Dynamic Emission Baffle Inspired by Horseshoe Bat Noseleaves

The evolution of bats is characterized by a combination of two key innovations - powered flight and biosonar - that are unique among mammals. Bats still outperform engineered systems in both capabilities by a large margin. Bat biosonar stands out for its ability to encode and extract sensory information using various mechanisms such as adaptive beam width control, dynamic sound emission and reception, as well as cognitive processes. Due to the highly integrated and sophisticated design of their active sonar system, bats can survive in complex and dense environments using just a few simple smart acoustic elements. On the sound emission side, significant features that distinguish bats from the current man-made sonar system are the time-variant shapes of the noseleaves. Noseleaves are baffles that surround the nostrils in bats with nasal pulse emission such as horseshoe bats and can undergo non-rigid deformations large enough to affect their acoustic properties significantly. Behavioral studies have shown that these movements are not random byproducts, but are due to specific muscular action. To understand the underlying physical and engineering principles of the dynamic sensing in horseshoe bats, two experimental prototypes ,i.e. intact noseleaf and simplified noseleaf, have been used. We have integrated techniques of data acquisition, instrument control, additive manufacturing, signal processing, airborne acoustics, 3D modeling and image processing to facilitate this research. 3D models of horseshoe bat noseleaves were obtained by tomographic imaging, reconstructed, and modified in the digital domain to meet the needs of additive manufacturing prototype. Nostrils and anterior leaf were abstracted as an elliptical outlet and a concave baffle in the other prototype. As a reference, a circular outlet and a straight baffle designed. A data acquisition and instrument control system has been developed and integrated with transducers to characterize the dynamic emission system acoustically as well as actuators for recreating the dynamics of the horseshoe bat noseleaf. A conical horn and tube waveguide was designed to couple the loudspeaker to the outlet of bat noseleaf and simplified baffles. A pan-tilt was used to characterize the acoustic properties of the deforming prototypes over direction. By using those techniques, the dynamic effect of the noseleaf was reproduced and characterized. It was suggested that the lancet rotation induced both beam-gain and beamwidth changes. Narrow outlet produced an isotropic beampattern and concave baffle had a significant time-variant and frequency-variant effect with just a small displacement. All those results cast light on the possible functions of the biological morphology and provided new thoughts on the engineering device's design.