The electromechanical response of a symmetric electret parallel-plates actuator

The electromechanical response of a symmetric electret parallel-plates actuator is analyzed. The actuator is constructed from a dielectric plate that is suspended by a linear spring between two electrodes of a planar capacitor. The dielectric plate is loaded with fixed charge, and is displaced due to the interaction between this charge and the electrostatic field. The electrostatic field that displaces the charged dielectric has three components: a field induced by the voltage difference across the capacitor plates, a field induced by the anti-symmetric part of charge, and a field induced by the combined effect of the symmetric part of charge and the displacement of the plate itself. The analysis shows that the displacement of the electret actuator is a linear function of the driving voltage, and that a full range of stable motion can be achieved. Furthermore, it is shown that all important characteristics of the fixed charge can be deduced from simple measurements.