Acoustic Metamaterials for Sub-wavelength, Broadband, and Perfect Absorption in Ventilated Problems

This chapter describes the possibilities given by acoustic metamaterialsAcoustic metamaterial to produce sub-wavelength, broadbandBroadband, and perfect absorption in ventilated problems, i.e., accounting for both reflected and transmitted wavesWaves. We discuss the problem of perfect acousticAcoustic absorption both in the reflection and ventilated problems reviewing the different acoustic metamaterialsAcoustic metamaterial described in the literature to achieve these two goals. The general one-dimensional reciprocal scattering problem is first considered to derive the rigorous perfect absorption conditions. The complex frequencyFrequency plane and the Argand diagrams are then introduced to interpret and visualize the perfect absorption conditions. Acoustic metamaterialsAcoustic metamaterial made of HelmholtzHelmholtz resonatorsResonator are subsequently introduced, paying special attention to slow-soundSound systems. Finally, two examples of acousticAcoustic metamaterialsAcoustic metamaterial based on these acoustic metamaterials are shown, exhibiting perfect absorption either with or without mirror symmetry.