@article{furst_dow_garrard_sohn_fixsen_rinehart_mentzell_veach_rizzo_dhabal_2016, title={Design and validation of the mounting structure for BETTII balloon-based telescope with thin-walled optics}, volume={2}, ISSN={["2329-4221"]}, DOI={10.1117/1.jatis.2.2.024001}, abstractNote={Abstract. The NASA Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) system is designed to study the infrared emissions from star formation and active galactic nuclei through a double-Fourier Michelson interferometer located on a balloon at an altitude of 37 km. The BETTII external optics include a pair of identical beam-reducing, four-mirror telescopes, each with a 522-mm aperture, nonrotationally symmetric primary mirror. These telescopes were designed and assembled at the North Carolina State University Precision Engineering Consortium and are composed entirely of thin-walled aluminum components. The mounting structure is designed to be light weight and stiff to reduce thermal equilibration time in the rarified air at the edge of space and to maintain robust alignment of the optical elements. The mounts also prevent deformation of the large optical elements via custom-built kinematic Kelvin couplings and fixed-load clamps; the maximum form error of the optical surfaces are 300 nm RMS. This work details the design of the thin mirrors and mounting structure as well as validation of the mount assembly process, mount stiffness, and the kinematic couplings.}, number={2}, journal={JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS}, author={Furst, Stephen and Dow, Tom and Garrard, Ken and Sohn, Alex and Fixsen, Dale and Rinehart, Stephen and Mentzell, Eric and Veach, Todd and Rizzo, Maxime and Dhabal, Arnab}, year={2016}, month={Apr} }
 @article{dhabal_rinehart_rizzo_mundy_fixsen_sampler_mentzell_veach_silverberg_furst_et al._2016, title={Optics of Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): delay lines and alignment}, volume={9907}, ISSN={["0277-786X"]}, DOI={10.1117/12.2230218}, abstractNote={We present the optics of Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) as it gets ready for launch. BETTII is an 8-meter baseline far-infrared (30-90 μm) interferometer mission with capabilities of spatially resolved spectroscopy aimed at studying star formation and galaxy evolution. The instrument collects light from its two arms, makes them interfere, divides them into two science channels (30-50 μm and 60-90 μm), and focuses them onto the detectors. It also separates out the NIR light (1-2.5 μm) and uses it for tip-tilt corrections of the telescope pointing. Currently, all the optical elements have been fabricated, heat treated, coated appropriately and are mounted on their respective assemblies. We are presenting the optical design challenges for such a balloon borne spatio- spectral interferometer, and discuss how they have been mitigated. The warm and cold delay lines are an important part of this optics train. The warm delay line corrects for path length differences between the left and the right arm due to balloon pendulation, while the cold delay line is aimed at introducing a systematic path length difference, thereby generating our interferograms from where we can derive information about the spectra. The details of their design and the results of the testing of these opto-mechanical parts are also discussed. The sensitivities of different optical elements on the interferograms produced have been determined with the help of simulations using FRED software package. Accordingly, an alignment plan is drawn up which makes use of a laser tracker, a CMM, theodolites and a LUPI interferometer.}, journal={OPTICAL AND INFRARED INTERFEROMETRY AND IMAGING V}, author={Dhabal, Arnab and Rinehart, Stephen A. and Rizzo, Maxime J. and Mundy, Lee and Fixsen, Dale and Sampler, Henry and Mentzell, Eric and Veach, Todd and Silverberg, Robert F. and Furst, Stephen and et al.}, year={2016} }
 @article{riede_york_furst_mueller_seelecke_2011, title={Elasticity and stress relaxation of a very small vocal fold}, volume={44}, ISSN={["1873-2380"]}, DOI={10.1016/j.jbiomech.2011.04.024}, abstractNote={Across mammals many vocal sounds are produced by airflow induced vocal fold oscillation. We tested the hypothesis that stress–strain and stress-relaxation behavior of rat vocal folds can be used to predict the fundamental frequency range of the species' vocal repertoire. In a first approximation vocal fold oscillation has been modeled by the string model but it is not known whether this concept equally applies to large and small species. The shorter the vocal fold, the more the ideal string law may underestimate normal mode frequencies. To accommodate the very small size of the tissue specimen, a custom-built miniaturized tensile test apparatus was developed. Tissue properties of 6 male rat vocal folds were measured. Rat vocal folds demonstrated the typical linear stress–strain behavior in the low strain region and an exponential stress response at strains larger than about 40%. Approximating the rat's vocal fold oscillation with the string model suggests that fundamental frequencies up to about 6 kHz can be produced, which agrees with frequencies reported for audible rat vocalization. Individual differences and time-dependent changes in the tissue properties parallel findings in other species, and are interpreted as universal features of the laryngeal sound source.}, number={10}, journal={JOURNAL OF BIOMECHANICS}, author={Riede, Tobias and York, Alexander and Furst, Stephen and Mueller, Rolf and Seelecke, Stefan}, year={2011}, month={Jul}, pages={1936–1940} }
