@article{ul shougat_kennedy_perkins_2023, title={A Self-Sensing Shape Memory Alloy Actuator Physical Reservoir Computer}, volume={7}, ISSN={["2475-1472"]}, DOI={10.1109/LSENS.2023.3270704}, abstractNote={A self-sensing shape memory alloy actuator is harnessed as a computational resource by utilizing it as a physical reservoir computer. Physical reservoir computing is a machine learning technique that takes advantage of the dynamics of a physical system for computation. Compared to recurrent neural networks, this architecture can be both fast and efficient with a cheaper training procedure. A shape memory alloy actuator is designed, fabricated, and tested for processing information. Voltage variation along the shape memory alloy wire is used as the reservoir's nodes. The physical reservoir is then used to predict the future trajectory of the actuator's end effector under various driving signals. This self-prediction method is also reconfigurable, as demonstrated by training the reservoir for one waveform but testing it for a different one. A nonlinear autoregressive moving average prediction task was also used to highlight the physical reservoir computer's abilities. Following this methodology, the soft actuator can be used for actuation and computation at the same time without altering its design.}, number={5}, journal={IEEE SENSORS LETTERS}, author={Ul Shougat, Md Raf E. and Kennedy, Scott and Perkins, Edmon}, year={2023}, month={May} }
 @article{ul shougat_li_shao_mcgarvey_perkins_2023, title={Hopf physical reservoir computer for reconfigurable sound recognition}, volume={13}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-023-35760-x}, abstractNote={AbstractThe Hopf oscillator is a nonlinear oscillator that exhibits limit cycle motion. This reservoir computer utilizes the vibratory nature of the oscillator, which makes it an ideal candidate for reconfigurable sound recognition tasks. In this paper, the capabilities of the Hopf reservoir computer performing sound recognition are systematically demonstrated. This work shows that the Hopf reservoir computer can offer superior sound recognition accuracy compared to legacy approaches (e.g., a Mel spectrum + machine learning approach). More importantly, the Hopf reservoir computer operating as a sound recognition system does not require audio preprocessing and has a very simple setup while still offering a high degree of reconfigurability. These features pave the way of applying physical reservoir computing for sound recognition in low power edge devices.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Ul Shougat, Md Raf E. and Li, XiaoFu and Shao, Siyao and McGarvey, Kathleen and Perkins, Edmon}, year={2023}, month={May} }
 @article{reed_abney_mishra_naik_perkins_vermillion_2023, title={Stability and Performance of an Undersea Kite Operating in a Turbulent Flow Field}, volume={31}, ISSN={["1558-0865"]}, DOI={10.1109/TCST.2023.3237614}, abstractNote={In this article, we examine the effects of flow disturbances resulting from turbulence on the dynamic behavior of an underwater energy-harvesting kite system that executes periodic figure-8 flight. Due to the periodic nature of the kite’s operation, we begin by assessing orbital stability using the Floquet analysis and stroboscopic intersection analysis of a Poincaré section, with the former analysis performed on a simplified “unifoil” model and the latter performed on a six-degree-of-freedom (6-DOF)/flexible tether model. With periodic stability established, a frequency-domain analysis based on a linearization about the kite’s path is used to predict the quality of flight path tracking as a function of the turbulence frequency. To validate the accuracy of these simulation-based predictions under flow disturbances, we compare the predictions of the kite’s behavior against the results of small-scale tow testing experiments performed in a controlled pool environment.}, number={4}, journal={IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY}, author={Reed, James and Abney, Andrew and Mishra, Kirti D. and Naik, Kartik and Perkins, Edmon and Vermillion, Chris}, year={2023}, month={Jul}, pages={1663–1678} }
 @article{ul shougat_perkins_2023, title={The van der Pol physical reservoir computer}, volume={3}, ISSN={["2634-4386"]}, DOI={10.1088/2634-4386/acd20d}, abstractNote={Abstract
               The van der Pol oscillator has historical and practical significance to spiking neural networks. It was proposed as one of the first models for heart oscillations, and it has been used as the building block for spiking neural networks. Furthermore, the van der Pol oscillator is also readily implemented as an electronic circuit. For these reasons, we chose to implement the van der Pol oscillator as a physical reservoir computer (PRC) to highlight its computational ability, even when it is not in an array. The van der Pol PRC is explored using various logical tasks with numerical simulations, and a field-programmable analog array circuit for the van der Pol system is constructed to verify its use as a reservoir computer. As the van der Pol oscillator can be easily constructed with commercial-off-the-shelf circuit components, this PRC could be a viable option for computing on edge devices. We believe this is the first time that the van der Pol oscillator has been demonstrated as a PRC.}, number={2}, journal={NEUROMORPHIC COMPUTING AND ENGINEERING}, author={Ul Shougat, Md Raf E. and Perkins, Edmon}, year={2023}, month={Jun} }
