# Ultra-thin Underwater Acoustic Metasurface with Multiply Resonant Units

## TL;DR

This paper introduces an ultra-thin underwater acoustic metasurface with multiply resonant units that effectively manipulate sound waves, enabling applications like anomalous reflection, focusing, and cloaking in water.

## Contribution

It presents a practical, water-compatible acoustic metasurface with multiple resonances and a novel unit design, overcoming limitations of previous rigid-material-based metasurfaces.

## Key findings

- Achieves effective anomalous reflection, focusing, and cloaking in water.
- Constructed using real materials, not relying on ideal rigid materials.
- Thickness is about two orders of magnitude smaller than the wavelength in water.

## Abstract

This paper describes a new kind of acoustic metasurface with multiply resonant units, which have previously been used to induce multiple resonances and effectively produce negative mass density and bulk/shear moduli. The proposed acoustic metasurface can be constructed using real materials and does not rely on an ideal rigid material. Therefore, it can work well in a water background. The thickness of the acoustic metasurface is about two orders of magnitude smaller than the acoustic wavelength in water. The design of a unit group is proposed to avoid the phase discretization becoming too fine in such a long-wavelength condition. We demonstrate that the proposed acoustic metasurface achieves good performance in anomalous reflection, focusing, and carpet cloaking.

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Source: https://tomesphere.com/paper/1907.09016