@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} }
 @inproceedings{hodgins_york_seelecke_2010, title={Electro-mechanical analysis of a deap actuator coupled to a negative-rate bias spring mechanism}, DOI={10.1115/smasis2010-3849}, abstractNote={This paper presents the design and analysis of a Negative-rate Bias Spring (NBS) paired with a Dielectric Electro-Active Polymer (DEAP). A NBS is a bi-stable mechanism with a negative slope region between its two stable configurations. The objective of this work is to demonstrate the increased stroke output of a DEAP actuator when biased by such a bistable mechanism. Possible devices that could use this actuation technology are lightweight, miniature pumps and valves. First, the NBS is mechanically tested and its bi-stable behavior is observed along with the negative slope region between the stable configurations. Then the NBS is coupled with a circular DEAP actuator (to provide the bias force) and is experimentally tested under a variety of loading conditions with a focus on the force and stroke capabilities. The stroke output of the device was approximately 1mm for a range of electrical loading rates (0.1Hz, 1Hz, and 10Hz). The measured force and stroke are then correlated to the force vs. displacement data observed during the mechanical characterization experiments. Additionally, the force vs. displacement behavior of the NBS-DEAP is analytically modeled and showed good comparison with the results.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol. 1}, author={Hodgins, M. and York, A. and Seelecke, S.}, year={2010}, pages={315–322} }
 @article{york_dunn_seelecke_2010, title={Experimental characterization of the hysteretic and rate-dependent electromechanical behavior of dielectric electro-active polymer actuators}, volume={19}, ISSN={["0964-1726"]}, DOI={10.1088/0964-1726/19/9/094014}, abstractNote={Dielectric electro-active polymers (DEAPs) can achieve substantial deformation (>300% strain) while sustaining, compared to their ionic counterparts, large forces. This makes them attractive for various actuation and sensing applications such as in light weight and energy efficient valve and pumping systems. Many applications operate DEAP actuators at higher frequencies where rate-dependent effects influence their performance. This motivates the seeking of dynamic characterization of these actuators beyond the quasi-static regime. This paper provides a systematic experimental investigation of the quasi-static and dynamic electromechanical properties of a DEAP actuator. In order to completely characterize the fully coupled behavior, force versus displacement measurements at various constant voltages and force versus voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the electrical dynamics and viscoelastic relaxation inherent in DEAP actuators. This study is intended to provide information, including high frequency performance analysis, useful to anyone designing dynamic actuator systems using DEAPs.}, number={9}, journal={SMART MATERIALS & STRUCTURES}, author={York, A. and Dunn, J. and Seelecke, S.}, year={2010}, month={Sep} }
 @article{lien_york_fang_buckner_2010, title={Modeling piezoelectric actuators with Hysteretic Recurrent Neural Networks}, volume={163}, ISSN={["0924-4247"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-78049473465&partnerID=MN8TOARS}, DOI={10.1016/j.sna.2010.08.013}, abstractNote={This paper describes the application of Hysteretic Recurrent Neural Networks (HRNNs) to the modeling of polycrystalline piezoelectric actuators. Because piezoelectric materials exhibit voltage/strain relationships that are hysteretic and rate-dependent, the HRNN is composed of neurons with activation functions that incorporate these characteristics. Individual neurons are shown to agree with existing models of ideal single-crystal piezoelectric behavior. The combination of many such neurons into a network allows prediction of the heterogeneous behavior of polycrystalline materials. This model is shown to approximate the strain and polarization of an unloaded commercial stack actuator at multiple loading rates. A comparison is made to a recurrent Radial Basis Function Network model, and the HRNN is demonstrated to more accurately generalize across data sets. The model is further shown to execute on a PC platform at rates over 100 Hz, fast enough to support its application to real-time control.}, number={2}, journal={SENSORS AND ACTUATORS A-PHYSICAL}, author={Lien, J. P. and York, Alexander and Fang, Tiegang and Buckner, Gregory D.}, year={2010}, month={Oct}, pages={516–525} }
 @inproceedings{york_seelecke_2010, title={Towards self-sensing of deap actuators: Capacitive sensing experimental analysis}, DOI={10.1115/smasis2010-3847}, abstractNote={Dielectric Electro-Active Polymers (DEAP’s) have become attractive material for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. The materials ability to act as both and actuator and a sensor enable DEAP actuators to have “self-sensing” capabilities. This advancement provides low cost actuator systems that do not require external sensors for feedback control. This paper explores the capacitive sensing capabilities of a DEAP actuator under loading conditions typical for pumping and valve applications. The capacitive sensing capabilities of the actuator are tested using a method similar to that used by Jung et al. [1] which uses the DEAP actuator as a variable capacitor in a high pass filter circuit. This sensing circuit produces a direct voltage output when the actuator is displaced. The sensing response of this system is experimentally investigated under mechanical loading. The sensor is shown to have an effective sensitivity of .041 (V/Vexc) / mm. In addition, the initial results of a dual sensing and actuating system are presented.}, booktitle={Proceedings of the ASME Conference on Smart Materials, Adaptive Structures and Intelligent Systems, 2010, vol. 1}, author={York, A. and Seelecke, S.}, year={2010}, pages={307–314} }
 @inproceedings{york_hodgins_seelecke_2009, title={Electro-mechanical analysis of a biased dielectric EAP actuator}, DOI={10.1115/smasis2009-1441}, abstractNote={Dielectric Electro-Active Polymers (DEAP’s) can achieve substantial deformation (>300% strain) while, compared to their ionic counterparts, sustaining large forces. This makes them attractive for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems. This paper provides a systematic experimental investigation of the quasi-static and dynamic electro-mechanical properties of a commercially available dielectric EAP actuator. In order to completely characterize the fully coupled behavior force vs. displacement measurements at various constant voltages and force vs. voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and rate-dependent material behavior. These experiments provide insight into the viscoelastic and electrostatic behavior inherent in DEAP material. Typical operating conditions of the actuator require it to have a biased force, such as a spring. Experiments are conducted to observe the actuators performance under these conditions. The force and stroke capabilities are investigated while the actuator is loaded with different springs and at a variety of pre-stretch levels. The resulting behavior of the spring loaded actuator is then correlated to the viscoelastic effects observed during the electro-mechanical characterization.}, booktitle={SMASIS 2009, vol 1}, author={York, A. and Hodgins, M. and Seelecke, S.}, year={2009}, pages={289–297} }