Large reconfigurable microphone array for transmit beam pattern measurements of echolocating bats

Abstract

Measurements of the transmit beam patterns in bats have previously been limited to a single cross-sectional plane or averaged over multiple in-flight approaches with sparse microphone arrays. No high-resolution measurements have been published to date of individual transmitted beams jointly in azimuth and elevation. Toward this goal, a high density microphone array was designed and constructed using low-cost ultrasonic microphones and custom electronic circuitry. The planar array is 1.83 meters wide by 1.42 meters tall with sensors positioned on a 2.54 cm square grid. The system can record up to 228 channels simultaneously at a 500 kHz sampling rate. Big brown bats (Eptesicus fuscus) were trained to echolocate pairs of virtual targets in a two-alternative forced choice discrimination task while their signals were being recorded by the array. Visualizations of the beam patterns during the task will be presented along with some advanced signal processing techniques used in the analysis. [funded by ONR and N...