During the past decade, the passive metasurfaces enabling vortex beams carrying orbital angular momentum have drawn great interest in the fields of electromagnetic and acoustic wave. In the underwater environment, however, the elastic metasurface with a certain bandwidth is more difficult to be realized due to the strong fluid-solid interaction and rigorous impedance matching. To overcome this challenge, an inverse-design strategy is proposed to systematically construct a single-phase underwater metasurface for converting the incident plane waves into vortex beams on demand. All topology-optimized metasurface elements, possessing both the positive/negative effective dynamic properties for the full phase control, can support the desired phase modulation and high transmission. We numerically and experimentally demonstrate the acoustic functionality of converting the plane waves in free space to the first-order vortex modes. The present passive single-phase metasurface by inverse design may offer opportunities for underwater acoustic communication.

在过去十年中，使涡旋光束携带轨道角动量的被动超表面引起了电磁波和声波领域的极大兴趣。然而在水下环境中，由于强流固相互作用和严格的阻抗匹配，具有一定带宽的弹性超表面更难实现。为了克服这一挑战，提出了一种逆向设计策略来系统地构建单相水下超曲面，以按需将入射平面波转换为涡旋光束。所有拓扑优化的超表面元件都具有用于全相位控制的正/负有效动态特性，可以支持所需的相位调制和高传输。我们通过数值和实验证明了将自由空间中的平面波转换为一阶涡旋模式的声学功能。目前通过逆向设计的无源单相超表面可能为水声通信提供机会。