Bioinspired Conformal Transformation Acoustics

Abstract

Transformation theory is a powerful tool for material design to control waves in electromagnetics, acoustics, and elastic mechanics. Deformable materials are demonstrated to guide the propagation of ultrasonic waves freely. Toothed whales, such as dolphins and porpoises, may manipulate directional beams by simply deforming their foreheads. However, existing materials face great challenges in realizing their bioacoustic function. Here, we propose a bioinspired semianalytical conformal acoustics that can predict the evolution of acoustic functions strictly. Based on this method, we design a series of acoustic steering and collimation models. The sound-speed distribution functions can be determined by conformal mappings, and the acoustic-beam steering and expansion are numerically confirmed. We further experimentally fabricate acoustic steering and collimation devices by using metamaterials. The experimental results show good agreement with theoretical predictions. The proposed bioinspired conformal acoustics may bridge the gap between an animal's biosonar and artificial materials, which show potential application value in underwater acoustics, medical ultrasonography, and other related applications.