A novel amplifier-based transmissive space-time-coding metasurface is presented to realize strongly nonlinear controls of electromagnetic (EM) waves in both space and frequency domains, which can manipulate the propagation directions and adjust enhancements of nonlinear harmonic waves and break the Lorenz reciprocity due to the nonreciprocity of unilateral power amplifiers. By cascading the power amplifier between patches placed on two sides of the metasurface, the metasurface can transmit the spatial EM waves in the forward direction while blocking it in the backward direction. Two status of power amplifier biased at the standard working voltage and zero voltage are represented as codes "1" and "0," respectively. By periodically setting adequate code sequences and proportions in the temporal dimension, according to the space-time coding strategy, the amplitudes and phases of the harmonic transmission coefficients can be adjusted in a programmable way. A metasurface prototype is fabricated and measured in the microwave frequency to validate the concept and feasibility. The experimental results show good agreement with the theoretical predictions and numerical simulations. The proposed metasurface can achieve controllable harmonic power enhancements for flexibly configuring the power intensities in space, which enlarge and manipulate the quality of transmitting signals.

A 1-bit digital reconfigurable reflective metasurface (RRM) with 20 × 20 cells is presented, fabricated and measured for beam-scanning performance in this paper. The cell is designed with a single layer structure and one varactor diode, controlled electronically. The cell's phase compensation is over 180 • between 3 GHz and 4 GHz and the two states with 180 • phase difference are selected as coding "0" and coding "1". By the fuzzy quantification theory, all the elements on the RRM are set to be coding "0" or coding "1" according to the phase compensation calculated by MATLAB. Furthermore, by changing the coding of the RRM, it can achieve beam-scanning. The simulation results show that the beam-scanning range is over ±60 • . The RRM prototype is fabricated and experimentally tested for principle. The gain of the RRM is 18 dB and the 3 dB bandwidth is about 16.6%. The 1-bit digital RRM is preferred in practical implementations due to less error and much easier bias voltage control. The proposed RRM successfully balances the performance and system complexity, especially in the large-scale antenna designs. The experimental and simulated results are in good agreement to prove the correctness and feasibility of the design of the 1-bit digital RRM.

In the last two decades, metamaterials and metasurfaces have introduced many new electromagnetic (EM) theory concepts and inspired contemporary design methodologies for EM devices and systems. This review focuses on the recent advances in metamaterials (MMs) for simultaneous wireless information and power transmission (SWIPT) technology. In the increasingly complex EM world, digital coding and programmable metamaterials and metasurfaces have enabled commercial opportunities with a broad impact on wireless communications and wireless power transfer. In this review, we first introduce the potential technologies for SWIPT. Then, it is followed by a comprehensive survey of various research efforts on metamaterial-based wireless information transmission (WIT), wireless power transmission (WPT), wireless energy harvesting (WEH) and SWIPT technologies. Finally, it is concluded with perspectives on the rapidly growing SWIPT requirement for 6G. This review is expected to provide researchers with insights into the trend and applications of metamaterial-based SWIPT technologies to stimulate future research in this emerging domain.

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This article presents a holographic metasurface antenna with stochastically distributed surface impedance, which produces randomly frequency-diverse radiation patterns. Low mutual coherence electric field patterns generated by the holographic metasurface antenna can cover the K-band from 18 to 26 GHz with 0.1 GHz intervals. By utilizing the frequency-diverse holographic metasurface (FDHM) antenna, we build a near-field microwave computational imaging system based on reflected signals in the frequency domain. A standard horn antenna is adopted to acquire frequency domain signals radiated from the proposed FDHM antenna. A detail imaging restoration process is presented, and the desired targets are correctly reconstructed using the 81 frequency-diverse patterns through full-wave simulation studies. Compressed sensing technique and iterative shrinkage/thresholding algorithms are applied for the imaging reconstruction. The achieved compressive ratio of this computational imaging system on the physical layer is 30:1.