3D FEM simulations of perforated MEMS gas dampers

A 3D Navier-Stokes FEM solver was used to study the damping forces due to air flow in a perforated damper in translational motion normal to surfaces. Several damper topologies with square surfaces having 16 or 64 square holes were simulated. Dimensions of micromechanical devices were used and thus a slightly rarefied gas flow was considered using slip velocity boundary conditions. Incompressible and inertialess flow with small pressure differences was assumed. The damping forces acting on various parts of the perforated structure and on the ground surface were studied extensively. For each geometry, the grid refinement ratio and the number of elements was varied. The simulation results show that the damping force acting on the perforated body and on the ground surface approach each other when the element count is increased. In spite of the large element count (ap 10⁶), the force on the perforated body did not reach grid convergence. The study shows also that a certain moderate grid refinement ratio gives results that depend less on the number of elements. Using this refinement ratio, grid convergence for the force on the ground surface could be reached with ap 3 ldr 10⁵ elements.