 @article{kennedy_vlajic_perkins_2022, title={Cosserat modeling for deformation configuration of shape memory alloy unimorph actuators}, volume={8}, ISSN={["1530-8138"]}, DOI={10.1177/1045389X221109256}, abstractNote={ Shape memory alloys (SMAs) can contract their length via a crystalline phase transition that is dependent upon their temperature and stress state. SMAs have been used as linear micro-actuators due to their high strength to weight ratio and compact structure. However, the relatively low linear contraction ([Formula: see text]4%–5% in length) limits their use. To remedy this, the SMA can be offset from a passive structure, which acts to magnify the deformation. The resulting amount of deformation depends upon the material properties and geometry of both the SMA and the passive structure. In this work, geometrically exact beam theory (also known as Cosserat theory) is coupled with SMA constitutive relations to model the maximum deformation configuration of these actuators. Four of these actuators of various lengths were fabricated and tested to verify the model. For the four actuators tested, the mean squared error between the experimental results and the Cosserat model were between 0.0702 mm (0.1% error) for the shortest actuator (66 mm in length) and 3.59 mm (2.7% error) for the longest actuator (135 mm in length). These results show that the closed form solution derived for this Cosserat beam model can accurately model the deformation of these active structures. }, journal={JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES}, author={Kennedy, Scott and Vlajic, Nicholas and Perkins, Edmon}, year={2022}, month={Aug} }
 @article{mollik_kennedy_ul shougat_li_fitzgerald_echols_kirk_silverberg_perkins_2022, title={Discrete element method simulator for joint dynamics: a case study using a red-tailed hawk's hallux digit}, volume={6}, ISSN={["1573-272X"]}, DOI={10.1007/s11044-022-09828-x}, journal={MULTIBODY SYSTEM DYNAMICS}, author={Mollik, Tushar and Kennedy, Scott and Ul Shougat, Md Raf E. and Li, Xiaofu and Fitzgerald, Timothy and Echols, Scott and Kirk, Nick and Silverberg, Larry and Perkins, Edmon}, year={2022}, month={Jun} }
 @article{ul shougat_li_perkins_2022, title={Dynamic effects on reservoir computing with a Hopf oscillator}, volume={105}, ISSN={["2470-0053"]}, DOI={10.1103/PhysRevE.105.044212}, abstractNote={Limit cycle oscillators have the potential to be resourced as reservoir computers due to their rich dynamics. Here, a Hopf oscillator is used as a physical reservoir computer by discarding the delay line and time-multiplexing procedure. A parametric study is used to uncover computational limits imposed by the dynamics of the oscillator using parity and chaotic time-series prediction benchmark tasks. Resonance, frequency ratios from the Farey sequence, and Arnold tongues were found to strongly affect the computation ability of the reservoir. These results provide insights into fabricating physical reservoir computers from limit cycle systems.}, number={4}, journal={PHYSICAL REVIEW E}, author={Ul Shougat, Md Raf E. and Li, XiaoFu and Perkins, Edmon}, year={2022}, month={Apr} }
 @article{mollik_geng_ul shougat_fitzgerald_perkins_2022, title={Genetic algorithm shape optimization to manipulate the nonlinear response of a clamped-clamped beam}, volume={8}, ISSN={["2405-8440"]}, DOI={10.1016/j.heliyon.2022.e11833}, abstractNote={Dynamical systems, which are described by differential equations, can have an enhanced response because of their nonlinearity. As one example, the Duffing oscillator can exhibit multiple stable vibratory states for some external forcing frequencies. Although discrete systems that are described by ordinary differential equations have helped to build fundamental groundwork, further efforts are needed in order to tailor nonlinearity into distributed parameter, continuous systems, which are described by partial differential equations. To modify the nonlinear response of continuous systems, topology optimization can be used to change the shape of the mechanical system. While topology optimization is well-developed for linear systems, less work has been pursued to optimize the nonlinear vibratory response of continuous systems. In this paper, a genetic algorithm implementation of shape optimization for continuous systems is described. The method is very general, with flexible objective functions and very few assumptions; it is applicable to any continuous system. As a case study, a clamped-clamped beam is optimized to have a more nonlinear or less nonlinear vibratory response. This genetic algorithm implementation of shape optimization could provide a tool to improve the performance of many continuous structures, including MEMS sensors, actuators, and macroscale civil structures.}, number={11}, journal={HELIYON}, author={Mollik, Tushar and Geng, Ying and Ul Shougat, Md Raf E. and Fitzgerald, Timothy and Perkins, Edmon}, year={2022}, month={Nov} }
 @article{li_kallepalli_mollik_ul shougat_kennedy_frabitore_perkins_2022, title={The pendulum adaptive frequency oscillator}, volume={179}, ISSN={["1096-1216"]}, DOI={10.1016/j.ymssp.2022.109361}, abstractNote={Adaptive oscillators are a type of nonlinear oscillator that are capable of learning and storing information in plastic states. Here, a typical mechanical pendulum is modified to have an adjustable rod length to create a pendulum adaptive frequency oscillator. Since the resonance frequency of the pendulum is a function of the rod length, this allows the pendulum to learn and encode frequency information from an external source. An experimental pendulum adaptive frequency oscillator is designed and constructed, and its performance is compared to numerical simulations. This nonlinear pendulum was approximated as a Duffing oscillator through the method of multiple scales to determine the physical constants of the experiment by using a curve fit. Utilizing the pendulum adaptive frequency oscillator’s dynamics, this system is able to learn a resonance condition and store this information in the rod length. This causes the system to seek resonance, even with considerable nonlinearity. As pendulums can be used to harvest energy, this type of adaptation could be used to further exploit vibratory energy sources.}, journal={Mechanical Systems and Signal Processing}, author={Li, XiaoFu and Kallepalli, Pawan and Mollik, Tushar and Ul Shougat, Md Raf E and Kennedy, Scott and Frabitore, Sean and Perkins, Edmon}, year={2022}, month={Nov}, pages={109361} }
