A specific type of Microsystems or MEMS is the so called RF-MEMS switch. In contrast to MEMS resonators switches generally do not operate in a vacuum. Therefore at the small scales of MEMS fluid (or air) damping is the most dominant damping form. This means that if one is interested in transient or frequency behavior a proper damping model is required. This paper presents a way of using the non-linear Reynolds equation to model the squeeze film damping that is often the type of fluid damping present in these switches. The formulation is provided ready for FEM implementation. Also the tangent matrices required for linearized eigen frequencies are derived. The equations are tested on a model of simple micro switch. The results show that with this model it is possible to predict the damped motion as well as the frequency behavior. The frequency results also show that damping shifts the zero frequency point away from the pull-in point. With a simple mechanical contact model it is also possible to model the closing and opening transient of a microsystem.

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