Electrostatic Transducers with Solid Dielectric

Abstract

Recent studies of electrostatic transducers with solid dielectric have led to significant advances in electrostatic transduction. Electrostatic earphones have been constructed with multiple layers of solid dielectric. The use of multiple layers provides a total air gap that is more uniform over the area of the backplate and thus increases sensitivity and decreases mechanical distortion of the unit. The electrical distortion of these earphones can be reduced by use of a push-pull arrangement in which the foils are placed between two perforated metal plates. The external dc bias, which is required in most conventional condenser transducers, can be eliminated by the use of foil electrets. The foil electret is a 14-mil Mylar foil that is prepolarized in a dc field by a special process that is described. Such foil electrets have been used for push-pull earphones, as well as microphones. The use of thin foils in microphones gives a desirable high capacitance. The resulting lower impedance makes it possible to couple the output of the microphone directly to a conventional transistor amplifier. The well-known advantages of conventional condenser transducers are preserved in the described systems.