Novel inversion theory and sensor structure of biomimicry directional microphone

Micromachined directional microphones (sound source localization sensor) mimicking an auditory organ of Ormia ochracea have been intensively studied based on center-supported, marginally free 1-D or 2-D diaphragm structures. This paper first describes an exact mathematical theory of sound source localization based on the partial differential equation (PDE) formulation of the problem and the weighted integral method to obtain an exact direct algebraic solution of the sound distance and direction. This theory shows a Gaussian weight function on the diaphragm is inevitable in the transduction of 1st and 2nd moments. An analysis was performed to obtain the weight distribution assuming an arbitrary thickness distribution of a shell-structured diaphragm. The best result was a marginally-supported face-to-face cantilever structure. We fabricated this structure using SOI wafer and RIE. The experimental results show a strong dependence of the vibration pattern on both zenith and azimuth angles, and a greatly enhanced sensitivity to inclined sound pressure.