Active Willis metamaterials for ultra-compact non-reciprocal linear acoustic devices

Abstract

Willis materials are complex media characterized by four macroscopic material parameters, the conventional mass density, and 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 article, we show experimentally that linear active Willis metamaterials breaking these constraints enable highly non-reciprocal sound transport in very subwavelength structures, a feature unachievable through other methods. 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 allowed to vary independently. The approach presented here will enable a new generation of Willis materials for enhanced sound control and improved acoustic imaging and signal processing.

arXiv comment5 pages, 5 figures

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Cited by in corpus (9)

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• Digitally virtualized atoms for acoustic metamaterials
• Symmetry Breaking Creates Electro-Momentum Coupling in Piezoelectric Metamaterials
• Broadband nonreciprocal linear acoustics through nonlocal active media
• Acoustic amplifying diode using non-reciprocal Willis coupling
• Exact analogue of the Hatano-Nelson model in 1D continuous nonreciprocal systems
• Symmetry-driven Phononic Metamaterials
• Fundamental principles for generalized Willis metamaterials
• Acoustic Willis metamaterials beyond the passivity bound