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Unidirectional zero sonic reflection in passive 𝓟𝓣-symmetric Willis media

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2018-11-15
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American Physical Society (APS)
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In an effective medium description of acoustic metamaterials, the Willis coupling plays the same role as the bianisotropy in electromagnetism. Willis media can be described by a constitutive matrix composed of the classical effective bulk modulus and density and additional cross-coupling terms defining the acoustic bianisotropy. Based on a unifying theoretical model, we unite the properties of acoustic Willis coupling with PT-symmetric systems under the same umbrella and show in either case that an exceptional point hosts a remarkably pronounced scattering asymmetry that is accompanied by one-way zero reflection for sound waves. The analytical treatment is backed up by experimental input in asymmetrically side-loaded waveguides showing how gauge transformations and loss biasing can embrace both Willis materials and non-Hermitian physics to tailor unidirectional reflectionless acoustics, which is appealing for purposeful sound insulation and steering.
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Acoustic metamaterials, Electromagnetism, Bianisotropic media, Optics
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Physical review B, 98(20), 201102(R), Nov. 2018,