Sound energy enhancement via impedance-matched anisotropic metamaterial

Abstract

Sound energy enhancement realized by electronic circuit designs plays a vital part in many fields, including acoustic communication, medical imaging, acoustic positioning and sound energy harvesting. The same effect, actually, can be achieved based on anisotropic acoustic meta-structures without electronic components, which has rarely been studied before. Fabricated by 3D printing technology, a two-way spiral-shaped metamaterial and its two-dimensional array are designed in the study, which is capable to realize sound energy enhancement. Due to the impedance matching design, the meta-structure shows almost opposite transmission behaviors in orthogonal directions. The sound wave compression and resonance effects come from the high-refractive-index medium, leading to enlarged acoustic signals inside the waveguide. For the array with an inside point sound source, an energy enhancement phenomenon occurs in the wave emission area outside the structure. Through experimental results and numerical simulations, it is revealed that the sound intensity of the emission wave can be increased more than fifteen-fold compared with the insulation condition in the range of 4.8–5.8 kHz, when the anisotropic metamaterial array is applied. The flexibility of the anisotropic meta-structure and corresponding array designs enables versatile applications demanding excellent sound signal and broadband performance.