FBG sensor located between the two bonds. Based on understanding the ultrasound coupling mechanism through two adhesive bonds, we test the self-referencing ultrasound with the presence of a damage in a structure, examining the output FBG response that contains a combined signal of distorted and reference signals extracted through each bond.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2020}, author={Wee, Junghyun and Alexander, Kevin and Peters, Kara}, year={2020} }
 @article{hackney_goode_seng_pankow_schultz_peters_2020, title={Survivability of integrated fiber Bragg grating sensors in ballistic protection fabrics for high velocity impact testing}, volume={60}, ISSN={["1095-9912"]}, DOI={10.1016/j.yofte.2020.102356}, abstractNote={This research demonstrates that fiber Bragg grating (FBG) strain sensors can survive and provide useful strain information when integrated into a woven fabric subjected to ballistic impact testing. In this work, FBGs were integrated into a single-layer, Kevlar® fabric, sensing mat, placed between a 30-layer Kevlar® fabric shoot pack and clay backing material, and then impacted with an 8.23 g, 12.69 mm diameter, steel ball bearing at velocities up to 285 m/s. Three different optical fiber types, with differing fiber coatings and fiber diameters, were tested. The FBG strain response was determined from the full-spectrum FBG response which was interrogated at 100 kHz throughout the impact event. The difference in FBG strain response for the different coatings and fiber diameters were compared. Additionally, the degradation of the coatings after repeated impacts were visually characterized, showing that smaller diameter fibers behaved better with a more elastic coating.}, journal={OPTICAL FIBER TECHNOLOGY}, author={Hackney, D. and Goode, T. and Seng, F. and Pankow, M. and Schultz, S. and Peters, K.}, year={2020}, month={Dec} }
 @article{wee_hackney_wells_bradford_peters_2020, title={Ultrasonic Lamb wave measurement sensitivity of aligned carbon nanotube coated fiber Bragg grating}, volume={2}, ISSN={["2515-7647"]}, DOI={10.1088/2515-7647/ab525e}, abstractNote={Fiber Bragg grating (FBG) sensors are typically bonded on the surface of a structure using an adhesive to collect ultrasonic waves for damage detection in structural health monitoring applications. However, the ultrasonic wave transfer from structure to optical fiber suffers signal attenuation due to the adhesive bond layer, which has a significantly different acoustic impedance than the optical fiber. Therefore, this paper develops a systematic procedure to fabricate an aligned carbon nanotube (CNT)-wrapped FBGs for acoustic impedance matching. Specifically, we first develop an automated CNT winding system to fabricate CNT-wrapped FBGs with varying CNT layer thickness, which are bonded to an aluminum plate for ultrasonic sensitivity testing. We demonstrate that CNT wrapped FBGs do not necessarily produce an increased sensitivity as compared to a reference polyimide-coated FBG, however some outliers are observed with a significant improvement. Using a scanning electron microscopy we examine the cross-section of CNT/adhesive layers, identifying a unique CNT/adhesive bonding morphology with a stiff exterior shell and a relatively compliant inner layer. Finite element simulation validates that this two-layered bonding geometry is most likely the source of the increased FBG ultrasonic sensitivity for the outliers.}, number={1}, journal={JOURNAL OF PHYSICS-PHOTONICS}, author={Wee, Junghyun and Hackney, Drew and Wells, Brian and Bradford, Philip D. and Peters, Kara}, year={2020}, month={Jan} }
 @article{valle_peters_2019, title={Finite Element Modeling of Pulse Phase Thermography of an Approximate Model of Low Velocity Impact Induced Damage in Carbon Fiber Reinforced Polymer Structures}, volume={10990}, ISSN={["1996-756X"]}, DOI={10.1117/12.2513434}, abstractNote={In this work, we apply the finite element (FE) method to simulate an approximate low velocity impact induced model. One important characteristic of low velocity impact damage is the presence of multiple defects located at different depths, creating overshadowing among each other, affecting the thermal diffusion and therefore the blind frequency and temperature distribution on the surface, understanding this phenomenon is paramount in order to quantify the magnitude of under-the-surface damages. In this paper, we create a representative geometry of a defect using the meshing code CUBIT and solve the finite element model in ARIA thermal code in order to simulate the phase component of reflected thermal waves. The phase and thermal data collected from the FE solution on the surface above each defect is post processed and linearly correlated, in conjunction with a two-point strategy to provide information about the defect below the surface of interest. We also present a comparison with a single defect representation of the defect, proving that single model defect is not accurate to represent damage created by low velocity impact.}, journal={COMPUTATIONAL IMAGING IV}, author={Valle, Saul Hernandez and Peters, Kara}, year={2019} }
 @article{guo_pankow_peters_2019, title={High-Speed Interrogation Approach for FBG Sensors Using a VCSEL Array Swept Source}, volume={19}, ISSN={["1558-1748"]}, DOI={10.1109/JSEN.2019.2927901}, abstractNote={This paper presents a fiber Bragg grating (FBG) interrogator based on vertical surface cavity emitting lasers (VCSEL). A Fabry–Pérot filter technique is developed to directly calibrate the dynamic wavelength behavior of VCSELs at both low and high sweep rates. A broad bandwidth light source is constructed by multiplexing five VCSELs together to increase the number of FBGs that can be tracked. Scanning of the VCSEL-array is accomplished by a high-speed electronic switch circuit. The developed interrogator achieves a sweep bandwidth of 10 nm at a scanning rate of 4 kHz. Low-velocity impact testing of a composite plate with a surface mounted FBG sensor shows that the wavelength detection error was 2.7% when compared with the FBG strain obtained by a high-speed swept laser.}, number={21}, journal={IEEE SENSORS JOURNAL}, author={Guo, Guodong and Pankow, Mark and Peters, Kara}, year={2019}, month={Nov}, pages={9766–9774} }
 @article{wee_hackney_peters_2019, title={Preferential directional coupling to ultrasonic sensor using adhesive tape}, volume={58}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.58.7.072003}, abstractNote={Abstract. For structural health monitoring applications, recent studies have demonstrated an increased ultrasonic detection sensitivity of fiber Bragg grating (FBG) sensors through remote bonding of the FBG to a structure. In this case, the S0 or A0 Lamb waves in a structure are coupled to guided L01 waves in an optical fiber at the adhesive bond location, resulting in L01 modes of equal amplitudes propagating in both directions along the optical fiber. We demonstrate that when the adhesive bond is replaced with adhesive tape the S0 mode couples to the same L01 modes, however, with a preferential direction. Therefore, our study investigates the mechanism causing the preferential direction. We first identify different ultrasonic coupling pathways from a plate to an FBG through adhesive tape, demonstrating that both direct and indirect pathways are active, but that the indirect pathway produces the directional coupling. Then we test different adhesive tape parameters through experiments and simulations, demonstrating that flexural rigidity and bond length are parameters that can be used to control the directionality. The results of this work could be applied to design multiplexed FBG sensor arrays with specified signal pathways through the optical fiber networks.}, number={7}, journal={OPTICAL ENGINEERING}, author={Wee, Junghyun and Hackney, Drew and Peters, Kara}, year={2019}, month={Jul} }
 @article{guo_hackney_pankow_peters_2019, title={Shape reconstruction of woven fabrics using fiber bragg grating strain sensors}, volume={28}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665X/ab4ba3}, abstractNote={In this paper we develop a methodology that uses in-plane strain measurements to determine out-of-plane deflection for woven fabrics using an optical fiber based sensor network. A multiplexed fiber Bragg grating (FBG) network is used to collect strain at discrete locations in the fabric. To simplify the problem a circularly shaped two-dimensional woven fabric material under a spherical indenter load is studied. A finite element (FE) model of the fabric behavior, derived from benchmark testing, was used to help develop reconstruction algorithms, some of which account for slipping of the fabric at the clamped boundaries. Due to the large deflections, complex material behavior of the fabric and slipping of the fabric at the outer boundaries, a modified empirical approximation approach was found to be the optimal choice for the deflection reconstruction. Experiments are performed to evaluate one of the algorithms on strain data from FBG sensors for two test cases: bonded to and woven into the fabric. Despite the complex strain on the FBGs bonded to the fabric, the empirical approach well predicts the out-of-plane deflection, except in the region under the indentor, where the fabric deformation was different than that modeled in the FE simulations. This result is promising for structural applications were direct observations of the out-of-plane deflections are not possible. To increase the maximum deflection of the fabric that could be measured, weaving of the FBGs into the fabric is also attempted. This method was less successful, due to the large amount of relative slipping between the optical fiber and the fabric, drastically reducing the strain measured by the FBGs.}, number={12}, journal={SMART MATERIALS AND STRUCTURES}, author={Guo, Guodong and Hackney, Drew and Pankow, Mark and Peters, Kara}, year={2019}, month={Dec} }
 @article{goode_shoemaker_schultz_peters_pankow_2019, title={Soft body armor time-dependent back face deformation (BFD) with ballistics gel backing}, volume={220}, ISSN={["1879-1085"]}, DOI={10.1016/j.compstruct.2019.04.025}, abstractNote={This paper presents a method for obtaining time dependent back face deformation (BFD) data for body armor during ballistic impact using a clear ballistics gelatin backing and high-speed cameras to capture the deformation profile. Using this method, baseline fabric characterization data was obtained for samples comprised of varying layers of 467 g/m2 Kevlar K29 fabric impacted with 8.24 g steel ball projectile and backed with NATO standard 20% clear ballistics gelatin. For these tests, deformation depths were seen to increase with increasing impact energy and decreasing total areal density. A limited study of the various test parameters was performed by testing one additional fabric, projectile, and ballistics gelatin. From these comparisons, it was observed that 122 g/m2 Kevlar KM2+ fabric performs better per weight than 467 g/m2 Kevlar K29 fabric in terms of BFD, 9 mm FMJ projectiles produce deeper BFDs than 12.7 mm steel ball projectiles, and backing a sample with FBI standard 10% ballistics gel increases the BFD considerably over NATO standard 20% ballistics gel.}, journal={COMPOSITE STRUCTURES}, author={Goode, T. and Shoemaker, G. and Schultz, S. and Peters, K. and Pankow, M.}, year={2019}, month={Jul}, pages={687–698} }
 @article{kuznetsov_pankow_peters_huang_2019, title={Strain state dependent anisotropic viscoelasticity of tendon-to-bone insertion}, volume={308}, ISSN={0025-5564}, url={http://dx.doi.org/10.1016/j.mbs.2018.12.007}, DOI={10.1016/j.mbs.2018.12.007}, abstractNote={Tendon-to-bone insertion tissues may be considered as functionally-graded connective tissues, providing a gradual transition from soft tendon to hard bone tissue, and functioning to alleviate stress concentrations at the junction of these tissues. The tendon-to-bone insertion tissues demonstrate pronounced viscoelastic behavior, like many other biological tissues, and are designed by the nature to alleviate stress at physiological load rates and strains states. In this paper we present experimental data showing that under biaxial tension tendon-to-bone insertion demonstrates rate-dependent behavior and that stress-strain curves for the in-plane components of stress and strain become less steep when strain rate is increased, contrary to a typical viscoelastic behavior, where the opposite trend is observed. Such behavior may indicate the existence of a protective viscoelastic mechanism reducing stress and strain during a sudden increase in mechanical loading, known to exist in some biological tissues. The main purpose of the paper is to show that such viscoelastic stress reduction indeed possible and is thermodynamically consistent. We, therefore, propose an anisotropic viscoelasticity model for finite strain. We identify the range of parameters for this model which yield negative viscoelastic contribution into in-plane stress under biaxial state of strain and simultaneously satisfy requirements of thermodynamics. We also find optimal parameters maximizing the observed protective viscoelastic effect for this particular state of strain. This model will be useful for testing and describing viscoelastic materials and for developing interfaces for dissimilar materials, considering rate effect and multiaxial loadings.}, journal={Mathematical Biosciences}, publisher={Elsevier BV}, author={Kuznetsov, Sergey and Pankow, Mark and Peters, Kara and Huang, Hsiao-Ying Shadow}, year={2019}, month={Feb}, pages={1–7} }
 @article{wee_hackney_peters_2019, title={Ultrasonic Lamb wave mode conversion to optical fiber guided mode with varying input conditions}, volume={10970}, ISSN={["1996-756X"]}, DOI={10.1117/12.2514057}, abstractNote={In structural health monitoring (SHM) applications, one of the advantages of utilizing a surface bonded fiber Bragg grating (FBG) sensor for damage detection is its increased sensitivity in collecting ultrasonic waves. Recent studies have demonstrated that for a certain bonding condition the output FBG response can be increased by bonding the optical fiber at a distance away from the FBG to collect optical fiber guided wave (L01 mode) that is converted from S0 Lamb wave, referred as remote bonding. However in order to apply the remote bonding configuration in practical situations, the S0 mode conversion to L01 mode through an adhesive bond under various conditions must be characterized. This work investigates how the coupled L01 mode changes with varying input S0 mode frequency and angle of incidence through an adhesive bond. The goal of this work is to better understand the S0 mode conversion to the L01 mode in order to implement the remote bonding configuration for an improved SHM of a structure.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2019}, author={Wee, Junghyun and Hackney, Drew and Peters, Kara}, year={2019} }
 @article{peters_jakoby_myers_yang_foss_fansler_yacoot_2018, title={Announcing the 2017 Measurement Science and Technology Outstanding Paper Awards}, volume={29}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/aacf51}, number={9}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Peters, Kara and Jakoby, Bernhard and Myers, John and Yang, Wuqiang and Foss, John and Fansler, Todd and Yacoot, Andrew}, year={2018}, month={Sep} }
 @article{stewart_weisler_macleod_powers_defreitas_gritter_anderson_peters_gopalarathnam_bryant_et al._2018, title={Design and demonstration of a seabird-inspired fixed-wing hybrid UAV-UUV system}, volume={13}, ISSN={1748-3190}, url={http://dx.doi.org/10.1088/1748-3190/aad48b}, DOI={10.1088/1748-3190/aad48b}, abstractNote={This paper looks to the natural world for solutions to many of the challenges associated with the design of fixed-wing cross-domain vehicles. One example is the common murre, a seabird that flies from nesting locations to feeding areas, dives underwater to catch prey and returns. This hunting expedition provides an outline of a possible mission for a cross-domain vehicle. While the challenges of cross-domain vehicles are many, the focus of this paper was on buoyancy management and propulsion. Potential solutions to each challenge, inspired by multiple animals that cross between aerial and underwater domains, are investigated. From these solutions, three design concepts are considered, a quadrotor/fixed-wing hybrid, a vertical takeoff and landing (VTOL) tailsitter aircraft, and a waterjet-assisted takeoff vehicle. A comparison was made between the capability of each concept to complete two missions based on the common murres’ hunting expedition. As a result of this comparison, the VTOL tailsitter design was selected for further study. In-depth design was conducted and a prototype vehicle was built. The completed vehicle prototype successfully conducted submerged operation as well as four air flights. Flights consisted of egress from water, flight in air, ingress into water in each flight, and water locomotion. A total of 11 min, 23 s of flight time was recorded as well as underwater swims down to 12 ft (3.7 m) below the surface.}, number={5}, journal={Bioinspiration & Biomimetics}, publisher={IOP Publishing}, author={Stewart, William and Weisler, Warren and MacLeod, Marc and Powers, Thomas and Defreitas, Aaron and Gritter, Richard and Anderson, Mark and Peters, Kara and Gopalarathnam, Ashok and Bryant, Matthew and et al.}, year={2018}, month={Aug}, pages={056013} }
 @article{wee_hackney_bradford_peters_2018, title={Effect of continuous optical fiber bonding on ultrasonic detection using fiber Bragg grating}, volume={10598}, ISSN={["1996-756X"]}, DOI={10.1117/12.2295833}, abstractNote={For laboratory demonstrations, Lamb wave detection using fiber Bragg grating (FBG) sensors is typically performed with only the grating location spot bonded and with the fiber axis aligned with the ultrasonic propagation direction. However, in reality, the entire length of fiber is often bonded to protect the fiber from any environmental damage, referred to here as continuous bonding. Theoretically, the Lamb wave signal can couple to the guided traveling wave in the optical fiber at any adhered location, which could potentially produce output signal distortion. In this paper, we investigate the impact of continuously bonding a long length of optical fiber on the measured Lamb wave signal detected by an FBG. Therefore, an experiment is performed to measure the Lamb wave signals excited from a PZT actuator using a surface bonded FBG with varying optical fiber bond length, indicating that the output FBG response remains constant with changing length. The second experiment investigates the FBG angular response to the traveling wave in the optical fiber, and compares to the conventional case where FBG directly measures the Lamb waves with varying angle. Specifically, the optical fiber is bonded to the plate at a distance away from the FBG. The Lamb wave is launched to the bond location with varying angles, which is coupled to traveling wave, then measured with FBG. The results indicate that the mechanism of the Lamb wave transfer to the directly bonded FBG is through displacement matching, whereas that of the traveling wave is through a forced excitation.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2018}, author={Wee, Junghyun and Hackney, Drew and Bradford, Philip and Peters, Kara}, year={2018} }
 @article{wee_hackney_bradford_peters_2018, title={Experimental Study on Directionality of Ultrasonic Wave Coupling Using Surface-Bonded Fiber Bragg Grating Sensors}, volume={36}, ISSN={["1558-2213"]}, DOI={10.1109/jlt.2017.2769960}, abstractNote={Recent studies demonstrated the potential of increasing the Lamb wave detection sensitivity of fiber Bragg grating (FBG) sensors by bonding the optical fiber away from the grating location, instead of the conventional method of bonding the FBG directly. The FBG located at a remote location further along the optical fiber collects the guided traveling wave in the optical fiber generated from the Lamb wave signal. This remote bonding method could potentially be extended to a series of multiplexed FBGs. However, previous experiments also detected coupling to guided traveling waves in both directions in the optical fiber, which could have significant effects on multiplexed signals. In this paper, we measure the coupled signal amplitudes in both forward and backward directions, when ultrasonic waves couple from a thin plate to an optical fiber and from an optical fiber to a thin plate. The forward- and backward-induced modes are measured in both the optical fiber and the plate. The same experiment is then performed for the case when ultrasonic signal is coupled from the optical fiber to the plate. In addition, two different types of bonding, cyanoacrylate adhesive and frictional bond, are explored to investigate how the signal conversion depends on the bonding method. The results demonstrate that the coupling of ultrasonic waves from a thin structure to an optical fiber and from an optical fiber to the structure is complex. The coupling does not only occur in the direction of the wave propagation, but can be coupled into both forward and backward modes, depending on the bonding configuration used.}, number={4}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Wee, Junghyun and Hackney, Drew and Bradford, Philip and Peters, Kara}, year={2018}, month={Feb}, pages={932–938} }
 @article{wu_pankow_huang_peters_2018, title={High-speed polarization imaging of dynamic collagen fiber realignment in tendon-to-bone insertion region}, volume={23}, ISSN={1083-3668}, url={http://dx.doi.org/10.1117/1.JBO.23.11.116002}, DOI={10.1117/1.JBO.23.11.116002}, abstractNote={Abstract. A high-speed polarization imaging instrument is demonstrated to be capable of measuring the collagen fiber alignment orientation and alignment strength during high-displacement rate dynamic loading at acquisition rates up to 10 kHz. The implementation of a high-speed rotating quarter wave plate and high-speed camera in the imaging system allows a minimum measurement acquisition time of 6 ms. Sliced tendon-to-bone insertion samples are loaded using a modified drop tower with an average maximum displacement rate of 1.25  m  /  s, and imaged using a high-speed polarization imaging instrument. The generated collagen fiber alignment angle and strength maps indicate the localized deformation and fiber realignment in tendon-to-bone samples during dynamic loading. The results demonstrate a viable experimental method to monitor collagen fiber realignment in biological tissue under high-displacement rate dynamic loading.}, number={11}, journal={Journal of Biomedical Optics}, publisher={SPIE-Intl Soc Optical Eng}, author={Wu, Xianyu and Pankow, Mark and Huang, Hsiao-Ying Shadow and Peters, Kara}, year={2018}, month={Nov}, pages={1} }
 @article{kim_wee_peters_huang_2018, title={Multiphysics Coupling in Lithium-Ion Batteries with Reconstructed Porous Microstructures}, volume={122}, ISSN={1932-7447 1932-7455}, url={http://dx.doi.org/10.1021/ACS.JPCC.7B12388}, DOI={10.1021/ACS.JPCC.7B12388}, abstractNote={For an energy storage application such as electrical vehicles (EVs), lithium-ion batteries must overcome limited lifetime and performance degradation under specific conditions. Particularly, lithiu...}, number={10}, journal={The Journal of Physical Chemistry C}, publisher={American Chemical Society (ACS)}, author={Kim, Sangwook and Wee, Junghyun and Peters, Kara and Huang, Hsiao-Ying Shadow}, year={2018}, month={Feb}, pages={5280–5290} }
