@article{proctor_richards_shen_skorczewski_wang_zhang_zhong_massad_smith_2010, title={Design of RF MEMS Switches without Pull-in Instability}, volume={7644}, ISSN={["1996-756X"]}, DOI={10.1117/12.848045}, abstractNote={Micro-electro-mechanical systems (MEMS) switches for radio-frequency (RF) signals have certain advantages over solid-state switches, such as lower insertion loss, higher isolation, and lower static power dissipation. Mechanical dynamics can be a determining factor for the reliability of RF MEMS. The RF MEMS ohmic switch discussed in this paper consists of a plate suspended over an actuation pad by four double-cantilever springs. Closing the switch with a simple step actuation voltage typically causes the plate to rebound from its electrical contacts. The rebound interrupts the signal continuity and degrades the performance, reliability and durability of the switch. The switching dynamics are complicated by a nonlinear, electrostatic pull-in instability that causes high accelerations. Slow actuation and tailored voltage control signals can mitigate switch bouncing and effects of the pull-in instability; however, slow switching speed and overly-complex input signals can significantly penalize overall system-level performance. Examination of a balanced and optimized alternative switching solution is sought. A step toward one solution is to consider a pull-in-free switch design. In this paper, determine how simple RC-circuit drive signals and particular structural properties influence the mechanical dynamics of an RF MEMS switch designed without a pull-in instability. The approach is to develop a validated modeling capability and subsequently study switch behavior for variable drive signals and switch design parameters. In support of project development, specifiable design parameters and constraints will be provided. Moreover, transient data of RF MEMS switches from laser Doppler velocimetry will be provided for model validation tasks. Analysis showed that a RF MEMS switch could feasibly be designed with a single pulse waveform and no pull-in instability and achieve comparable results to previous waveform designs. The switch design could reliably close in a timely manner, with small contact velocity, usually with little to no rebound even when considering manufacturing variability.}, journal={BEHAVIOR AND MECHANICS OF MULTIFUNCTIONAL MATERIALS AND COMPOSITES 2010}, author={Proctor, W. Cyrus and Richards, Gregory P. and Shen, Chongyi and Skorczewski, Tyler and Wang, Min and Zhang, Jingyan and Zhong, Peng and Massad, Jordan E. and Smith, Ralph}, year={2010} }
 @article{massad_smith_2005, title={A homogenized free energy model for hysteresis in thin-film shape memory alloys}, volume={489}, ISSN={["1879-2731"]}, DOI={10.1016/j.tsf.2005.04.079}, abstractNote={Thin-film shape memory alloys (SMAs) have become excellent candidates for microactuator fabrication in microelectromechanical systems due to their capability to achieve very high work densities, produce large deformations, and generate high stresses. In general, the material behavior of SMAs is nonlinear and hysteretic. To achieve the full potential of SMA actuators, it is necessary to develop models that characterize the nonlinearities and hysteresis inherent to the constituent materials. We develop a model that quantifies the nonlinearities and hysteresis inherent to SMAs. The fully thermomechanical model is based on free energy principles combined with stochastic homogenization techniques. It predicts rate-dependent, polycrystalline SMA behavior, and it accommodates heat transfer issues pertinent to thin-film SMAs. The main advantages of this model are that it admits a simple, low-order formulation suitable for implementation and subsequent control design, and that most of the model parameters are identifiable directly from standard measurements. We illustrate aspects of the model through comparison with thin-film SMA superelastic and shape memory effect hysteresis data.}, number={1-2}, journal={THIN SOLID FILMS}, author={Massad, JE and Smith, RC}, year={2005}, month={Oct}, pages={266–290} }
 @article{massad_smith_2003, title={A  domain wall model for hysteresis in ferroelastic materials}, volume={14}, DOI={10.1177/104538903035235}, number={7}, journal={Journal of Intelligent Material Systems and Structures}, author={Massad, J. E. and Smith, Ralph}, year={2003}, pages={455–471} }