Discrete metasurface for extreme sound transmission through water-air interface

TL;DR

This paper introduces a discrete metasurface designed via topology optimization to significantly enhance sound transmission across the water-air interface, outperforming continuous metasurfaces and improving acoustic communication efficiency.

Contribution

The study presents a novel discrete metasurface design with optimized unit cells for extreme sound transmission, validated through experiments and numerical analysis.

Findings

Discrete metasurface achieves higher sound transmission than continuous metasurface.

Experimental results align with numerical simulations when considering viscosity effects.

Frequency shifts are caused by random unit cell immersion and bending effects.

Abstract

The mismatch of acoustic impedance at water-air interface can lead a low transmitted sound energy. In this paper, we propose a discrete metasurface for extreme sound transmission based on the impedance matching theory. 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. 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 metasurface, respectively. The present work suggests an alternative way for improving the efficiency of water-air acoustic communication.