Gas Damping in Capacitive MEMS Transducers in the Free Molecular Flow Regime

We present a novel analysis of gas damping in capacitive MEMS transducers that is based on a simple analytical model, assisted by Monte-Carlo simulations performed in Molflow+ to obtain an estimate for the geometry dependent gas diffusion time. This combination provides results with minimal computational expense and through freely available software, as well as insight into how the gas damping depends on the transducer geometry in the molecular flow regime. The results can be used to predict damping for arbitrary gas mixtures. The analysis was verified by experimental results for both air and helium atmospheres and matches these data to within 15% over a wide range of pressures.

Numerical analysis of flows past two parallel flat plates in the free-molecular regime

A numerical investigation is presented for a free-molecular flow past two parallel circular flat plates using the test particle Monte Carlo (TPMC) method, with flow shadowing and multiple reflections analyzed. Flow shadowing and multiple reflections have a significant effect on aerodynamic forces, and the distance-to-radius ratio of the two plates has a considerable influence on flow shadowing and multiple reflections. As the distance-to-radius ratio increases, flow shadowing and multiple reflections become weaker. Different distance-to-radius ratios result in different surface pressure distributions.