 @article{ul shougat_li_mollik_perkins_2021, title={A Hopf physical reservoir computer}, volume={11}, ISSN={["2045-2322"]}, DOI={10.1038/s41598-021-98982-x}, abstractNote={AbstractPhysical reservoir computing utilizes a physical system as a computational resource. This nontraditional computing technique can be computationally powerful, without the need of costly training. Here, a Hopf oscillator is implemented as a reservoir computer by using a node-based architecture; however, this implementation does not use delayed feedback lines. This reservoir computer is still powerful, but it is considerably simpler and cheaper to implement as a physical Hopf oscillator. A non-periodic stochastic masking procedure is applied for this reservoir computer following the time multiplexing method. Due to the presence of noise, the Euler–Maruyama method is used to simulate the resulting stochastic differential equations that represent this reservoir computer. An analog electrical circuit is built to implement this Hopf oscillator reservoir computer experimentally. The information processing capability was tested numerically and experimentally by performing logical tasks, emulation tasks, and time series prediction tasks. This reservoir computer has several attractive features, including a simple design that is easy to implement, noise robustness, and a high computational ability for many different benchmark tasks. Since limit cycle oscillators model many physical systems, this architecture could be relatively easily applied in many contexts.}, number={1}, journal={SCIENTIFIC REPORTS}, author={Ul Shougat, Md Raf E. and Li, XiaoFu and Mollik, Tushar and Perkins, Edmon}, year={2021}, month={Sep} }
 @article{li_ul shougat_kennedy_fendley_dean_beal_perkins_2021, title={A four-state adaptive Hopf oscillator}, volume={16}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0249131}, abstractNote={Adaptive oscillators (AOs) are nonlinear oscillators with plastic states that encode information. Here, an analog implementation of a four-state adaptive oscillator, including design, fabrication, and verification through hardware measurement, is presented. The result is an oscillator that can learn the frequency and amplitude of an external stimulus over a large range. Notably, the adaptive oscillator learns parameters of external stimuli through its ability to completely synchronize without using any pre- or post-processing methods. Previously, Hopf oscillators have been built as two-state (a regular Hopf oscillator) and three-state (a Hopf oscillator with adaptive frequency) systems via VLSI and FPGA designs. Building on these important implementations, a continuous-time, analog circuit implementation of a Hopf oscillator with adaptive frequency and amplitude is achieved. The hardware measurements and SPICE simulation show good agreement. To demonstrate some of its functionality, the circuit’s response to several complex waveforms, including the response of a square wave, a sawtooth wave, strain gauge data of an impact of a nonlinear beam, and audio data of a noisy microphone recording, are reported. By learning both the frequency and amplitude, this circuit could be used to enhance applications of AOs for robotic gait, clock oscillators, analog frequency analyzers, and energy harvesting.}, number={3}, journal={PLOS ONE}, author={Li, XiaoFu and Ul Shougat, Md Raf E. and Kennedy, Scott and Fendley, Casey and Dean, Robert N. and Beal, Aubrey N. and Perkins, Edmon}, year={2021}, month={Mar} }
 @article{ul shougat_li_mollik_perkins_2021, title={An Information Theoretic Study of a Duffing Oscillator Array Reservoir Computer}, volume={16}, ISSN={["1555-1415"]}, DOI={10.1115/1.4051270}, abstractNote={Abstract
               Typically, nonlinearity is considered to be problematic and sometimes can lead to dire consequences. However, the nonlinearity in a Duffing oscillator array can enhance its ability to be used as a reservoir computer. Machine learning and artificial neural networks, inspired by the biological computing framework, have shown their immense potential, especially in the real-time temporal data processing. Here, the efficacy of a Duffing oscillator array is explored as a reservoir computer by using information theory. To do this, a reservoir computer model is studied numerically, which exploits the dynamics of the array. In this system, the complex dynamics stem from the Duffing term in each of the identical oscillators. The effects of various system parameters of the array on the information processing ability are discussed from the perspective of information theory. By varying these parameters, the information metric was found to be topologically mixed. Additionally, the importance of asynchrony in the oscillator array is also discussed in terms of the information metric. Since such nonlinear oscillators are used to model many different physical systems, this research provides insight into how physical nonlinear oscillatory systems can be used for dynamic computation, without significantly modifying or controlling the underlying dynamical system. To the authors' knowledge, this is the first use of Shannon's information rate for quantifying a reservoir computer of this kind, as well as the first comparison between synchronization phenomena and the computing ability of a reservoir.}, number={8}, journal={Journal of Computational and Nonlinear Dynamics}, author={Ul Shougat, Md. Raf E. and Li, XiaoFu and Mollik, Tushar and Perkins, Edmon}, year={2021}, month={Aug}, pages={081004} }
 @inproceedings{perkins_2021, title={Flexible Tensegrity Reservoir Computing Robots}, author={Perkins, Edmon}, year={2021} }
