Microwave and Acoustic Absorption Metamaterials

Using the framework of causal constraint and impedance matching, the authors take an unorthodox approach to surveying the literature on microwave and acoustic metamaterial absorbers on a unified basis. This perspective has the advantage of highlighting the potential of some particular approaches and ways to improve absorption toward a target absorption spectrum. The last section of the review focuses on current and developing methods to circumvent the causal constraint, with the goal of attaining absorption performance previously considered impossible.