We consider squeeze film gas damping during microbeam motion away and toward a substrate as occurs during opening and closing of RF switches and other MEMS devices. The numerical solution of the gas damping problem in two-dimensional geometries is obtained based on the Boltzmann-ESBGK equation. The difference in damping force between downward and upward moving beams is shown to vary from as little from as 5% for low beam velocities of 0.1m/s to more than 200% at 2.4m/s. For a constant velocity magnitude of 0.8m/s, this difference increases from 60% to almost 90% when the pressure is reduced by an order of magnitude. The numerical simulations are consistent with earlier observations of a significantly higher damping force during the closing of a capacitive RF MEMS switch reported by Steeneken et al. (JMM, 15, 176-184, 2005). The physical mechanism leading to this non-linear dependence of the damping force on velocity has been attributed to the differences in the flow rarefaction regime for the gas in the microgap.
Date of this Version
Chigullapalli, S; Weaver, A; and Alexeenko, Alina A., "Nonlinear Effects in Squeeze Film Gas Damping on Microbeams" (2012). School of Aeronautics and Astronautics Faculty Publications. Paper 4.