 @article{valle_peters_2018, title={Numerical simulation of phase images and depth reconstruction in pulsed phase thermography}, volume={10661}, ISSN={["1996-756X"]}, DOI={10.1117/12.2301959}, abstractNote={In this work we apply the finite element (FE) method to simulate the results of pulsed phase thermography experiments on laminated composite plates. Specifically, the goal is to simulate the phase component of reflected thermal waves and therefore verify the calculation of defect depth through the identification of the defect blind frequency. The calculation of phase components requires a higher spatial and temporal resolution than that of the calculation of the reflected temperature. An FE modeling strategy is presented, including the estimation of the defect thermal properties, which in this case is represented as a foam insert impregnated with epoxy resin. A comparison of meshing strategies using tetrahedral and hexahedral elements reveals that temperature errors in the tetrahedral results are amplified in the calculation of phase images and blind frequencies; we investigate the linearity of the measured diffusion length (based on the blind frequency) as a function of defect depth. The simulations demonstrate a nonlinear relationship between the defect depth and diffusion length, calculated from the blind frequency, consistent with previous experimental observations. And finally a two-point strategy is presented to better estimate the defect depth and thickness.}, journal={THERMOSENSE: THERMAL INFRARED APPLICATIONS XL}, author={Valle, Saul Hernandez and Peters, Kara}, year={2018} }
 @article{weisler_stewart_anderson_peters_gopalarathnam_bryant_2018, title={Testing and Characterization of a Fixed Wing Cross-Domain Unmanned Vehicle Operating in Aerial and Underwater Environments}, volume={43}, ISSN={0364-9059 1558-1691 2373-7786}, url={http://dx.doi.org/10.1109/JOE.2017.2742798}, DOI={10.1109/JOE.2017.2742798}, abstractNote={This paper presents test results and performance characterization of the first fixed-wing unmanned vehicle capable of full cross-domain operation in both the aerial and underwater environments with repeated transition and low-energy loitering capabilities. This vehicle concept combines the speed and range of an aircraft with the persistence, diving capabilities, and stealth of a submersible. The paper describes the proof-of-concept vehicle including its concept of operations, the approaches employed to achieve the required functions, and the main components and subsystems. Key subsystems include a passively flooding and draining wing, a single motor and propeller combination for propulsion in both domains, and aerodynamic–hydrodynamic control surfaces. Experiments to quantify the vehicle performance, control responses, and energy consumption in underwater, surface, and flight operation are presented and analyzed. Results of several full-cycle tests are presented to characterize and illustrate each stage of operation including surface locomotion, underwater locomotion, water egress, flight, and water ingress. In total, the proof-of-concept vehicle demonstrated 12 full-cycle cross-domain missions including both manually controlled and autonomous operation.}, number={4}, journal={IEEE Journal of Oceanic Engineering}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Weisler, Warren and Stewart, William and Anderson, Mark B. and Peters, Kara J. and Gopalarathnam, Ashok and Bryant, Matthew}, year={2018}, month={Oct}, pages={969–982} }
 @article{kieffer_peters_2018, title={The effect of short range order on the thermal output and gage factor of Ni3FeCr strain gages}, volume={54}, ISSN={["1475-1305"]}, DOI={10.1111/str.12253}, abstractNote={Abstract}, number={1}, journal={STRAIN}, author={Kieffer, T. P. and Peters, K. J.}, year={2018}, month={Feb} }
 @article{mabry_seracino_peters_2018, title={The effects of accelerated Freeze-Thaw conditioning on CFRP strengthened concrete with pre-existing bond defects}, volume={163}, DOI={10.1016/j.conbuildmat.2017.12.017}, abstractNote={Despite demonstrated success in both the laboratory and in the field, significant questions remain unanswered regarding the durability of Carbon Fiber Reinforced Polymer (CFRP) for strengthened concrete members. Little is known about the impact of pre-existing bond defects when subjected to harsh environmental conditions. The results from a study observing the performance of 18 small-scale CFRP-to-concrete pull test specimens is presented herein. Half of the sample set was stored in ambient laboratory conditions while the remaining sample set was subjected to 50 freeze–thaw cycles. Repeated for each condition were 3 specimens prepared without any intentional bond defects and 3 specimens containing 645 mm2 Teflon inserts, for comparison purposes. It was found that, not only did the freeze–thaw conditioning reduce the debonding capacity of the externally bonded CFRP, but that the presence of defects resulted in a greater reduction in debonding capacity following the environmental conditioning, when compared to specimens exposed to ambient conditions only. Nondestructive evaluation of the bonded interface was also performed by using Pulse Phase Thermography (PPT).}, journal={Construction and Building Materials}, author={Mabry, N. J. and Seracino, R. and Peters, Kara}, year={2018}, pages={286–295} }
 @article{guo_hackney_pankow_peters_2017, title={A spectral profile multiplexed FBG sensor network with application to strain measurement in a Kevlar woven fabric}, volume={10168}, ISSN={["1996-756X"]}, DOI={10.1117/12.2260114}, abstractNote={A spectral profile division multiplexed fiber Bragg grating (FBG) sensor network is described in this paper. The unique spectral profile of each sensor in the network is identified as a distinct feature to be interrogated. Spectrum overlap is allowed under working conditions. Thus, a specific wavelength window does not need to be allocated to each sensor as in a wavelength division multiplexed (WDM) network. When the sensors are serially connected in the network, the spectrum output is expressed through a truncated series. To track the wavelength shift of each sensor, the identification problem is transformed to a nonlinear optimization problem, which is then solved by a modified dynamic multi-swarm particle swarm optimizer (DMS-PSO). To demonstrate the application of the developed network, a network consisting of four FBGs was integrated into a Kevlar woven fabric, which was under a quasi-static load imposed by an impactor head. Due to the substantial radial strain in the fabric, the spectrums of different FBGs were found to overlap during the loading process. With the developed interrogating method, the overlapped spectrum would be distinguished thus the wavelength shift of each sensor can be monitored.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2017}, author={Guo, Guodong and Hackney, Drew and Pankow, Mark and Peters, Kara}, year={2017} }
 @article{foss_peters_yang_2017, title={Announcing the 2016 Measurement Science and Technology Outstanding Paper Awards}, volume={28}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/aa726e}, abstractNote={Since 1991, Measurement Science and Technology (MST) has awarded a Best Paper prize. The Editorial Board of this journal believe that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented ‘Outstanding Paper Awards’. This year awards were presented in the areas of Fluid Mechanics, Optical and Laser-based Techniques and Measurement Science. Although the categories broadly mirror subject sections in the journal, the Editorial Board consider articles from all categories in the selection process.}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Foss, John and Peters, Kara and Yang, Wuqiang}, year={2017}, month={Jul} }
 @article{wee_hackney_bradford_peters_2017, title={Bi-directional ultrasonic wave coupling to FBGs in continuously bonded optical fiber sensing}, volume={56}, ISSN={["2155-3165"]}, DOI={10.1364/ao.56.007262}, abstractNote={Fiber Bragg grating (FBG) sensors are typically spot-bonded onto the surface of a structure to detect ultrasonic waves in laboratory demonstrations. However, to protect the rest of the optical fiber from any environmental damage during real applications, bonding the entire length of fiber, called continuous bonding, is commonly done. In this paper, we investigate the impact of continuously bonding FBGs on the measured Lamb wave signal. In theory, the ultrasonic wave signal can bi-directionally transfer between the optical fiber and the plate at any adhered location, which could potentially produce output signal distortion for the continuous bonding case. Therefore, an experiment is performed to investigate the plate-to-fiber and fiber-to-plate signal transfer, from which the signal coupling coefficient of each case is theoretically estimated based on the experimental data. We demonstrate that the two coupling coefficients are comparable, with the plate-to-fiber case approximately 19% larger than the fiber-to-plate case. Finally, the signal waveform and arrival time of the output FBG responses are compared between the continuous and spot bonding cases. The results indicate that the resulting Lamb wave signal output is only that directly detected at the FBG location; however, a slight difference in signal waveform is observed between the two bonding configurations. This paper demonstrates the practicality of using continuously bonded FBGs for ultrasonic wave detection in structural health monitoring (SHM) applications.}, number={25}, journal={APPLIED OPTICS}, author={Wee, Junghyun and Hackney, Drew and Bradford, Philip and Peters, Kara}, year={2017}, month={Sep}, pages={7262–7268} }
 @article{chandrasekaran_pankow_peters_huang_2017, title={Composition and structure of porcine digital flexor tendon-bone insertion tissues}, volume={105}, ISSN={1549-3296}, url={http://dx.doi.org/10.1002/jbm.a.36162}, DOI={10.1002/jbm.a.36162}, abstractNote={Abstract}, number={11}, journal={Journal of Biomedical Materials Research Part A}, publisher={Wiley}, author={Chandrasekaran, Sandhya and Pankow, Mark and Peters, Kara and Huang, Hsiao-Ying Shadow}, year={2017}, month={Aug}, pages={3050–3058} }
 @article{wu_huang_pankow_peters_2017, title={Dynamic Polarization Microscopy for In-Situ Measurements of Collagen Fiber Realignment During Impact}, ISBN={["978-3-319-41350-1"]}, ISSN={["2191-5652"]}, DOI={10.1007/978-3-319-41351-8_9}, abstractNote={The long term goal of this work is to better understand the tendon-to-bone insertion injury due to medium strain rate impact (e.g. sports activity). Specifically, we imaged collagen fiber realignment during impact, to investigate the ability of the tendon-to-bone insertion to these survive harsh dynamic events. A polarized light microscopy (PLM) setup was built in the lab and used to monitor the birefringence property changes of a known material under changing stress conditions. Initially polycarbonate dogbone specimens were tested quasi-statically to validate the setup and analysis algorithm. Polarized light retardation and alignment direction images are generated to quantitatively analyze the birefringence property change under different stress and compared to theoretical predictions. To perform dynamic experiments a drop weight tower was modified for medium strain rate testing (10–100 %/s) and the PLM setup is being incorporated for imaging. Several dynamic experiments have been conducted using this modified drop tower on porcine tendon specimens. A high-speed camera is used to record their dynamic response and deformation.}, journal={MECHANICS OF BIOLOGICAL SYSTEMS AND MATERIALS, VOL 6}, author={Wu, Xianyu and Huang, Hsiao-Ying Shadow and Pankow, Mark and Peters, Kara}, year={2017}, pages={61–66} }
 @article{van hoe_oman_van steenberge_stan_schultz_peters_2017, title={High-Speed Interrogation of Multiplexed Fiber Bragg Gratings With Spectral Distortion}, volume={17}, ISSN={["1558-1748"]}, DOI={10.1109/jsen.2017.2750327}, abstractNote={Fiber Bragg grating (FBG) sensors can be multiplexed in large numbers to monitor the performance of large structures. This paper addresses the collection of FBG reflection spectra from wavelength division multiplexed sensors at fast acquisition rates. The spectral and temporal resolution is first derived as a function of the tunable filter and measurement system properties. The method is applied to impact loading investigations of a stiffened composite skin panel. The reflected spectrum of each FBG in an array, embedded in the panel, is collected at 100 kHz during the impact events with a spectral resolution down to 40 pm. Visualization of the FBG responses to these impact events, including the presence of spectral distortion in some FBG spectra, is presented. Future analyses based on the full-spectral data sets can enable the assessment of the localized progression of internal damage in such structures.}, number={21}, journal={IEEE SENSORS JOURNAL}, author={Van Hoe, Bram and Oman, Kyle G. and Van Steenberge, Geert and Stan, Nikola and Schultz, Stephen M. and Peters, Kara J.}, year={2017}, month={Nov}, pages={6941–6947} }
 @article{wells_kumar_reynolds_peters_bradford_2017, title={Highly anisotropic magneto-transport and field orientation dependent oscillations in aligned carbon nanotube/epoxy composites}, volume={111}, ISSN={["1077-3118"]}, DOI={10.1063/1.4999503}, abstractNote={Carbon nanotubes (CNTs) have been widely investigated as additive materials for composites with potential applications in electronic devices due to their extremely large electrical conductivity and current density. Here, highly aligned CNT composite films were created using a sequential layering fabrication technique. The degree of CNT alignment leads to anisotropic resistance values which varies >400× in orthogonal directions. Similarly, the magnetoresistance (MR) of the CNT composite differs depending upon the relative direction of current and the applied magnetic field. A suppression of negative to positive MR crossover was also observed. More importantly, an overall positive magnetoresistance behavior with localized +/− oscillations was discovered at low fields which persists up to room temperature when the current (I) and in-plane magnetic field (B) were parallel to the axis of CNT (B∥I∥CNT), which is consistent with Aharonov-Bohm oscillations in our CNT/epoxy composites. When the current, applied magnetic field, and nanotube axis are aligned, the in-plane MR is positive instead of negative as observed for all other field, current, and tube orientations. Here, we provide in-depth analysis of the conduction mechanism and anisotropy in the magneto-transport properties of these aligned CNT-epoxy composites.}, number={26}, journal={APPLIED PHYSICS LETTERS}, author={Wells, Brian and Kumar, Raj and Reynolds, C. Lewis, Jr. and Peters, Kara and Bradford, Philip D.}, year={2017}, month={Dec} }
 @article{guo_hackney_pankow_peters_2017, title={Interrogation of a spectral profile division multiplexed FBG sensor network using a modified particle swarm optimization method}, volume={28}, ISSN={["1361-6501"]}, DOI={10.1088/1361-6501/aa637f}, abstractNote={This paper applies the concept of spectral profile division multiplexing to track each Bragg wavelength shift in a serially multiplexed fiber Bragg grating (FBG) network. Each sensor in the network is uniquely characterized by its own reflected spectrum shape, thus spectral overlapping is allowed in the wavelength domain. In contrast to the previous literature, spectral distortion caused by multiple reflections and spectral shadowing between FBG sensors, that occur in serial topology sensor networks, are considered in the identification algorithm. To detect the Bragg wavelength shift of each FBG, a nonlinear optimization function based on the output spectrum is constructed and a modified dynamic multi-swarm particle swarm optimizer is employed. The multiplexing approach is experimentally demonstrated on data from multiplexed sensor networks with up to four sensors. The wavelength prediction results show that the method can efficiently interrogate the multiplexed network in these overlapped situations. Specifically, the maximum error in a fully overlapped situation in the specific four sensor network demonstrated here was only 110 pm. A more general analysis of the prediction error and guidelines to optimize the sensor network are the subject of future work.}, number={5}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Guo, Guodong and Hackney, Drew and Pankow, Mark and Peters, Kara}, year={2017}, month={May} }
 @article{wee_hackney_bradford_peters_2017, title={Mechanisms of signal coupling to optical fiber for FBG sensor detection of Lamb waves}, volume={10323}, ISSN={["1996-756X"]}, DOI={10.1117/12.2263278}, abstractNote={One of the major challenges when using fiber Bragg grating sensors (FBGs) to detect Lamb wave or acoustic emission signals in structures is the low sensitivity of these sensors to surface waves propagating in the structure. The authors have previously demonstrated that remote bonding of the optical fiber away from the FBG can increase the measured signal amplitude. In this paper we investigate the potential mechanisms for this increase through finite element simulations and demonstrate that the shear lag effect through the adhesive is the major source of the signal amplitude difference between the direct and remote bonding cases.}, journal={2017 25TH INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS (OFS)}, author={Wee, Junghyun and Hackney, Drew and Bradford, Philip and Peters, Kara}, year={2017} }
 @article{wee_hackney_bradford_peters_2017, title={Simulating increased Lamb wave detection sensitivity of surface bonded fiber Bragg grating}, volume={26}, ISSN={["1361-665X"]}, DOI={10.1088/1361-665x/aa646b}, abstractNote={Fiber Bragg grating (FBG) sensors are excellent transducers for collecting ultrasonic wave signals for structural health monitoring (SHM). Typically, FBG sensors are directly bonded to the surface of a structure to detect signals. Unfortunately, demodulating relevant information from the collected signal demands a high signal-to-noise ratio because the structural ultrasonic waves have low amplitudes. Our previous experimental work demonstrated that the optical fiber could be bonded at a distance away from the FBG location, referred to here as remote bonding. This remote bonding technique increased the output signal amplitude compared to the direct bonding case, however the mechanism causing the increase was not explored. In this work, we simulate the previous experimental work through transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. The model is first constructed without an adhesive to assume an ideal bonding condition, investigating the difference in excitation signal coherence along the FBG length between the two bonding configurations. A second model is constructed with an adhesive to investigate the effect of the presence of the adhesive around the FBG. The results demonstrate that the amplitude increase is originated not from the excitation signal coherence, but from the shear lag effect which causes immature signal amplitude development in the direct bonding case compared to the remote bonding case. The results also indicate that depending on the adhesive properties the surface-bonded optical fiber manifests varying resonant frequency, therefore resulting in a peak amplitude response when the input excitation frequency is matched. This work provides beneficial reference for selecting adhesive and calibrating sensing system for maximum ultrasonic detection sensitivity using the FBG sensor.}, number={4}, journal={SMART MATERIALS AND STRUCTURES}, author={Wee, J. and Hackney, D. A. and Bradford, P. D. and Peters, K. J.}, year={2017}, month={Apr} }
 @inproceedings{wee_hackney_bradford_peters_2017, title={The adhesive effect on ultrasonic Lamb wave detection sensitivity of remotely-bonded fiber Bragg grating sensors}, volume={10168}, DOI={10.1117/12.2260009}, abstractNote={Fiber Bragg grating (FBG) sensors are excellent transducers for ultrasonic signal detection in structural health monitoring (SHM) application. While the FBG sensors are typically bonded directly on the surface of a structure to collect signals, one of the major challenges arises from demodulating relevant information from the low amplitude signal. The authors have experimentally demonstrated that the ultrasonic wave detection sensitivity of FBG sensors can be increased by bonding optical fiber away from the FBG location. This configuration is referred to here as remote bonding. However the mechanism causing this phenomenon has not been explored. In this work, we simulate the previous experimental work through a transient analysis based on the finite element method, and the output FBG response is calculated through the transfer matrix method. We first model an optical fiber bonded on the surface of an aluminum plate with an adhesive. The consistent input signal is excited to the plate, which is detected by the directly and remotely-bonded FBGs. The effect of the presence of the adhesive around the FBG is investigated by analyzing strain and displacement along the length of the FBGs at the locations of direct and remote bonding cases, and the consequent output FBG responses. The result demonstrates that the sensitivity difference between the direct and remote bonding cases is originated from shear lag effect due to adhesive.}, booktitle={Sensors and smart structures technologies for civil, mechanical, and aerospace systems 2017}, author={Wee, J. and Hackney, D. A. and Bradford, P. D. and Peters, Kara}, year={2017} }
 @article{peters_yang_tadigadapa_jakoby_2016, title={Announcing the 2015 Measurement Science and Technology outstanding paper awards}, volume={27}, ISSN={0957-0233 1361-6501}, url={http://dx.doi.org/10.1088/0957-0233/27/7/070101}, DOI={10.1088/0957-0233/27/7/070101}, abstractNote={a measurements in high-enthalpy, hypersonic flow condition. Large carbon cluster (LCC) based thin film gauges for the measurement of the heat transfer rates in hypersonic shock tunnels are presented. The thermal sensors are deposited on Macor substrate inserts by the pyrolysis of benzene and ferrocene at 1023 K. Morphological characterization of the films is presented using scanning electron images while active carbon identification was confirmed using Raman Spectra. LCC film based thermistor characterization is presented and thermal models on Macor substrate are presented. LCC thermal gauges have been used to measure the stagnation point heat flux rate over a space-capsule recovery experiment model and a 120 ° apex angle blunt cone body at flow Mach number of 6.8. Under these test conditions, the LCC layer of the thermal gauge encounters high shear forces and a hostile environment for test durations in the range of few milliseconds. The measured temperature values are found to match well with the theoretical estimates. Furthermore the performance of the LCC thin film gauges has been compared with the performance of traditional platinum thin film gauges by simultaneously measuring the heat transfer rates over the 120 ° apex angle blunt cone model in hypersonic flow using the two types of gauges. As compared to platinum thin film gauges, the LCC based thin film thermal gauges show better stability and faster response.}, number={7}, journal={Measurement Science and Technology}, publisher={IOP Publishing}, author={Peters, Kara and Yang, Wuqiang and Tadigadapa, Srinivas and Jakoby, Bernhard}, year={2016}, month={May}, pages={070101} }
 @article{hackney_peters_black_costa_moslehi_2016, title={Fiber Bragg gratings as transient thermal gradient sensors}, volume={55}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.55.11.114102}, abstractNote={We experimentally subject a fiber Bragg grating to an unknown, variable temperature gradient. We use the full-spectral response of the grating to determine the magnitude of the gradient over the length of the grating via the full width at quarter maximum bandwidth. The experimental bandwidth and spectrum deformation were compared with a numerical model consisting of an analytical heat transfer model, a finite element analysis model, and the transfer matrix (T-matrix) method. The numerical model showed excellent agreement with the experimental results when the T-matrix method was modified to include the slope of the gradient in addition to the magnitude of the gradient.}, number={11}, journal={OPTICAL ENGINEERING}, author={Hackney, Drew A. and Peters, Kara J. and Black, Richard J. and Costa, Joannes M. and Moslehi, Behzad}, year={2016}, month={Nov} }
