Acoustic rainbow trapping through perforated structures

Acoustic rainbow trapping (ART) metamaterials are a type of artificial materials that allows intensive energy trapping and spatial-spectral modulation of broadband sound waves, by providing strong acoustic wave dispersions lacking in natural materials. However, previous studies on ART metamaterials are all based on 2D unit cells and thus require the structure size in the third dimension to be much larger than the wavelength, which limits their further applications. Here we would like to present an ART model that is constructed using 3D hole structures. Full wave numerical simulation result shows that incident plane waves of different frequencies are effectively converted into a highly-dispersive structure-induced surface waves (SSAWs) mode and trapped at different positions, inducing greatly enhanced sound fields, which is in good agreement with our theoretical prediction. Such ART metamaterials with 3D unit cells can be easily developed into practical use and may also be extended multi-dimensional case.