A BEM technique for free-molecule flows in high frequency MEMS resonators

A boundary element approach is proposed for the analysis of free-molecule flows in order to evaluate mechanical dissipation in micro-systems working at low pressure. The formulation is first presented for the general case of large perturbations and then adapted to the typical working conditions of micro-electro-mechanical-systems (MEMS). Since polysilicon micro-systems are addressed, the high surface roughness justifies the adoption of a diffuse reflection model at surfaces. The final linear boundary integral methods (BIE), which represents a flow balance of molecules on the surface, is implemented for medium scale 3D problems and validated against both analytical and experimental results with very promising results.