 @article{black_costa_zarnescu_hackney_moslehi_peters_2016, title={Fiber-optic temperature profiling for thermal protection system heat shields}, volume={55}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.55.11.114101}, abstractNote={To achieve better designs for spacecraft heat shields for missions requiring atmospheric aero-capture or entry/reentry, reliable thermal protection system (TPS) sensors are needed. Such sensors will provide both risk reduction and heat-shield mass minimization, which will facilitate more missions and enable increased payloads and returns. This paper discusses TPS thermal measurements provided by a temperature monitoring system involving lightweight, electromagnetic interference-immune, high-temperature resistant fiber Bragg grating (FBG) sensors with a thermal mass near that of TPS materials together with fast FBG sensor interrogation. Such fiber-optic sensing technology is highly sensitive and accurate, as well as suitable for high-volume production. Multiple sensing FBGs can be fabricated as arrays on a single fiber for simplified design and reduced cost. Experimental results are provided to demonstrate the temperature monitoring system using multisensor FBG arrays embedded in a small-size super-light ablator (SLA) coupon which was thermally loaded to temperatures in the vicinity of the SLA charring temperature. In addition, a high-temperature FBG array was fabricated and tested for 1000°C operation, and the temperature dependence considered over the full range (cryogenic to high temperature) for which silica fiber FBGs have been subjected.}, number={11}, journal={OPTICAL ENGINEERING}, author={Black, Richard J. and Costa, Joannes M. and Zarnescu, Livia and Hackney, Drew A. and Moslehi, Behzad and Peters, Kara J.}, year={2016}, month={Nov} }
 @article{wee_wells_hackney_bradford_peters_2016, title={Increasing signal amplitude in fiber Bragg grating detection of Lamb waves using remote bonding}, volume={55}, ISSN={["2155-3165"]}, DOI={10.1364/ao.55.005564}, abstractNote={Networks of fiber Bragg grating (FBG) sensors can serve as structural health monitoring systems for large-scale structures based on the collection of ultrasonic waves. The demodulation of structural Lamb waves using FBG sensors requires a high signal-to-noise ratio because the Lamb waves are of low amplitudes. This paper compares the signal transfer amplitudes between two adhesive mounting configurations for an FBG to detect Lamb waves propagating in an aluminum plate: a directly bonded FBG and a remotely bonded FBG. In the directly bonded FBG case, the Lamb waves create in-plane and out-of-plane displacements, which are transferred through the adhesive bond and detected by the FBG sensor. In the remotely bonded FBG case, the Lamb waves are converted into longitudinal and flexural traveling waves in the optical fiber at the adhesive bond, which propagate through the optical fiber and are detected by the FBG sensor. A theoretical prediction of overall signal attenuation also is performed, which is the combination of material attenuation in the plate and optical fiber and attenuation due to wave spreading in the plate. The experimental results demonstrate that remote bonding of the FBG significantly increases the signal amplitude measured by the FBG.}, number={21}, journal={APPLIED OPTICS}, author={Wee, Junghyun and Wells, Brian and Hackney, Drew and Bradford, Philip and Peters, Kara}, year={2016}, month={Jul}, pages={5564–5569} }
 @article{peters_2016, title={Networking of optical fiber sensors for extreme environments}, volume={9803}, ISSN={["1996-756X"]}, DOI={10.1117/12.2225296}, abstractNote={One of the major benefits of optical fiber sensors for applications to structural health monitoring and other structural measurements is their inherent multiplexing capabilities, meaning that a large number of sensing locations can be achieved with a single optical fiber. It has been well demonstrated that point wise sensors can be multiplexed to form sensor networks or optical fibers integrated with distributed sensing techniques. The spacing between sensing locations can also be tuned to match different length scales of interest. This article presents an overview of directions to adapt optical fiber sensor networking techniques into new applications where limitations such as available power or requirements for high data acquisition speeds are a driving factor. In particular, the trade-off between high fidelity sensor information vs. rapid signal processing or data acquisition is discussed.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2016}, author={Peters, Kara}, year={2016} }
 @article{shin_webb_peters_2016, title={Pulsed phase thermography imaging of fatigue-loaded composite adhesively bonded joints}, volume={79}, ISSN={["1879-1174"]}, DOI={10.1016/j.ndteint.2015.11.008}, abstractNote={We applied pulsed phase thermography to image and size damage in adhesively bonded joints. Specifically, the initiation and propagation of fatigue-induced damage in single lap joints with carbon fiber epoxy adherends was investigated. Lap joint specimens with various levels of manufacturing defects were fabricated and loaded in low-cycle fatigue. A calibration specimen with artificial defects was used to design a threshold algorithm for sizing of the damaged regions. The dominant failure mode in specimens without manufacturing defects was fiber-failure, whereas joints failing prematurely demonstrated adhesive failure. Imaging of the lap joints after regular number of fatigue cycles revealed that manufacturing defects could be detected and the resulting, imminent adhesive failure could be identified prior to joint failure. Additionally, the extent of this damage could be accurately estimated through the sizing algorithm. Due to the brittle nature of fiber-failure, it could not be detected prior to failure of the joint, however this was not critical, as the goal was to identify premature failure of the adhesively bonded joint.}, journal={NDT & E INTERNATIONAL}, author={Shin, Peter H. and Webb, Sean C. and Peters, Kara J.}, year={2016}, month={Apr}, pages={7–16} }
 @article{wee_hackney_peters_wells_bradford_2016, title={Sensitivity of contact-free fiber Bragg grating sensors to ultrasonic Lamb waves}, volume={9803}, ISSN={["1996-756X"]}, DOI={10.1117/12.2218924}, abstractNote={Networks of fiber Bragg grating (FBG) sensors can serve as structural health monitoring (SHM) systems for large-scale structures based on the collection of ultrasonic waves. The demodulation of structural Lamb waves requires a high signal-to-noise ratio because Lamb waves have a low amplitude. This paper investigates the signal transfer between Lamb waves propagating in an aluminum plate collected by an optical fiber containing a FBG. The fiber is bonded to the plate at locations away from the FBG. The Lamb waves are converted into longitudinal and flexural traveling waves propagating along the optical fiber, which are then transmitted to the Bragg grating. The signal wave amplitude is measured for different distances between the bond location and the Bragg grating. Bonding the optical fiber away from the FBG location and closer to the signal source produces a significant increase in signal amplitude, here measured to be 5.1 times that of bonding the Bragg grating itself. The arrival time of the different measured wave coupling paths are also calculated theoretically, verifying the source of the measured signals. The effect of the bond length to Lamb wavelength ratio is investigated, showing a peak response as the bond length is reduced compared to the wavelength. This study demonstrates that coupling Lamb waves into guided traveling waves in an optical fiber away from the FBG increases the signal-to-noise ratio of Lamb wave detection, as compared to direct transfer of the Lamb wave to the optical fiber at the location of the FBG.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2016}, author={Wee, Junghyun and Hackney, Drew and Peters, Kara and Wells, Brian and Bradford, Philip}, year={2016} }
 @article{seng_hackney_goode_shumway_hammond_shoemaker_pankow_peters_schultz_2016, title={Split Hopkinson bar measurement using high-speed full-spectrum fiber Bragg grating interrogation}, volume={55}, ISSN={["2155-3165"]}, DOI={10.1364/ao.55.007179}, abstractNote={The development and validation of a high-speed, full-spectrum measurement technique is described for fiber Bragg grating (FBG) sensors. A FBG is surface-mounted to a split-Hopkinson tensile bar specimen to induce high strain rates. The high strain gradients and large strains that indicate material failure are analyzed under high strain rates up to 500  s-1. The FBG is interrogated using a high-speed full-spectrum solid-state interrogator with a repetition rate of 100 kHz. The captured deformed spectra are analyzed for strain gradients using a default interior point algorithm in combination with the modified transfer matrix approach. This paper shows that by using high-speed full-spectrum interrogation of an FBG and the modified transfer matrix method, highly localized strain gradients and discontinuities can be measured without a direct line of sight.}, number={25}, journal={APPLIED OPTICS}, author={Seng, Frederick and Hackney, Drew and Goode, Tyler and Shumway, LeGrand and Hammond, Alec and Shoemaker, George and Pankow, Mark and Peters, Kara and Schultz, Stephen}, year={2016}, month={Sep}, pages={7179–7185} }
 @article{foss_peters_yacoot_jakoby_mcgrath_2015, title={Announcing the 2014 Measurement Science and Technology outstanding paper awards}, volume={26}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/26/7/070202}, abstractNote={Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented 'Outstanding Paper Awards'. This year awards were presented in the areas of 'Measurement Science' and 'Fluid Mechanics'. Although the categories mirror subject sections in the journal, the Editorial Board consider articles from all categories in the selection process. 2012 Award Winners—Measurement Science Physical characterization and performance evaluation of an x-ray micro-computed tomography system for dimensional metrology applications J Hiller1, M Maisl2 and L M Reindl3 1 Department of Mechanical Engineering, Technical University of Denmark (DTU), Produktionstorvet, Building 425, 2800 Kgs Lyngby, Denmark 2 Development Center for X-Ray Technology (EZRT), Fraunhofer Institute for Non-Destructive Testing (IZFP), Campus E3 1, 66123 Saarbrucken, Germany 3 Laboratory for Electrical Instrumentation, Institute for Microsystem Technology (IMTEK), University of Freiburg, Georges-Kohler-Allee 103, 79110 Freiburg, Germany This year's award goes to another paper [1] dealing with micro-measurements, using a scientific measurement technique that is both old and traditional. However, it is the advent of modern technology with computational techniques that have offered new insights into the capability of the measurement method. The paper describes an x-ray computed tomography (CT) system. Such systems are increasingly used in production engineering, where non-destructive measurements of the internal geometries of workpieces can be made with high information density. CT offers important alternatives to tactile or optical measurement systems which sometimes cannot reach internal features. The subject discussed is very important for measurement science. It is concerned with the many factors that affect precision and accuracy in CT metrology. These include issues in the scanning and reconstruction process, the image processing, and the 3D data evaluation. They all influence the dimensional measurement properties of the system as a whole. Therefore, as the authors point out, it is important to know what leads to, and what are the consequences of, such things as experimental geometrical misalignment of the scanner system, or image unsharpness (blurring), or noise or image artefacts. This paper is therefore directed at the implementation of a modern CT system, identifying what is important with implementation of the technique, and what are the likely sources of systematic and random error. After a useful introduction, the paper carefully describes a 3D micro-CT system developed at the Fraunhofer Institute for Non-Destructive Testing in Saarbrucken, Germany, to carry out dimensional measurements on small plastic and metal parts. Considerable emphasis is placed on the characterization of the x-ray tube, with discussion about the effective focal spot size and focus drift. Likewise, there is a detailed account of the flat-panel detector, before examining the contrast and noise transfer properties in the measuring volume. These features are important for achieving short term accuracy, whilst a later section discusses temperature measurements that affect long term accuracy. As a consequence, the image sharpness, noise or image artefacts, are evaluated. In a simple example, the length measurement property of the scanner for a given set of scanning parameters was obtained by using a calibrated ball-bar with a reference length of 8.7678 mm. Two different approaches for systematic error compensation were applied. They obtained an expanded measurement uncertainty of 6.9 µm down to 1.0 µm, which confirms the excellent dimensional measurement that can be achieved with a micro-CT scanner. The paper concludes with a useful summary of their characterization and performance studies. It also sets down possible future research activities in CT metrology. In particular, it identifies the need for development of CT scanning planning strategies to reduce measurement uncertainties in general and to minimize user influence in particular. This paper is excellent in its presentation and scientific description. Issues have been clearly described, and the paper should help establish x-ray micro-computed CT as a fully accepted measuring system in manufacturing engineering. Its contents were supported by 66 references. This helps to put the contribution into context with contributions from previous research papers. The nomination for this paper was supported by seven panel members, higher than any other paper, and it was rated as excellent during the refereeing process. 2012 Award Winners—Fluid Mechanics Polynomial element velocimetry (PEV): a technique for continuous in-plane velocity and velocity gradient measurements for low Reynolds number flows C R Samarage1,2, J Carberry2, G J Sheard2 and A Fouras1,2 1 Laboratory for Dynamic Imaging, Monash University, Melbourne, VIC 3800, Australia 2 Department of Mechanical and Aerospace Engineering, Monash University, Melbourne, VIC 3800, Australia The technique proposed in this article [2] is highly relevant to the wide community of experimentalists that make use of particle image velocimetry. The authors have addressed the issue of how to accurately measure the velocity field and the velocity gradient distribution. The method proposed is elegant and innovative in that it introduces polynomial base functions to represent the spatially varying velocity field within an 'element'. The working principle is clearly described and illustrated. It is noted that the authors have taken a modest position by limiting their conclusions to the case of low Reynolds number flows. It is expected that further developments of this work could lead to successful applications at higher Reynolds numbers and turbulent flows. For the cases analyzed in this work, the authors have achieved a significant improvement in describing the velocity and the vorticity in proximity of the wall. Lastly, the authors have discussed with an open attitude the possible shortcomings of the method. They have indicated the points that will deserve attention when further research efforts are dedicated to the topic. Given the above considerations, the MST outstanding paper selection committee for measurements in fluids, chaired by Professor John Foss, has nominated this article for the MST 2012 outstanding paper award. The chairmen would like to thank the authors for choosing to publish their work in Measurement Science and Technology, and hope that other researchers enjoy reading these works and feel encouraged to submit their own best work to the journal. References [1] Hiller J, Maisl M and Reindl L M 2012 Physical characterization and performance evaluation of an x-ray micro-computed tomography system for dimensional metrology applications Meas. Sci. Technol. 23 085404 (18pp) [2] Samarage C R, Carberry J, Sheard G J and Fouras A 2012 Polynomial element velocimetry (PEV): a technique for continuous in-plane velocity and velocity gradient measurements for low Reynolds number flows Meas. Sci. Technol. 23 105304 (16pp)}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Foss, John and Peters, Kara and Yacoot, Andrew and Jakoby, Bernhard and McGrath, John}, year={2015}, month={Jul} }
 @inproceedings{stewart_van hoe_van steenberge_schultz_peters_2015, title={Correction factors for cross-correlation processing of FBG sensor network data}, volume={9436}, url={http://dx.doi.org/10.1117/12.2084829}, DOI={10.1117/12.2084829}, abstractNote={This paper outlines a demodulation technique developed for low-bandwidth, high sensor density fiber Bragg grating (FBG) applications. Currently there are no such demodulation techniques that can be easily scaled to large networks of sensors. The technique takes advantage of known differences in FBG spectral profiles to uniquely identify each multiplexed grating. Known grating profiles are individually cross-correlated with the measured spectrum to locate each Bragg peak. Cross-correlation was used because of its rapid processing speed. This paper covers preliminary experimental validations to identify accuracy limits, as well as investigations into a correction factor for improved accuracy.}, booktitle={Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2015}, publisher={SPIE}, author={Stewart, William and Van Hoe, Bram and Van Steenberge, Geert and Schultz, Stephen and Peters, Kara}, editor={Peters, Kara J.Editor}, year={2015}, month={Mar} }
 @article{mabry_peters_seracino_2015, title={Depth Detection of Bond Defects in Multilayered Externally Bonded CFRP-to-Concrete Using Pulse Phase Thermography}, volume={19}, ISSN={["1943-5614"]}, DOI={10.1061/(asce)cc.1943-5614.0000551}, abstractNote={AbstractAlthough the practice of repairing or strengthening concrete infrastructure with externally bonded carbon-fiber-reinforced polymer (CFRP) has become common, the development of robust guidelines and techniques for its quality assurance, inspection, and monitoring is lagging significantly. Whereas common inspection methods (e.g., visual inspection or acoustic sounding) are sufficient to broadly identify deboned regions, it is difficult to reliably and accurately define the boundaries of bond defects, as is often required by acceptance criteria. Infrared thermography is a more sophisticated alternative, but the results of its application are influenced by ambient environmental conditions and operator interpretation of the data. Further, for applications in which multiple layers of CFRP are required, none of these techniques are capable of fully characterizing existing bond defects, including the depth through the thickness. To this end, pulse phase thermography (PPT) has the potential to more reliabl...}, number={6}, journal={JOURNAL OF COMPOSITES FOR CONSTRUCTION}, author={Mabry, Nehemiah J. and Peters, Kara J. and Seracino, Rudolf}, year={2015}, month={Dec} }
 @article{hamouda_seyam_peters_2015, title={Evaluation of the integrity of 3D orthogonal woven composites with embedded polymer optical fibers}, volume={78}, ISSN={["1879-1069"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84927642175&partnerID=MN8TOARS}, DOI={10.1016/j.compositesb.2015.03.092}, abstractNote={Abstract Due to their high flexibility, high tensile strain and high fracture toughness, polymer optical fibers (POF) are excellent candidates to be utilized as embedded sensors for structure health monitoring of fiber reinforced composites. In 3D orthogonal woven structures yarns are laid straight and polymer optical fiber can be easily inserted during preform formation either as a replacement of constituents or between them. The results of the previous paper indicated how an optic fiber sensor can be integrated into 3D orthogonal woven preforms with no signal loss. This paper addresses whether incorporating POF into 3D orthogonal woven composites affects their structure integrity and performance characteristics. Range of 3D orthogonal woven composites with different number of layers and different weft densities was fabricated. The samples were manufactured with and without POF to determine the effect of embedding POF on composite structure integrity. Bending, tensile strength tests, and cross section analysis were conducted on the composite samples. Results revealed that integrity of 3D orthogonal woven composite was not affected by the presence of POF. Due to its high strain, embedded POF was able to withstand the stresses without failure as a result of conducting destructive tests of the composite samples. Micrograph of cross-section of composite samples showed that minimum distortion of the yarn cross-section in vicinity of POF and no presence of air pocked around the embedded POF which indicates that 3D woven preform provided a good host for embedded POF.}, journal={COMPOSITES PART B-ENGINEERING}, author={Hamouda, Tamer and Seyam, Abdel-Fattah M. and Peters, Kara}, year={2015}, month={Sep}, pages={79–85} }
 @article{oman_van hoe_aly_peters_van steenberge_stan_schultz_2015, title={Instrumentation of integrally stiffened composite panel with fiber Bragg grating sensors for vibration measurements}, volume={24}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84938117649&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/24/8/085031}, abstractNote={We evaluate the performance of fiber Bragg grating (FBG) sensors for the measurement of dynamic strains in complex composite structures. The particular structure used in this study is an integrally stiffened composite panel for which the stiffeners and skin are fabricated in a single layup and cure process. Surface-mounted FBG sensors are bonded to the panels after curing, whereas embedded FBG sensors are successfully incorporated during the fabrication process. A finite element model was also constructed of the stiffened panel. The panels were subjected to repeated impacts and the post-impact vibration response of the panel was measured through the FBG sensor responses. Little change to the global response of the panel was observed after the repeated impacts, through the dynamic response of the surface-mounted FBGs. Pulsed phase thermography and micro-computer-tomography imaging of the panel confirmed that the damage was localized near the impact locations, producing negligible changes to the global response of the panel. All of the embedded FBG sensors survived the fabrication and multiple impacts; however, as these were embedded close to the neutral axis of the panel, they were not very sensitive to the vibration modes. Excitation of the panel near the first natural frequency did produce a measurable response in the FBG sensors, confirming their functionality.}, number={8}, journal={SMART MATERIALS AND STRUCTURES}, author={Oman, Kyle and Van Hoe, Bram and Aly, Karim and Peters, Kara and Van Steenberge, Geert and Stan, Nikola and Schultz, Stephen}, year={2015}, month={Aug} }
 @article{hamouda_seyam_peters_2015, title={Investigating the Loss of an Embedded Perfluorinated Optical Fiber for Different Resin's Gel Time}, volume={16}, ISSN={["1875-0052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84945385553&partnerID=MN8TOARS}, DOI={10.1007/s12221-015-5534-0}, number={10}, journal={FIBERS AND POLYMERS}, author={Hamouda, Tamer and Seyam, Abdel-Fattah M. and Peters, Kara}, year={2015}, month={Oct}, pages={2135–2140} }
 @article{yang_harrysson_west_cormier_park_peters_2015, title={Low-energy drop weight performance of cellular sandwich panels}, volume={21}, ISSN={["1758-7670"]}, DOI={10.1108/rpj-08-2013-0083}, abstractNote={
               Purpose
                – The aim of this study is to perform a comparative study on sandwich structures with several types of three-dimensional (3D) reticulate cellular structural core designs for their low-energy impact absorption abilities using powder bed additive manufacturing methods. 3D reticulate cellular structures possess promising potentials in various applications with sandwich structure designs. One of the properties critical to the sandwich structures in applications, such as aerospace and automobile components, is the low-energy impact performance. 
