Resolving bearing ambiguity with a single bio-inspired direction finding microelectromechanical system acoustic sensor

Abstract

Microelectromechanical systems (MEMS) directional sound sensors have been developed to mimic the unique hearing mechanism of the parasitoid fly Ormia ochracea. The fly analyzes the superposition of the two natural oscillation modes (rocking and bending) of its coupled eardrums to identify the incident direction of a cricket chirp. The incident sound generates unequal oscillation amplitudes of the eardrums depending on the direction of incidence. The MEMS sensor consisted of two wings connected by a bridge which is attached to a substrate using two torsional legs. For electronic readout of the oscillation amplitude of the wings, a comb finger capacitor was integrated to each wing. The amplitudes of oscillation of the two wings were independently measured to probe the coupling between the rocking and bending modes. The measurement of the sensor response was performed optically, using a scanning laser vibrometer, and electronically using a capacitance to voltage converter. It was found that the oscillation amplitudes of the two wings are strongly affected by the incident direction of sound. In addition, higher wing deflection occurred on the side closest to the incident sound source indicating the ability of the sensor to detect the direction of sound without the right-left ambiguity.