Design of metasurfaces to enable shear horizontal wave trapping

We propose a simple method to design a wave trapping mechanism, referred to as an elastic open cavity, for shear horizontal waves using the concept of metasurfaces. Conventional open cavity designs have utilized bulk metamaterial media with negative refractive indices at certain frequencies. Here, we show that wave trapping can be attained depending on the incident angle with a suitable design and arrangement of several metasurfaces. This design strategy can be applied to waves with various incident angles and frequencies. We show that the incident angles and the number of metasurfaces are closely related. In addition, connections between the characteristic length of the metasurfaces and the resonance frequency are discussed. As an illustration, we theoretically derive the wave fields for an elastic open cavity with six metasurfaces. Numerical simulations based on the finite element calculations are performed to verify the correctness and consistency of the theory. Instead of using reflecting walls to localize energy, this wave trapping mechanism stores mechanical energy via constructive interference by guiding wave fronts that travel around closed contours. The demonstration of this concept could be a potential guide to design new energy harvesting devices.