Hybridization of underwater acoustic diffusion and absorption for the reduction of scattering cross section.

Abstract

Different approaches have been proposed to reduce the scattering cross section (SCS) of objects, including the approach based on the absorption, the diffusion, and the coordinate transformation. However, for underwater acoustic waves, there exists two main challenges: the lack of a valid mechanism to unify these approaches and the existence of the coupling between the shear waves inside the solid and pressure waves in water. To break these limits, an elastic decoupling mechanism and a cross section-based manipulation mechanism are proposed to design unit cells using the soft solid material, and with the aid of two involved resonances of different absorption abilities, we propose a hybrid diffusion and absorption mechanism to design a metasurface for the reduction of SCS. Owing to the hybrid mechanism, the bandwidth of measured monostatic SCS reduction below -10  dB covers from 4 to 22 kHz, the corresponding FBW is 138.5%, and the thickness of fabricated sample approximates to 0.42λc, with λc being the central wavelength of working bandwidth.