Underwater Acoustic Stealth by a Broadband 2-Bit Coding Metasurface

Underwater acoustic stealth is of significance for hiding targets. Since perfect cloaking achieved by carpet cloaks or metasurface carpet cloaks may only be suitable for static targets, here we propose a broadband 2-bit coding metasurface to reduce the scattering cross section (SCS) of an object by the destructive interferences among waves scattered by different coding elements. A simple and easy fabricated design is developed by drilling square holes into a steel plate. Utilizing the antiresonance induced by couplings among four square holes of the unit cell, we achieve an approximate 95.62% fractional bandwidth of acoustic stealth with the SCS reduction below -10 dB, which has been confirmed by both the theoretical prediction and experimental measurement. Compared with the previously proposed underwater acoustic carpet cloaks by the transformation acoustics, the bandwidth of SCS reduction is greatly expanded by the destructive interferences. In addition, simulations have demonstrated that the proposed metasurface may also be suitable for an object with a nonplanar surface.

Automated summary

The paper proposes a broadband 2-bit coding metasurface to reduce the scattering cross section of an object by destructive interferences among waves scattered by different coding elements, achieving a high fractional bandwidth of 95.62% and SCS reduction exceeding -10 dB for acoustic stealth. Compared to previous underwater acoustic carpet cloaks, this method greatly expands the bandwidth of SCS reduction through destructive interferences.