Effects of local shape features on the beampatterns of a dynamic biomimetic baffle

Abstract

Horseshoe bats have mobile pinnae that can change their shapes as a result of active actuation. A common pattern is an alteration between an upright and a bent-tip geometrical configuration. Numerical predictions of reception beampatterns associated with these different shape geometries have indicated that the upright configurations are associated with beampatterns dominated by a single mainlobe whereas the bent-tip configurations have prominent sidelobes. Using a biomimetic baffle prototype, we have found that this effect can be reproduced qualitatively with just a plain obliquely truncated cone that is fabricated from flexible material (rubber) and bent at the tip. However, local shape features can have a strong impact on the quantitative expression of this effect. The three features studied here were a vertical ridge, an equivalent to the bat's antitragus, and a lateral incision into the baffle rim. The effects of these features on the beampatterns where found to interact with each other and also depend strongly on the deformation stage of the baffle shape. Hence the corresponding biological features may offer bats an opportunity to fine-tune their beampatterns as a function of deformation stage. However, control strategies for biomimetic devices with variable beampatterns have yet to be developed.