Piezoresistive Semiconductor Microphone

Abstract

A microphone using the piezoresistive effect of n-type germanium has been designed and constructed with a cantilever beam arrangement. Frequency response curves were taken in a sound field of 10 microbars with the microphone in a bridge type circuit and biased with 9 and 18 milliamperes. The microphone produces 10−11 watt in the flat low frequency range and peaks to 10−9 watt at a resonance at 2570 cps with a total bias of 18 ma in a bridge type circuit. Other designs of transducers and different types of semiconductor material are discussed. The performance of a germanium rod microphone is compared with a standard carbon button transmitter.