Non-reciprocal wave propagation in space-time modulated media

TL;DR

This paper demonstrates how space-time modulated media can achieve non-reciprocal wave propagation by breaking time-reversal symmetry, leading to unidirectional band gaps, supported by asymptotic analysis and numerical simulations.

Contribution

It provides a theoretical framework and analysis for non-reciprocal wave behavior in space-time modulated media, highlighting the role of band structure folding and degeneracy breaking.

Findings

Non-reciprocal wave propagation is achievable in space-time modulated media.

Modulation causes band structure folding and potential degeneracies.

Breaking time-reversal symmetry opens unidirectional band gaps.

Abstract

We prove the possibility of achieving non-reciprocal wave propagation in space-time modulated media and give an asymptotic analysis of the non-reciprocity property in terms of the amplitude of the time-modulation. Such modulation causes a folding of the band structure of the material, which may induce degenerate points. By breaking time-reversal symmetry, we show that these degeneracies may open into non-symmetric, unidirectional band gaps. Finally we illustrate our results by several numerical simulations.