Large displacement parallel plate electrostatic actuator with saturation type characteristic

We report on a long travel electrostatic actuator operated by parallel plate electrodes. The actuator architecture is based on a folded suspension composed of initially curved beams with an actuating force applied along the beams. The straightening of the beams, which are used simultaneously as motion amplifiers and suspension elements, is transformed into the long stroke lateral motion of the actuator and much smaller axial displacement of the beams' ends. Small distances between electrodes are therefore possible, improving actuator effectiveness. Steep increase in the stiffness of the straightened beams improves actuator stability and leads to the saturation type voltage-displacement dependence. In the vicinity of the inflection point the voltage-displacement dependence is practically linear and therefore of importance for applications. The exact extensible elastica and approximate reduced order models of the actuator are used for the stability analysis. For some range of parameters multistability of the actuator is possible. Actuators of varying configurations were fabricated using SOI wafers and deep reactive ion etching (DRIE). The comparison between the experimental and model results reveals good agreement between the two.