MANIPULATION OF SOUND PROPERTIES BY ACOUSTIC METASURFACE AND METASTRUCTURE

Abstract

Using the mathematical method called transformation acoustics, researchers have demonstrated acoustic metamaterials with unusual sound properties and phenomena. Here we extend the concept of metamaterial to metasurface and metastructure, which are made from assemblies of various elements fashioned from traditional materials such as copper or membrane. Different from metamaterial which enables abnormal sound properties inside itself, metasurface is a thin-layer structure which allows the change of sound properties right at its surface. Thus, instead of gradual change in metamaterial, acoustic waves seem to have an abrupt change after touching metasurface. Besides, inasmuch as acoustic metamaterial is based on transformation acoustics, the conformal mapping of coordinates inevitably leads to complex parameters. We also propose the concept of acoustic metastructure, which does not rely on transformation acoustics. By a unique design, the acoustic metastructure has a much accessible layout and does not have components of microscopic or smaller scales.