Design of broadband active sound isolators based on acoustic bianisotropic metamaterials

Abstract

The acoustic wave propagation through conventional materials is controlled by two parameters: the mass density and the bulk modulus. It has been shown that two additional parameters called Willis coupling terms are needed in order to describe the dynamics of certain complex media called bianisotropic (Willis) materials. The few bianisotropic (Willis) materials reported so far have experimentally demonstrated the ability of these complex media to control the propagation of sound beyond what is possible with conventional media. For instance, it has been shown that bianisotropic materials could control reflection and transmission coefficients independently and enable high-efficiency sound beam steering devices. In this presentation, we will describe a previously unexplored property of acoustic bianisotropy. Namely, we will present a design of ultra-compact active bianisotropic metamaterials that can serve as excellent sound isolators. In addition, we will discuss the bandwidth and stability of our design. We will show that unlike conventional active sound control devices, active bianisotropic materials are stable even in dynamically changing environments without employing any instability mitigation algorithms.