A new approach to tackle noise issue in miniature directional microphones: bio-inspired mechanical coupling

摘要

When using microphone array for sound source localization, the most fundamental step is to estimate the time difference of arrival (TDOA) between different microphones. Since TDOA is proportional to the microphone separation, the localization performance degrades with decreasing size relative to the sound wavelength. To address the size constraint of conventional directional microphones, a new approach is sought by utilizing the mechanical coupling mechanism found in the superacute ears of the parasitic fly Ormia ochracea. Previously, we have presented a novel bio-inspired directional microphone consisting of two circular clamped membranes structurally coupled by a center pivoted bridge, and demonstrated both theoretically and experimentally that the fly ear mechanism is replicable in a man-made structure. The emphasis of this article is on theoretical analysis of the thermal noise floor of the bio-inspired directional microphones. Using an equivalent two degrees-of-freedom model, the mechanical-thermal noise limit of the structurally coupled microphone is estimated and compared with those obtained for a single omni-directional microphone and a conventional microphone pair. Parametric studies are also conducted to investigate the effects of key normalized parameters on the noise floor and the signal-to-noise ratio (SNR).