Subminiature hearing aid microphones

Electret microphones have played a key role in the miniaturization of hearing aids since 1970. With the passage of time their good stability finally is being confirmed with measured values of only 1.5dB loss in output after 15 years. Today's electrets help to fit hearing aids into the ear canal without sacrifice of performance even though the receiver is placed much closer. New microphones use a diaphragm 1 to 2 micron in thickness to reduce vibration-induced distortion and feed back from the receiver. Teflon back-electrets provide bias and close-coupled preamps impedance matching to the amplifier.