High‐Efficiency Synthesizer for Spatial Waves Based on Space‐Time‐Coding Digital Metasurface

Abstract

Space‐time modulated metasurfaces enable efficient manipulations of nonlinear harmonics with more degrees of freedom than conventional materials by simply controlling the element geometries and modulation signals. The theoretical analyses reveal that a group of harmonics in reflected waves could be generated by the metasurface under the incidence of monochromatic wave with the rapid change of surface reflectivity, while the fundamental spectrum is greatly suppressed. However, it remains a great challenge to synthesize a high‐quality single‐tone signal for the reflected waves with excellent rejection ratio for higher‐order harmonics, which is highly desired for applications like wireless communications and radar detection. Here, a new scheme to overcome this limit, which experimentally realizes high‐efficiency frequency conversion from the fundamental harmonic to the +1st/−1storder harmonic of reflected waves, and beam shaping based on the space‐time joint coding strategy are proposed. The measured results show that the maximum conversion efficiency is greater than 88%. This design can also find widespread applications in THz frequencies when the active metasurface for periodical phase modulations is further developed.

Smart Doppler Cloak Operating in Broad Band and Full Polarizations

“…Recently, time-modulated metasurfaces have been verified that can be used to control dynamically the spectrum distribution of EM waves. [23][24][25][26][27][28][29][30] In particular, when the modulation waveform enables continuously linear variation of the reflection phase of metasurface in one modulation period T m , the incident frequency f i will be converted efficiently to a new frequency component f r upon reflection, and thus create a frequency shift Δf t = f r -f i (f r is the frequency of reflected waves). Under this modulation, the linearly varying reflection phase ϕ(t) of the metasurface is described as…”

Full Manipulation of the Power Intensity Pattern in a Large Space‐Time Digital Metasurface: From Arbitrary Multibeam Generation to Harmonic Beam Steering Scheme

“…Therefore, Equation (25) is valid for the harmonics with scan angle lower than that given by the limiting case as expressed by Equation (32).…”

“…By designing phase-only metaparticles as a physical coding element and by encoding proper time-varying spatial codes, based on the presented formalism, our proposed structure can be implemented in space-time digital metasurface based systems. [31][32][33][34] Finally, at the end of the article, four investi-gations have been conducted to determine the limits of the validity range of the assumptions. The proposed straightforward approach is expected to broaden the applications of digital coding metasurfaces significantly and exposes a new opportunity for various applications such as multiple-target radar systems and Non-Orthogonal-Multiple_Access (NOMA) communication.…”

Programmable Controls to Scattering Properties of a Radiation Array

“…The programmable and real‐time manipulations of EM waves by the programmable metasurface have been demonstrated in space and time domains, [ 35–40 ] leading to many novel applications such as holographic imaging, diffuse scattering, vortex beams in the visible spectral and microwave regions, conversions between propagation waves and surface waves, anomalous reflection and transmission, information processing, harmonic beam steering in space and frequency domains, and new architectures of wireless communication systems. [ 41–57 ] More recently, a thin self‐feeding Janus metasurface and digital‐coding‐feeding metasurface have been proposed for manipulating incident waves and emitting radiations simultaneously, which exhibit multiple functions including polarization conversion, scattering manipulation, EM wave radiation, and beam scanning. [ 58,59 ] However, the scattering properties cannot be programmable controlled.…”