Simulating bat sonar using vector sound intensity

Abstract

In general bats use ultrasound to determine their surroundings and to detect flying insects. Generally the beam width of ultrasonic signals emitted by bats is too wide to distinguish closely-spaced objects and the receiving pattern of bats' ears is similar (J. A. Simmons, "Directionality of biosonar broadcasts and reception by the ears", Tutorial Lecture, ASA Spring Meeting, 2002). To locate an object requires knowing both distance and direction. Distance can be readily determined using time-of-flight. How a bat determines direction is less clear. In this presentation, an ultrasonic device is demonstrated that measures both distance and direction (R. Hickling, "Method and Apparatus for Echolocation" US Patent No. 7,054,226, May 2006). This uses a combination of a pulsed ultrasonic source and a vector sound-intensity probe. The probe has four ultrasonic receivers at the vertices of a regular tetrahedron and determines direction from the sound-intensity vector, using finite-difference approximations and the cross-spectral formulation. The frequencies of the echoes received by the probe have to be heterodyned down to lower frequencies for accuracy in the finite-difference approximations. Echolocation data using the device are presented.