Year: 2019
Type: article
Abstract: Willis materials are complex media characterized by four macroscopic material parameters, the conventional mass density, the bulk modulus, and two additional Willis coupling terms, which have been shown to enable unsurpassed control over the propagation of mechanical waves. However, virtually all previous studies on Willis materials involved passive structures which have been shown to have limitations in terms of achievable Willis coupling terms. In this Rapid Communication, we show experimentally that linear active Willis metamaterials breaking these constraints enable highly nonreciprocal sound transport in very subwavelength structures. Furthermore, we present an experimental procedure to extract the effective material parameters expressed in terms of acoustic polarizabilities for media in which the Willis coupling terms are not constrained by the relationship holding in unbiased passive materials. The approach presented here will enable a generation of ultracompact Willis materials for enhanced sound control and improved acoustic imaging and signal processing.
Authors: Yuxin Zhai, Hyung-Suk Kwon, Bogdan-Ioan Popa
Institution: University of Michigan
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2910860676