Ultrathin broadband acoustic reflection metasurface based on meta-molecule clusters

Abstract

The control of sound waves by metasurfaces is an interesting research topic in the metamaterial technology field. Based on existing research about the acoustic metamaterials constructed using meta-molecules, we propose a theoretical model of a deep subwavelength acoustic reflection metasurface. We further verify this model via simulations and experiments. The designed broadband acoustic metasurface consists of ‘meta-atoms’, ‘meta-molecules’, ‘meta-molecule clusters’ and ‘meta-molecule cluster sets’, in the aforementioned order. The structural parameters of the two meta-atom types can be adjusted to regulate the acoustic reflection phase, and the meta-molecule are sufficient to realise the discrete phase shifts that cover the complete 2π span. Meta-molecule clusters comprise meta-molecules that can adjust certain geometric parameters of the meta-atoms to achieve abnormal and negative reflections. In addition, ‘meta-molecule cluster sets’ enable the metasurface to achieve a broad multi-frequency response by combining two types of meta-atoms’ regulative modes. We construct a meta-molecule cluster set consist of two clusters enable the broadband metasurface achieve 800 Hz bandwidth abnormal reflection. Our ultrathin acoustic meta-molecule metasurface combines a simple and highly-integrated structure with a thickness equal to only 1/16th of the acoustic wavelength. We additionally design a subwavelength-thickness acoustic axicon by arranging meta-molecule structure. The proposed ultrathin acoustic metasurface exhibits considerable potential for applications in acoustic devices such as acoustic cloaking and absorption.