Normal and tangential impact in micro electromechanical structures

Abstract

Micro-electromechanical structures made of polycrystalline silicon (poly-Si) have been fabricated, analyzed, and tested for repetitive impact at frequencies of up to 14 kHz and for durations of 46 continuous hours in order to characterize both normal and tangential impact on the microscale. Nonlinear dynamic models of the impact bumper and target impact wall have been formulated using coefficients of restitution for both normal and tangential impact. It was estimated that the coefficient of restitution can be very small (0-0.25), which indicates that the impact of poly-Si microstructures can, under certain circumstances, dissipate substantial kinetic energy. An analytic model assuming Coulomb friction and no sliding during oblique impact has been formulated, and it is believed that slipping indeed exists, requiring a more complicated model. A wear test has been carried out with a design of a microstructure to generate large surface contact stress (approximately 2 GPa) resulting from impact. After 12 hours of testing, a surface defect in the impacting surface is observable.<>