 @article{larson_perkins_oldfather_zabala_2021, title={Local dynamic stability of the lower-limb as a means of post-hoc injury classification}, volume={16}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0252839}, abstractNote={Since most sporting injuries occur at the lower extremity (50% to 66%) and many of those injuries occur at the knee (30% to 45%), it is important to have robust metrics to measure risk of knee injury. Dynamic measures of knee stability are not commonly used in existing metrics but could provide important context to knee health and improve injury screening effectiveness. This study used the Local Dynamic Stability (LDS) of knee kinematics during a repetitive vertical jump to perform a post-hoc previous injury classification of participants. This study analyzed the kinematics from twenty-seven female collegiate division 1 (D1) soccer, D1 basketball, and club soccer athletes from Auburn University (height = 171 ± 8.9cm, weight = 66.3 ± 8.6kg, age = 19.8 ± 1.9yr), with 7 subjects having sustained previous knee injury requiring surgery and 20 subjects with no history of injury. This study showed that LDS correctly identified 84% of previously injured and uninjured subjects using a multivariate logistic regression during a fatigue jump task. Findings showed no statistical difference in kinematic position at maximum knee flexion during all jumps between previously injured and uninjured subjects. Additionally, kinematic positioning at maximum knee flexion was not indicative of LDS values, which would indicate that future studies should look specifically at LDS with respect to injury prevention as it cannot be effectively inferred from kinematics. These points suggest that the LDS preserves information about subtle changes in movement patterns that traditional screening methods do not, and this information could allow for more effective injury screening tests in the future.}, number={6}, journal={PLoS One}, author={Larson, Jacob and Perkins, Edmon and Oldfather, Taylor and Zabala, Michael}, year={2021}, pages={e0252839} }
 @article{zhao_perkins_li_bond_marghitu_2021, title={Nonlinear vibratory properties of additive manufactured continuous carbon fiber reinforced polymer composites}, volume={117}, ISSN={["1433-3015"]}, DOI={10.1007/s00170-021-07456-x}, journal={The International Journal of Advanced Manufacturing Technology}, author={Zhao, Jing and Perkins, Edmon and Li, XiaoFu and Bond, Arthur and Marghitu, Dan}, year={2021}, pages={1077–1089} }
 @article{li_shougat_mollik_beal_dean_perkins_2021, title={Stochastic effects on a Hopf adaptive frequency oscillator}, volume={129}, ISSN={["1089-7550"]}, DOI={10.1063/5.0050819}, abstractNote={This paper explores the stochastic dynamics of a Hopf adaptive frequency oscillator when driven by noise. Adaptive oscillators are nonlinear oscillators that store information via plastic states. As noise is ubiquitous in physical systems, it is important to gain an understanding of the stochastic effects on adaptive oscillators. Previously, it has been shown that a simplified analysis of the Fokker–Planck equation results in affecting the plastic frequency state of these oscillators. However, when the full Fokker–Planck equation is considered, new behaviors are observed due to changes in oscillation amplitudes in addition to frequencies. The plastic frequency state of these oscillators may benefit from enhanced learning due to small amplitudes of noise, converge to incorrect values for medium amplitudes of noise, and even collapse to zero in the limit of large amplitudes of noise. Interestingly, not all averaged states collapse equally, which leads a two dimensional limit cycle to collapse into single dimensional oscillations when considering the averaged dynamics. These behaviors are compared analytically through the Fokker–Planck equation, numerically using the Euler–Maruyama simulations, and finally validated experimentally using an analog, electronic circuit. These results show that noise can enhance, mislead, or even reduce the dimensionality of the averaged adaptive Hopf oscillator.}, number={22}, journal={JOURNAL OF APPLIED PHYSICS}, author={Li, XiaoFu and Shougat, Md. Raf E. Ul and Mollik, Tushar and Beal, Aubrey N. and Dean, Robert N. and Perkins, Edmon}, year={2021}, month={Jun} }
 @inproceedings{bond_bottenfield_dean_adams_zhao_li_flowers_perkins_2020, title={3D Printed MEMS-Scale Vibration Isolators}, ISBN={9780791884546}, url={http://dx.doi.org/10.1115/imece2020-24357}, DOI={10.1115/imece2020-24357}, abstractNote={Abstract
               Mechanical vibration isolation is an important element for many traditional MEMS devices, (e.g., MEMS inertial sensors and micro-optics) that are deployed in harsh environments (e.g., aerospace applications or automotive applications). Without suitable vibration isolation, environmental vibrations can potentially damage these devices. Micro-scale mechanical vibration isolators usually consist of a center proof mass pad, a suspension system, and a surrounding frame. The isolator functions as a mechanical low-pass filter that provides useful attenuation of high frequency environmental vibrations between the frame and the proof mass pad, to which the vibration sensitive device is attached. These vibration isolators are usually fabricated with either laser processing or silicon micromachining techniques. Although these traditional techniques produce high quality vibration isolators, these methods take time to develop for specific sensor applications, and the batch size is typically large. This paper has two key highlights. First, the efficacy of 3D printing as a prototyping tool for small batch MEMS sensor vibration isolation applications is considered. Twenty-five mechanical vibration isolators were tested for this investigation, using both SLA and FDM printers. The resulting test data demonstrated that the MEMS-scale 3D printed mechanical vibration isolators can be a valid option for real-world vibration isolation applications. Second, it is unclear whether the bulk material properties are valid for MEMS-scale 3D printed structures, since these bulk material properties are typically calculated using tensile tests on macro-scale dog-bone specimens. Considerable variation in vibratory system parameters was found, even when the same printer, print orientation, material, and post-processing were used.}, booktitle={Volume 7A: Dynamics, Vibration, and Control}, publisher={American Society of Mechanical Engineers}, author={Bond, Arthur and Bottenfield, Brent D. and Dean, Robert N. and Adams, Mark L. and Zhao, Jing and Li, XiaoFu and Flowers, George T. and Perkins, Edmon}, year={2020}, month={Nov} }
 @inproceedings{mollik_perkins_2020, title={A Neural NARX Network Controller for a Pneumatic Artificial Muscle Driven Translational System}, author={Mollik, Tushar and Perkins, Edmon}, year={2020} }
 @inproceedings{crifasi_roy_perkins_2020, title={Additively Manufactured 2D Truss Demonstration"}, author={Crifasi, Daniel and Roy, Chandan and Perkins, Edmon}, year={2020} }
