Loss Compensation in Time-Dependent Elastic Metamaterials

TL;DR

This paper derives an exact expression for wave amplitude in lossy, time-modulated elastic materials, revealing conditions where temporal modulation compensates for dissipation, enabling lossless wave propagation.

Contribution

It introduces a novel analytical framework for loss compensation in time-dependent elastic metamaterials, linking band-gap properties and viscosity to achieve amplitude stability.

Findings

Waves can maintain constant amplitude despite material losses.

A general condition for loss compensation is derived.

Design guidelines for lossless mechanical metamaterials are provided.

Abstract

Materials with properties that are modulated in time are known to display wave phenomena showing energy increasing with time, with the rate mediated by the modulation. Until now there has been no accounting for material dissipation, which clearly counteracts energy growth. This paper provides an exact expression for the amplitude of elastic or acoustic waves propagating in lossy materials with properties that are periodically modulated in time. It is found that these materials can support a special propagation regime in which waves travel at constant amplitude, with temporal modulation compensating for the normal energy dissipation. We derive a general condition under which amplification due to time-dependent properties offsets the material dissipation. This identity relates band-gap properties associated with the temporal modulation and the average of the viscosity coefficient, thereby providing a simple recipe for the design of loss-compensated mechanical metamaterials.