Damping of micro electrostatic torsion mirror caused by air-film viscosity

Abstract

A method of analyzing the damping characteristics of electrostatically driven torsion mirror actuators which have deep grooves on their electrodes is described. The damping force is caused by viscous friction of the gas film between a moving mirror plate and the electrodes. The grooves decrease the damping force and enable the moving plate to be driven at high speed and low driving voltage. To calculate the damping force correctly, it is necessary to consider the viscous friction not only on the moving plate and electrodes, but also on the sidewalls of the grooves. For that purpose, the idea of hydraulic mean depth is introduced and is applied to the Reynolds equation. The calculated damping force shows good agreement with the measured damping force of the developed torsion mirror actuator for optical heads.