Sound field enhancement based on multiple-cavity metamaterial

Abstract

Owing to the low energy density of sound energy in nature, it is difficult to realize the local enhancement effect of sound field in air. Therefore, it is of great significance to explore new physical mechanisms and methods to achieve sound field enhancement. In recent years, artificial Mie resonance structure as a kind of acoustic metamaterial has attracted considerable attention, which has a variety of resonant modes, such as monopolar, dipolar, quadrupolar and higher multipolar modes. Compared with local resonance, acoustic Mie resonance mode has strong acoustic interaction, which can effectively enhance the acoustic field by the coupling of the Mie resonance. In this paper, we design an acoustic metamaterial composed of multiple-cavity unit cells, which is capable of realizing sound field enhancement. The multiple-cavity unit is circular in external shape and it is composed of a circular central cavity and twelve resonators. The twelve resonators are evenly distributed around the circular central cavity, with three resonators combined into a group. This exotic function arises from the compound monopole Mie resonance introduced by mutual coupling between the system structure and the monopole Mie resonance of each unit cell. Symmetric and asymmetric metamaterials are constructed by arranging several multiple-cavity unit cells in different forms. These two kinds of metamaterials can be used to achieve sound field enhancement with different effects. The results show that due to the symmetry of metamaterial structure, the symmetric metamaterials with square, circle, rectangle and regular hexagon shapes can realize the sound field enhancement, which is independent of the direction of incident wave. However, for the asymmetric metamaterial with equilateral triangle shape, the sound intensity in the center of the system varies with incident direction, which indicates that the designed asymmetric metamaterial has a strong dependence on the direction of incident wave. These two kinds of metamaterials constructed in this research can possess a number of potential applications such as in sound insulation, acoustic sensor, noise location, acoustic communication and asymmetric acoustic device. These two kinds of metamaterials constructed in this research can possess a number of potential applications such as in sound insulation.