Bifunctional superlens for simultaneous flexural and acoustic wave superfocusing

Abstract

Superfocusing of acoustic and elastic waves is generally achieved by the combination of negative refraction and the enhancement of the evanescent waves. Here, we numerically and experimentally demonstrate the bifunctionality of a superlens that can simultaneously focus acoustic and flexural waves beyond the diffraction limit. The designed structure is composed of a two-dimensional arrangement of pillars that act as rigid scatterers for the sound waves and as resonant scatterers for the flexural waves. The band structure presents modes with negative dispersion bands allowing negative refraction for both types of waves within the frequency range of 6.9–7.4 kHz, which is induced by the Bragg scattering effect. Edge modes that enhance the evanescent waves through resonant coupling appear around 7.2 kHz for the flexural and sound wave. The simultaneous superlensing is then observed at this frequency. Our finding will enlighten multiphysical and multifunctional wave manipulations and could have pragmatic applications involving multiwave devices.