 @article{furst_dow_garrard_sohn_2010, title={Automated Part Centering With Impulse Actuation}, volume={132}, ISSN={["1528-8935"]}, DOI={10.1115/1.4000681}, abstractNote={Centering a part on a spindle for precision machining is a tedious, time-consuming task. Currently, a skilled operator must measure the run-out of a part using a displacement gauge, then tap the part into place using a plastic or rubber hammer. This paper describes a method to automatically center a part on a vacuum chuck with initial run-out as large as 2.5 mm. The method involves measuring the magnitude and direction of the radial run-out and then actuating the part until the part and spindle centerlines are within 5 μm of each other. The run-out can be measured with either a touch probe mounted to a machine axis or an electronic gauge. The part is tapped into place with a linear actuator driven by a voice coil motor. This paper includes an analysis of run-out measurement uncertainty as well as the design, performance modeling, and testing of the alignment actuator. This actuator was employed for part realignment and successfully positioned a hemispherical part with an initial run-out of 1–2.5 mm to within 5 μm of the spindle centerline. This capability shows that the run-out of a part manually placed on flat vacuum chuck can be automatically corrected.}, number={1}, journal={JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING-TRANSACTIONS OF THE ASME}, author={Furst, S. J. and Dow, T. A. and Garrard, K. and Sohn, A.}, year={2010}, month={Feb} }
 @inproceedings{hangekar_furst_seelecke_2010, title={Development of a 6-channel power controller for simultaneous actuation and resistance measurement of SMA wires}, DOI={10.1115/smasis2010-3846}, abstractNote={The use of ‘multifunctional’ Shape Memory Alloy wires as embedded actuators and sensors has been proposed for numerous novel applications. The SMA wires are actuated as a result of the Joule heating induced by passing electric current through it. The resistance of the SMA wire can simultaneously be measured during its actuation enabling it to be used as sensor data that relates to the strain and temperature of the wire. In order to control actuation stroke from the SMA wire, the Joule heating (electric power supplied to the SMA wire) of the wire needs to be controlled. Therefore, a 6-channel power controller device has been developed that simultaneously controls the power supplied to six different SMA wires and measures the resistance of these wires during excitation. This paper continues from the previously presented concept of a multi-channel power controller implementation. The focus of this paper is to discuss the operation, calibration methods and optimization techniques to improve the performance and robustness of the device and to eliminate the issues in multi-channel implementation. Further, this device is implemented in a test setup to study the position control of SMA wire using resistance feedback. Results of these tests can be utilized in practical applications involving SMA wires as embedded actuators and sensors, such as Smart Inhaler system being developed at North Carolina State University.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol 2}, author={Hangekar, R. and Furst, S. and Seelecke, S.}, year={2010}, pages={461–470} }
 @article{furst_hangekar_seelecke_2010, title={Development, Assembly, and Validation of an SMA-Actuated 2-Joint Nozzle and 6-Channel Power Supply for Use in a Smart Inhaler System}, volume={7643}, ISSN={["0277-786X"]}, DOI={10.1117/12.853399}, abstractNote={The Smart Inhaler design concept recently developed at NC State University has the potential to target the delivery of inhaled aerosol medication to specified locations within the lung system. This targeted delivery could help patients with pulmonary ailments by reducing the exposure of healthy lung tissue to potentially harmful medications. However, controlled delivery can only be accomplished if medication is injected at a precise location in an inhaled stream of properly conditioned laminar flow. In particular, the medication must be injected into the inhaled flow using a small nozzle that can be positioned without disturbing the flow. This paper outlines the procedure used to assemble and control a key component of the smart inhaler: a shape memory alloy (SMA) based dual-joint flexible nozzle that exploits the sensing and actuating capabilities of thermally activated SMA wires. A novel 6-channel power-supply is used to control input power and measure the resistance across the SMA. Since a practical fabrication process may result in SMA wires with different contact resistances, the power supply employs an initialization procedure to self-calibrate and provide normalized power distribution 6 SMA wires simultaneously. Furthermore, a robust control scheme is used to ensure that a constant current is provided to the wires. In validation tests, a LabVIEW-based video positioning system was used to measure the deflection of the nozzle tip and joint rotation. Results show that the carefully controlled assembly of a stream-lined nozzle can produce a practical smart structure, and joint rotation is predictable and repeatable when power input is also controlled. Future work will assess the use of the SMA-resistance measurement as position feedback and PID position control power as a measurement of the convective cooling that results from the moving airflow.}, journal={ACTIVE AND PASSIVE SMART STRUCTURES AND INTEGRATED SYSTEMS 2010, PTS 1 AND 2}, author={Furst, Stephen J. and Hangekar, Rohan and Seelecke, Stefan}, year={2010} }