 @article{rhea_harrison_werner_perkins_dean_2020, title={Approximating an Exactly Solvable Chaotic Oscillator Using a Colpitts Oscillator Circuit}, volume={68}, ISSN={1549-7747 1558-3791}, url={http://dx.doi.org/10.1109/tcsii.2020.3024147}, DOI={10.1109/TCSII.2020.3024147}, abstractNote={An alternative approximate implementation of an exactly solvable chaotic oscillator circuit is presented. In this implementation, the previously used op amp based NIC sinusoidal oscillator subcircuit was replaced with a single BJT Colpitts oscillator subcircuit. Although this change resulted in an increase in the order of the chaotic system and introduced additional nonlinearities, simulation and hardware testing results indicated that its performance was equivalent to that of the mathematical model for the exactly solvable chaotic system. It also demonstrated equivalent performance to previous op amp based designs, while mitigating some of the performance limitations inherent with op amp based NICs. Evaluation of the resulting 18.9 kHz oscillator circuit demonstrated chaotic dynamics comparable to those from the ideal exactly solvable chaotic system.}, number={3}, journal={IEEE Transactions on Circuits and Systems II: Express Briefs}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Rhea, Benjamin K. and Harrison, R. Chase and Werner, Frank T. and Perkins, Edmon and Dean, Robert N.}, year={2020}, pages={1–1} }
 @article{tucker_perkins_2020, title={Asphaltophones: Modeling, analysis, and experiment}, volume={148}, ISSN={0001-4966}, url={http://dx.doi.org/10.1121/10.0001575}, DOI={10.1121/10.0001575}, abstractNote={The asphaltophone is a musical instrument consisting of (1) a specially designed road surface topology, (2) the tire's contact patch, and (3) the vehicle itself. Each of these components in the asphaltophone has an analogy in the phonograph, which is composed of (1) a record, (2) a stylus, and (3) an amplification device. Asphaltophones are an enjoyable and inexpensive method to keep drivers alert and develop tourism. In this paper, a simplified quarter-car model is proposed to study the effects of the asphaltophone on a vehicle. An analytical solution of the simplified quarter-car model to the most common asphaltophone profiles is derived. This analytical solution is used to determine the relationship between the asphaltophone's profile and the signal quality. An experimental installment is analyzed. The asphaltophone experiment was fabricated and installed on a college campus. The fabrication process used a laser cutter to cut predefined sections from a strip of asphalt marking tape. To the authors' knowledge, very little research has been pursued on this instrument.}, number={1}, journal={The Journal of the Acoustical Society of America}, publisher={Acoustical Society of America (ASA)}, author={Tucker, Alex and Perkins, Edmon}, year={2020}, month={Jul}, pages={236–242} }
 @article{tucker_perkins_2020, title={Cover Art}, volume={148}, url={https://asa.scitation.org/action/showLargeCover?doi=10.1121%2Fjas.2020.148.issue-1}, number={1}, journal={Journal of Acoustical Society of America}, author={Tucker, Alex and Perkins, Edmon}, year={2020}, month={Jul} }
 @inproceedings{marghitu_perkins_2020, place={Switzerland}, series={Applied Mechanics and Materials}, title={Dynamics of a Linkage Mechanism Using Sample Entropy}, DOI={10.4028/www.scientific.net/AMM.896.67}, abstractNote={The dynamics of a slider-crank mechanism is developed using Kane's equations of motion. The motor torque is a function of the derivative of the generalized coordinate. The nonlinear equations of motion are solved using MATLAB numerical techniques. The sample entropy is calculated for different angular velocities of the crank.}, booktitle={Achievements and solutions in mechanical engineering II : selected, peer reviewed papers from the 5th International Conference of Mechanical Engineering (ICOME) 2019, October 24-25, 2019, Craiova, Romania}, publisher={Trans Tech Publications}, author={Marghitu, Dan and Perkins, Edmon}, editor={Dumitru, Nicolae and Craciunoiu, Nicolae and Rosca, Adrian SorinEditors}, year={2020}, pages={67–74}, collection={Applied Mechanics and Materials} }
 @inproceedings{carpenter_zabala_perkins_larson_marino_2020, title={Frequency Characterization of Thigh Soft Tissue Artifact During a Relaxed and Activated State}, author={Carpenter, Scot and Zabala, Michael and Perkins, Edmon and Larson, Jacob and Marino, Anthony}, year={2020} }
 @inproceedings{li_shougat_fendley_dean_perkins_2020, title={Stochastic Response of Hopf Adaptive Frequency Oscillator}, booktitle={10th European Nonlinear Dynamics Conference}, author={Li, XiaoFu and Shougat, Md Raf E Ul and Fendley, Casey and Dean, Robert and Perkins, Edmon}, year={2020} }
 @article{weatherall_boone_caldwell_cole_cattley_lascola_clark‐price_farag_perkins_hanson_2020, title={Tensile strength and early healing of self‐locking and surgeon's knots}, volume={49}, ISSN={0161-3499 1532-950X}, url={http://dx.doi.org/10.1111/vsu.13497}, DOI={10.1111/vsu.13497}, abstractNote={AbstractObjectiveTo compare the biomechanical properties and healing of ventral midline celiotomies (VMC) closed with a self‐locking knot combination and forwarder start and Aberdeen end (F‐A) vs a traditional knot combination and surgeon's start and end (S‐S).Study designIn vivo, experimental.AnimalsTwenty‐one horses.MethodsFourteen horses underwent VMC, which was closed with either an F‐A (n = 7) or an S‐S (n = 7) knot combination. Incisions were subjectively graded by masked evaluators for dehiscence, edema, and drainage. Biomechanical testing was performed on three abdominal segments, and histology was performed on one segment from each animal after humane euthanasia 10 days post‐VMC. The abdominal wall of control horses (n = 7, no celiotomy) was collected for biomechanical testing.ResultsForwarder start and Aberdeen end and S‐S horses had less tensile strength compared with control horses (P ≤ .001). No differences were detected between treatment groups for any variable evaluated, including tensile strength (P = .975), location of failure (P = .240), and histologic healing at the knot (P = .600).ConclusionClosure of VMC with self‐locking knots resulted in biomechanical and healing features similar to those with a traditional closure technique, with neither restoring the tensile strength of the linea alba.Clinical significanceResults of this study provide evidence to support a clinical trial to evaluate long‐term performance of the F‐A self‐locking knot closure in horses.}, number={8}, journal={Veterinary Surgery}, publisher={Wiley}, author={Weatherall, Kathleen M. and Boone, Lindsey H. and Caldwell, Fred J. and Cole, Robert C. and Cattley, Russell C. and Lascola, Kara M. and Clark‐Price, Stuart C. and Farag, Ramsis and Perkins, Edmon and Hanson, R. Reid}, year={2020}, month={Aug}, pages={1580–1589} }
