SUMMARY

Silicon micromachined microphones with diffraction-based optical displacement detection and integrated optoelectronics are presented. Both omnidirectional and directional microphone designs are described and tested. Omnidirectional microphones share similarities with existing capacitive micromachined microphones. The novel, biomimetically inspired, directional microphones were supplied by the State University of New York at Binghamton and accomplish directionality by imitating the intertympanal mechanical coupling of the fly, Ormia ochracea. A modular packaging architecture, suitable for testing both types of microphones and comparable to measurement microphone packages, is designed to impose minimal disturbance to measured acoustic fields. Results from the omnidirectional optical microphone structure demonstrate the capability of resolving 150fm/√Hz (5µPa/√Hz) across much of the audio bandwidth. This resolution, limited primarily by relative laser intensity noise, allows the 2mm diameter omnidirectional microphone to achieve a 26dBA noise floor. The biomimetic directional optical microphone, which has an equivalent port spacing of 1mm, is able to resolve 2.5pm/√Hz (1.5x10-5 Pa/√Hz) at 1kHz. The noise floor of this microphone is measured to be 34dBA and is limited by the thermal mechanical noise level of the soft differential diaphragm. An array of two biomimetic directional optical microphones located on the same silicon chip and separated by less than 5mm is also implemented and measured to have directivity indices of 4.6 and 3.5. These results confirm the micro-optical detection method as an alternative to capacitive detection especially for miniaturized microphone applications and suggest that this method in its modular packaging architecture is competitive with industry leading measurement microphones.