Abstract:
MEMS devices employ the mechanical behavior of microstructures for sensing, controlling, and actuating. Their function, reliability, and fatigue life greatly depend on the microstructure’s mechanical behavior. Microstructures have an infinitesimal stiffness and high surface-to-volume ratio. Consequently, its behavior is influenced by surface forces and forces arising from the external fields/sources. The undesirable/excessive forces hinder MEMS function and act as a disturbance. Therefore, their assessment and control are crucial for the design of MEMS devices. Microstructures experience sliding motion in MEMS devices, where friction force is dominant. In this study, the contact behavior and friction force of a microwire are evaluated numerically for the push-pull sliding motion against two opposite microprobes. The microwire is manipulated against microprobes by a Double Beam Cantilever (DBC), where one end of the microwire is attached at the tip of the DBC and the other end is supported between microprobes by frictional contact. The microwire's friction force and contact behavior are evaluated numerically by the FEA tool ANSYS Workbench. The results are validated by comparing with the experimental results available in the literature. The effects of variation of the contact pressure, size, and boundary conditions of the microwire on the friction force are also investigated. The vibrational characteristics of DBC are evaluated numerically and compared with Single Beam Cantilever (SBC) for MEMS manipulation. Besides, the electrostatic and adhesive forces between the microwire and microprobe are assessed for a single contact, where the available experimental deformations of the microwire under electrostatic and adhesive force are used as boundary conditions of the numerical analysis. The numerical analysis is performed in the absence of all disturbance forces other than friction force. Therefore, the difference between the available experimental and numerical results reveals the sum of all surface and external disturbance forces in the microwire. The surface forces, such as adhesive, electrostatic, etc., and the sum of disturbance forces arising from the external sources/fields are predicted by comparing numerical results with the experimental results. This study's results reveal that the friction force in sliding microstructures can be controlled by suitable size and boundary conditions besides surface asperity. This study will help to evaluate friction force and contact behavior in other microstructures, such as microbars, microplates, etc., for sliding motion, and to select the appropriate type and length of the cantilever for MEMS application. Besides, it will aid in achieving MEMS devices' reliability and fatigue life by assessing surface and external disturbance forces in microstructures.