            }, number={4}, journal={RAPID PROTOTYPING JOURNAL}, author={Yang, Li and Harrysson, Ola A. and West, Harvey A., II and Cormier, Denis R. and Park, Chun and Peters, Kara}, year={2015}, pages={433–442} }
 @article{wu_peters_2015, title={Non-Destructive Inspection of Adhesively Bonded Joints using Amplitude Modulated Thermography}, volume={55}, ISSN={["1741-2765"]}, DOI={10.1007/s11340-015-9997-0}, number={8}, journal={EXPERIMENTAL MECHANICS}, author={Wu, X. and Peters, K.}, year={2015}, month={Oct}, pages={1485–1501} }
 @article{hernandez-valle_peters_2015, title={Numerical simulation of phase images and depth reconstruction in pulsed phase thermography}, volume={26}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/26/11/115602}, abstractNote={In this work we apply the finite element (FE) method to simulate the results of pulsed phase thermography experiments on laminated composite plates. Specifically, the goal is to simulate the phase component of reflected thermal waves and therefore verify the calculation of defect depth through the identification of the defect blind frequency. The calculation of phase components requires a higher spatial and temporal resolution than that of the calculation of the reflected temperature. An FE modeling strategy is presented, including the estimation of the defect thermal properties, which in this case is represented as a foam insert impregnated with epoxy resin. A comparison of meshing strategies using tetrahedral and hexahedral elements reveals that temperature errors in the tetrahedral results are amplified in the calculation of phase images and blind frequencies. Finally, we investigate the linearity of the measured diffusion length (based on the blind frequency) as a function of defect depth. The simulations demonstrate a nonlinear relationship between the defect depth and diffusion length, calculated from the blind frequency, consistent with previous experimental observations.}, number={11}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Hernandez-Valle, Saul and Peters, Kara}, year={2015}, month={Nov} }
 @article{hamouda_seyam_peters_2015, title={Polymer optical fibers integrated directly into 3D orthogonal woven composites for sensing}, volume={24}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84921802387&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/24/2/025027}, abstractNote={This study demonstrates that standard polymer optical fibers (POF) can be directly integrated into composites from 3D orthogonal woven preforms during the weaving process and then serve as in-situ sensors to detect damage due to bending or impact loads. Different composite samples with embedded POF were fabricated of 3D orthogonal woven composites with different parameters namely number of y-/x-layers and x-yarn density. The signal of POF was not affected significantly by the preform structure. During application of resin using VARTM technique, significant drop in backscattering level was observed due to pressure caused by vacuum on the embedded POF. Measurements of POF signal while in the final composites after resin cure indicated that the backscattering level almost returned to the original level of un-embedded POF. The POF responded to application of bending and impact loads to the composite with a reduction in the backscattering level. The backscattering level almost returned back to its original level after removing the bending load until damage was present in the composite. Similar behavior occurred due to impact events. As the POF itself is used as the sensor and can be integrated throughout the composite, large sections of future 3D woven composite structures could be monitored without the need for specialized sensors or complex instrumentation.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Hamouda, Tamer and Seyam, Abdel-Fattah M. and Peters, Kara}, year={2015}, month={Feb} }
 @inproceedings{mabry_seracino_peters_2015, title={Pulse phase thermography inspection of bond defects in environmentally conditioned FRP-to-concrete specimens}, DOI={10.12783/shm2015/55}, abstractNote={Externally bonded fiber-reinforced polymer (FRP) composite systems have emerged over the last few decades as an effective means for strengthening concrete structures. Typically these systems are installed by a process known as wet lay-up which involves the saturation of dry fibers with epoxy and applying them to the surface of a concrete member. This in-situ manual process is widely susceptible to a number of defects along the bondline due to entrapped air, moisture and other foreign inclusions. While current guidelines suggest acceptable defect sizes without the need for repair, significant research is still needed that examines the non-destructive evaluation (NDE) of such defects and the durability of FRP strengthened structures in extreme environments. Due to the speed and ease of application, acoustic sounding (hammer tapping) is among the most common inspection methods, but it is considered insufficient due to the limited information it provides and its accuracy depends on user interpretation. To this end, many have turned to Infrared Thermography (IRT) as an alternative whose use has been demonstrated by several researchers. However, its effectiveness is also affected by the operating environment. Occurrences such as surface reflection, humidity and non-uniform heating can lead to false readings that produce an inaccurate assessment of bond quality. Pulse Phase Thermography (PPT), a derivative technique, has been shown to overcome such issues by performing a Fourier Transform on the thermal data captured during the cooling period. PPT not only enables the removal of thermal noise by observing the phase values in the frequency domain, it also enjoys the benefit of rapid deployment by using shorter heating periods. This paper presents the results from a study involving the environmental conditioning of small scale, single-lap FRP-to-concrete pull-test specimens. Fifteen specimens were manufactured with and without pre-existing bond defects and were subjected to water submersion and freeze-thaw protocols. PPT inspection images were taken before and after the conditioning to observe the growth of defected areas as a result of conditioning. Also the tested performance of these specimens was examined to assess the criticality of discovered flaws. Finally, conclusions are made on the durability of the FRP-to-concrete interface when defects are initially present. doi: 10.12783/SHM2015/55}, booktitle={Structural health monitoring 2015: system reliability for verification and implementation, vols. 1 and 2}, author={Mabry, N. and Seracino, R. and Peters, Kara}, year={2015}, pages={424–431} }
 @inproceedings{peters_webb_2015, title={Rapid processing of full-spectral data from embedded FBG sensors}, DOI={10.12783/shm2015/216}, abstractNote={This paper addresses the inversion of applied non-uniform strain fields from measured FBG reflection spectra. With recent advances in instrumentation that can measure such reflected spectra dynamically, these spectra can now be tied to different failure modes in composite structures. This unique capability is particularly useful when the FBG sensors are embedded in composite materials and therefore subjected to highly non-uniform strain fields. The calculation of an arbitrary applied strain field from a measured reflection spectrum remains a significant computational effort, however, due to the need for an optimization algorithm. Therefore this data processing has not been applied to FBG reflected spectra collected from dynamic events, due to the large amount of spectra that must be processed. In this article we present a linearization method to calculate the applied strain field, provided that the measured reflection spectra are collected at a sufficiently high acquisition rate. doi: 10.12783/SHM2015/216}, booktitle={Structural health monitoring 2015: system reliability for verification and implementation, vols. 1 and 2}, author={Peters, Kara and Webb, S.}, year={2015}, pages={1729–1736} }
 @article{stewart_van hoe_van steenberge_schultz_peters_2015, title={Spectral profile tracking of multiplexed fiber Bragg grating sensors}, volume={357}, ISSN={["1873-0310"]}, DOI={10.1016/j.optcom.2015.08.083}, abstractNote={Abstract This paper outlines a demodulation technique for fiber Bragg grating (FBG) sensors based on combined spectral profile division multiplexing and wavelength division multiplexing. The advantage to this technique is that more FBG sensors can be compressed in a fixed bandwidth, as compared to pure wavelength division multiplexing, in which separate wavelength window is required for each sensor. To identify each FBG sensor, the cross-correlation algorithm of the original sensor spectral profile with the measured full-spectrum from the sensor array is calculated for rapid signal processing. The demodulation method is tested on simulated and experimental data. The demodulation generally performed well, except for cases where a significant amount of spectral distortion due to multiplexing was present. Finally, a correction factor based on the prior location of each sensor at the previous time step is added to compensate for inherent uncertainties in the cross-correlation algorithm. The correction factor improved some predictions, but made others worse, and therefore needs further investigation for practical applications.}, journal={OPTICS COMMUNICATIONS}, author={Stewart, William and Van Hoe, Bram and Van Steenberge, Geert and Schultz, Stephen and Peters, Kara}, year={2015}, month={Dec}, pages={113–119} }
 @article{foss_dewhurst_yacoot_tadigadapa_peters_2014, title={Announcing the 2013 Measurement Science and Technology Outstanding Paper Awards}, volume={25}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/25/7/070201}, abstractNote={Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believe that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented ‘Outstanding Paper Awards’. This year awards were presented in the areas of Fluid Mechanics, Measurement Science, Precision Measurement, Sensors and Sensing Systems, and Optical and Laser-based Techniques. Although the categories mirror subject sections in the journal, the Editorial Board consider articles from all categories in the selection process. 2013 Award Winner—Fluid Mechanics Extraction of skin-friction fields from surface flow visualizations Tianshu Liu Department of Mechanical and Aerospace Engineering, Western Michigan University, Kalamazoo, MI 49008, USA The skin friction or wall shear stress, τ w, for a wall bounded turbulent flow is a quantity of fundamental importance. It is the basis for the wall unit, ν/u τ (kinematic viscosity/friction velocity: [τ w/ρ ]1/2), which establishes the intrinsic length scale in the flow. The selected paper [1] provides a comprehensive review of—and builds upon—prior techniques to obtain τ w values over an area of interest for flow past complex geometries. The quantities that can be measured by optical imaging are shown to be related to the skin friction by the optical flow equation, which in turn is solved numerically as an inverse problem via the variational approach. The paper provides a well defined set of guidelines for other investigators. Detailed examples of skin-friction measurements using luminescent oil films as well as temperature- and pressure-sensitive paints are presented. Quantitative uncertainty estimates are included in the paper. Given the importance of the wall shear stress (skin friction) in fluid mechanics and the notorious difficulty of measuring this quantity directly, this paper is expected to be a seminal contribution. The paper was one of four in the special feature on Wall Shear Stress organized by Professor A Naguib in the December 2013 issue. 2013 Award Winner—Measurement Science Analysis of calibration-free wavelength-scanned wavelength modulation spectroscopy for practical gas sensing using tunable diode lasers K Sun, X Chao, R Sur, C S Goldenstein, J B Jeffries and R K Hanson High Temperature Gasdynamics Laboratory, Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA In the previous two years, the Measurement Science Award has gone to important papers in diagnostic fields, namely particle image velocimetry (PIV [2]) and x-ray micro-computed tomographic systems [3]. This year’s award [4] goes to another diagnostic field, infrared spectroscopy for practical gas sensing. Infrared spectroscopy is a very important topic for measurement science, concerned with the monitoring of gases in our environment. Over two decades, this form of spectroscopy has been enabled with the development of tunable diode lasers (TDLs). Hence, tunable diode laser absorption spectroscopy (TDLAS) is now an established method for in situ measurements of gas composition, temperature, pressure and velocity. Gases such as ammonia, methane, carbon dioxide and monoxide, hydrogen chloride, hydrogen fluoride and sulfur dioxide can all be monitored by commercially available systems. Some advances have been associated with improvements in infrared detectors or in the properties of some diode lasers. For homogeneous gases, the interpretation using the Beer–Lambert law and direct absorption (DA) is quite straightforward. DA is the preferred method when an absorption line can be found in the infrared region with an isolated transition of sufficient strength, and with a linewidth small enough to allow the laser to be wavelength-scanned on the absorption line, and just off it (as a reference baseline). Otherwise, wavelength modulation spectroscopy (WMS) is used for those cases where the gas offers small absorbance, or high pressure or for absorbers with closely spaced transitions, which are blended in the wings precluding measurement of a non-absorbing baseline. WMS is a powerful technique, but the interpretation is more complex, and the authors explain in their introduction the strategies that are normally adopted for data interpretation. In this new paper, the authors explain a new strategy for wavelength modulation spectroscopy. The strategy is different in two significant ways. Firstly, the measured laser intensity is used to simulate the transmitted laser intensity. Secondly, digital lock-in and low-pass filter software is used to expand both simulated and measured transmitted laser intensities into harmonics of the modulation frequency. In this way, the analysis scheme does not require an isolated transition; instead it recovers the lineshape for absorption from unresolved blended transitions. The paper goes on to describe an example using this novel method. It discusses the analysis of WMS absorption detection using water as an example. The advantages of the new method are explained, and a comparison is made with the more usual Fourier analysis approach. This paper is excellent in its clarity, presentation and scientific description. Issues have been clearly identified, and a new method of analysis has been presented with some evidence of validation. Its conclusions contain an in-depth summary, and the following 42 references are informative and representative of what is a very large field of study. It was voted as the best paper from a shortlist of 12 nominated papers. 2013 Award Winner—Precision Measurement Interferometric diameter determination of a silicon sphere using a traceable single laser frequency synthesizer Xuejian Wu, Yan Li, Haoyun Wei, Honglei Yang, Guoce Yang and Jitao Zhang State Key Lab of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University, Beijing 100084, People’s Republic of China This paper [5] describes the determination of the absolute diameter of a silicon sphere for the Avogadro project using a phase shifting interferometer based on a flat etalon. The absolute diameter is attained by combining the fractional and integral measurement results, which are measured with phase shifting interferometry and frequency sweeping interferometry using laser frequency tuning, respectively. An optical frequency comb is used as the frequency ruler to measure and control the frequency of an external cavity diode laser in order to reduce the uncertainty contribution from the laser frequency on the phase steps to an insignificant level. The Carré algorithm with arbitrary but equal phase steps is used to calculate the fractional interference phases according to the characteristic of single laser frequency synthesiser. The paper provides a comprehensive description of the measurement techniques together with an uncertainty budget for the measurement of a silicon sphere. An overall measurement uncertainty of 5 nm is achieved. This paper has been downloaded more than 130 times since its publication. The selection committee members on the Precision Measurement Award, Dr A Yacoot, Dr P Williams, Dr H Bosse, Professor X Chen and Dr T Eom, selected this paper from a strongly competitive list of several candidates. Considering its impact on accurate evaluation of the measurement of silicon spheres, the paper was selected as the winner of the Precision Measurement Award for 2013. 2013 Award Winner—Sensors and Sensing Systems Enhancing the dynamic range of ultrasound imaging velocimetry using interleaved imaging C Poelma1 and K H Fraser 2 1Laboratory for Aero and Hydrodynamics (3ME-P&E), Delft University of Technology, Leeghwaterstraat 21, 2628 CA Delft, The Netherlands 2Department of Bioengineering, Imperial College London, South Kensington Campus, SW7 2AZ London, UK This paper [6] presents an innovative interleaved imaging technique to overcome the dynamic velocity range limitation of current ultrasound imaging velocimetry. Due to the nature of the recording of ultrasound images, the conversion from pixel displacement to velocities is less straightforward since the lines of an image are not recorded at the same time, so the inter-frame time needs to be corrected for any displacement. The upper limit of displacement velocities is widely reported in the literature as a major problem with the best measured in-vivo flow rates of ~ 70–80 cm s−1 or by restricting the field of view to as high as 140 cm s−1. In this study, the authors introduce a novel imaging method that enhances the dynamic range of ultrasound imaging velocimetry by an interleaved read-out approach. Using this technique, the inter-frame time is no longer fixed to the imaging rate and allows for the displacement of fast flows to be reduced by choosing an appropriate image offset parameter. The authors show that this technique allows for measurement of flows of up to 140 cm s−1 with the maximum lateral field of view and unrestricted depth. In their winning paper the authors have very clearly articulated the dynamic range limitations of the flow measurement using ultrasound imaging velocimetry and have very elegantly described the theory and experimental implementation of the interleaved imaging technique. The superior performance of the proposed method is clearly demonstrated through experimental results and images analyzed using the necessary mathematical transforms. The improved dynamic flow rate measurements using ultrasound imaging velocimetry made feasible using this technique are likely to have a significant impact on non-invasive blood flow monitoring for clinical screening and post-operative monitoring. 2013 Award Winner—Optical and Laser-based Techniques Dete}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Foss, John and Dewhurst, Richard and Yacoot, Andrew and Tadigadapa, Srinivas and Peters, Kara}, year={2014}, month={Jul} }
 @article{webb_shin_peters_zikry_stan_chadderdon_selfridge_schultz_2014, title={Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 1. Experiments}, volume={23}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84892404653&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/23/2/025016}, abstractNote={In this study we measure the in situ response of a fiber Bragg grating (FBG) sensor embedded in the adhesive layer of a single composite lap joint, subjected to harmonic excitation after fatigue loading. After a fully reversed cyclic fatigue loading is applied to the composite lap joint, the full-spectral response of the sensor is interrogated at 100 kHz during two loading conditions: with and without an added harmonic excitation. The full-spectral information avoided dynamic measurement errors often experienced using conventional peak wavelength and edge filtering techniques. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. The dynamic response of the FBG sensor indicated a transition to strong nonlinear dynamic behavior as fatigue-induced damage progressed. The ability to measure the dynamic response of the lap joint through sensors embedded in the adhesive layer can provide in situ monitoring of the lap joint condition.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Webb, S. and Shin, P. and Peters, K. and Zikry, M. A. and Stan, N. and Chadderdon, S. and Selfridge, R. and Schultz, S.}, year={2014}, month={Feb} }
 @article{webb_shin_peters_zikry_stan_chadderdon_selfridge_schultz_2014, title={Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 2. Simulations}, volume={23}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84892411813&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/23/2/025017}, abstractNote={In this paper, we simulate the response of fiber Bragg grating (FBG) sensors embedded in the adhesive layer of a composite lap that is subjected to harmonic excitation. To simulate accumulated fatigue damage at the adhesive layer, two forms of numerical nonlinearities are introduced into the model: (1) progressive plastic deformation of the adhesive and (2) changing the boundary of an interfacial defect at the adhesive layer across the overlap shear area. The simulation results are compared with previous measurements of the dynamic, full-spectral response of such FBG sensors for condition monitoring of the lap joint. Short-time Fourier transforms (STFT) of the locally extracted axial strain time histories reveal a transition to nonlinear behavior of the composite lap joint by means of intermittent frequencies that were observed in the experimental measurements and are not associated with the external excitation. The simulation results verify that the nonlinear changes in measured dynamic FBG responses are due to the progression of damage in the lap joint.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Webb, S. and Shin, P. and Peters, K. and Zikry, M. A. and Stan, N. and Chadderdon, S. and Selfridge, R. and Schultz, S.}, year={2014}, month={Feb} }
