Optical Differential Microphone
This invention involves a differential microphone that utilizes an optical means of converting the sound-induced motion of the diaphragm into an electronic signal. The majority of high-performance microphones, and particularly miniature microphones used in cellular telephones and hearing aids, use capacitive sensing to detect the diaphragm motion. This involves detecting the change in capacitance between the pressure-sensitive diaphragm and a back plate electrode. In order to detect this change in capacitance, it is first necessary to impose a bias voltage between the back plate and the diaphragm. This voltage creates practical constraints on the mechanical design of the diaphragm that compromise its effectiveness in detecting sound. The aim of this invention is to overcome these performance limitations by the use of an optical detection scheme. The optical detection scheme uses 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.
- The optical design permits the use of much more flexible and smaller diaphragms, which can be made using silicon micro-fabrication techniques.
- It achieves higher signal to noise ratios than are possible in capacitive sensing schemes.
- It has a much lower noise detection floor relatively low power consumption, and is lightweight.
U.S. 7,826,629; 8,503,701
Binghamton Univeristy RB220