 @inproceedings{furst_hangekar_seelecke_2010, title={Practical implementation of resistance feedback measurement for position control of a flexible smart inhaler nozzle}, DOI={10.1115/smasis2010-3840}, abstractNote={Many “smart materials” have the capacity to be used simultaneously as both an actuator and sensor. For example, SMA actuator wires can be heated by Joule heating to induce contraction; at the same time, the resistance across the SMA wire can be measured to give the user some indication of the strain in the wire. This multi-functional capability enables the design of applications requiring extremely light-weight and streamlined embedded sensors and actuators. One such “smart structure” application is the flexible nozzle used in the Smart Inhaler system under development at North Carolina State University. The Smart Inhaler allows a doctor to control the locations within the pulmonary system that are medicated by controlling the location at which medication is injected into an inhaled airflow. This can reduce the amount of healthy tissue that is exposed to potentially toxic medications, such as those used to treat lung cancer. However, the practical challenge of injecting medication into a flow without disturbing the flow requires a highly controllable yet non-obstructive nozzle. This paper presents a scheme that correlates the resistance measurement across an SMA actuator wire to the wire strain and the resulting deformation of the flexible nozzle. The relationship between resistance and nozzle deformation is nonlinear and hysteretic; however, the repeatability of the relationship allows the user to calibrate the feedback measurement. This enables the wire to be used as both position sensor and positioning actuator. The results represent the first experiments that exploit the multi-functional capabilities of SMA wires in the context of a practical embedded sensor and actuator application.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol 2}, author={Furst, S. J. and Hangekar, R. and Seelecke, S.}, year={2010}, pages={205–213} }
 @inproceedings{furst_bumgarner_seelecke_2009, title={Quantification of the effectiveness of various conductive and non-conductive epoxies as an attachment method for small SMA wires}, DOI={10.1115/smasis2009-1450}, abstractNote={The discovery of thermoelastic behavior in shape memory alloys (SMA) such as Nitinol enabled the conceptualization of many applications where actuators and sensors are embedded into a structural component. These so called “adaptive structures” can be extremely compact and energy efficient. SMA wires show characteristics similar to that of muscle fibers, and thus enable replication of an animal’s musculoskeletal system. Also, SMA wires are extremely attractive in the biomedical field where compact robotic elements can reduce the invasiveness of some surgical procedures. Unfortunately, widespread implementation of adaptive structures actuated by small SMA-wires in industry has been hindered by two significant challenges. First, SMA wires exhibit hysteretic behavior during heating and cooling that can be difficult to model without substantial computation. Second, attaching a small (∼50–100 μm diameter) SMA wire is extremely difficult because standard methods such as crimping are infeasible. The goal of this study is to quantify the effectiveness of using adhesives to hold a small SMA wire. A wide range of commercially available adhesives are tested under the conditions relevant to an application where SMA-wires are embedded directly within a structure. Epoxies are tested so that the adhesive will bond to both plastic and metallic elements. The experimental setup is designed to test the failure shear stress between an SMA wire and adhesive. A wire is encapsulated in a small drop of adhesive. Then the area of the wire that is exposed to the adhesive is measured under a microscope and the wire is pulled as a load cell measures the tensile load. The force that causes failure of the bond is recorded and used to calculate the failure shear stress between the adhesive and wire. The effects of using wires with different surface temperatures, and handling procedures (i.e. washing with acetone and handling with latex gloves) are also tested. Measurements under each set of parameters are repeated and quantitative results are obtained.}, booktitle={SMASIS 2009, vol 2}, author={Furst, S. J. and Bumgarner, D. and Seelecke, S.}, year={2009}, pages={409–418} }
 @article{xi_zhang_furst_chen_pei_2008, title={Electrochemical Synthesis and Photovoltaic Property of Cadmium Sulfide-Polybithiophene Interdigitated Nanohybrid Thin Films}, volume={112}, ISSN={["1932-7447"]}, DOI={10.1021/jp807868j}, abstractNote={Interdigitated hybrid films consisting of cadmium sulfide (CdS) nanorod arrays and interpenetrating polybithiophene have been synthesized by electrochemical depositions. The vertically aligned CdS nanorods were self-assembled on gold-coated glass substrates through a simple cathodic process of an electrolyte solution containing cadmium sulfate and potassium thiocyanate, without the use of any templates. The conjugated polymer polybithiophene was deposited into the nanorod arrays by in situ electrochemical polymerization. The resulting interdigitated nanohybrid films showed dense packing of the polymer in the nanorod arrays with a filling ratio estimated to be 76%. Raman spectroscopy and Fourier transform infrared revealed charge-transfer between the polymer and the CdS nanorods, consistent with the high filling ratio and improved polymer−CdS interface. Solar cells based on these hybrid films with vapor-deposited aluminum cathode exhibited a diode characteristic with a rectification ratio of 103 at ± 1 V. ...}, number={49}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Xi, Dongjuan and Zhang, Han and Furst, Stephen and Chen, Bin and Pei, Qibing}, year={2008}, month={Dec}, pages={19765–19769} }