 @article{webb_peters_zikry_stan_chadderdon_selfridge_schultz_2014, title={Fiber Bragg grating spectral features for structural health monitoring of composite structures}, volume={9157}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84903169877&partnerID=MN8TOARS}, DOI={10.1117/12.2059625}, abstractNote={We demonstrate the measurement of and applications for reflected spectral signatures obtained from FBG sen- sors in dynamic environments. Three uses of the spectral distortion measurements for monitoring of airframe structures are presented: the measurement of the dynamic response of a laminated plate to an impact event; the measurement of damage induced spectral distortion in a thin plate during vibration loading; and the measurement of the change in dynamic response of an adhesively bonded joint with the progression of fatigue damage.}, journal={23RD INTERNATIONAL CONFERENCE ON OPTICAL FIBRE SENSORS}, author={Webb, Sean and Peters, Kara and Zikry, Mohammed and Stan, Nikola and Chadderdon, Spencer and Selfridge, Richard and Schultz, Stephen}, year={2014} }
 @inproceedings{hackney_peters_black_costa_moslehi_zarnescu_2014, title={Fiber bragg gratings for heat flux measurements in thermal protection systems under a steady conductive thermal load}, booktitle={Proceedings of the ASME Conference on Smart Materials Adaptive Structures and Intelligent Systems - 2013, vol 2}, author={Hackney, D. A. and Peters, K. J. and Black, R. J. and Costa, J. M. and Moslehi, B. and Zarnescu, L.}, year={2014} }
 @article{stan_bailey_chadderdon_webb_zikry_peters_selfridge_schultz_2014, title={Increasing dynamic range of a fibre Bragg grating edge-filtering interrogator with a proportional control loop}, volume={25}, ISSN={["1361-6501"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84899634683&partnerID=MN8TOARS}, DOI={10.1088/0957-0233/25/6/065206}, abstractNote={We present a fibre Bragg grating (FBG) interrogator that uses a microcontroller board and a tunable optical filter in a proportional control loop to increase dynamic range and achieve high strain sensitivity. It is an edge-filtering interrogator with added proportional control loop that locks the operating wavelength to the mid-reflection point on the FBG spectrum. The interrogator separates low-frequency (LF) components of strain and measures them with extended dynamic range, while at the same time measuring high-frequency (HF) strain without loss in strain sensitivity. In this paper, we describe the implementation of the interrogator and analyse the characteristics of individual components, such as the speed and voltage resolution of the microcontroller and the tunable optical filter. We measure the performance of the proportional control loop at frequencies up to 1 kHz and characterize the system using control theory. We illustrate the limitation of the conventional interrogator to measure strains greater than 40 μϵ and demonstrate successful application of the proposed interrogator for simultaneous measurement of 450 μϵ LF strain at 50 Hz superimposed with 32 kHz HF strain.}, number={6}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Stan, Nikola and Bailey, D. C. and Chadderdon, S. L. and Webb, S. and Zikry, M. and Peters, K. J. and Selfridge, R. H. and Schultz, S. M.}, year={2014}, month={Jun} }
 @article{webb_oman_peters_stan_chadderdon_selfridge_schultz_2014, title={Localized measurements of composite dynamic response for health monitoring}, volume={9062}, ISSN={["1996-756X"]}, DOI={10.1117/12.2045255}, abstractNote={We demonstrate the measurement of and applications for full-spectral measurements collected from FBG sensors in dynamic loading environments. The measurement of the dynamic response of a laminated plate to an impact event highlights the information gained during the event as compared to after the event. The measurement of damage induced spectral distortion in a thin plate during vibration loading demonstrates the capability of separating spectral distortion due to multiple effects, including damage and vibration loading. Finally, the measurement of the change in dynamic response of an adhesively bonded joint highlights the capability to measure the progression of fatigue damage. Confirmation that the change in FBG response is due to fatigue damage is performed through independent pulsed phase thermography imaging of the adhesively bonded joint.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS INTEGRATION 2014}, author={Webb, Sean and Oman, Kyle and Peters, Karsa and Stan, Nikola and Chadderdon, Sspencer and Selfridge, Richard and Schultz, Stephen}, year={2014} }
 @article{foss_dewhurst_yacoot_regtien_peters_2013, title={Announcing the 2012 Measurement Science and Technology Outstanding Paper Awards}, volume={24}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/24/7/070101}, abstractNote={Since 1991, Measurement Science and Technology has awarded a Best Paper prize. The Editorial Board of this journal believes that such a prize is an opportunity to thank authors for submitting their work, and serves as an integral part of the on-going quality review of the journal. The current breadth of topical areas that are covered by MST has made it advisable to expand the recognition of excellent publications. Hence, since 2005 the Editorial Board have presented 'Outstanding Paper Awards'. This year awards were presented in the areas of 'Measurement Science' and 'Fluid Mechanics'. Although the categories mirror subject sections in the journal, the Editorial Board consider articles from all categories in the selection process. 2012 Award Winners—Measurement Science Physical characterization and performance evaluation of an x-ray micro-computed tomography system for dimensional metrology applications J Hiller1, M Maisl2 and L M Reindl3 1 Department of Mechanical Engineering, Technical University of Denmark (DTU), Produktionstorvet, Building 425, 2800 Kgs Lyngby, Denmark 2 Development Center for X-Ray Technology (EZRT), Fraunhofer Institute for Non-Destructive Testing (IZFP), Campus E3 1, 66123 Saarbrücken, Germany 3 Laboratory for Electrical Instrumentation, Institute for Microsystem Technology (IMTEK), University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg, Germany This year's award goes to another paper [1] dealing with micro-measurements, using a scientific measurement technique that is both old and traditional. However, it is the advent of modern technology with computational techniques that have offered new insights into the capability of the measurement method. The paper describes an x-ray computed tomography (CT) system. Such systems are increasingly used in production engineering, where non-destructive measurements of the internal geometries of workpieces can be made with high information density. CT offers important alternatives to tactile or optical measurement systems which sometimes cannot reach internal features. The subject discussed is very important for measurement science. It is concerned with the many factors that affect precision and accuracy in CT metrology. These include issues in the scanning and reconstruction process, the image processing, and the 3D data evaluation. They all influence the dimensional measurement properties of the system as a whole. Therefore, as the authors point out, it is important to know what leads to, and what are the consequences of, such things as experimental geometrical misalignment of the scanner system, or image unsharpness (blurring), or noise or image artefacts. This paper is therefore directed at the implementation of a modern CT system, identifying what is important with implementation of the technique, and what are the likely sources of systematic and random error. After a useful introduction, the paper carefully describes a 3D micro-CT system developed at the Fraunhofer Institute for Non-Destructive Testing in Saarbrücken, Germany, to carry out dimensional measurements on small plastic and metal parts. Considerable emphasis is placed on the characterization of the x-ray tube, with discussion about the effective focal spot size and focus drift. Likewise, there is a detailed account of the flat-panel detector, before examining the contrast and noise transfer properties in the measuring volume. These features are important for achieving short term accuracy, whilst a later section discusses temperature measurements that affect long term accuracy. As a consequence, the image sharpness, noise or image artefacts, are evaluated. In a simple example, the length measurement property of the scanner for a given set of scanning parameters was obtained by using a calibrated ball-bar with a reference length of 8.7678 mm. Two different approaches for systematic error compensation were applied. They obtained an expanded measurement uncertainty of 6.9 µm down to 1.0 µm, which confirms the excellent dimensional measurement that can be achieved with a micro-CT scanner. The paper concludes with a useful summary of their characterization and performance studies. It also sets down possible future research activities in CT metrology. In particular, it identifies the need for development of CT scanning planning strategies to reduce measurement uncertainties in general and to minimize user influence in particular. This paper is excellent in its presentation and scientific description. Issues have been clearly described, and the paper should help establish x-ray micro-computed CT as a fully accepted measuring system in manufacturing engineering. Its contents were supported by 66 references. This helps to put the contribution into context with contributions from previous research papers. The nomination for this paper was supported by seven panel members, higher than any other paper, and it was rated as excellent during the refereeing process. 2012 Award Winners—Fluid Mechanics Polynomial element velocimetry (PEV): a technique for continuous in-plane velocity and velocity gradient measurements for low Reynolds number flows C R Samarage1,2, J Carberry2, G J Sheard2 and A Fouras1,2 1 Laboratory for Dynamic Imaging, Monash University, Melbourne, VIC 3800, Australia 2 Department of Mechanical and Aerospace Engineering, Monash University, Melbourne, VIC 3800, Australia The technique proposed in this article [2] is highly relevant to the wide community of experimentalists that make use of particle image velocimetry. The authors have addressed the issue of how to accurately measure the velocity field and the velocity gradient distribution. The method proposed is elegant and innovative in that it introduces polynomial base functions to represent the spatially varying velocity field within an 'element'. The working principle is clearly described and illustrated. It is noted that the authors have taken a modest position by limiting their conclusions to the case of low Reynolds number flows. It is expected that further developments of this work could lead to successful applications at higher Reynolds numbers and turbulent flows. For the cases analyzed in this work, the authors have achieved a significant improvement in describing the velocity and the vorticity in proximity of the wall. Lastly, the authors have discussed with an open attitude the possible shortcomings of the method. They have indicated the points that will deserve attention when further research efforts are dedicated to the topic. Given the above considerations, the MST outstanding paper selection committee for measurements in fluids, chaired by Professor John Foss, has nominated this article for the MST 2012 outstanding paper award. The chairmen would like to thank the authors for choosing to publish their work in Measurement Science and Technology, and hope that other researchers enjoy reading these works and feel encouraged to submit their own best work to the journal. References [1] Hiller J, Maisl M and Reindl L M 2012 Physical characterization and performance evaluation of an x-ray micro-computed tomography system for dimensional metrology applications Meas. Sci. Technol. 23 085404 (18pp) [2] Samarage C R, Carberry J, Sheard G J and Fouras A 2012 Polynomial element velocimetry (PEV): a technique for continuous in-plane velocity and velocity gradient measurements for low Reynolds number flows Meas. Sci. Technol. 23 105304 (16pp)}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Foss, John and Dewhurst, Richard and Yacoot, Andrew and Regtien, Paul and Peters, Kara}, year={2013}, month={Jul} }
 @article{webb_shin_peters_zikry_chadderdon_stan_selfridge_schultz_2013, title={Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors}, volume={8693}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84878407243&partnerID=MN8TOARS}, DOI={10.1117/12.2010018}, abstractNote={In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor embedded at the adhesive layer of a single composite lap joint subjected to harmonic excitation after fatigue loading. After a fully-reversed cyclic fatigue loading is applied to the composite lap joint, the full spectral response of the sensor is interrogated in reflection at 100 kHz during two states: with and without an added harmonic excitation. The dynamic response of the FBG sensor indicates strong nonlinearities as damage progresses. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. Pulse-phase thermography indicates a progression in defect size at the adhesive layer that strongly suggests non-uniform loading of the FBG sensor.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS INTEGRATION 2013}, author={Webb, S. and Shin, P. and Peters, K. and Zikry, M. A. and Chadderdon, S. and Stan, N. and Selfridge, R. and Schultz, S.}, year={2013} }
 @inproceedings{webb_shin_peters_zikry_schultz_selfridge_2013, title={Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber bragg grating sensors}, booktitle={Structural Health Monitoring 2013, Vols 1 and 2}, author={Webb, S. and Shin, P. and Peters, K. and Zikry, M. and Schultz, S. and Selfridge, R.}, year={2013}, pages={1953–1960} }
 @article{pearson_labarbera_prabhugoud_peters_zikry_2013, title={Experimental and Computational Investigation of Low-Impact Velocity and Quasi-Static Failure of PMMA}, volume={53}, ISSN={["1741-2765"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84872276475&partnerID=MN8TOARS}, DOI={10.1007/s11340-012-9650-0}, number={1}, journal={EXPERIMENTAL MECHANICS}, author={Pearson, J. D. and LaBarbera, D. and Prabhugoud, M. and Peters, K. and Zikry, M. A.}, year={2013}, month={Jan}, pages={53–66} }
 @article{webb_peters_zikry_chadderdon_nikola_selfridge_schultz_2013, title={Full-Spectral Interrogation of Fiber Bragg Grating Sensors Exposed to Steady-State Vibration}, volume={53}, ISSN={["1741-2765"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84874796178&partnerID=MN8TOARS}, DOI={10.1007/s11340-012-9661-x}, number={4}, journal={EXPERIMENTAL MECHANICS}, author={Webb, S. and Peters, K. and Zikry, M. A. and Chadderdon, S. and Nikola, S. and Selfridge, R. and Schultz, S.}, year={2013}, month={Apr}, pages={513–530} }
 @inbook{webb_shin_peters_2013, title={Fusion of Global and Local Measurements of Damage in Bonded Joints}, ISBN={9783319007649 9783319007656}, ISSN={2191-5644 2191-5652}, url={http://dx.doi.org/10.1007/978-3-319-00765-6_3}, DOI={10.1007/978-3-319-00765-6_3}, abstractNote={In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor embedded at the adhesive layer of a single composite lap joint subjected to harmonic excitation after fatigue loading. After a fully-reversed cyclic fatigue loading is applied to the composite lap joint, the full spectral response of the sensor is interrogated in reflection at 100 kHz during two states: with and without an added harmonic excitation. The dynamic response of the FBG sensor indicates strong nonlinearities as damage progresses. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. Pulsed-phase thermography indicates a progression in defect size at the adhesive layer that strongly suggests non-uniform loading of the FBG sensor. These imaging results are applied to finite element modeling of the joint to simulate the non-linearities in the structural response.}, booktitle={Fracture and Fatigue, Volume 7}, publisher={Springer International Publishing}, author={Webb, Sean C. and Shin, Peter and Peters, Kara}, year={2013}, month={Jul}, pages={13–19} }
 @article{pawar_peters_2013, title={Hybrid imaging of damage progress in composites through thermal imaging and embedded sensing}, volume={8693}, ISSN={["1996-756X"]}, DOI={10.1117/12.2010016}, abstractNote={In this paper, we investigate the fusion of imaging data from pulsed phase thermography (PPT) with local temperature data obtained from embedded fiber Bragg grating (FBG) sensors for non-destructive evaluation of composite structures. We use the square pulse heating applied for the PPT imaging as the input thermal wave for both the imaging and sensing processes. In addition, the role of the local microstructure surrounding the FBG on the measured wavelength shift as a function of temperature is derived analytically. Fusing the FBG wavelength response with the PPT data at the corresponding pixel and depth is shown to provide a unique characterization of the local material condition.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS INTEGRATION 2013}, author={Pawar, S. and Peters, K.}, year={2013} }
 @article{shin_webb_peters_2013, title={Nondestructive inspection in adhesive-bonded joint CFRP using pulsed phase thermography}, volume={8705}, ISSN={["0277-786X"]}, DOI={10.1117/12.2018414}, abstractNote={Many forms of damages in fiber reinforcement polymer (FRP) composites are difficult to detect because they occurs in subsurface layers of the composites. One challenging need for inspection capabilities is in adhesively bonded joints between composite components, a common location of premature failure in aerospace structures. This paper investigates pulsed phase thermography (PPT) imaging of fatigue damage in these adhesively bonded joints. Simulated defects were created to calibrate parameters for fatigue loading conditions, PPT imaging parameters, and a damage sizing algorithm for carbon fiber reinforced polymer (CFRP) single lap joints. Afterwards, lap joint specimens were fabricated with varying quality of manufacturing. PPT imaging of the pristine specimens revealed defects such as air bubbles, adhesive thickness variations, and weak bonding surface between the laminate and adhesive. Next, fatigue testing was performed and acquired PPT imaging data identified fatigue induced damage prior to final failure cycles. After failure of each sample, those images were confirmed by visual inspections of failure surface.}, journal={THERMOSENSE: THERMAL INFRARED APPLICATIONS XXXV}, author={Shin, P. H. and Webb, S. C. and Peters, K. J.}, year={2013} }
 @article{webb_shin_peters_selfridge_schultz_2013, title={Nondestructive inspection of CFRP adhesively bonded joints using embedded FBG sensors}, volume={8722}, ISSN={["1996-756X"]}, DOI={10.1117/12.2018443}, abstractNote={One challenging need for inspection capabilities is in adhesively bonded joints between composite components, a common location of premature failure in aerospace structures. In this work we demonstrate that dynamic, full spectral scanning of FBG sensors embedded in the adhesive bond can identify changes in bond quality through the measurement of non-linear dynamics of the joint. Eighteen lap joint specimens were fabricated with varying manufacturing quality. Ten samples also included fiber Bragg grating (FBG) sensors embedded in the adhesive bond for real-time inspection during a simulated flight condition of these single-lap joints. Prior to testing, pulse phase thermography imaging of the pristine specimens revealed defects such as air bubbles, adhesive thickness variations, and weak bonding surface between the laminate and adhesive. The lap joint specimens were then subjected to fatigue loading, with regular interrogation of the FBG sensors at selected load cycle intervals. The FBG data was collected during vibration loading of the lap joint to represent an in-flight environment. Changes in the lap joint dynamic response, including the transition to non-linear responses, were measured from both the full-spectral and peak wavelength FBG data. These changes were correlated to initial manufacturing defects and the progression of fatigue-induced damage independently measured with pulse phase imaging and visual inspections of the failure surfaces.}, journal={FIBER OPTIC SENSORS AND APPLICATIONS X}, author={Webb, S. and Shin, P. and Peters, K. and Selfridge, R. and Schultz, S.}, year={2013} }
 @article{chen_peters_li_2013, title={Self-healing sandwich structures incorporating an interfacial layer with vascular network}, volume={22}, ISSN={["0964-1726"]}, DOI={10.1088/0964-1726/22/2/025031}, abstractNote={A self-healing capability specifically targeted for sandwich composite laminates based on interfacial layers with built-in vascular networks is presented. The self-healing occurs at the facesheet–core interface through an additional interfacial layer to seal facesheet cracks and rebond facesheet–core regions. The efficacy of introducing the self-healing system at the facesheet–core interface is evaluated through four-point bend and edgewise compression testing of representative foam core sandwich composite specimens with impact induced damage. The self-healing interfacial layer partially restored the specific initial stiffness, doubling the residual initial stiffness as compared to the control specimen after the impact event. The restoration of the ultimate specific skin strength was less successful. The results also highlight the critical challenge in self-healing of sandwich composites, which is to rebond facesheets which have separated from the core material.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Chen, Chunlin and Peters, Kara and Li, Yulong}, year={2013}, month={Feb} }
 @article{xu_rezvanian_peters_zikry_2013, title={The viability and limitations of percolation theory in modeling the electrical behavior of carbon nanotube-polymer composites}, volume={24}, ISSN={["1361-6528"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84875677113&partnerID=MN8TOARS}, DOI={10.1088/0957-4484/24/15/155706}, abstractNote={A new modeling method has been proposed to investigate how the electrical conductivity of carbon nanotube (CNT) reinforced polymer composites are affected by tunneling distance, volume fraction, and tube aspect ratios. A search algorithm and an electrical junction identification method was developed with a percolation approach to determine conductive paths for three-dimensional (3D) carbon nanotube arrangements and to account for electron tunneling effects. The predicted results are used to understand the limitations of percolation theory and experimental measurements and observations, and why percolation theory breaks down for specific CNT arrangements.}, number={15}, journal={NANOTECHNOLOGY}, author={Xu, S. and Rezvanian, O. and Peters, K. and Zikry, M. A.}, year={2013}, month={Apr} }
