Metasurfaces, which are planar arrays of subwavelength artificial structures, have emerged as excellent platforms for the integration and miniaturization of electromagnetic devices and provided ample possibilities for single-dimensional and multidimensional manipulations of electromagnetic waves. However, owing to the limited interactions between planar thin metallic nanostructures and electromagnetic waves as well as intrinsic losses in metals, metasurfaces exhibit disadvantages in terms of efficiency, controllability, and functionality. Recent advances in this field show that few-layer metasurfaces can overcome these drawbacks. Few-layer metasurfaces composed of more than one functional layer enable more degrees of design freedom. Hence, they possess unprecedented capabilities for electromagnetic wave manipulation, which have considerable impact in the area of nanophotonics. This article reviews recent advances in few-layer metasurfaces from the viewpoint of their scattering properties. The scattering matrix theory is briefly introduced, and the advantages and drawbacks of few-layer metasurfaces for the realization of arbitrary scattering properties are discussed. Then, a detailed overview of typical few-layer metasurfaces with various scattering properties and their design principles is provided. Finally, an outlook on the future directions and challenges in this promising research area is presented.

中文翻译：

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具有任意散射特性的几层超表面

超亚表面是亚波长人工结构的平面阵列，已成为电磁设备集成和小型化的绝佳平台，并为电磁波的一维和多维操纵提供了充足的可能性。然而，由于平面薄金属纳米结构与电磁波之间的相互作用有限，以及金属中的固有损失，超颖表面在效率，可控制性和功能性方面均表现出劣势。该领域的最新进展表明，很少层的超颖表面可以克服这些缺点。由不止一个功能层组成的几层超颖表面可以实现更大程度的设计自由度。因此，它们具有前所未有的电磁波处理能力，在纳米光子学领域有相当大的影响。本文从其散射特性的角度回顾了几层超表面的最新进展。简要介绍了散射矩阵理论，并讨论了用于实现任意散射特性的多层超表面的优缺点。然后，详细介绍了具有各种散射特性的典型几层超颖表面及其设计原理。最后，提出了对这个有前途的研究领域的未来方向和挑战的展望。并讨论了用于实现任意散射特性的多层超表面的优缺点。然后，详细介绍了具有各种散射特性的典型几层超颖表面及其设计原理。最后，提出了对这个有前途的研究领域的未来方向和挑战的展望。并讨论了用于实现任意散射特性的多层超表面的优缺点。然后，详细介绍了具有各种散射特性的典型几层超颖表面及其设计原理。最后，提出了对这个有前途的研究领域的未来方向和挑战的展望。