Hybridization of Guided Surface Acoustic Modes in Unconsolidated Granular Media by a Resonant Metasurface

Abstract

Elastic metasurfaces can manipulate the propagation of surface acoustic waves (SAWs) for applications as wave filters, including barriers for seismic surface waves---earthquake protection, that is. Efforts so far have focused on homogenous media, in crude approximation of the real world. The authors study the dynamics of an elastic metasurface in an unconsolidated granular medium, which presents an inhomogeneous stiffness profile. The metasurface's resonance hybridizes the lowest-order SAW and down-converts all higher-order SAWs, preventing the surface-wave delocalization seen in homogeneous media. These findings could impact protective designs for inhomogeneous stratified soils.