Bidirectional Electrostatic Actuator Operated With Charge Control

A method for driving an electrically floating, bidirectional electrostatic actuator using high-speed switching and charge control has been proposed and verified experimentally. A macroscopic experiment is used to model the operation of a surface-micromachined microelectromechanical systems (MEMS) device having the form of two parallel electrodes, one rigid, and the other flexible. The movable, or “free” electrode, is connected to ground via a switching device, and the stationary electrode is connected to a single voltage source. The free electrode is alternately charged by induction, then left floating and subjected to a field produced by the stationary electrode. This charge-control mode of operation overcomes the travel range limits associated with the well-known “snap-through” instability. Our proof-of-concept experiment shows that a periodic charging/driving cycle increases the possible travel range of the free electrode by a factor of two over that possible without charge control. The configuration has the potential for use in a variety of optical MEMS applications involving mirror surfaces that must be exposed to the outside world.