A dual-band staggered triangular checkerboard metasurface (STCM) with flexibility is proposed for the radar cross section (RCS) reduction. The designed STCM can obtain greater than 10 dB dual-broadband RCS reduction at the two side bands and high efficiency of mirror reflection in the center band whether in planar or cylindrical conformal cases. Compared with a traditional square checkerboard metasurface (TSCM) of the same size, the simulation results indicate that the STCM in the planar case shows stronger vertical RCS reduction, with a maximum improvement of 11.85 dB. Especially, the proposed STCM covered on the cylinder with the radius (R) of 90 mm can achieve over 10 dB RCS reduction in 8.2-11.4 GHz and 15.2-19.1 GHz, and the corresponding relative bandwidth (RB) is 32.7 % and 22.7 %, which is superior to other research results. The scattering characteristics of the cylinder conformal case become better ith the increase of R under the case of a certain size of the STCM. Furthermore, RCS reduction exceeding 7 dB can be obtained in 11.2-13.1 GHz (RB = 15.6 %) and 15.7-19.1 GHz (RB = 19.5 %) when the STCM is applied on the saddle surface. A prototype is fabricated and measured. The experiment result shows the STCM can achieve more than 10 dB RCS reduction in 8.6-11.7 GHz (RB = 30.5 %) and 15.2-18.7 GHz (RB = 20.6 %) when wrapped around a cylinder with R = 90 mm, which almost coincides with numerical simulation. The proposed STCM shows promising application prospects in electromagnetic (EM) stealth, microwave communication and conformable stealth devices.

A flexible, transparent and polarization-insensitive metasurface absorber (MA) with dual-broadband feature is proposed. The MA consists of absorption layer, transparent flexible polyvinyl chloride (PVC) dielectric layer, and indium tin oxide (ITO)/polyethylene terephthalate (PET) bottom plate. The dual-broadband characteristics are studied by transmission-line theory, numerical simulation and experiment. The experimental results indicate that over 90

A flexible dual‐band efficient polarization converter is realized by both coupled mode theory (CMT) analysis and numerical simulation in the microwave regime. The proposed structure can convert linearly polarized electromagnetic waves into their orthogonal components in the two sidebands. Moreover, a specular reflection performance is obtained in the central frequency band. The polarization conversion ratio (PCR) and operating bandwidth of dual band is dynamically modulated by vanadium dioxide (VO 2 ). In the simulation results, it is shown that the proposed metasurface can achieve linear polarization conversion in 8.17–12.87 and 14.63–18.92 GHz in the insulating phase. PCRs of the dual band are 97.06% and 98.13%, the corresponding relative bandwidths (RBs) are 44.68% and 25.58%. In the metallic phase, the PCRs in 6.81–13.95 and 16.23–18.16 GHz are 91.12% (RB = 68.79%) and 96.92% (RB = 11.22%). The analyses of the phase difference ( u–v coordinate system) and the surface current are given to explain the mechanisms of dual‐band and high PCR. The simulation results are in good agreement with those of CMT. Furthermore, the structure has a robust response to the oblique incidence angle (up to 30°) and has polarization insensitivity. The proposed metasurface has great potential applications in antenna radiation, biosensing, and stealth technology.

A bifunctional flexible metasurface with high polarization conversion ratio (PCR) and absorptivity based on graphene and vanadium dioxide (VO2) is proposed in microwave band, which consists of metallic resonator with two VO2 films in the diagonal, graphene resistance film layer, two polyimide (PI) dielectric layers and copper ground plate. The phase transition ability of VO2 enables switching between polarization conversion mode and absorption mode, and the graphene layer can improve the absorptivity in absorption mode. The design metasurface behaves as a polarization converter when the conductivity of VO2 (σvo2) is 10 S/m and the square resistance of graphene (Rg) is 900 Ω/sq. The PCR is 95.83% in 6.97-17.62 GHz with a broad relative bandwidth of 86.62%. For σvo2=2×105 S/m and Rg=30 Ω/sq, the metasurface is converted to absorption mode, the absorptivity is 95.18% in 13.33-19.47 GHz, corresponding relative bandwidth is 37.44%. The dual functions can be dynamically modulated by changing σvo2 and Rg. The influence of structural parameters, incident angles and polarization modes on its bifunctional features are investigated. The proposed bifunctional metasurface is expected to be applied in the fields of electromagnetic (EM) detection, microwave imaging, and stealth technology.

