While elastic metasurfaces offer a remarkable and very effective approach to the subwavelength control of stress waves, their use in practical applications is severely hindered by intrinsically narrow band performance. In applications to electromagnetic and photonic metamaterials, some success in extending the operating dynamic range was obtained by using nonlocality. However, while electronic properties in natural materials can show significant nonlocal effects, even at the macroscales, in mechanics, nonlocality is a higher-order effect that becomes appreciable only at the microscales. This study introduces the concept of intentional nonlocality as a fundamental mechanism to design passive elastic metasurfaces capable of an exceptionally broadband operating range. The nonlocal behavior is achieved by exploiting nonlocal forces, conceptually akin to long-range interactions in nonlocal material microstructures, between subsets of resonant unit cells forming the metasurface. These long-range forces are obtained via carefully crafted flexible elements, whose specific geometry and local dynamics are designed to create remarkably complex transfer functions between multiple units. The resulting nonlocal coupling forces enable achieving phase-gradient profiles that are functions of the wavenumber of the incident wave. The identification of relevant design parameters and the assessment of their impact on performance are explored via a combination of semianalytical and numerical models. The nonlocal metasurface concept is tested, both numerically and experimentally, by embedding a total-internal-reflection design in a thin-plate waveguide. Results confirm the feasibility of the intentionally nonlocal design concept and its ability to achieve a fully passive and broadband wave control.

尽管弹性超颖表面为应力波的亚波长控制提供了一种卓越且非常有效的方法，但其固有的窄带性能严重阻碍了它们在实际应用中的使用。在电磁和光子超材料的应用中，通过使用非局部性在扩展操作动态范围方面取得了一些成功。但是，尽管天然材料的电子特性即使在宏观尺度上也可能显示出显着的非局部效应，但在力学上，非局部性是一种高级效应，仅在微尺度上才变得明显。这项研究引入了有意非局部性的概念，将其作为设计具有异常宽带工作范围的被动弹性超颖表面的基本机制。通过利用非本地力量来实现非本地行为，从概念上讲，它类似于形成超表面的共振晶胞子集之间的非局部材料微观结构中的远程相互作用。这些远程力是通过精心设计的柔性元件获得的，这些元件的特定几何形状和局部动力学设计为在多个单元之间创建非常复杂的传递函数。所产生的非局部耦合力使得能够实现作为入射波的波数的函数的相位梯度分布。通过半分析和数值模型的组合，探索了相关设计参数的识别及其对性能影响的评估。通过将全内反射设计嵌入薄板波导中，对非局部超表面概念进行了数值和实验测试。