A implantable sealed microphone (50) includes a diaphragm (52) having a thin central region (54) surrounded by a thicker rim (56). One side of sheet electret material (72) is bonded to the diaphragm (52) while the other side contacts a roughened plate (82). The rim (56) is bonded to a housing (112) thereby...http://www.google.es/patents/US5881158?utm_source=gb-gplus-sharePatente US5881158 - Microphones for an implantable hearing aid
