EQUIVALENT-CIRCUIT MODEL OF THE SQUEEZED GAS FILM IN A SILICON ACCELEROMETER

We present a new electric equivalent circuit for the forces created by a squeezed gas film between vertically moving planar surfaces. The model is realized with frequency-dependent resistors and inductors. Circuit analysis tools are applied to calculate the response of a micromechanical silicon capacitive accelerometer in both the frequency and the time domains. The simulations are shown to match the measured frequency responses in an excellent way. We utilize the circuit model to calculate the effective viscosity in a narrow gap between the moving surfaces. The results are compared with different slip-flow equations discussed in the literature. We present a simple approximate equation of the pressure-dependent viscosity that is valid for both viscous and molecular damping regions, and has 5% accuracy.