A tunable bifunctional metasurface absorber based on vanadium dioxide (VO2) and photoconductive silicon (PSi) is proposed in a terahertz (THz) band. When the conductivities of VO2 (sigma vo2) and PSi (sigma PSi) are 10 S m-1 and 1 x 105 S m-1, the designed absorber has a function of dual-broadband absorption. The absorptivity rate of over 90% is in the dual-broadband of 2.47-3.71 THz and 8.90-10.62 THz, corresponding to relative bandwidths (RBs) of 40.13% and 17.62%, respectively. When sigma vo2 and sigma PSi are equal to 2 x 105 S m-1 and 1 x 105 S m-1, the proposed design has a function of single-broadband absorption. More than 90% absorptivity is achieved in 4.69-7.72 THz (RB = 48.83%). Furthermore, the absorptivity under the dual- and single-broadbands is manipulated by changing sigma PSi. An impedance matching theory, equivalent transmission-line (TL) model and electric field distribution are used to reveal the tunable bifunctional absorption mechanism. The influences of structure parameters, polarization mode and incidence angle on the dual- and single-broadband absorption are investigated. The dual- and single-broadband absorption performances are maintained within the incident angles of 55 degrees and 60 degrees, which also possess polarization insensitivity. The proposed absorber has a potential application value in multifunctional devices such as modulation, sensing and electromagnetic (EM) stealth.

Flow rate and holdup are two essential parameters to describe oil-water two-phase flow. The distribution of oil-water two-phase flow in the pipeline is very uneven, and there is a significant slippage between the phases. This makes it difficult to measure these two flow parameters. In this paper, a new measurement method of flow rate and holdup based on phase state regulation is proposed. The oil-water two-phase flow is adjusted to oil or water single-phase flow according to the time sequence by the phase state regulation, and the oil-water phase interface is measured with a conductance sensor. A wavelet transform based phase inflection point detection model is proposed to detect the oil-water phase change point. The experimental results show that the maximum measurement error of the flow rate of water is 3.73%, the maximum measurement error of the flow rate of oil is 3.68%, and the flow rate measurement repeatability is 0.0002. The accuracy of the measurement holdup is better than 3.23%, and the repeatability of the measurement holdup is 0.0003. The prototype designed based on this method has two advantages. One is that it is small in size, the other is that it does not depend on the accuracy of the sensor. Therefore, it can be widely used in oilfield ground measurement.

A dual-broadband and high-efficiency polarization conversion metasurface based on asymmetric transmission is proposed, which is composed of two orthogonal metal gratings, metal resonator and FR-4 dielectric spacer. The simulated results show that the designed metasurface can convert x-polarized incident waves into y-polarized waves in the frequency ranges of 4.64-14.37 GHz and 17.02-37.23 GHz, and the corresponding polarization conversion ratio (PCR) exceeds 90%. The relative bandwidths of the two bands are 102.37% and 74.51%, respectively. The influence of structural parameters on the transmissive polarization conversion performance is studied. The bandwidths of the two bands can be easily modulated by varying the structural parameters of l, n, m and w. The excellent performance of dual-broadband and high-efficiency covers C, X, Ku, K and Ka bands, which can also be well maintained in the oblique incidence range of 0 degrees -50 degrees. Moreover, the mechanism of transmissive polarization conversion is analyzed. The prototype is fabricated and the experimental results are basically consistent with the numerical simulation. The proposed metasurface has potential application value in polarization imaging radar or radiometer, radar, transmission array antennas and filter.

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, 240, and $350~\Omega $ /sq, respectively. For $R_{s} = 240\,\,\Omega $ /sq, RCS reduction in the conformal case is better than 10 dB in 8.52–16.98 GHz, and 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 becomes better with the increase of curvature radius when the metasurface size is fixed. The proposed metasurface initiates a new way for research and development of multifunctional metasurface devices, which has important application in EM stealth in microwave band.

