Microwave and Acoustic Absorption Metamaterials

Abstract

Wave-absorption metamaterials have been an enduring topic over the past two decades, propelled not only by scientific advances, but also by their extensive application potential. In this review, we aim to provide some general insights into the absorption mechanism common to both microwave and acoustic systems. By establishing a universal model for resonance-based metamaterials, we present the theoretical conditions for broadband impedance matching and introduce the fundamental causal limit as an evaluation tool for absorption performance. Under this integrated framework, we survey recent advances in metamaterial absorption in both microwave and acoustic systems, with a focus on those that have pushed the overall performance close to the causal limit. We take note of some emerging metastructures that can circumvent the constraints imposed by causal limit, thereby opening an avenue to low-frequency absorption. This review concludes by discussing the existing challenges with possible solutions and the broad horizon for future developments.