Control of reflected waves that meet surfaces from oblique directions is crucial, for instance, in closed spaces. Metasurfaces composed of Helmholtz resonators can be efficient and compact absorbers but have limited ability to achieve high absorption over a wide incidence angle range, especially when designed for high performance in the region approaching grazing incidence. In turn, sonic crystals can be used to manipulate wave propagation direction at low frequencies. We propose a type of absorber that combines a surface of 2D Helmholtz resonators and a 2D sonic crystal with cylindrical scatterers arranged in a hexagonal lattice. The combined effect of both structures yields a metasurface that can achieve high absorption over a broad range of incidence angles. Here, an analytic model to estimate the behavior of the absorbers for wavelengths that are much longer than the unit cell dimensions is presented. The model is used in combination with an optimization strategy to realize designs for single frequency and octave-band performance. The test cases show that surfaces with absorption coefficient values above 0.9 for the range of incidence angle extending from until can be realized. The performance of the absorbers is verified with a finite element model and experimentally.

中文翻译：

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用于在广泛的波入射角范围内吸声的超表面

例如，在封闭空间中，控制从倾斜方向接触表面的反射波至关重要。由亥姆霍兹谐振器组成的超表面可以是高效且紧凑的吸收器，但在较宽的入射角范围内实现高吸收的能力有限，特别是当设计用于接近掠入射的区域中的高性能时。反过来，声波晶体可用于操纵低频波的传播方向。我们提出了一种吸收器，它将 2D 亥姆霍兹谐振器表面和 2D 声波晶体与排列成六角形晶格的圆柱形散射体相结合。两种结构的综合作用产生了一种超表面，可以在较宽的入射角范围内实现高吸收。这里提出了一个分析模型，用于估计比晶胞尺寸长得多的波长下吸收体的行为。该模型与优化策略结合使用，实现单频和倍频程性能的设计。测试案例表明，对于从 到 的入射角范围，可以实现吸收系数值高于 0.9 的表面。吸波器的性能通过有限元模型和实验进行了验证。