Coding metasurfaces are a kind of metasurface that can combine artificial structures with digital codes “0” and “1.” By digitally programming the arrangements of structural units, they can manipulate the transmitted or reflected waves into arbitrary patterns. Recently, coding metasurfaces have been demonstrated to realize fascinating functions in acoustics, including far-field modulation, focusing, and vortex beam generation. However, the previous acoustic coding metasurfaces work at a single frequency and have only one function under a specific arrangement, limiting the efficiency and capacity of manipulation to a low quality. To overcome these shortcomings, here we propose frequency-selected bifunctional coding acoustic metasurfaces. Dual-layer Helmholtz-like resonators are utilized to produce a 0 and $\pi$ phase difference, corresponding to the “0” and “1” codes, respectively. Owing to the design of the dual-layer resonators, the two working frequencies are integrated on a single unit with a subwavelength thickness, which eliminates the long-wavelength limitations. Frequency-selected anomalous reflection, diffusion, and Airy-beam generation are further demonstrated to prove its availability. The results are shown through theoretical predictions, simulations, and experiments, which show good correspondence. The proposed frequency-selected bifunctional coding acoustic metasurfaces can be used in acoustic information preservation and provide an alternative way to achieve multispectral acoustic devices.

中文翻译：

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频率选择双功能编码声超表面

编码超表面是一种可以将人工结构与数字代码“ 0”和“ 1”组合在一起的超表面。通过对结构单元的布置进行数字编程，它们可以将透射或反射的波操纵为任意模式。最近，已经证明编码超表面可以实现声学上令人着迷的功能，包括远场调制，聚焦和涡流束生成。然而，先前的声学编码超表面以单一频率工作，并且在特定布置下仅具有一种功能，从而将操纵的效率和能力限制为低质量。为了克服这些缺点，我们在此提出频率选择的双功能编码声学超表面。双层亥姆霍兹型谐振器用于产生0和$\pi$相位差，分别对应于“ 0”和“ 1”码。由于双层谐振器的设计，两个工作频率被集成在具有亚波长厚度的单个单元中，从而消除了长波长限制。进一步证明了频率选择的异常反射，扩散和艾里光束的产生，以证明其可用性。通过理论预测，模拟和实验显示了结果，这些结果显示出良好的对应性。所提出的频率选择双功能编码声学超表面可用于声学信息保存，并提供实现多光谱声学设备的替代方法。