 @article{vibratory response characteristics of high-frequency shape memory alloy actuators_2020, url={https://asmedigitalcollection.asme.org/vibrationacoustics/article/142/1/011004/975366?casa_token=hjh0F6kLUvYAAAAA:v2exhZOXFfKRoVAmKj69YQCxz_xIesg3LnMpMw61mnRwoOpW6UMBoZS9Cy_Kou1CRShpCtGO}, journal={Journal of Vibration and Acoustics}, year={2020} }
 @inproceedings{toner_garton_perkins_2019, title={1088 hours}, author={Toner, Tyler and Garton, Max and Perkins, Edmon}, year={2019} }
 @inproceedings{stevens_dean_perkins_li_beal_flowers_2019, title={A Nonlinear MEMS Resonator for Generating AC Voltages Without Electronics}, ISBN={9781728101378}, url={http://dx.doi.org/10.1109/southeastcon42311.2019.9020649}, DOI={10.1109/southeastcon42311.2019.9020649}, abstractNote={High temperature applications exists where AC voltage generation would be useful, but the operating temperature is too high for many semiconductor electronic devices to operate reliably. Micromachined Si devices can operate at these elevated temperatures. The nonlinear characteristics of the MEMS parallel plate actuator can be exploited to realize a self-oscillating resonator by placing the PPA in series with a large value resistor and a DC voltage source with a voltage greater than or equal to the pull-in voltage of the PPA. In addition to generating an oscillating proof mass motion, the voltage across the PPA also oscillates with the same fundamental frequency. This phenomenon was modelled in MATLAB Simulink and investigated experimentally.}, booktitle={2019 SoutheastCon}, publisher={IEEE}, author={Stevens, Colin B. and Dean, Robert N. and Perkins, Edmon and Li, Chong and Beal, Aubrey N. and Flowers, George T.}, year={2019}, month={Apr} }
 @inproceedings{rhea_harrison_dean_perkins_2019, place={Fountain Hills, AZ}, title={A Technique for Reducing System Form Factor in Electronic Systems}, author={Rhea, Benjamin and Harrison, Remington and Dean, Robert and Perkins, Edmon}, year={2019} }
 @inproceedings{harrison_rhea_ramsey_dean_perkins_2019, title={A True Random Number Generator based on a Chaotic Jerk System}, ISBN={9781728101378}, url={http://dx.doi.org/10.1109/southeastcon42311.2019.9020442}, DOI={10.1109/southeastcon42311.2019.9020442}, abstractNote={We present a scheme for true random number generation by directly sampling a chaotic jerk system. A method for determination of the maximum Lyapunov exponent, and thus the maximum bit rate for true random number generation, of the jerk system of interest is shown. The system is tested over a wide range of sampling parameters in order to simulate possible hardware configurations. This system is readily implemented in high speed electronics and is well suited for random number generation due to its high dynamic complexity, long term aperiodicity, and extreme sensitivity to initial conditions.}, booktitle={2019 SoutheastCon}, publisher={IEEE}, author={Harrison, R. Chase and Rhea, Benjamin K. and Ramsey, Ariel N. and Dean, Robert N. and Perkins, J. Edmon}, year={2019}, month={Apr} }
 @inproceedings{tucker_arnold_perkins_2019, title={Asphaltophone Profile Design}, author={Tucker, Alex and Arnold, Tim and Perkins, Edmon}, year={2019} }
 @book{flowers_perkins_zhang_2019, title={Compact Circular Acoustic Lens of Transmissive Sound Beam for Wide Frequency Band}, number={62/878,503}, author={Flowers, George and Perkins, Edmon and Zhang, Fuxi}, year={2019} }
 @book{flowers_perkins_zhang_2019, title={Compact Labyrinth Element Acoustic Metamaterials for Broadband Low-frequency Attenuation}, number={62/878,510}, author={Flowers, George and Perkins, Edmon and Zhang, Fuxi}, year={2019} }
 @inproceedings{zhang_flowers_perkins_dean_suhling_roberts_2019, place={Fountain Hills, AZ}, title={Compact Labyrinth Element Acoustic Metamaterials for Broadband Low-frequency Attenuation}, author={Zhang, Fuxi and Flowers, George and Perkins, Edmon and Dean, Robert and Suhling, Jeffrey and Roberts, Jordan}, year={2019} }
 @article{compact acoustic metalens with sinusoidal sub-channels for directional far-field sound beams_2019, url={https://iopscience.iop.org/article/10.7567/1882-0786/ab2ff4}, DOI={10.7567/1882-0786/ab2ff4}, abstractNote={A metasurface lens (i.e., metalens), composed of perforated sinusoidal channels evenly arrayed with sub-wavelength distances, is explored in this paper. Enhanced directional far-field sound transmission over a large frequency range was realized through using this compact metalens. Numerical simulations and experimental tests demonstrated a pronounced diffraction-limited sound beam from 7390 to 7600 Hz, which reached as far as 57.6 cm at 7551 Hz with a width of 9 cm. This metalens is a feasible candidate for directional sound projection and sound energy harvesting.}, journal={Applied Physics Express}, year={2019} }
 @inproceedings{weatherall_hanson_caldwell_cole_cattley_lascola_clark-price_farag_perkins_boone_et al._2019, title={Comparison of Tensile Strength of Self-Locking and Surgeon's Knots for Closure of Ventral Midline Celiotomy in Horses}, author={Weatherall, Kathleen and Hanson, Reid and Caldwell, Fred and Cole, Robert and Cattley, Russell and Lascola, Kara and Clark-Price, Stuart and Farag, Ramsis and Perkins, Edmon and Boone, Lindsey and et al.}, year={2019} }
 @inproceedings{kennedy_price_zabala_perkins_2019, title={High Frequency Shape Memory Alloy Actuators}, author={Kennedy, Scott and Price, Morgan and Zabala, Michael and Perkins, Edmon}, year={2019} }
