Direction finding using multiple MEMS acoustic sensors

Abstract : A microelectromechanical direction-finding sensor has been developed based on the mechanically coupled ears of the Ormia ochracea fly. Previous designs determined the direction of sound relative to the normal of the sensor by using the sound pressure level at the sensor. However, these designs suffered from a left-right ambiguity. To overcome these shortcomings, a dual sensor assembly was created. Two sensors co-located at an offset angle allow direction finding across 120 deg. This eliminated ambiguous angles and the requirement for a sound pressure level. For this study, the dual sensor assembly was fabricated using two custom circuit boards powered by a 9V battery and arranged on a 3D-printed mount. The resonant frequency of the sensors produced a 260 V/Pa output at 1.690 kHz +- 20 Hz. Experimental work was done in an anechoic chamber, and outputs were captured using lock-in amplifiers. The angle error ranged from less than 0.3 deg close to the normal axis (0 deg) to 3.4 deg at the limits of coverage, +- 60 deg. The outcome of this research is that it is possible to operate this microelectromechanical direction-finding sensor assembly to find the bearing of a signal on resonance over an angular range of 120 deg with a maximum uncertainty of 3.4 deg.