Klein-like tunneling of sound via negative index metamaterials

TL;DR

This paper demonstrates a classical analogue of Klein tunneling using acoustic metamaterials, enabling lossless, omnidirectional sound transmission without relying on quantum spinor structures.

Contribution

It introduces a novel mechanism for Klein-like tunneling in classical sound systems, independent of quantum pseudospin, and shows how anisotropy can achieve omnidirectional tunneling.

Findings

Simulated sound tunneling in acoustic metamaterials mimics quantum Klein tunneling.

Achieved omnidirectional tunneling by introducing specific anisotropy.

Potential for lossless, direction-independent sound transmission applications.

Abstract

Klein tunneling is a counterintuitive quantum-mechanical phenomenon, predicting perfect transmission of relativistic particles through higher energy barriers. This phenomenon was shown to be supported at normal incidence in graphene due to pseudospin conservation. Here I show that Klein tunneling analogue can occur in classical systems, and remarkably, not relying on mimicking graphene's spinor wavefunction structure. Instead, the mechanism requires a particular form of constitutive parameters of the penetrated medium, yielding transmission properties identical to the quantum tunneling in graphene. I demonstrate this result by simulating tunneling of sound in a two-dimensional acoustic metamaterial. More strikingly, I show that by introducing a certain form of anisotropy, the tunneling can be made unimpeded for any incidence angle, while keeping most of its original Klein dispersion properties. This phenomenon may be denoted by the omnidirectional Klein-like tunneling. The new tunneling mechanism and its omnidirectional variant may be useful for applications requiring lossless and direction-independent transmission of classical waves.