The optical design permits the use of much more flexible and smaller diaphragms, which can be made using silicon micro-fabrication techniques.
This micro-machined differential microphone utilizes an optical means to convert the sound-induced motion of a diaphragm into an electronic signal. Because it can be manufactured with high sensitivity and low noise, this lightweight microphone design offers a means to improve hearing aids and cellular phone applications. This invention overcomes changes in capacitance performance limitations by using an optical detection scheme based on a low-power semiconductor laser and optical gratings incorporated into the microphone diaphragm. Because the overall compliance of the microphone diaphragm is adjustable over a very wide range, it is possible to achieve high sensitivity and very low noise performance.