Space-time acoustic coding metasurfaces with scattering reduction characteristics.

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.