MEMS directional sound sensor with simultaneous detection of two frequency bands

Conventional directional sound sensing systems use an array of spatially separated microphones to achieve directional sensing by monitoring the arrival times and amplitudes at each microphone. The directional accuracy is then determined by the spatial separation of the microphones. In contrast, the Ormia ochracea fly´s ears are separated by merely 500 μm yet have remarkable sensitivity to the direction of sound even at wavelengths two orders of magnitude greater than the size of the fly´s hearing structure. The fly uses a unique system which consists of two identical wings hinged at the center to determine the direction of sound. Recently, our group demonstrated a MEMS-based directional sound sensor modeled on the hearing system of the fly. The sensor response has two resonant modes (rocking and bending) and a strong response was only achieved at the bending frequency since the amplitude of the rocking mode depends on the tiny pressure difference between the two wings. In this paper, we report achievement of dual-band sensing using asymmetric wings to enhance the response at the rocking frequency. The fabricated sensor showed nearly equal responses at the rocking and bending frequencies.