Multi-oil droplet target recognition is one of the applications of machine vision in the measurement of oil-water two-phase flow parameters, which could combine other algorithms to obtain the oil droplet velocity and the water holdup of oil water two-phase flow. Appropriate target representation features can improve the recognition effect of multiple oil droplets. However, due to shooting environment differences and quality differences of oil-water two-phase flow images, existing target representation features do not perform well in low-quality oil-water two-phase flow images. To improve the precision of multi-oil droplet target recognition in oil-water two-phase flow and reduce the miss rate, this paper constructs an integrated feature on the basis of aggregate channel features (ACF). The integrated feature named aggregate channel features with histogram of local gravitational feature（ACFHG） contains the color feature channels reflecting the overall color features of the oil droplet sample, the gradient amplitude channel reflecting the overall gradient of the oil droplet sample image, the gradient direction histogram feature channels reflecting the local gradient of the oil droplet sample image, and the local gravitational feature channels that ensure oil droplet target recognition in low quality photos and photos taken in complex shooting environments. Moreover, the rotation invariance is obtained by taking the oriented gradient histogram of the local gravitational feature to further improve the multi-oil droplet target recognition effect. Experiment results show that the average precision of multi-oil droplet target recognition using the integrated features is 83.38%, which is 9.93% higher than that with using ACF, and the miss rate is 9.13%, which is 57.18% lower than that with using ACF. Compared with other existing target detection methods, the method proposed in this paper still has an advantage in the rate of missed detection.

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.

In this paper, a highly efficient dual-band and dynamic regulated terahertz linear polarization converter is proposed. Based on the principle of electromagnetic (EM) wave polarization control, a periodic array metasurface composed of graphene split square ring and elliptical patches is designed to realize dual-band and high efficiency linear polarization conversion in terahertz band. The simulation results show that the polarization conversion ratio (PCR) is higher than 90% in the frequency range of 0.656-0.730 THz and 0.809-1.449 THz, and corresponding relative bandwidths are 10.7% and 56.7%, respectively. The dual-band performance is maintained within the incident angle of 50 degrees. In addition, the dynamic regulation of dual -band terahertz linear polarization converter is obtained by modifying the Fermi level and relaxation time of graphene. The designed dual-band terahertz linear polarization converter has a broad application prospect in terahertz communication, sensing and spectrum.

A flexible, dual-broadband, and polarization-insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1 bit coding units “0” and “1” are formed by the Pancharatnam–Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this communication can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26–12.87 and 14.84–19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained, while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

This paper proposes a new image encryption algorithm. First, time-domain and frequency-domain features of the user’s voice are extracted to generate a voice key. Second, the key is iterated through a chaotic map multiple times to map the key data to the chaotic oscillation region, and, subsequently, the parameters of the oscillation area are used to encrypt the user’s image. Third, at the time of decryption, the user’s latest voice data are re-extracted to generate a new voice key and decrypt the encrypted image. The encrypted image cannot be successfully decrypted if there are differences between the two extracted voices in the time or frequency domain. Finally, the experiments are performed using 80 groups of face images and voice data, all of which pass the encryption and decryption experiments. In addition, various safety tests have been carried out on the algorithm. The key sensitivity of the algorithm is verified by the normalized cross-correlation parameter Cncc. The effective anti-attack ability of the algorithm is verified by measuring the correlation between adjacent pixels, the number of changing pixel rate (NPCR) and the unified averaged changed intensity (UACI). The key space of the proposed algorithm is greater than 2100, and it has good anti-cracking ability.

A dual-band, high polarization conversion ratio (PCR) tunable flexible polarization conversion metasurface based on the reversible insulator-to-metal transition (IMT) of vanadium dioxide (VO2) is proposed. It consists of a pattern layer combining VO2 and copper, two flexible dielectric layers and a metallic ground. The simulation results show that the proposed metasurface can achieve linear polarization conversion in 8.17-12.87 GHz and 14.63-18.92 GHz in the insulting phase. And the PCRs of the two band are 97.06% and 98.13%, the corresponding relative bandwidths are 44.68% and 25.58%, respectively. In the metallic phase, the PCRs within 6.81-13.95GHz and 16.23-18.16 GHz are 91.12% and 96.92%, respectively. The dynamic regulation characteristics of PCR and operating bandwidth are realized by changing the conductivity of VO2. The surface current at the resonant frequency is simulated, and the mechanisms of dual-band and high PCR are analyzed. In addition, the polarization converter exhibits good robustness when the x- and y-polarized incident angle is up to 30°. The proposed metasurface has great potential applications in antenna radiation, biosensing and stealth technology.

