@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{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{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={Abstract}, 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{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{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{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{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{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{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{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{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} }
 @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{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} }