Causality and instability in wave propagation in random time-varying media

TL;DR

This paper presents a theoretical model for wave propagation in media with random, time-varying properties, deriving an exact average Green's function and analyzing different propagation regimes, with implications for dynamic metamaterials and imaging.

Contribution

The paper introduces a non-perturbative, exact solution for wave propagation in temporally disordered media, extending analysis to the thermodynamic limit and providing an effective medium description.

Findings

Exact expression for average Green's function in finite temporal disorder

Causality prevents recurrent scattering in time-varying media

Analysis of propagation regimes using effective medium theory

Abstract

We develop a theoretical model to investigate wave propagation in media with random time-varying properties, where temporal fluctuations lead to complex scattering dynamics. Focusing on the ensemble-averaged field, we derive an exact expression for the average Green's function in the presence of finite temporal disorder, and extend the analysis to the thermodynamic limit. In contrast to spatial disorder, causality prevents recurrent scattering, allowing us to achieve a non-perturbative solution. We introduce an effective medium description providing a simple analysis of the propagation regimes. Our findings offer new insights into wave dynamics in temporally disordered media, with potential applications in time-varying metamaterials, dynamic sensing, and imaging in turbulent or chaotic environments.