The big brown bat Eptesicus fuscus has pinnae with prominent ridge structures. Image used with permission © Merlin D. Tuttle, Bat Conservation International.
From paraboloid to pinna ridges. (a) A pair of paraboloids axially shifted by both focus incident acoustic planar wavefronts onto the ec. The two rectangular patches shown at top correspond to two ridge reflecting areas.
Vertical cross-sections through four paraboloidal patches model E. fuscus pinna containing four ridges. Dotted lines show horizontal connections between patches to construct ideal reflecting Fresnel lens. Dashed lines show geometric paths from ridges to ec. Heavy lines show corresponding ridge heights. Light lines show Fresnel lens heights that are lost to obtain geometric paths from ridges to ec. (a) Direct reflection into the ec. (b) Tragus acting as a secondary reflector as in a Cassegrain system results in more efficient Fresnel lens structure.
Ridge impulse response produced by random search and magnitude frequency responses. (a) Tapered impulse response weights show apodization. (b) Frequency responses. Dashed curve: response computed from impulse response in (a). Dotted curve: response if ridge components had equal weights (no apodization). Solid curve: apodized response modified by Rayleigh scattering efficiency correction.
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