Broadband directional resonant tunneling emission enhancement via acoustic anisotropic metamaterials

Abstract

Broadband directional acoustic emission enhancement is essential in practical applications, such as acoustic communication and medical imaging. In this paper, an anisotropic metamaterial array of meta-unit consisting of a straight channel and four symmetrical side branch cavities is proposed, aiming to achieve broadband directional resonant tunneling acoustic emission enhancement via the coupling of the transmission peaks in the y-direction. In the range of 3335–4625 Hz, the broadband anisotropic characteristic is reflected in the opposite transmission capacities of the meta-unit and periodic array in the orthogonal directions, which is caused by the different effective impedances due to resonant tunneling. Numerical simulation shows that for the anisotropic metamaterial array with a monopole source in the center, the broadband directional acoustic emission enhancement phenomenon appears in the y-direction. The experimental results confirm that at a distance of 35 cm from the point source, the SPL gain in the y-direction is 4 dB on average, and the SPL in the x-direction is reduced by an average of 12 dB. Based on the above results, the proposed anisotropic metamaterial array is expected to show significant potential applications in the fields where broadband acoustic signals are required.