High sensitive MEMS directional sound sensor with comb finger capacitor electronic readout

Abstract

The conventional directional sound sensing systems employ an array of spatially separated microphones to achieve directional sensing by monitoring the arrival times and amplitudes of different microphones. However, there are insects such as Ormia ochracea fly that can determine the direction of sound using its miniature-hearing organ much smaller than the wavelength of sound it detects. The fly’s eardrums that are coupled mechanically with separation merely by about 1 mm have remarkable sensitivity to the direction of sound. Our MEMS based sensor, which consists of two 1 mm2 wings connected in the middle, similar to the fly’s hearing system, was designed and fabricated using silicon on insulator (SOI) substrate. The vibration of the wings in response to incident sound at the bending resonance was measured using a laser vibrometer found to be about 1 μm/Pa. For measuring sensor response electronically, comb finger capacitors were integrated on to the wins and the measured output using a MS3110 capacitive to voltage converter was found to be about 25 V/Pa. The fabricated sensors showed cos2q directional response similar to a pressure gradient microphone. The directional response of the sensor was measured down to about 30 dB.