We theoretically and experimentally investigate a helical acoustic metasurface capable of providing a modulated sound-reflected wavefront and a continuously tunable broadband feature. Compared to existing metasurface designs, which mostly manipulate acoustic waves in a fixed or narrow frequency range, the matched screw-and-nut mechanism has added value and unusual properties, opening a realistic solution to achieve broadband tunability of acoustic metasurfaces with multifunctions. The conceived tunable metasurface is composed of identical units, which consist of matched screws rotated into helical channels from bottom to top to modulate the sound-reflected wavefront pattern. As a pragmatic example, we present the design details and functionalities of a flat metasurface operating at a wide working band. Then a sample of the metasurface is manufactured with the three-dimensional (3D)-printed cylindrical units to experimentally demonstrate the continuously tunable multifunction, including anomalous reflection, arbitrary focusing, and self-bending beams. All results are in good agreement. The proposed spiral matching concept could open up an alternative avenue for broadband tunable metasurfaces of reflected wavefront modulations and associated applications.

中文翻译：

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可调宽带反射声超表面

我们在理论上和实验上研究了能够提供调制的声反射波前和连续可调宽带特征的螺旋形声学超表面。与主要在固定或狭窄频率范围内操纵声波的现有超颖表面设计相比，匹配的螺帽和螺母机构具有附加值和非同寻常的特性，为实现具有多功能的声学超颖表面的宽带可调谐性提供了切实可行的解决方案。设想的可调超颖表面由相同的单元组成，这些单元由匹配的螺钉组成，这些螺钉从下到上旋转成螺旋形通道，以调制声反射波阵面模式。作为一个实用的示例，我们介绍了在较宽的工作范围内运行的平面超表面的设计细节和功能。然后，使用三维（3D）打印的圆柱单元制作超颖表面的样本，以实验证明连续可调的多功能功能，包括异常反射，任意聚焦和自弯曲光束。所有结果均吻合良好。所提出的螺旋匹配概念可以为反射波阵面调制及其相关应用的宽带可调超颖表面开辟一条替代途径。