 @article{high frequency realization of non-autonomous nonlinear transistor circuit_2019, url={https://aip.scitation.org/doi/full/10.1063/1.5100948}, DOI={10.1063/1.5100948}, abstractNote={In this paper, an electronic implementation of a non-autonomous nonlinear transistor circuit is presented. This nonlinear circuit topology requires a minimal number of components, which consists of two resistors, two capacitors, and a single NPN bipolar junction transistor (BJT). This topology is of interest because it is relatively simple to construct and could be used for potential applications such as random number generators (RNGs) or noise signal generators (NSGs). The transistor portion of the circuit was analyzed using the Ebers-Moll model for a BJT. Using this model, time domain and phase space plots that qualitatively match the original systems dynamics were created. This model was also used to create bifurcation diagrams of the base voltage versus both frequency and amplitude, where periodic and chaotic solutions exist. The hardware realization was built using commercial-off-the-shelf (COTS) components with two different printed circuit board (PCB) designs. This PCB included the forcing function on the board with the transistor circuit. This circuit topology functioned over a wide range of frequencies, with an upper limit of approximately 5.1 MHz. Many potential applications could benefit from this high operation frequency.}, journal={AIP Advances}, year={2019} }
 @inproceedings{mulholland_perry_geng_perkins_2019, title={Keyboard Technology: A 3D Printed Piano Action and Self-tuning Controller}, author={Mulholland, Rebecca and Perry, Isabel and Geng, Ying and Perkins, Edmon}, year={2019} }
 @inproceedings{larson_zabala_oldfather_perkins_2019, title={Maximum Lyapunov Exponent Analysis of a Repetitive Vertical Jump Task in Female Athletes}, author={Larson, Jacob and Zabala, Michael and Oldfather, Taylor and Perkins, Edmon}, year={2019} }
 @inproceedings{price_larson_perkins_2019, title={Modal Constructs}, publisher={Auburn University College of Engineering}, author={Price, Morgan and Larson, Jacob and Perkins, Edmon}, year={2019} }
 @inproceedings{jackson_perkins_2019, title={Musical Nano Surfaces}, publisher={Auburn University College of Engineering}, author={Jackson, Robert and Perkins, Edmon}, year={2019} }
 @inproceedings{perkins_2019, title={Mythic STEAM}, author={Perkins, Edmon}, year={2019} }
 @inproceedings{perkins_marghitu_crocker_maksotskaya_2019, title={Nonlinear Dynamic Analysis of Elements of Music}, author={Perkins, Edmon and Marghitu, Dan and Crocker, Malcolm and Maksotskaya, Margarita}, year={2019} }
 @inproceedings{rhea_dean_perkins_2019, title={Nonlinear Transistor PCB}, publisher={Auburn University College of Engineering}, author={Rhea, Benjamin and Dean, Robert and Perkins, Edmon}, year={2019} }
 @book{flowers_roberts_perkins_zhang_2019, title={Open-through Dual Expansion Chamber for High Sound Absorption with 9th Octave Frequency}, number={62/878,493}, author={Flowers, George and Roberts, Jordan and Perkins, Edmon and Zhang, Fuxi}, year={2019} }
 @article{restricted normal mode analysis and chaotic response of p-mode intrinsic localized mode_2019, url={https://link.springer.com/article/10.1007/s11071-019-05020-7}, DOI={10.1007/s11071-019-05020-7}, journal={Nonlinear Dynamics}, year={2019} }
 @book{dean_perkins_2019, title={Self-oscillating MEMS Resonator using a Gap-closing Actuator}, number={62/939,288}, author={Dean, Robert and Perkins, Edmon}, year={2019} }
 @inproceedings{wang_perkins_hung_2019, title={Trajectory Tracking Control for an Underwater Vehicle Manipulator System Using a Neural-adaptive Network}, ISBN={9781728101378}, url={http://dx.doi.org/10.1109/southeastcon42311.2019.9020372}, DOI={10.1109/southeastcon42311.2019.9020372}, abstractNote={A neural-adaptive trajectory tracking control strategy is proposed for an underwater vehicle manipulator system (UVMS). A feedback term based on a nominal dynamic model is used, and an adaptive neural network is utilized to approximate parametric uncertainties. The performance of this control scheme is demonstrated by applying it to a specific trajectory tracking task. The simulation results showed that the controller has a good performance under parametric uncertainty situations.}, booktitle={2019 SoutheastCon}, publisher={IEEE}, author={Wang, Jiliang and Perkins, Edmon and Hung, John Y.}, year={2019}, month={Apr} }
 @article{kennedy_price_zabala_perkins_2019, title={Vibratory Response Characteristics of High-Frequency Shape Memory Alloy Actuators}, volume={142}, ISSN={1048-9002 1528-8927}, url={http://dx.doi.org/10.1115/1.4044867}, DOI={10.1115/1.4044867}, abstractNote={Abstract
               This paper presents a shape memory alloy actuator design using a bimorph structure capable of high-speed actuation and low power consumption. Two active layers of shape memory alloy wires are separated by a passive layer of thermoplastic polyurethane. This structure results in a bending actuator when current is alternated between the two active shape memory alloy layers. Actuators of lengths 20, 25, 30, 35, and 40 mm were tested at peak current input of 110, 120, 130, and 140 mA. The 40-mm actuator was shown to have a natural frequency of 11.4 Hz with a bending displacement of 26.4 mm perpendicular to the neutral position and a power input of 0.78 W (140 mA peak current input). A relationship between the input current and the resulting vibratory characteristics was found. As the current increases, the natural frequency decreases and the damping ratio increases. The experimental results are compared with a finite element method (FEM) vibration analysis and an Euler–Bernoulli cantilever beam equations.}, number={1}, journal={Journal of Vibration and Acoustics}, publisher={ASME International}, author={Kennedy, Scott and Price, Morgan and Zabala, Michael and Perkins, Edmon}, year={2019}, month={Nov} }
