In this article, the frequency-selective rasorber (FSR) built on multilayer resistive sheets, which achieves a broad absorption band, was proposed. First, the detailed analysis of the absorption and transmission performance for FSR with the single-layer/multilayer resistive sheets based on the equivalent circuit model (ECM) was demonstrated, which proved that the FSR with the multilayer resistive sheets can obtain a broader absorption band. Second, the multilayer resonator (MR) of a smaller size and higher design freedom compared with single-layer resonator was proposed. Then, the FSR on the basis of multilayer resistive sheets using MR was designed. It consists of the three-layered metallic structures and separated by an air spacer. For the top and middle layers, the lumped-resistor-loaded metallic dipole with the MR inserted into the center was applied to generate a wide absorption band and transparent window, respectively. For the bottom layer, the square-slot frequency-selective surface was optimized to match the transmission band of the resistive sheet. Simulated and measured results show that the broad absorption band and transmission band with low insertion loss have been realized, and the proposed FSR yields the widest relative bandwidth $\vert S_{11}\vert \le -10$ dB of 145.2%.

This paper aims to achieve a high-transmittance varactor-tunable frequency selective surface (FSS). First, the impedance condition for the high-transmittance FSS is deduced. Next, a square-slot FSS loaded with varactors, owns the empirical formulas for equivalent circuit parameter extraction, is selected to demonstrate the proposed method for realizing a high-transmittance varactor-tunable FSS. Several conclusions are deduced and verified through the full-wave simulation. To illustrate the effectiveness of the proposed method, two FSSs operating at the same frequency are designed. The simulation and measurement results show that the FSS with the higher transmission rate follows the deduced conclusions. Note that the transmission rate of the varactor-tunable FSS is more than 77.8% (S21 = 1.09dB) from 4.84 to 5.9GHz when the bias voltage applied to the varactors is tuned from 5 to 20V. Compared to the reported tunable FSSs, the varactor-tunable FSS achieved in this paper obtains the highest transmission rate over the tunable transmission band.

This paper proposes a frequency selective rasorber (FSR) with anisotropic transmission band. At first, the analysis for realizing FSR with anisotropic transmission band based on equivalent circuit model (ECM) is demonstrated. Next, the FSR composed of a two-layered metallic structure with an air gap in the middle is proposed on account of the former analysis. At the top layer, split circle resonator (SCR) combined with metallic strip loaded with resistors is adopted to realize resistive sheet. At the bottom layer, a slot-type FSS with two kinds of slots is designed to match the passband of the resistive sheet. Full-wave simulation results show that the anisotropic transmission band with low insertion loss under TE and TM polarization is realized. To verify the correctness of analysis and simulation results, the proposed FSR is processed and measured. Good agreement between simulation and measurement results is obtained.

This letter presents a thermal-switchable absorbing metasurface (TSAM) based on the phase-change material vanadium dioxide (VO₂). A thin film of VO₂ was deposited on a sapphire substrate by a magnetron sputtering and then sliced into tiny chips, which can be regarded as thermal-switchable resistors. The surface structure of the thermal-switchable absorbing metasurface element is realized by loading four VO₂ chips into a square metallic loop. Polytetrafluoroethylene (PTFE) is used as the substrate due to its high thermal conductivity compared with foam. The TSAM is on “absorbing” mode when it is heated underneath, and is switched into “reflecting” mode at room temperature. The absorbing mode is characterized by a wideband absorption (8 - 22 GHz). A TSAM prototype was fabricated and measured to verify this design.

This article presents a thermal-switchable metamaterial absorber (TSMA) based on the phase-change material of vanadium dioxide (VO₂). VO₂ thin film was deposited on sapphire substrate by magnetron sputtering followed by vacuum annealing treatment. Then, the prepared VO₂ film was sliced into tiny chips for thermal-switchable elements. The surface structure of TSMA was realized by loading four VO₂ chips into a square metallic loop. The absorption frequency of TSMA was located at 7.3 GHz at room temperature and switched to 6.8 GHz when the temperature was heated above the critical phase transition temperature of VO₂. A VO₂-based TSMA prototype was fabricated and measured to verify this design. The design is expected to be used in metasurface antennas, sensors, detectors, etc.

With the rapid development of terahertz radar technology, the electromagnetic device for terahertz radar cross-section (RCS) reduction is worth investigating. However, the existing research concentrates on the RCS reduction metasurface with fixed performance working in the microwave band. This paper proposes a terahertz dynamic coding metasurface integrated with vanadium dioxide (VO₂) for dual-polarized, dual-band, and wide-angle RCS reduction. The simulation result indicates that by switching the state of the VO₂ between insulator and metal, the metasurface can realize the effective RCS reduction at 0.18 THz to 0.24 THz and 0.21 THz to 0.39 THz under the left-handed and right-handed circularly polarized incident waves. When the polar and azimuth angles of the incident wave vary from 0° to 40° and 0° to 360° respectively, this metasurface can maintain a 10 dB RCS reduction. This work has potential value in the terahertz stealth field.