A metasurface is an array of subwavelength units with modulated wave responses that show great potential for the control of refractive/reflective properties in compact functional devices. In this work, we propose an elastic metasurface consisting of a line of pillars with gradient heights, erected on a homogeneous plate. The change in the resonant frequencies associated with the height gradient allows us to achieve transmitted phase response covering a range of 2π, while the amplitude response remains at a relatively high level. We employ the pillared units to design a focusing metasurface and compare the properties of the focal spots through simulation and experiment. The subwavelength transverse and lateral full width at half maximum of the focusing intensity profiles are observed in both simulation and experiment, with the underlying mechanism being the interference and diffraction of the scattered waves from the resonant pillars as well as the boundaries (especially for experiment). The good correspondence between the experimental and simulated relative focal lengths shows the robustness of the focusing pillared metasurfaces with respect to fabrication imperfections. This proposed compact, simple, and robust metasurface with unaffected mechanical properties provides a new platform for elastic wave manipulation for energy harvesting, wave communication, sensing, and non-destructive testing among others.

中文翻译：

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用于弯曲波聚焦的柱状超表面的实验实现

超表面是具有调制波响应的亚波长单元阵列，在紧凑型功能器件中显示出控制折射/反射特性的巨大潜力。在这项工作中，我们提出了一个弹性超表面，由一排具有梯度高度的柱子组成，竖立在均匀的板上。与高度梯度相关的谐振频率的变化使我们能够实现覆盖 2π 范围的透射相位响应，而幅度响应保持在相对较高的水平。我们采用柱状单元来设计聚焦超表面，并通过模拟和实验比较焦点的特性。在模拟和实验中均观察到聚焦强度分布的亚波长横向和横向半高全宽，其潜在的机理是来自共振柱以及边界的散射波的干扰和衍射（特别是用于实验）。实验和模拟相对焦距之间的良好对应关系显示了聚焦柱形超颖表面相对于制造缺陷的鲁棒性。这种具有不受影响的机械性能的紧凑、简单和坚固的超表面为能量收集、波通信、传感和无损测试等弹性波操纵提供了一个新平台。实验和模拟的相对焦距之间的良好对应表明聚焦柱状超表面相对于制造缺陷的鲁棒性。这种具有不受影响的机械性能的紧凑、简单和坚固的超表面为能量收集、波通信、传感和无损测试等弹性波操纵提供了一个新平台。实验和模拟的相对焦距之间的良好对应表明聚焦柱状超表面相对于制造缺陷的鲁棒性。这种具有不受影响的机械性能的紧凑、简单和坚固的超表面为能量收集、波通信、传感和无损测试等弹性波操纵提供了一个新平台。