A metasurface absorber consisting of patterned graphene sandwich structure, transparent flexible polyvinyl chloride(PVC) dielectric layer and indium tin oxide(ITO) bottom plate is proposed in microwave band. The graphene layer is patterned as periodic strip bands with the same rectangular holes. The radar cross section(RCS) characteristics are studied by simulation and experiment. The results indicate that the proposed transparent flexible metasurface shows more than 10 dB RCS reduction in dual-band, wideband and single band when the sheet resistance( R_s ) of graphene is 70 Ω/sq, 240 Ω/sq and 350 Ω/sq, respectively. For R_s =240 Ω/sq, RCS reduction in the conformal case is better than 10 dB in 8.52-16.98 GHz, corresponding relative bandwidth is 66.35%. The regulation characteristics are attributed to the strong interference at the resonant frequency or in the broadband. It effectively captures the incident electromagnetic(EM) waves in the metasurface, and the incident wave energies are dissipated with high ohmic loss. Moreover, the RCS suppression ability of the conformal metasurface become better with increase of curvature radius when the metasurface size is fixed. The proposed metasurface initiates a new way for research and development of multi-functional metasurface devices, which has important application in EM stealth in microwave band.

In this work, a metasurface with the symmetrical double C-shaped narrow ring connected with the central cross structure is investigated by simulation, theory and experiment, which can near-perfectly convert linearly polarized electromagnetic waves into their orthogonal components in the frequency ranges from 9.38 to 13.36 GHz and 14.84 to 20.36 GHz. And the corresponding fractional bandwidths within the two bands are 35.00% and 31.36%, respectively. The influences of structural parameters on the polarization conversion performance are studied. The results show that the central frequencies and bandwidths of the two bands can be easily modulated by varying the structural parameters of r and θ. The high-efficiency and dual-broadband characteristics can also be well maintained in the oblique incidence range of 0-45°. Meanwhile, the mechanisms of polarization conversion are analysed, and several formulas are used to calculate the reflection coefficients of the co- and cross-polarization under the normal incident y-polarized electromagnetic waves based on the phase difference of the reflection coefficients of the u- and v-polarized conversions. The experiment results are in good agreement with those of simulations and theoretical analysis. The proposed metasurface has important applications in novel polarization control devices.

The injection of CO₂ to displace CH₄ in coal seams is an effective method to exploit coalbed methane (CBM), for which the CO₂ injection temperature and pressure are important influential factors. We performed simulations, using COMSOL Multiphysics to determine the effect of CO₂ injection temperature and pressure on CO₂-enhanced coalbed methane (CO₂-ECBM) recovery, according to adsorption/desorption, seepage, and diffusion of binary gas (CO₂ and CH₄) in the coal seam, and deriver a thermal–hydraulic–mechanical coupling equation of CO₂-ECBM. The simulation results show that, as CO₂ injection pressure in CO₂-ECBM increases, the molar concentration and displacement time of CH₄ in the coal seam significantly decrease. With increasing injection temperature, the binary gas adsorption capacity in the coal seam decreases, and CO₂ reserves and CH₄ production decrease. High temperatures are therefore not conducive for CH₄ production.

A wideband low-scattering metasurface with optical transparency and flexibility is proposed by using the combination of phase cancellation and absorption mechanisms. Electromagnetic (EM) diffusion is achieved through the random phase distribution design of the two coding elements. The enhanced energy absorption can be obtained in a wide spectrum by using indium tin oxide (ITO) with suitable sheet resistance in the supercells. The experimental results show that the radar cross section (RCS) reductions of less than −10 dB under the planar and conformal cases are in 6.65-19.40 GHz and 6.11-17.37 GHz, corresponding relative bandwidth are 97.89% and 95.91%, respectively. Both theoretical analysis and simulated results are good accordance with the experiment. Furthermore, the analyses of the surface current, EM field distribution and power loss density are given to explain the hybrid RCS reduction mechanism. The proposed composite transparent flexible coding metasurface (CTFCM) maintains good angular stability within 0°-60° oblique incidence and has polarization insensitivity. The CTFCM has excellent flexibility and high optical transparency, which provides a way to reduce RCS in a wider band and has important application potential for stealth aircraft cockpit and transparent radome.

A dual-broadband and high-efficiency reflective linear polarization converter based on an anisotropic metasurface is presented. The device consists of two symmetrical, double-slotted metallic split-rings and one criss-cross structure, a dielectric layer, and a completely reflective metallic ground. The converter exhibits four resonances and can near-perfectly convert x- or y-polarized incident waves into cross-polarized waves in the frequency ranges of 9.38–13.36 GHz and 14.84–20.36 GHz. The polarization conversion ratios (PCRs) of the two bands are 98.21% and 99.32%, respectively. The energy conversion ratio (ECR) for energy loss measurement is almost 100% in these frequency bands. The polarization conversion principle is studied. The bandwidths and PCRs of the two bands are determined by varying the dielectric layer thickness. The simulation results are consistent with experimental observations. The designed dual-broadband and high-efficiency metasurface has great potential in the application of electromagnetic polarization control.