 @article{perkins_fitzgerald_2018, title={Continuation Method on Cumulant Neglect Equations}, volume={13}, ISSN={1555-1415 1555-1423}, url={http://dx.doi.org/10.1115/1.4038895}, DOI={10.1115/1.4038895}, abstractNote={For stochastic systems, the Fokker–Planck equation (FPE) is used to describe the system dynamics. The FPE is a partial differential equation, which is a function of all the variables in state space and of time. To solve the FPE, several methods are used, including finite elements, moment neglect methods, and cumulant neglect methods. This paper will study the cumulant neglect equations, which are derived from the FPE. It will be shown that the cumulant neglect method, while being a useful and popular tool for studying the system response, introduces several nonphysical artifacts.}, number={9}, journal={Journal of Computational and Nonlinear Dynamics}, publisher={ASME International}, author={Perkins, Edmon and Fitzgerald, Tim}, year={2018}, month={Jul} }
 @inproceedings{perkins_2018, title={Energy Localization in Nonlinear Dynamical Systems: Design, Measurement, and Control}, author={Perkins, Edmon}, year={2018} }
 @inproceedings{rhea_harrison_dean_perkins_2018, title={Non-autonomous Chaotic Circuit that Integrates a Variable Forcing Function onto a Single PCB}, author={Rhea, Benjamin and Harrison, Remington and Dean, Robert and Perkins, Edmon}, year={2018} }
 @inproceedings{crifasi_ergle_özdeş_perkins_2018, title={Vibratory System Identification of 3D Printed Cantilever}, ISBN={9780791852040}, url={http://dx.doi.org/10.1115/imece2018-86840}, DOI={10.1115/imece2018-86840}, abstractNote={Although 3D printing has become a widespread method of fabrication, the vibratory properties of thermoplastic composites are poorly understood. This is, in part, due to the anisotropies introduced by the 3D printing process, the composite materials used, and the geometry. In this study, an attempt has been made to characterize the vibratory response of a 3D printed thermoplastic cantilever, in order to determine the damping ratio and natural frequency. The cantilevered beams were 3D printed, with a range of varied parameters. These parameters include the inclusion and exclusion of continuous carbon fiber reinforcement, as well as the three orthogonal build directions. Impact tests and frequency sweeps were used to gain information about the vibratory response of these cantilevers. This information was used to model the effects of the carbon fiber and anisotropy introduced by the different build parameters. During the experiments, a high-speed camera was used to record the response of the cantilevers. These videos were then post-processed with image analysis tools to quantify the response. Then, a point near the tip of the cantilever was used as the time-dependent variable for a reduced order model. By proceeding in this described method, the damping ratio and natural frequency of the system may be written as a function of the build parameters.}, booktitle={Volume 4B: Dynamics, Vibration, and Control}, publisher={American Society of Mechanical Engineers}, author={Crifasi, Daniel and Ergle, Matthew and Özdeş, Hüseyin and Perkins, Edmon}, year={2018}, month={Nov} }
 @article{perkins_2017, title={Effects of noise on the frequency response of the monostable Duffing oscillator}, volume={381}, number={11}, journal={Physics Letters A}, publisher={Elsevier}, author={Perkins, Edmon}, year={2017}, pages={1009–1013} }
 @inproceedings{perkins_2017, title={Frequency response of p-mode intrinsic localized mode}, author={Perkins, Edmon}, year={2017} }
 @inproceedings{perkins_2017, title={Stochastic Effects on a Chaotic Duffing Oscillator}, author={Perkins, Edmon}, year={2017} }
 @article{perkins_kimura_hikihara_balachandran_2016, title={Effects of noise on symmetric intrinsic localized modes}, volume={85}, number={1}, journal={Nonlinear Dynamics}, publisher={Springer}, author={Perkins, Edmon and Kimura, Masayuki and Hikihara, Takashi and Balachandran, Balakumar}, year={2016}, pages={333–341} }
 @article{perkins_balachandran_2015, title={Effects of phase lag on the information rate of a bistable Duffing oscillator}, volume={379}, number={4}, journal={Physics Letters A}, publisher={Elsevier}, author={Perkins, Edmon and Balachandran, Balakumar}, year={2015}, pages={308–313} }
 @phdthesis{perkins_2015, title={Noise-influenced dynamics of nonlinear oscillators}, author={Perkins, Edmon}, year={2015} }
 @article{balachandran_perkins_fitzgerald_2015, title={Response localization in micro-scale oscillator arrays: influence of cubic coupling nonlinearities}, volume={3}, number={2}, journal={International Journal of Dynamics and Control}, publisher={Springer}, author={Balachandran, Balakumar and Perkins, Edmon and Fitzgerald, Timothy}, year={2015}, pages={183–188} }
 @inproceedings{perkins_balachandran_2015, title={Restricted Normal Mode Analysis of the P-Mode Intrinsic Localized Mode}, booktitle={Proceedings of the International Symposium on Nonlinear Theory and Its Applications}, publisher={NOLTA Society}, author={Perkins, Edmon and Balachandran, Balakumar}, year={2015}, pages={793–796} }
 @inproceedings{perkins_balachandran_2014, place={Newport Beach, CA}, title={Noise-Influenced Dynamics in Nonlinear Systems}, author={Perkins, Edmon and Balachandran, Balakumar}, year={2014} }
 @inproceedings{perkins_balachandran_2013, title={Noise-influenced dynamics of a vertically excited pendulum}, booktitle={ASME 2013 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference}, author={Perkins, Edmon and Balachandran, Balakumar}, year={2013}, pages={V07BT10A025-V07BT10A025} }
 @article{perkins_chabalko_balachandran_2013, title={Noise-influenced transient energy localization in an oscillator array}, volume={4}, number={3}, journal={Nonlinear Theory and Its Applications, IEICE}, publisher={The Institute of Electronics, Information and Communication Engineers}, author={Perkins, Edmon and Chabalko, Chris and Balachandran, Balakumar}, year={2013}, pages={232–243} }
 @article{perkins_balachandran_2012, title={Noise-enhanced response of nonlinear oscillators}, volume={5}, journal={Procedia IUTAM}, publisher={Elsevier}, author={Perkins, Edmon and Balachandran, Balakumar}, year={2012}, pages={59–68} }
 @inproceedings{telly_perkins_shrestha_balachandran_2010, place={Blacksburg, VA, Virginia Tech}, title={Noise Enhanced Performance of Coupled Oscillators: Entropy Studies}, author={Telly, Saliou and Perkins, Edmon and Shrestha, Dibesh and Balachandran, Balakumar}, year={2010} }