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.


This is the published version of [Chigullapalli, S.*, Weaver, A. B.*, and Alexeenko, A. A.]. (2012). “Non-linear Effects in Squeeze-Film Gas Damping on Microbeams”. First published in the Journal of Micromechanics and Microengineering and is available online at: http://dx.doi.org/10.1088/0960-1317/22/6/065010.

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