 @article{pawar_peters_2013, title={Through-the-thickness identification of impact damage in composite laminates through pulsed phase thermography}, volume={24}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/24/11/115601}, abstractNote={In this paper we demonstrate through-the-thickness imaging of barely visible impact damage in a two-dimensional woven, carbon fiber epoxy laminate using pulsed phase thermography (PPT). Specifically we calibrate the defect depth with blind frequency for the particular material system using a specimen with simulated defects in the form of polymer foam inclusions. The calibrated depth versus blind frequency relation is then applied to specimens with barely visible impact damage due to low-velocity impacts. The polymer foam reproduces the irregular boundaries and thin nature of the delaminations, but does not reproduce through-the-thickness variations. The extent of delamination at different depths was reconstructed as a function of depth for varying levels of impact energy. The extent of damage imaged using PPT corresponded well with visual observations and microscopy images.}, number={11}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Pawar, Sachin S. and Peters, Kara}, year={2013}, month={Nov} }
 @article{park_peters_2012, title={Comparison of damage measures based on fiber Bragg grating spectra}, volume={23}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/23/2/025105}, abstractNote={We compare the performance of four different damage measures based on the full spectral response of fiber Bragg grating (FBG) sensors: spectral bandwidth, number of peaks, cross-correlation coefficient and fractal dimension. These damage measures provide a rapid indication of the extent of damage near the FBG sensor. Each damage measure is applied to data simulating the response of a FBG to a pure strain gradient and experimental data from FBG sensors embedded in a laminate subjected to multiple impacts. The cross-correlation coefficient and number of peaks did not perform well for the experimental data. The spectral bandwidth presented a low sensitivity to noise and a high sensitivity to rapidly increasing strain fields, whereas the fractal dimension was more sensitive to more gradually changing strain fields. Ultimately, the best strategy would be to fuse the results of the spectral bandwidth and fractal dimension damage measures to incorporate the strengths of each approach. At the same time, this study highlighted the challenges in using such spectral data from FBG sensors embedded in structural materials, primarily due to the variability in response between sensors exposed to the same damage states.}, number={2}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Park, Chun and Peters, Kara}, year={2012}, month={Feb} }
 @article{hamouda_peters_seyam_2012, title={Effect of resin type on the signal integrity of an embedded perfluorinated polymer optical fiber}, volume={21}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84860708768&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/21/5/055023}, abstractNote={Polymer optical fibers (POF) hold many advantages for embedded sensing, such as their low cost, flexibility, high tensile strain limits and high fracture toughness. POF sensors may therefore be integrated into fiber reinforced composite structures for monitoring structural behavior. Since POFs do not require a protective coating, it is critical to verify that the resin system does not have a negative impact on the noise level or performance of POF sensors during composite manufacture. This study measured the effect of vinylester and epoxy resin systems on the signal loss of embedded perfluorinated, graded index POFs. Photon-counting optical time domain reflectometry (OTDR) was used to monitor the signal attenuation and backscattering level of the POFs throughout the resin curing cycle. Fourier transform infrared spectrometry (FTIR) and cross section analyses using scanning electronic microscope (SEM) images were also conducted to investigate whether the resin system caused chemical and physical changes of the POF. This study showed that vinylester resin caused a significant increase in the backscattering level of POF sensors and therefore induced high fiber signal losses. On the other hand, the POF treated with epoxy showed no change in backscattering level, indicating that no chemical or physical change had occurred to the POF.}, number={5}, journal={SMART MATERIALS AND STRUCTURES}, author={Hamouda, Tamer and Peters, Kara and Seyam, Abdel-Fattah M.}, year={2012}, month={May} }
 @article{webb_peters_zikry_chadderdon_nikola_selfridge_schultz_2012, title={Full-spectral interrogation of fiber Bragg grating sensors for measurements of damage during steady-state vibration}, volume={8346}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84901266148&partnerID=MN8TOARS}, DOI={10.1117/12.915150}, abstractNote={In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor subjected to a non-uniform static strain state and simultaneously exposed to vibration loading. The full spectral response of the sensor is interrogated in reflection at 100 kHz during two loading cases: with and without an added vibration load spectrum. The static tensile loading is increased between each test, in order to increase the magnitude of the non-uniform strain field applied to the FBG sensor. During steady-state vibration, the behavior of the spectral shape of the FBG reflection varies depending on the extent of non-uniform strain. With high-speed full spectral interrogation, it is potentially possible to separate this vibration-induced spectral change from spectral distortions due to non-uniform strain. Such spectral distortion contains valuable information on the static damage state of the surrounding host material.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS INTEGRATION 2012}, author={Webb, S. and Peters, K. and Zikry, M. A. and Chadderdon, S. and Nikola, S. and Selfridge, R. and Schultz, S.}, year={2012} }
 @article{peters_2012, title={Full-spectrum FBG analysis of inhomogeneous, fast-varying strain effects}, volume={8351}, ISSN={["1996-756X"]}, DOI={10.1117/12.916010}, abstractNote={Embedded sensors provide a high sensitivity to sub-surface damage due to their proximity to the damage features. In particular, fiber Bragg gratings (FBG) are easily embedded into laminates with a minimum of perturbation to the surrounding material microstructure. In this paper we summarize some recent advances derived from full-spectral interrogation of FBG sensors for structural health monitoring and damage identification in composites. In particular we present signals from the FBG reflected spectra that have been correlated to the progression of delamination due to multiple low-velocity impacts in woven composite laminates and foam-core sandwich composites. We also discuss recent advances in interrogation systems for these sensors which have permitted dynamic evaluation of these parameters. Finally, spectral distortion can lead to errors in the interpretation of strain values from the peak wavelength measurement when peak waveforms are assumed. We demonstrate that full-spectral interrogation can provide sensor specific error compensation for these measurements.}, journal={THIRD ASIA PACIFIC OPTICAL SENSORS CONFERENCE}, author={Peters, Kara}, year={2012} }
 @article{park_peters_2012, title={Optimization of Embedded Sensor Placement for Structural Health Monitoring of Composite Airframes}, volume={50}, ISSN={["0001-1452"]}, DOI={10.2514/1.j051729}, abstractNote={Thisstudy develops anoptimization methodspecifically for embeddedsensors forstructural health monitoring of a composite laminated aircraft structure. The chosen cost function is the component lifetime, balancing both the positive benefits of the condition-based monitoring enabled by the sensor information with the negative costs of the structural-performance degradation.Theoptical-fiberspacingisoptimized,ratherthantheplacement ofindividual sensors. Sensor interaction with damage and sensor-feature extraction are included into the optimization problem through experimentally derived probabilistic models. The resulting sensor-placement optimization has regions of decreasing laminate lifetime and regions of increasing laminate lifetime as a function of sensor spacing. A critical sensor spacing is also calculated, below which sensors are not recommended to be embedded.}, number={11}, journal={AIAA JOURNAL}, author={Park, Chun and Peters, Kara}, year={2012}, month={Nov}, pages={2536–2545} }
 @article{fugon_chen_peters_2012, title={Self-Healing Sandwich Composite Structures}, volume={8345}, ISSN={["0277-786X"]}, DOI={10.1117/12.915165}, abstractNote={Previous research demonstrated that a thin self-healing layer is effective in recovering partial sandwich composite performance after an impact event. Many studies have been conducted that show the possibility of using Fiber Bragg Grating (FBG) sensors to monitor the cure of a resin through strain and temperature monitoring. For this experiment, FBG sensors were used to monitor the curing process of a self-healing layer within a twelve-layer fiberglass laminate after impact. First, five self-healing sandwich composite specimens were manufactured. FBG sensors were embedded between the fiberglass and foam core. Then the fiberglass laminate was impacted with the use of a drop tower and the curing process was monitored. The collected data was used to compare the cure of the resin and fiberglass alone to the cure of the resin from a self-healing specimen. For the low viscosity resin system tested, these changes were not sufficiently large to identify different polymerization states in the resin as it cured. These results indicate that applying different resin systems might increase the efficiency of the self-healing in the sandwich composites.}, journal={SENSORS AND SMART STRUCTURES TECHNOLOGIES FOR CIVIL, MECHANICAL, AND AEROSPACE SYSTEMS 2012, PTS 1 AND 2}, author={Fugon, D. and Chen, C. and Peters, K.}, year={2012} }
 @article{song_peters_2012, title={Self-repairing waveguide sensor with highly repeatable strain response}, volume={8346}, ISSN={["1996-756X"]}, DOI={10.1117/12.914904}, abstractNote={In this article we present experimental demonstrations of a self-writing polymer waveguide strain sensor that can selfrepair after failure. The original sensor is fabricated between two multi-mode optical fibers by ultraviolet (UV) lightwaves in the photopolymerizable resin system via a self-writing process. After the original sensor fails, the repaired sensor is grown from the existing waveguide to bridge the gap between the two optical fibers. Multiple self-repairs of a single sensor were demonstrated. When the sensor was packaged within a polyimide capillary, the cyclic response showed almost no hysteresis and the response over the entire strain range was monotonic.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS INTEGRATION 2012}, author={Song, Young and Peters, Kara}, year={2012} }
 @article{song_peters_2012, title={Self-repairing, interferometric waveguide sensor with a large strain range}, volume={51}, ISSN={["2155-3165"]}, DOI={10.1364/ao.51.006886}, abstractNote={We demonstrate a polymer waveguide, Fabry-Perot interferometer strain sensor fabricated through a self-writing process in a photopolymerizable resin bath between two silica optical fibers. The measurable strain range is extended through sensor self-repair and strain measurements are demonstrated up to 150% applied tensile strain. The sensor fabrication and repair is performed in the ultraviolet wavelength range, while the sensor interrogation is performed in the near-infrared wavelength range. A hybrid sensor is fabricated by splicing a short segment of multimode optical fiber to the input single-mode optical fiber. The hybrid sensor provides the high quality of waveguide fabrication previously demonstrated through self-writing between multimode optical fibers with the high fringe visibility of single-mode propagation. The peak frequency shift of the reflected spectrum Fabry-Perot sensor is extremely linear with applied strain for the hybrid sensor, with a sensitivity of 2.3×10(-3) per nanometer per percent strain. The calibrated peak frequency shift with applied strain is the same for both the original sensor and the repaired sensor; therefore, the fact that the sensor has self-repaired does not need to be known. Additionally, this calibration is the same between multiple sensor fabrications. In contrast to a conventional air gap Fabry-Perot cavity sensor, no decrease in the fringe visibility is observed over the measurable strain range.}, number={28}, journal={APPLIED OPTICS}, author={Song, Young J. and Peters, Kara J.}, year={2012}, month={Oct}, pages={6886–6895} }
 @article{song_peters_2011, title={A self-repairing polymer waveguide sensor}, volume={20}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/20/6/065005}, abstractNote={This paper presents experimental demonstrations of a self-repairing strain sensor waveguide created by self-writing in a photopolymerizable resin system. The sensor is fabricated between two multi-mode optical fibers via lightwaves in the ultraviolet (UV) wavelength range and operates as a sensor through interrogation of the power transmitted through the waveguide in the infrared (IR) wavelength range. After failure of the sensor occurs due to loading, the waveguide re-bridges the gap between the two optical fibers through the UV resin. The response of the original sensor and the self-repaired sensor to strain are measured and show similar behaviors.}, number={6}, journal={SMART MATERIALS AND STRUCTURES}, author={Song, Young J. and Peters, Kara J.}, year={2011}, month={Jun} }
 @article{peters_2011, title={Analysis of fiber Bragg grating spectral features for in-situ assessment of Composites}, volume={7982}, ISSN={["1996-756X"]}, DOI={10.1117/12.881149}, abstractNote={Embedded sensors provide a high sensitivity to sub-surface damage due to their proximity to the damage features. In particular, fiber Bragg gratings (FBG) are easily embedded into laminates with a minimum of perturbation to the surrounding material microstructure. This paper summarizes some recent advances derived from full-spectral interrogation of FBG sensors for structural health monitoring and damage identification in composites. In particular we will present signals from the FBG reflected spectra that have been correlated to stress concentrations near crack tips, curing conditions during processing of composite laminates and the progression of delamination due to multiple low-velocity impacts in woven composite laminates and foam-core sandwich composites. Recent advances in interrogation systems for these sensors will also be discussed which have permitted dynamic evaluation of these parameters. Finally, spectral distortion can lead to errors in the interpretation of strain values from the peak wavelength measurement when peak waveforms are assumed. This distortion is highly dependent upon the local microstructure surrounding the sensor and therefore cannot be compensated a-priori through a calibration factor. This article demonstrates that full-spectral interrogation can provide sensor specific error compensation for these measurements. These results demonstrate the richness of information that can be obtained from full-spectral interrogation of FBG sensors in a complex, multiple stress component environment.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2011}, author={Peters, Kara}, year={2011} }
 @article{hackney_peters_2011, title={Damage Identification After Impact in Sandwich Composites Through Embedded Fiber Bragg Sensors}, volume={22}, ISSN={["1530-8138"]}, DOI={10.1177/1045389x11414220}, abstractNote={ Based on the full-spectral response of fiber Bragg grating sensors, embedded at the facesheet-core interface, we identify the progression of failure modes in foam core sandwich composites during multiple, low-velocity impacts. By considering the characteristic shape of the reflected spectrum from the FBG sensor in the post-impact, residual strain state, it is shown that we can classify the extent of damage into one of three states. Unlike the previous FBG peak wavelength measurements; this identification does not require the full strain history to identify the current state of damage in the composite. The disparate material properties between the facesheet and core materials, which create significant challenges for conventional non-destructive evaluation methods, enhance the damage detection through large deformations in the core at the impact location with sharp strain gradients. }, number={12}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Hackney, D. and Peters, K.}, year={2011}, month={Aug}, pages={1305–1316} }
 @article{webb_noevere_peters_zikry_vella_chadderdon_selfridge_schultz_2011, title={Full-spectral interrogation of fiber Bragg grating sensors for damage identification}, volume={7982}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79956068726&partnerID=MN8TOARS}, DOI={10.1117/12.881093}, abstractNote={In this study we evaluate the measurements of a fiber Bragg grating (FBG) sensor subjected to a non-uniform static strain state and simultaneously exposed to vibration loading. The full spectral response of the sensor is interrogated in reflection at 100 kHz during two loading cases: with and without an added vibration load spectrum. The static tensile loading is increased between each test, in order to increase the magnitude of the non-uniform strain field applied to the FBG sensor. The spectral distortion due to non-uniform strain is observed to change once the sensor is exposed to a non-transient 150 Hz vibration spectrum. With high-speed full spectral interrogation, it is potentially possible to separate this vibration-induced spectral change from spectral distortions due to non-uniform strain. Such spectral distortion contains valuable information on the static damage state of the surrounding host material.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2011}, author={Webb, S. and Noevere, A. and Peters, K. and Zikry, M. A. and Vella, T. and Chadderdon, S. and Selfridge, R. and Schultz, S.}, year={2011} }
 @misc{peters_2011, title={Polymer optical fiber sensors-a review}, volume={20}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/20/1/013002}, abstractNote={Polymer optical fibers (POFs) have significant advantages for many sensing applications, including high elastic strain limits, high fracture toughness, high flexibility in bending, high sensitivity to strain and potential negative thermo-optic coefficients. The recent emergence of single-mode POFs has enabled high precision, large deformation optical fiber sensors. This article describes recent advances in both multi-mode and single-mode POF based strain and temperature sensors. The mechanical and optical properties of POFs relevant to strain and temperature applications are first summarized. POFs considered include multi-mode POFs, solid core single-mode POFs and microstructured single-mode POFs. Practical methods for applying POF sensors, including connecting and embedding sensors in structural materials, are also described. Recent demonstrations of multi-mode POF sensors in structural applications based on new interrogation methods, including backscattering and time-of-flight measurements, are outlined. The phase–displacement relation of a single-mode POF undergoing large deformation is presented to build a fundamental understanding of the response of single-mode POF sensors. Finally, this article highlights recent single-mode POF based sensors based on polymer fiber Bragg gratings and microstructured POFs.}, number={1}, journal={SMART MATERIALS AND STRUCTURES}, author={Peters, Kara}, year={2011}, month={Jan} }
 @article{song_peters_2011, title={Self-repairing polymer optical fiber sensor}, volume={7753}, ISSN={["1996-756X"]}, DOI={10.1117/12.885147}, abstractNote={This article presents experimental demonstrations of a self-repairing strain sensor waveguide created by self-writing in a photopolymerizable resin system. The sensor fabricates between two multi-mode optical fibers via lightwaves in the ultraviolet (UV) wavelength range and operates as a sensor through interrogation of the power transmitted through the waveguide in the infrared (IR) wavelength range. After failure of the sensor occurs due to loading, the waveguide rebridges the gap between the two optical fibers through the UV resin. The response of the original sensor and the selfrepaired sensor to strain are measured and show similar behaviors.}, journal={21ST INTERNATIONAL CONFERENCE ON OPTICAL FIBER SENSORS}, author={Song, Young and Peters, Kara}, year={2011} }
 @article{abdi_peters_kowalsky_hassan_2011, title={Validation of a single-mode polymer optical fiber sensor and interrogator for large strain measurements}, volume={22}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/22/7/075207}, abstractNote={A single-mode polymer optical fiber (POF) in a Mach–Zehnder interferometer configuration is validated for the measurement of tensile nominal elongation of the POF up to 10%. The single-mode POF sensors were unmounted and surface mounted on aluminum tensile coupons for strain measurements. The measured strains from the POF sensors were compared to extensometer measurements for validation. The phase response of the interferometer was measured with a 3 × 3 coupler interrogator. The coupler arrangement was configured to permit the extraction of potential intensity changes in the sensor arm. The phase-shift–strain response of the POF sensors was repeatable for the loading and unloading measurements. The nonlinearity of the phase-shift–strain response was greater than that measured during pure tensile loading of the POF, presumably due to the behavior of the adhesive between the optical fiber and the aluminum coupons.}, number={7}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Abdi, Omid and Peters, Kara and Kowalsky, Mervyn and Hassan, Tasnim}, year={2011}, month={Jul} }
 @article{webb_peters_zikry_vella_chadderdon_selfridge_schultz_2011, title={Wavelength hopping due to spectral distortion in dynamic fiber Bragg grating sensor measurements}, volume={22}, ISSN={0957-0233 1361-6501}, url={http://dx.doi.org/10.1088/0957-0233/22/6/065301}, DOI={10.1088/0957-0233/22/6/065301}, abstractNote={We demonstrate the measurement of wavelength hopping in dynamic fiber Bragg grating (FBG) sensor measurements and its effect on the interpretation of the dynamic behavior of a composite laminate. Strain measurements are performed with FBG sensors embedded in laminates, subjected to low-velocity impacts, with data acquired using a commercial peak wavelength following controller and a high-speed full-spectral interrogator recently developed by the authors. The peak follower response is theoretically predicted from the full-spectral interrogator measurements. We demonstrate that dynamic wavelength hopping does occur, that it changes the apparent dynamic behavior of the composite and that it can be directly predicted from the dynamic spectral distortion. We also demonstrate that full-spectral data acquisition at speeds lower than those required to fully resolve the dynamic event creates apparent measurement errors due to wavelength hopping as well.}, number={6}, journal={Measurement Science and Technology}, publisher={IOP Publishing}, author={Webb, S and Peters, K and Zikry, M and Vella, T and Chadderdon, S and Selfridge, R and Schultz, S}, year={2011}, month={May}, pages={065301} }
