Recent advances of space-time-coding digital metasurfaces demonstrate powerful capabilities in the generation of nonlinear harmonics and the accurate control of the corresponding wavefronts. However, to date the near field manipulation and the experiment characterization are still not explored. In this paper, we propose a space-time-digital coding metasurface to realize accurate manipulation of the near fields at the fundamental and $+1$st ($-1$st) harmonics simultaneously, by properly controlling the initial phase and time delay of the time varying reflectivity. A novel mapping system is established to measure the nonlinear near field distributions of multiharmonics. Both the simulation and experimental results demonstrate the validity of the proposed method.

中文翻译：

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通过装有pin二极管的有源超表面来控制谐波近场分布

时空编码数字超表面的最新进展证明了在产生非线性谐波和精确控制相应波阵面方面的强大功能。然而，迄今为止，仍未探索近场操纵和实验表征。在本文中，我们提出了一种时空数字编码超表面，以实现对基波和基波附近场的精确操纵。$+\mathrm{1个}$英石 （$-\mathrm{1个}$通过适当控制时变反射率的初始相位和时间延迟，可以同时产生谐波。建立了一种新颖的测绘系统，用于测量多谐波的非线性近场分布。仿真和实验结果均证明了该方法的有效性。