A linear polarization conversion coding metasurface (MS) is proposed for the radar cross section (RCS) reduction of an object. The designed MS has both wideband RCS reduction and high efficiency of mirror reflection in different frequency bands. The cells are arranged according to different 1 bit coding sequences, and the characteristics of RCS reduction are verified by emulations and experiments. The simulation results indicate that the 01/10 coding MSs possess RCS reduction of greater than 10 dB in 9.5-13.9 and 15.2-20.4 GHz, and the 01/10 coding MS is less sensitive to polarization under normal incidence. The experiment results show that 10 dB RCS reduction is achieved in 10.2-14.0 and 15.3-20.7 GHz under normal incidence, and the relative bandwidth (BW) is 32% and 30%, while high efficiency of mirror reflection is obtained from 14.0 to 15.3 GHz. The experimental results are in good agreement with the numerical simulations. Additionally, for the 01/10 coding MS, the dual-broadband performance is also well maintained under 0 degrees-45 degrees oblique incidence. It is a new and practical method to suppress the scattering of metal objects by the combination of scattering and reflection, which has significant potential in the applications of antenna designs or stealth technology fields.

A dual-wideband coding metasurface based on the polarization conversion for radar cross section (RCS) reduction is proposed. An anisotropic element with rotational symmetry is denoted as '0' or '1' in 1-bit coding sequences. The unit cells are arranged according to a binary coded matrix formed by simulated annealing algorithm. The optimal coding metasurface possesses RCS reduction of greater than 10 dB in 9.9-14.1 and 15.6-20.6 GHz while simultaneously maintaining an effective specular reflection performance from 14.1 to 15.6 GHz underx-polarized normal incidence. This shows that the designed optimal coding metasurface has the performance of frequency selectivity. Additionally, the proposed optimal coding metasurface in this paper has polarization insensitive characteristics. The experiment results of the prepared prototype are found to be in line with the numerical simulation results. It is a novel and practical method to achieve low-backward scattering by a combination of diffusion and reflection. The optimal coding metasurface offers huge potential applications for complex electromagnetic wave manipulation, such as stealth fields and antenna designs.

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.

Velocity is an important parameter for fluid flow characteristics in profile logging. Particle tracking velocimetry (PTV) technology is often used to study the flow characteristics of oil wells with low flow velocity and high water cut, and the key to PTV technology is particle matching. The existing particle matching algorithms of PTV technology do not meet the matching demands of oil drops in the oil phase velocity measurement of oil-water two-phase flow with low velocity and high water cut. To raise the particle matching precision, we improved the particle matching algorithm from the oriented FAST and the rotated BRIEF (ORB) feature description and the random sample consensus (RANSAC) algorithm. The simulation and experiment were carried out. Simulation results show that the improved algorithm not only increases the number of matching points but also reduces the computation. The experiment shows that the improved algorithm in this paper not only reduces the computation of the feature description process, reaching half of the computation amount of the original algorithm, but also increases the number of matching results, thus improving the measurement accuracy of oil phase velocity. Compared with the SIFT algorithm and the ORB algorithm, the improved algorithm has the largest number of matching point pairs. And the variation coefficient of this algorithm is 0.039, which indicates that the algorithm is stable. The mean error of oil phase velocity measurement of the improved algorithm is 1.20 %, and the maximum error is 6.16 %, which is much lower than the maximum error of PTV, which is 25.89 %. The improved algorithm overcomes the high computation cost of the SIFT algorithm and achieves the precision of the SIFT algorithm. Therefore, this study contributes to the improvement of the measurement accuracy of oil phase velocity and provides reliable production logging data for oilfield.

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.

In this work, Cr-doped ZnO thin films with the hexagonal wurtzite structure and c-axis preferred orientation are prepared with the radio frequency magnetron sputtering technique. The variation of working pressure, from 1.3 Pa to 1.9 Pa, produces variations in the structural, optical and electrical properties of the films. X-ray diffraction results indicate that the intensity of the (002) peak in the films first increases, and then decreases, with an increase in the working pressure. Cr-doped ZnO thin films deposited at 1.5 Pa have perfect optical and electrical properties, a maximal crystal size of 13.43 nm, a transmittance of 85.40%, a minimal dislocation density of 5.544 × 1015 lines m−2, a quality factor of 7.43 × 104 S cm−1, a small residual stress of −0.135 GPa and a low resistivity of 1.15 × 10−3 Ω cm. The band gaps of the films increase with an increase in the working pressure. The results show that the working pressure influences the structural, optical and electrical properties of Cr-doped ZnO thin films.