Characterization of the time-variant behavior of a biomimetic beamforming baffle

Abstract

Horseshoe bats can actively change the shapes of their noseleaves and outer ears on time scales that are comparable to the duration of the biosonar pulses and echoes. When the shape deformations and the emission or reception of the ultrasonic signals overlap in time, the result is a time-variant diffraction process. Such a dynamic process provides additional flexibility that could potentially be used to enhance the encoding of sensory information. However, such a function remains hypothetical at present. To investigate the time-variant properties of deforming baffles such as the outer ears of horseshoe bats, the acoustic behavior of a biomimetic microphone baffle modeled on these biological structures has been investigated. The methods employed to characterize this device included representations in the time-delay domain as well as in the time-frequency domain. It was found that characterization methods which do not employ Fourier transforms revealed even more substantial time-variant effects than were apparent from time-frequency domain characterizations such as beampatterns obtained for different times in the deformation cycle. Furthermore, conspicuous correlates of asymmetries in the time-variant physical shapes were found in some characterizations that could be used to link dynamic baffle geometry with acoustic behavior.