# Space-time acoustic coding metasurfaces with scattering reduction characteristics

## TL;DR

This paper introduces a new type of metasurface that can reduce sound scattering in 3D space by manipulating acoustic waves using time-modulation strategies.

## Contribution

The novel contribution is the development of space-time acoustic coding metasurfaces (STAMs) with scattering reduction capabilities through harmonic manipulation.

## Key findings

- STAMs can reduce sound pressure levels by about 22 dB compared to traditional acoustic coding metasurfaces.
- The proposed STAM unit cells maintain a 180° phase difference at the operation frequency by varying acoustic impedance.
- The space-time modulation mechanism enables flexible acoustic wavefront manipulation for applications like noise control and acoustic stealth.

## Abstract

In recent years, constructing space-time joint modulation acoustic metasurfaces with harmonic manipulation capabilities to achieve excellent scattering reduction within three-dimensional (3D) space has remained a significant challenge. Here, space-time acoustic coding metasurfaces (STAMs) with harmonic manipulation in 3D space are demonstrated, which consist of two types of sub-wavelength unit cells. By changing acoustic impedance of proposed unit cells, the phase difference between these unit cells can maintain 180° in the operation frequency. Both theoretical calculations and numerical simulations verified that compared with acoustic coding metasurfaces of the same size with spatial coding sequence M1(0000 …), the maximum sound pressure level (SPL) of the STAM can decrease about 22 dB. The proposed space-time joint modulation mechanism can provide a method for achieving flexible acoustic wavefront manipulation, which has potential applications in acoustic stealth technology, noise control, and other relevant applications.

•A time-modulation strategy for flexible regulation of harmonic energy is proposed•STAM unit cell with reflection phase varying with acoustic impedance•STAM exhibits excellent scattering reduction capability for acoustic wave energy

A time-modulation strategy for flexible regulation of harmonic energy is proposed

STAM unit cell with reflection phase varying with acoustic impedance

STAM exhibits excellent scattering reduction capability for acoustic wave energy

Physics; Acoustics