Abstract
Abstract Time-domain digital coding metasurfaces have been proposed recently to achieve efficient frequency conversion and harmonic control simultaneously; they show considerable potential for a broad range of electromagnetic applications such as wireless communications. However, achieving flexible and continuous harmonic wavefront control remains an urgent problem. To address this problem, we present Fourier operations on a time-domain digital coding metasurface and propose a principle of nonlinear scattering-pattern shift using a convolution theorem that facilitates the steering of scattering patterns of harmonics to arbitrarily predesigned directions. Introducing a time-delay gradient into a time-domain digital coding metasurface allows us to successfully deviate anomalous single-beam scattering in any direction, and thus, the corresponding formula for the calculation of the scattering angle can be derived. We expect this work to pave the way for controlling energy radiations of harmonics by combining a nonlinear convolution theorem with a time-domain digital coding metasurface, thereby achieving more efficient control of electromagnetic waves.
Highlights
Considerable efforts have been invested towards controlling electromagnetic (EM) fields in desired fashions
We present Fourier operations on a timedomain digital coding metasurface and propose a principle of nonlinear scattering-pattern shift using a convolution theorem that facilitates the steering of scattering patterns of harmonics to arbitrarily predesigned directions
We expect this work to pave the way for controlling energy radiations of harmonics by combining a nonlinear convolution theorem with a time-domain digital coding metasurface, thereby achieving more efficient control of electromagnetic waves
Summary
Considerable efforts have been invested towards controlling electromagnetic (EM) fields in desired fashions. It is worth noting that Liu et al proposed a linear scattering-pattern shift for the first time by performing convolution operations on a space-domain digital coding metasurface [42], thereby providing an efficient method to achieve the predesigned co-frequency scattering beams Their method cannot be adopted to control harmonic propagation behaviors, and currently, there is no literature available on nonlinear convolution operations for harmonic control. By introducing a time-delay gradient into the time-domain digital coding metasurface, as shown, we can achieve a dual-beam harmonic scattering and steer it to an arbitrarily pre-determined direction, with negligible distortion to the shape of the far-field scattering patterns To validate this theory, we first propose a broadband time-domain digital coding metasurface composed of active meta-atoms possessing tunable reflection states to realize nonlinear phenomena with high efficiency using phase modulation (PM).
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