@article{ouyang_mcdonald_zhu_2013, title={Temperature-dependent material properties of Z-shaped MEMS thermal actuators made of single crystalline silicon}, volume={23}, ISSN={["1361-6439"]}, DOI={10.1088/0960-1317/23/12/125036}, abstractNote={MEMS thermal actuators have been employed in a broad range of applications, often operating in different environments (e.g. vacuum, air or liquid). Since the involved heat dissipation mechanisms are different in different operating environments, the device performances are expected to be different. In this paper, we report experimental measurement and multiphysics modeling of device performance metrics of a recently introduced thermal actuator, the Z-shaped thermal actuator, including temperature distribution, electric resistance and displacement in both air and vacuum environments. The temperature measurement was based on Raman scattering in air. Fully 3D multiphysics (coupled thermo-electro-mechanical) simulations were performed to treat both air and vacuum environments. Heat conduction through air to neighboring devices is important, while heat convection to air is negligible. The experimental and modeling results agreed well, which demonstrated the accuracy of the temperature-dependent material properties used in the modeling. Fully 3D multiphysics modeling combined with valid material property parameters will enable the exploration of the design space and the optimization of performances of the MEMS thermal actuators for different operating environments.}, number={12}, journal={JOURNAL OF MICROMECHANICS AND MICROENGINEERING}, author={Ouyang, Jing and McDonald, Margaret and Zhu, Yong}, year={2013}, month={Dec} }
 @article{ouyang_zhu_2012, title={Z-Shaped MEMS Thermal Actuators: Piezoresistive Self-Sensing and Preliminary Results for Feedback Control}, volume={21}, ISSN={["1941-0158"]}, DOI={10.1109/jmems.2012.2189361}, abstractNote={Feedback control of microactuators holds potential to significantly improve their performance and reliability. A critical step to realize the feedback control of microactuators is feedback sensing. In this paper, we report the feasibility of using a Z-shaped thermal actuator (ZTA) as a simultaneous force or displacement sensor. An in situ scanning electron microscope nanomanipulation process is used to characterize the piezoresistive response of ZTAs, which shows that ZTAs can be used as piezoresistive sensors. The experimental results agree very well with multiphysics (electric-thermal-structural-piezoresistive) simulations. A new feedback scheme is further explored, where the ZTA is treated as a two-input (applied current and external force) and two-output (displacement and electric resistance) system. Based on the calibrated relationships between the inputs and the outputs, a feedback system is developed, which can simultaneously sense the external force and generate updated current to actuate the ZTA to the desired position. We demonstrate preliminary results of this feedback control by holding the ZTA at a constant position under various external forces. The device and method presented in this paper are valuable for a range of microelectromechanical systems applications, including on-chip nanoscale mechanical testing and nanopositioning.}, number={3}, journal={JOURNAL OF MICROELECTROMECHANICAL SYSTEMS}, author={Ouyang, Jing and Zhu, Yong}, year={2012}, month={Jun}, pages={596–604} }