Non-Reciprocal Willis Coupling in Zero-Index Moving Media

Abstract

Mechanical motion can break the symmetry in which sound travels in a medium, but significant non-reciprocity is typically achieved only for very large motion speeds. Here we combine moving media with zero-index acoustic propagation, yielding extreme non-reciprocity and induced bianisotropy for modest applied speeds. The metamaterial is formed by an array of waveguides loaded by Helmholtz resonators, and it exhibits opposite signs of the refractive index sustained by asymmetric Willis coupling for propagation in opposite directions. We use this response to design a non-reciprocal acoustic lens focusing only when excitation from one side, with applications for imaging and ultrasound technology.

References in corpus (7)

• Possible Realization of Directional Optical Waveguides in Photonic Crystals with Broken Time-Reversal Symmetry
• Epsilon-Near-Zero (ENZ) Metamaterials and Electromagnetic Sources: Tailoring the Radiation Phase Pattern
• An optical diode made from a `flying' photonic crystal
• Extraordinary Sound Transmission through Density-Near-Zero Ultranarrow Channels
• Asymmetric Wave Propagation in Nonlinear Systems
• Maximum Willis Coupling in Acoustic Scatterers
• Analytical formulation of 3D dynamic homogenization for periodic elastic systems

Cited by in corpus (8)

• Experimental Observation of Efficient Nonreciprocal Mode Transitions via Spatiotemporally-Modulated Acoustic Metamaterials
• Nonreciprocal phonon blockade
• Acoustic amplifying diode using non-reciprocal Willis coupling
• CPA-Lasing in Thin-Elastic Plates via Exceptional Points
• Band Structure and Effective Properties of One-Dimensional Thermoacoustic Bloch Waves
• Symmetry-driven Phononic Metamaterials
• Acoustic Willis metamaterials beyond the passivity bound
• Experimental Realization of Acoustic Bianisotropic Gratings