 @inproceedings{hackney_webb_peters_2010, title={Analysis of fiber Bragg grating spectral features for in-situ assessment of sandwich composites}, DOI={10.1115/smasis2010-3886}, abstractNote={In this paper we summarize recent advances derived from full-spectral interrogation of FBG sensors for structural health monitoring and damage identification in composites. Previous work has correlated signals from FBG reflected spectra to stress concentrations near crack tips, curing conditions during processing of composite laminates and the progression of delamination due to multiple low-velocity impacts in woven composite laminates. In this paper we investigate the information gained from FBG sensors embedded at the facesheet-core interface in foam-core sandwich composites subjected to low-velocity impact loading. We also discuss recent advances in interrogation systems for these sensors which will permit dynamic evaluation of these parameters. These results demonstrate the richness of information that can be obtained from full-spectral interrogation of FBG sensors in a complex, multiple stress component environment.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol 2}, author={Hackney, D. and Webb, S. and Peters, Kara}, year={2010}, pages={813–820} }
 @article{propst_peters_zikry_schultz_kunzler_zhu_wirthlin_selfridge_2010, title={Assessment of damage in composite laminates through dynamic, full-spectral interrogation of fiber Bragg grating sensors}, volume={19}, ISSN={["0964-1726"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-74849118513&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/19/1/015016}, abstractNote={In this study, we demonstrate the full-spectral interrogation of a fiber Bragg grating (FBG) sensor at 535 Hz. The sensor is embedded in a woven, graphite fiber–epoxy composite laminate subjected to multiple low-velocity impacts. The measurement of unique, time dependent spectral features from the FBG sensor permits classification of the laminate lifetime into five regimes. These damage regimes compare well with previous analysis of the same material system using combined global and local FBG sensor information. Observed transient spectral features include peak splitting, wide spectral broadening and a strong single peak at the end of the impact event. Such features could not be measured through peak wavelength interrogation of the FBG sensor. Cross-correlation of the measured spectra with the original embedded FBG spectrum permitted rapid visualization of average strains and the presence of transverse compressive strain on the optical fiber, but smeared out the details of the spectral profile.}, number={1}, journal={SMART MATERIALS AND STRUCTURES}, author={Propst, A. and Peters, K. and Zikry, M. A. and Schultz, S. and Kunzler, W. and Zhu, Z. and Wirthlin, M. and Selfridge, R.}, year={2010}, month={Jan} }
 @article{hackney_peters_2010, title={Embedded fiber Bragg sensors for damage identification in sandwich composites after impact}, volume={7648}, ISSN={["1996-756X"]}, DOI={10.1117/12.848351}, abstractNote={The use and viability of fiber Bragg grating sensors in sandwich composite structures for the purpose of structural health monitoring under low velocity impact. Initially, a group of twelve specimens were tested to characterize the impact response of sandwich composite structures. Each specimen test consisted of repeated impacts at a constant impact energy to measure and observe damage progression. Once this was completed, a single optical fiber with a fiber Bragg grating was embedded in the structure between the core and the faceplate to and measured using a laser. The shift and deformation of the reflected spectrum from the fiber Bragg grating sensor resulting from each strike was analyzed and the corresponding strain was measured. The peak wavelength shift measurements did not have a strong correlation to the accumulation of damage in the sandwich laminate. However, the spectral distortion did evolve throughout the initial accumulation of damage in the laminate. Further analysis of the spectrum is needed to correlate the spectral response to the damage modes.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2010}, author={Hackney, Drew A. and Peters, Kara J.}, year={2010} }
 @article{vella_chadderdon_selfridge_schultz_webb_park_peters_zikry_2010, title={Full-spectrum interrogation of fiber Bragg gratings at 100 kHz for detection of impact loading}, volume={21}, ISSN={["1361-6501"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77958167493&partnerID=MN8TOARS}, DOI={10.1088/0957-0233/21/9/094009}, abstractNote={This paper explains key innovations that allow monitoring of detailed spectral features of an FBG in response to impact loading. The new system demonstrates capture of FBG spectral data at rates of 100 kHz. Rapid capture of the entire reflection spectrum at such high reading rates shows important features that are missed when using systems that merely track changes in the peak location of the spectrum. The update rate of 100 kHz allows resolution of features that occur on transient time scales as short as 10 µs. This paper gives a detailed description of the unique features of the apparatus and processes used to capture the data at such a rapid rate. Furthermore, we demonstrate this interrogation scheme on a composite laminate system during impact.}, number={9}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Vella, T. and Chadderdon, S. and Selfridge, R. and Schultz, S. and Webb, S. and Park, C. and Peters, K. and Zikry, M.}, year={2010}, month={Sep} }
 @article{jiang_dawood_peters_rizkalla_2010, title={Global and Local Fiber Optic Sensors for Health Monitoring of Civil Engineering Infrastructure Retrofit with FRP Materials}, volume={9}, ISSN={["1741-3168"]}, DOI={10.1177/1475921709352989}, abstractNote={ Fiber-reinforced polymer (FRP) materials are currently used for strengthening civil engineering structures and bridges. The effectiveness of the strengthening system is highly dependent on the bond characteristics of the FRP material to the external surface of the structure. This article presents the application of two types of fiber optic sensors, which can be embedded in FRP materials to monitor the global and local behavior of the strengthened structure, respectively. The global sensor is designed to evaluate the overall condition of a structure based on the measured elongation of the FRP layer along the entire span of the structure. The success of this low-cost global sensor has been demonstrated using a full-scale prestressed concrete bridge girder that was loaded up to failure. The test results indicate that this type of sensor can be used to identify major changes in the overall behavior of the structure such as cracking of prestressed members or yielding of the internal reinforcement. The second sensor component consists of fiber Bragg grating sensors. The sensors were used to monitor the behavior of steel double-lap shear specimens tested under tensile loading up to failure. The measurements were used to identify abnormal structural behaviors such as epoxy cracking and/or FRP debonding. The test results compared well to the numerical values obtained from a three dimensional shear-lag model that was previously developed to predict the sensor response. }, number={4}, journal={STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL}, author={Jiang, Guoliang and Dawood, Mina and Peters, Kara and Rizkalla, Sami}, year={2010}, month={Jul}, pages={309–322} }
 @article{webb_peters_zikry_vella_chadderdon_selfridge_schultz_2010, title={Impact induced damage assessment in composite laminates through embedded fiber Bragg gratings}, volume={7648}, ISSN={["1996-756X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77953525959&partnerID=MN8TOARS}, DOI={10.1117/12.847543}, abstractNote={In this study we evaluate the measurements of fiber Bragg sensor spectra from a sensor embedded in a composite laminate subjected to multiple low velocity impacts. The full-spectral response of the sensor is interrogated in reflection at 100 kHz during the impact events. The measurement of the time dependent spectra features are compared with previous results obtained at a 534 Hz interrogation rate. With the increased interrogation rate, we can observe a smooth transition in the full-spectra response of the sensor between strikes and the presence of peak-splitting due to transverse compression from the beginning of the laminate lifetime. Finally, at the 100 kHz acquisition rate, it is possible to determine the maximum wavelength and accurately determine the duration of the impact event for all of the strikes.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2010}, author={Webb, S. and Peters, K. and Zikry, M. A. and Vella, T. and Chadderdon, S. and Selfridge, R. and Schultz, S.}, year={2010} }
 @article{park_peters_zikry_haber_schultz_selfridge_2010, title={Peak wavelength interrogation of fiber Bragg grating sensors during impact events}, volume={19}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77949894501&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/19/4/045015}, abstractNote={In this paper, we embed fiber Bragg grating (FBG) sensors in graphite fiber–epoxy woven composite laminates to detect evolving damage modes. The peak wavelengths of the FBG sensors are interrogated at 625 and 295 kHz, while the laminates are subjected to 11.0 J low-velocity impact events. It is demonstrated that 295 kHz interrogation is sufficient for accurately collecting the dynamic response of the sensors. The FBG sensors embedded at the laminate midplanes successfully reconstructed the global laminate response to impact. The maximum and full width at half-maximum (FWHM) for the relative strain histories demonstrated the same trends as the maximum and FWHM of the contact force histories measured from the impactor. More noise was present in the strain histories obtained from the FBG sensors than the contact force histories, as the embedded FBGs were sensitive to local perturbations in the stress state. The FBG sensors embedded below the midplane of the laminate were closer to the damage regions and measured complex strain histories. In one case, this strain history revealed the presence of delamination.}, number={4}, journal={SMART MATERIALS AND STRUCTURES}, author={Park, Chun and Peters, Kara and Zikry, Mohammed and Haber, Todd and Schultz, Stephen and Selfridge, Richard}, year={2010}, month={Apr} }
 @article{joshi_peters_2010, title={SMASIS Symposium on Structural Health Monitoring Preface}, volume={21}, ISSN={["1045-389X"]}, DOI={10.1177/1045389x09359109}, abstractNote={This special issue presents a selection of papers presented at the first ASME Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 2008) Symposium on Structural Health Monitoring held at the Turf Valley Resort in Ellicott City, MD on October 28 30, 2008. The ability to diagnose and predict structural failures in complex structural and material systems through embedded sensing, actuation, and data management can reduce operating costs while increasing safety. The key commercialization drivers for the technology are life-cycle cost, avoidance of catastrophic failure, and inspection of difficult-to-access locations. As of now, aerospace, ground, and sea vehicles are primarily driving the development of the technology. Continuous or on-demand inspection of bridges, buildings, off-shore structures, and oil drilling machinery are also among the first non-aerospace applications. This symposium focused on the system level hurdles including algorithms, sensor networks, data management, and experimental demonstrations of structural health monitoring or nondestructive evaluation for structural systems. Additionally, the optimization of sensor locations and energy harvesting for powering of structural health monitoring systems were also addressed. The symposium included 38 technical publications, of which 14 were selected for publication in this special issue. These papers were selected based on peer review and referee recommendations. The guest editors would like to thank both the authors who submitted extended papers for publication in this special issue as well as the numerous reviewers who dedicated their time to evaluating the manuscripts. We would also like to gratefully acknowledge the support of ASME, the Conference General Chair, Chris Lynch, and the Conference Technical Chair, Diann Brei, for all of their help in organizing the symposium. Finally, we also express our gratitude to the Journal Editors, Dr Daniel Inman and Dr Norman Wereley for providing the opportunity for this publication and for their collaboration in the preparation of this special issue.}, number={3}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Joshi, Shiv and Peters, Kara}, year={2010}, month={Feb}, pages={223–223} }
 @article{song_peters_2010, title={Self-repairing polymer optical fiber sensor}, volume={7648}, ISSN={["1996-756X"]}, DOI={10.1117/12.847631}, abstractNote={This article presents experimental demonstrations of a self-writing waveguide in a photopolymerizable resin system. The waveguide will be embedded in a structure and serve as a self-repairing strain sensor. The sensor would fabricate via lightwaves in the ultraviolet (UV) wavelength range and operate as a sensor in the infrared (IR) wavelength range. Optimized self-written waveguides are obtained by varying the input UV laser power and testing the repeatability of the waveguide fabrication between two optical fibers. An IR laser output is then transmitted between two MM fibers during the fabrication process to quantify the response of the self-repaired optical sensor by measuring the transmitted IR power. The IR power is successfully transmitted through a self-written waveguide; however problems with optical fiber alignment and bending of the waveguide can induce loss of IR transmission.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2010}, author={Song, Young J. and Peters, Kara J.}, year={2010} }
 @article{park_peters_zikry_2010, title={The Effects of Embedded Optical Fiber Density on the Impact Response and Lifetime of Laminated Composites}, volume={21}, ISSN={["1530-8138"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78650907528&partnerID=MN8TOARS}, DOI={10.1177/1045389x10390250}, abstractNote={ Graphite fiber/epoxy, two-dimensional woven composite laminates were fabricated with various densities of embedded optical fibers at the midplane. The specimens were subjected to multiple low-velocity impacts until failure, as the energy dissipated by the laminate and the maximum contact force were measured for each impact event. Cumulative probability distributions were calculated for each embedded optical fiber density, from which probability distribution functions in terms of embedded optical fiber density were extrapolated. At low fiber densities, the total energy dissipated by the specimen and the total maximum contact force over the lifetime of the specimen decreased rapidly with increasing optical fiber density. After a threshold embedded optical fiber density, the optical fibers dominated the failure mode of the laminate and the laminate lifetime, and the overall stiffness was not affected by the embedded optical fiber density. The obtained probability distribution functions could be applied for future optimization of embedded sensor placement for smart composite structures. }, number={18}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Park, Chun and Peters, Kara and Zikry, Mohammed}, year={2010}, month={Dec}, pages={1819–1829} }
 @article{park_peters_zikry_2010, title={The Role of Embedded Sensors in Damage Assessment of Composite Laminates}, volume={7648}, ISSN={["0277-786X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77953489216&partnerID=MN8TOARS}, DOI={10.1117/12.847634}, abstractNote={Various densities of optical fibers are embedded into a total of eighty woven, graphite fiber-epoxy composite laminates, for which the response to low velocity impacts are evaluated. The goal of this work is to determine the role of hostsensor interaction on the lifetime of the host material system. The woven composites are subjected to multiple impacts at 14.5 J until perforation of the specimen. We obtain the energy dissipated by the laminate and the maximum contact force between the impactor laminate for each strike. From these experimental data we calculate the statistical distribution of the total energy dissipated at failure as a function of embedded optical fiber density. The total dissipated energy, a measure of the specimen lifetime, decreased with increasing embedded optical fiber density, however remained constant after a threshold density was reached. The total maximum contact force per specimen, a measure of the specimen stiffness, continued to decrease with the number of embedded optical fibers.}, journal={SMART SENSOR PHENOMENA, TECHNOLOGY, NETWORKS, AND SYSTEMS 2010}, author={Park, Chun and Peters, Kara and Zikry, Mohammed}, year={2010} }
 @article{pawar_peters_2010, title={Transient infrared thermography for damage evaluation in aerospace composites}, volume={7649}, ISSN={["0277-786X"]}, DOI={10.1117/12.847789}, abstractNote={In this paper we investigate the performance of defect detection using long duration transient thermography for woven composite laminates subjected to low-velocity impacts. Two types of defects are studied: inclusions represented by foam tabs inserted into the laminate during fabrication and barely visible impact damage due to low-velocity impacts. These defects represent the expected damage states that are necessary for inspection during the service life of a woven composite aircraft component. The long duration transient thermography is demonstrated to successfully detect the embedded inclusions, with a dimension to depth ratio detection capability of approximately 3. It is also demonstrated that the detection of low velocity impact damage with the transient thermography is less successful due to uneven emissivity of the surface. Therefore, processing of the image using a self referencing algorithm is performed which improves the damage detection clarity.}, journal={NONDESTRUCTIVE CHARACTERIZATION FOR COMPOSITE MATERIALS, AEROSPACE ENGINEERING, CIVIL INFRASTRUCTURE, AND HOMELAND SECURITY 2010}, author={Pawar, S. and Peters, K.}, year={2010} }
 @article{kiesel_peters_hassan_kowalsky_2009, title={Calibration of a single-mode polymer optical fiber large-strain sensor}, volume={20}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/20/3/034016}, abstractNote={We calibrate the phase shift as a function of applied displacement in a polymethylmethacrylate (PMMA) single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm. The phase sensitivity is measured up to 15.8% nominal strain in the fiber. The measured phase–displacement response is compared to a previous analytical formulation for the large deformation response of the polymer optical fiber strain sensor. The formulation includes both the finite deformation of the optical fiber and nonlinear strain-optic effects at large deformations. Using previously measured values for the linear and nonlinear mechanical response of the fiber, the nonlinear strain-optic effects are calibrated from the current experimental data. This calibration demonstrates that the nonlinearities in the strain-optic effect are of the same order of magnitude as those in the mechanical response of the PMMA optical fiber sensor.}, number={3}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2009}, month={Mar} }
 @article{abdi_wong_hassan_peters_kowalsky_2009, title={Cleaving of solid single mode polymer optical fiber for strain sensor applications}, volume={282}, ISSN={["1873-0310"]}, DOI={10.1016/j.optcom.2008.11.046}, abstractNote={Abstract Single mode polymer optical fibers (smPOFs) can be applied for measuring large strains in numerous applications, such as civil engineering infrastructure assessment and health monitoring. Because of the large light attenuation of solid smPOFs, small lengths of the fiber would need to be coupled to silica optical fibers (SOFs) for practical applications of the smPOF as a strain sensor. This coupling requires smooth cleaving of the smPOFs. In this work, several cleaving techniques previously demonstrated to provide smooth cross-sections of multimode POFs were applied to the smPOF. From these techniques, hot-knife cutting was determined to be a feasible method for cleaving when the blade was heated to 80 °C and the smPOF heated in the range of 30 °C to 40 °C. In addition, focused ion beam machining which produces high-precision cleaves of the solid smPOF cross-section, was performed to set a bench mark and thus evaluate the quality of cleaving from other methods used in this study.}, number={5}, journal={OPTICS COMMUNICATIONS}, author={Abdi, O. and Wong, K. C. and Hassan, T. and Peters, K. J. and Kowalsky, M. J.}, year={2009}, month={Mar}, pages={856–861} }
 @article{anderson_peters_2009, title={Finite Element Simulation of Self-Writing Waveguide Formation Through Photopolymerization}, volume={27}, ISSN={["0733-8724"]}, DOI={10.1109/JLT.2009.2031823}, abstractNote={This article presents the simulation of the dynamics of the self-writing waveguide phenomenon in photopolymerizable resin systems using the finite element method. The rate equation of the photopolymerization process, mechanical shrinkage in the resin and lightwave propagation through the waveguide are included in the finite element model. An emphasis is placed on the simulation of processes occuring at multiple time scales and the introduction of mechanical shrinkage through an equivalent body force. Simulation results predict the features of self-writing previously observed including nonuniformities in the final polymerized waveguide.}, number={24}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Anderson, Aliesha and Peters, Kara}, year={2009}, month={Dec}, pages={5529–5536} }
 @article{schultz_kunzler_zhu_wirthlin_selfridge_propst_zikry_peters_2009, title={Full-spectrum interrogation of fiber Bragg grating sensors for dynamic measurements in composite laminates}, volume={18}, ISSN={["1361-665X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-70350668824&partnerID=MN8TOARS}, DOI={10.1088/0964-1726/18/11/115015}, abstractNote={This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop-tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict the remaining lifetime in composite laminate structures.}, number={11}, journal={SMART MATERIALS AND STRUCTURES}, author={Schultz, S. and Kunzler, W. and Zhu, Z. and Wirthlin, M. and Selfridge, R. and Propst, A. and Zikry, M. and Peters, K.}, year={2009}, month={Nov} }
