C6.1 - Hearing Aid Microphones: From Electret to Piezoelectret Transducers

G. M. Sessler & J. Hillenbrand
For several decades, most hearing aids have been equipped with electret microphones. These transducers are of simple design. They consist of an electret, mostly a thin polytetrafluoroethylene film cemented to a back electrode, and a membrane, often a metallized polymer film, separated by a shallow air gap from the electret. Some years ago, a new type of electret microphone, based on cellular piezoelectrets, was introduced and characterized. Piezoelectrets consist of closed-cell foams, often of polypropylene...