Broadband tunable sound transparency via underwater metasurfaces

Sound waves have consistently served as vital carriers of information in the physical world. However, in the realms of hydroacoustics and medical ultrasound, the impedance mismatch between the solid and liquid poses significant challenges, resulting in energy dissipation that hinders the effective transmission of information. Hence, achieving underwater sound transparency holds tremendous significance for advancing underwater acoustic communication technology and fostering innovations in the research and development of medical ultrasound equipment. This research endeavor leverages multimode coupling to transcend the limitations of previous narrow-band sound transparency designs. Confirmed by experiments, this work achieves broadband sound transparency spanning from $170$ to $230\phantom{\rule{0.2em}{0ex}}\mathrm{kHz}$. Furthermore, leveraging the abundance of geometric parameters and the flexibility of degrees of freedom, we introduce a dual broadband design, which exhibits dual broadband sound transparency with passbands of $280--350\phantom{\rule{0.2em}{0ex}}\mathrm{kHz}$ and $450--510\phantom{\rule{0.2em}{0ex}}\mathrm{kHz}$. Crucially, our research serves as a stepping stone towards realizing broadband acoustic underwater metasurfaces, thereby paving the way for advancements in ultrasonic imaging and underwater acoustic communications.