 @article{garrett_peters_zikry_2009, title={In-situ impact-induced damage assessment of woven composite laminates through a fibre Bragg grating sensor network}, volume={113}, ISSN={["0001-9240"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-68349093775&partnerID=MN8TOARS}, DOI={10.1017/S0001924000003031}, abstractNote={Abstract}, number={1144}, journal={AERONAUTICAL JOURNAL}, author={Garrett, R. C. and Peters, K. J. and Zikry, M. A.}, year={2009}, month={Jun}, pages={357–370} }
 @inproceedings{propst_garrett_park_peters_zikry_2009, title={Sensor networks for in-situ failure identification in woven composites}, volume={7293}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-66749128673&partnerID=MN8TOARS}, DOI={10.1117/12.815743}, abstractNote={This paper presents experimental measurements of the response of woven composite laminates to multiple low-velocity impacts. Damage initiation and progression occur at multiple physical and temporal scales in heterogeneous materials, including fiber breakage, matrix cracking, delamination and matrix relaxation. The sensor/interrogators were therefore chosen specifically to provide insight into the order and progression of different failure modes. Measurements of the contact force between the impactor and composite are measured throughout impact. Additionally, the dissipated energy per impact event is also calculated from the impactor velocity. Surface mounted and embedded fiber Bragg grating sensors are used for the measurement of the laminate response. Peak wavelength measurements are performed during impact at 1 kHz, while full-spectral scanning is performed at 5 Hz during relaxation period of the laminate immediately after impact and quasi-statically to measure post-impact residual strain states within the laminate. The results highlight the depth of information embedded within the FBG full-spectral data sensors, as well as the added insight to be gained from combined global-local measurements.}, booktitle={SMASIS 2009, vol 2}, author={Propst, A. and Garrett, R. and Park, C. and Peters, K. and Zikry, M.}, year={2009}, pages={477–485} }
 @article{jiang_peters_2008, title={A shear-lag model for three-dimensional, unidirectional multilayered structures}, volume={45}, ISSN={["0020-7683"]}, DOI={10.1016/j.ijsolstr.2008.02.018}, abstractNote={A shear-lag model is derived for unidirectional multilayered structures whose constituents vary throughout the cross-section through the extension of an existing optimal shear-lag model suitable for two-dimensional planar structures. Solution algorithms for a variety of boundary conditions are discussed. Numerical predictions for a single-fiber composite and a unidirectional laminated composite are presented. Comparison of the predicted interfacial shear stresses and average normal stresses to finite element analysis demonstrates that this shear-lag model can be used to rapidly estimate the average normal stress distribution in the various constituents, although the interfacial shear stresses are less accurate. Possible applications and limitations of the new model are finally discussed.}, number={14-15}, journal={INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES}, author={Jiang, Guoliang and Peters, Kara}, year={2008}, month={Jul}, pages={4049–4067} }
 @article{kiesel_peters_hassan_kowalsky_2008, title={Large deformation in-fiber polymer optical fiber sensor}, volume={20}, ISSN={["1941-0174"]}, DOI={10.1109/LPT.2008.916929}, abstractNote={We demonstrate the measurement of the phase shift in a polymethylmethacrylate single-mode optical fiber interferometer, operating at a wavelength of 632.8 nm, up to 15.8% nominal strain in the fiber. The phase-displacement sensitivity is measured to be 1.39 x10 radldrm-1 for this strain range. This strain range is well beyond the yield strain of the polymer fiber and that previously measured for polymer Bragg gratings and silica optical fiber sensors.}, number={5-8}, journal={IEEE PHOTONICS TECHNOLOGY LETTERS}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2008}, pages={416–418} }
 @article{kiesel_peters_hassan_kowalsky_2007, title={Behaviour of intrinsic polymer optical fibre sensor for large-strain applications}, volume={18}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/18/10/S16}, abstractNote={This paper derives the phase response of a single-mode polymer optical fibre for large-strain applications. The role of the finite deformation of the optical fibre and nonlinear strain optic effects are derived using a second order strain assumption and shown to be important at strain magnitudes as small as 1%. In addition, the role of the core radius change on the propagation constant is derived, but it is shown to be negligible as compared to the previous effects. It is shown that four mechanical and six opto-mechanical parameters must be calibrated to apply the sensor under arbitrary axial and transverse loading. The mechanical nonlinearity of a typical single-mode polymer optical fibre is experimentally measured in axial tension and is shown to be more significant than that of their silica counterpart. The mechanical parameters of the single-mode polymer optical fibre are also measured for a variety of strain rates, from which it is demonstrated that the strain rate has a strong influence on yield stress and strain. The calibrated constants themselves are less affected by strain rate.}, number={10}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Kiesel, Sharon and Peters, Kara and Hassan, Tasnim and Kowalsky, Mervyn}, year={2007}, month={Oct}, pages={3144–3154} }
 @article{prabhugoud_peters_2007, title={Finite element analysis of multi-axis strain sensitivities of Bragg gratings in PM fibers}, volume={18}, ISSN={["1045-389X"]}, DOI={10.1177/1045389X06074680}, abstractNote={ This article presents a numerical analysis of the sensitivity of fiber Bragg grating (FBG) sensors written into polarization maintaining fibers to transverse and thermal loading. These sensors are typically applied for the measurement of multiple strain components for the monitoring of civil structures. The finite element analysis includes both the optical and mechanical variations in the optical fiber. Five fiber types typically used in FBG sensors (elliptical core, D-fiber, elliptical core SAP, Bow-Tie, and Panda) are compared. It is shown that when only the fiber geometry is considered while the material parameters are approximately the same, the D-fiber demonstrates the highest sensitivity to transverse loading. In addition, it is shown that reducing the fiber cladding diameter significantly improves the sensitivities of the FBG sensor to transverse loads. All fiber types exhibit approximately the same sensitivity to thermal loading. }, number={8}, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Prabhugoud, Mohanraj and Peters, Kara}, year={2007}, month={Aug}, pages={861–873} }
 @article{pearson_zikry_prabhugoud_peters_2007, title={Global-local assessment of low-velocity impact damage in woven composites}, volume={41}, ISSN={["1530-793X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-35448962064&partnerID=MN8TOARS}, DOI={10.1177/0021998307078734}, abstractNote={ Global measurements from low-velocity impact experiments and local strain measurements from embedded and surface mounted optical fiber Bragg grating (FBG) sensors were used to obtain failure maps for two- and three dimensional woven composites. These maps delineated five distinct regimes spanning behavior from initial impact to complete penetration. Sensor and host damage were separated by signal intensity and the evolution of Bragg peaks due to repeated impact loads. The results indicate that a local-global framework can be used to monitor damage progression in different host materials, and hence it can be potentially used to mitigate damage. }, number={23}, journal={JOURNAL OF COMPOSITE MATERIALS}, author={Pearson, J. D. and Zikry, M. A. and Prabhugoud, M. and Peters, K.}, year={2007}, month={Dec}, pages={2759–2783} }
 @article{prabhugoud_peters_pearson_zikry_2007, title={Independent measurement of strain and sensor failure features in Bragg grating sensors through multiple mode coupling}, volume={135}, ISSN={["0924-4247"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34047170478&partnerID=MN8TOARS}, DOI={10.1016/j.sna.2006.08.021}, abstractNote={This article presents the interrelated measurements of Bragg reflection, cladding and radiation modes to obtain the applied strain and integrity of a short period Bragg grating sensor. While the Bragg reflection is known to be sensitive to applied strain, the relative strength of the cladding and radiation mode coupling is shown to be sensitive to damage such as debonding from the host structure. Furthermore, the length of the Bragg grating debonded from the surrounding medium is quantitatively related to the coupling to continuum radiation modes from the core mode. While the sensitivity of the radiation mode coupling to microcracking in the optical fiber is shown to be relatively low, maximum intensity measurements provide sufficient information on local fractures of the optical fiber. These results provide intelligent self-diagnostic capabilities within the Bragg grating sensor without additional measurements, and also permit the separate identification of sensor failure from the failure of the host structure.}, number={2}, journal={SENSORS AND ACTUATORS A-PHYSICAL}, author={Prabhugoud, Mohanraj and Peters, Kara and Pearson, James and Zikry, Mohammed A.}, year={2007}, month={Apr}, pages={433–442} }
 @article{pearson_zikry_prabhugoud_peters_2007, title={Measurement of low velocity and quasi-static failure modes in PMMA}, volume={28}, ISSN={["0272-8397"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34250820545&partnerID=MN8TOARS}, DOI={10.1002/pc.20287}, abstractNote={Abstract}, number={3}, journal={POLYMER COMPOSITES}, author={Pearson, J. D. and Zikry, M. A. and Prabhugoud, M. and Peters, K.}, year={2007}, month={Jun}, pages={381–391} }
 @article{jiang_van vickle_peters_knight_2007, title={Oscillator interrogated time-of-flight optical fiber interferometer for global strain measurements}, volume={135}, ISSN={["0924-4247"]}, DOI={10.1016/j.sna.2006.08.023}, abstractNote={In this paper, we demonstrate an oscillator interrogated time-of-flight optical fiber interferometer that provides global strain information for large-scale structures. The sensing resolution of the interferometer is sufficient for many structural applications, while the system is relatively inexpensive and durable as compared to previous methods. The measurable displacement range is determined by the oscillator frequency and can therefore be designed to be significantly larger than that of current systems. An optical length change resolution of 9.5 mm and range of 1.39 m are demonstrated experimentally. To easily embed the interferometer in structures and effectively increase the fiber sensing length, a commercially available prefabricated fiber ribbon is used. Results from static loading tests of a FRP strengthened reinforced concrete beam with embedded fiber ribbons show the feasibility of this technique for monitoring infrastructure systems.}, number={2}, journal={SENSORS AND ACTUATORS A-PHYSICAL}, author={Jiang, Guoliang and Van Vickle, Patrick and Peters, Kara and Knight, Victor}, year={2007}, month={Apr}, pages={443–450} }
 @book{sensor systems and networks: phenomena, technology and applications for nde and health monitoring 2007_2007, ISBN={9780819466518}, publisher={Bellingham, Wash.: SPIE}, year={2007} }
 @article{prabhugoud_peters_2006, title={Finite element model for embedded fiber Bragg grating sensor}, volume={15}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/15/2/038}, abstractNote={This paper presents an integrated formulation for the calculation of the spectral response of a fiber Bragg grating sensor embedded in a host material system, as a function of the loading applied to the host structure. In particular, the calculation of the transverse strain sensitivity of a fiber Bragg grating sensor through the calculation of the change in effective index (or indices) of refraction of the fiber cross-section due to the applied load is presented in detail. For the calculation of the fiber propagation constants, a two-step finite element formulation is used incorporating the optical, geometric and material properties of the cross-section. Once the propagation constants and principal optical axes are known along the fiber, a modified transfer matrix method is applied to calculate the spectral response of the FBG. It is shown that the FE formulation yields close agreement with previous methods for benchmark diametrical compression cases. However, the current method provides the potential to evaluate the effects of high strain gradients across the optical fiber core present in some loading applications.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Prabhugoud, M and Peters, K}, year={2006}, month={Apr}, pages={550–562} }
 @book{inaudi_ecke_culshaw_peters_udd_2006, title={Smart structures and materials 2006: Smart sensor monitoring systems and applications (SPIE; 6167)}, ISBN={0819462209}, publisher={Bellingham, Wash.: SPIE}, author={Inaudi, D. and Ecke, W. and Culshaw, B. and Peters, K. J. and Udd, E.}, year={2006} }
 @inbook{prabhugoud_peters_2005, title={Birefringence and Transverse Strain Sensitivity in Bragg Grating Sensors}, ISBN={1402036604}, url={http://dx.doi.org/10.1007/1-4020-3661-2_43}, DOI={10.1007/1-4020-3661-2_43}, booktitle={Sensing Issues in Civil Structural Health Monitoring}, publisher={Springer-Verlag}, author={Prabhugoud, Mohanraj and Peters, Kara}, year={2005}, month={Nov}, pages={433–442} }
 @article{gill_peters_studer_2004, title={Genetic algorithm for the reconstruction of Bragg grating sensor strain profiles}, volume={15}, ISSN={["1361-6501"]}, DOI={10.1088/0957-0233/15/9/027}, abstractNote={This paper presents a genetic algorithm for the interrogation of optical fibre Bragg grating strain sensors. The method encodes the axial strain distribution along the Bragg grating, here represented through the local period distribution, into a gene. To facilitate rapid calculation of the grating reflected intensity spectrum, the transfer-matrix approach is applied. The genetic algorithm inversion method presented requires only intensity information from the sensor and reconstructs non-linear and discontinuous distributions well, including regions with significant gradients. The development of this algorithm will permit the use of Bragg grating sensors for structural damage identification, allowing them to be located in regions where strong strain non-uniformities occur.}, number={9}, journal={MEASUREMENT SCIENCE AND TECHNOLOGY}, author={Gill, A and Peters, K and Studer, M}, year={2004}, month={Sep}, pages={1877–1884} }
 @article{prabhugoud_peters_2004, title={Modified transfer matrix formulation for Bragg grating strain sensors}, volume={22}, ISSN={["1558-2213"]}, DOI={10.1109/JLT.2004.833281}, abstractNote={This paper presents a formulation for the application of the transfer matrix method to Bragg grating strain sensors. A modified T-matrix representation is detailed for the sensor problem based on an effective period derived from the coupling coefficients. This modified T-matrix formulation is shown to converge to the coupled-mode equations solution for a large number of grating segments, even in the presence of significant strain gradients. Several numerical examples are presented to demonstrate the importance of inclusion of the strain gradient in the calculation. In addition, the current formulation is validated by application to previously published experimental data.}, number={10}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Prabhugoud, M and Peters, K}, year={2004}, month={Oct}, pages={2302–2309} }
 @article{studer_peters_2004, title={Multi-scale sensing for damage identification}, volume={13}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/13/2/006}, abstractNote={Damage identification is important for the lifetime prediction of any structure. In a composite structure, damage can occur at several material scales from micro-cracking to global buckling or delamination. This makes the identification of damage difficult with a single sensing device. In this paper, we propose to monitor a structural volume with an embedded optical fiber sensor network measuring strain, integrated strain, and strain gradients. Two methods are also compared for data fusion of the multi-scale data in order to determine damage parameters. The first calculates strain maps directly from the data; the second method uses a neural network. As an example, an isotropic, homogeneous structural volume with a localized crack is modeled. The results demonstrate that (a) the multi-scale sensing approach improves damage identification and (b) the neural network is a method well adapted for the multi-scale data fusion and significantly improves the damage identification capability.}, number={2}, journal={SMART MATERIALS AND STRUCTURES}, author={Studer, M and Peters, K}, year={2004}, month={Apr}, pages={283–294} }
 @article{prabhugoud_peters_2003, title={Efficient simulation of Bragg grating sensors for implementation to damage identification in composites}, volume={12}, ISSN={["1361-665X"]}, DOI={10.1088/0964-1726/12/6/008}, abstractNote={A computationally efficient method is proposed to interpret optical fiber sensor data collected from Bragg grating sensors embedded in composites. The method divides the composite into remote field and critical field regions with respect to any developed damage. These regions are defined via non-uniformities in the sensor response. The remote field response is treated via an optimal shear-lag theory first presented by Mendels and Nairn. This formulation provides a rapid solution of the average fiber axial stress at the location of each sensor. The critical field region is modeled via a finite element sensor model including the effects of multi-axis loading on the sensor and an optical loss due to local fiber curvature. The response of the Bragg grating sensor to the effects of axial, bending and shear loading are simulated for inclusion in the model. The bending loss response as a function of fiber curvature is experimentally measured. The application of this method is demonstrated through a numerical example, simulating the response of sensors embedded in a lamina to the presence of a transverse crack.}, number={6}, journal={SMART MATERIALS AND STRUCTURES}, author={Prabhugoud, M and Peters, K}, year={2003}, month={Dec}, pages={914–924} }
 @article{studer_peters_botsis_2003, title={Method for determination of crack bridging parameters using long optical fiber Bragg grating sensors}, volume={34}, ISSN={["1879-1069"]}, DOI={10.1016/S1359-8368(03)00004-0}, abstractNote={The state of the local fiber–matrix interface highly influences the propagation of cracks in fiber-reinforced composites and thus the stress distribution in any bridging fiber. This paper demonstrates that by embedding a long optical fiber Bragg grating into a reinforcing fiber and using an established model of the grating response to non-uniform stress distributions, one can determine key parameters of a crack bridging model. The grating extending into the epoxy on each side of the crack is subject to a strain function as a result of all micro-mechanical phenomena acting along the fiber. Furthermore, this technique does not require that one knows a priori the exact location of the crack. Two types of central crack specimens with an artificial crack were fabricated and tested, one with a strong interface and one with a weaker interface resulting in frictional sliding. The results demonstrate that this technique is efficient for the measurement of the bridging forces through validation by previous measurements using short Bragg gratings and the deduction of interface parameters. Analysis also shows that the sensitivity of the Bragg grating sensor to the bridging force is sufficient, even for the more realistic case of an initially zero-width crack e.g. grown by fatigue.}, number={4}, journal={COMPOSITES PART B-ENGINEERING}, author={Studer, M and Peters, K and Botsis, J}, year={2003}, pages={347–359} }
 @article{peters_pattis_botsis_2002, title={Novel technique to measure axial strain distribution along fiber during pullout test}, volume={21}, ISSN={["0261-8028"]}, DOI={10.1023/A:1015734914877}, number={11}, journal={JOURNAL OF MATERIALS SCIENCE LETTERS}, author={Peters, K and Pattis, P and Botsis, J}, year={2002}, month={Jun}, pages={887–891} }
 @article{studer_pietrzyk_peters_botsis_giaccari_2002, title={Studies on bridging tractions - simultaneous bridging tractions and COD measurements}, volume={114}, ISSN={["0376-9429"]}, DOI={10.1023/A:1015798126787}, abstractNote={The main objective of this work is to investigate the bridging tractions in a model composite using optical fiber Bragg grating (FBG) sensors written into selected reinforcing fibers. Simultaneously, the crack opening displacement (COD) is measured using a speckle interferometry technique. The measurements are useful in the verification of the relation between the COD and bridging tractions established with the use of the weight function method. Center crack specimens made of epoxy and reinforced with one layer of optical fibers are prepared and tested under remote tension parallel to the fibers. Bragg gratings of 0.17 to 0.38 mm in length are introduced in selected fibers for direct, non invasive, local measurements of axial strains in these fibers. A controlled central crack, bridged by intact fibers, is introduced by a laser technique such that the FBGs are located between the crack faces. The results on the forces obtained from the FBGs and the COD-weight function method show good agreement. The experimental results also compare very well with 3-dimensional numerical simulations of the actual specimen geometry and loading configuration.}, number={4}, journal={INTERNATIONAL JOURNAL OF FRACTURE}, author={Studer, M and Pietrzyk, J and Peters, K and Botsis, J and Giaccari, P}, year={2002}, month={Apr}, pages={379–399} }
 @article{peters_studer_botsis_iocco_limberger_salathe_2001, title={Embedded optical fiber Bragg grating sensor in a nonuniform strain field: Measurements and simulations}, volume={41}, ISSN={["0014-4851"]}, DOI={10.1007/BF02323100}, number={1}, journal={EXPERIMENTAL MECHANICS}, author={Peters, K and Studer, M and Botsis, J and Iocco, A and Limberger, H and Salathe, R}, year={2001}, month={Mar}, pages={19–28} }