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Direction Finding System Using MEMS Sound Sensors

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 accuracy of the directionality in this case is determined by the extent of spatial separation of the microphones making them bulky. On the other hand, the ears of Ormia ochracea fly are separated mere 0.5 mm yet it has remarkable sensitivity to direction of sound. The fly’s unique ear structure consists of two eardrums coupled at the center. The incident sound generates directionally dependent oscillations of the eardrums with large amplitudes at normal modes of the coupled system. In this work, a narrowband MEMS direction finding sensor has been developed based on the fly’s hearing system. The sensor consists of two wings coupled at the middle and attached to a substrate using two legs. The sensor operates at its bending resonance frequency and has cosine directional characteristics similar to that of a pressure gradient microphone. Thus, the directional response of the sensor is symmetric about the normal axis making the determination of the direction ambiguous. To overcome this shortcoming two sensors were assembled with a canted angle similar to that employed in radar bearing locators. The outputs of two sensors were processed together allowing direction finding with no requirement of knowing the incident sound pressure level. At the bending resonant frequency of the sensor an output voltage of about 10 V/Pa was measured which three orders of magnitude larger than conventional MEMS microphones. The accuracy of the bearing of sound is found to be about 2°. These findings indicate the great potential to use dual MEMS direction finding sensor assemblies to locate sound sources with high accuracy.

Inventors: 
Patent Number: 
US 9,843,858
Technology Type(s): 
Electronics
Patent Status: 
Active
Patent Issue Date: 
December 12, 2017
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