Discrete Metasurface for Extreme Sound Transmission Through Water-Air Interface

Abstract

This paper proposes a discrete metasurface for extreme sound transmission based on the impedance matching theory. The aim is to overcome the mismatch of acoustic impedance at water-air interface. By employing topology optimization, discrete unit cells with different aspect ratios are designed with unitary sound transmission. The unit cell of continuous metasurface is also obtained for comparison. After analyzing the wide-angle performance of discrete unit cells, samples of both discrete and continuous metasurfaces are fabricated. Then the enhancement of sound transmission of the samples at water-air interface is measured in the experiment and the reason of the frequency shifts in the experiment is discussed. It can be found that in the experiment, the sound transmission enhancement of discrete metasurface is clearly measured compared to the bare water-air interface. And the amplitude is relatively larger than that of the continuous sample. Experimental results are in general agreement with numerical ones when viscosity of the sample is considered. Furthermore, the frequency shifts between experiment and simulation are attributed to the random immersion of unit cells for discrete metasurface and the bending of continuous one, respectively.

Keywords: Discrete metasurface, extreme sound transmission, water-air interface, Impedance matching, Topology optimization