High-efficiency Reflective Polarization Research Articles

Research on beam manipulate and RCS reduction based on terahertz ultra-wideband polarization conversion metasurface

Metasurfaces exhibit promising capacities in the manipulation of electromagnetic (EM) waves, as to diverse dimensions like amplitude, phase, and polarization. Despite many methods have been used to improve regulatory capabilities of EM waves, the efficiency and working bandwidth has yet to be developed. In this paper, an ultra-wideband and high-efficiency reflective polarization converter metasurface (PCM) is proposed. Both theoretical analysis and simulation results show that the polarization conversion ratio (PCR) is above 89% in the ultra-wideband from 2.28 THz to 6.75 THz, and the relative bandwidth reaches 99%. Moreover, the multi-bit digital coding metasurface elements are designed by using Pancharatnam–Berry (PB) phase principle. The coding metasurface arrays are designed by using different coding sequences, which can be used to realize the free adjustment of scattering angle of the reflected EM waves. In addition, the radar cross section (RCS) reduction performances of the designed metasurface array antennas based on different coding elements are studied. The results present that it can significantly reduce the RCS by −20 dB over a wide frequency range from 2.1 THz to 6.9 THz. The proposed metasurface has great application potential in manipulation of terahertz wave and contributes to RCS reduction.

Multi-functional high-efficiency reflective polarization converter based on an ultra-thin graphene metasurface in the THz band

In this study, an ultra-thin reflective metasurface is proposed for polarization conversion in the terahertz band. Each unit cell of metasurface is composed of graphene ribbons lying diagonally on silicon substrate. A reflective metal is also placed at the bottom of the structure. Our polarization converter works as a linear polarization converter (LPC) and linear to circular polarization converter (LTC-PC) by variation of the chemical potential of graphene, which can actively be changed by chemical doping or electrical bias of the graphene. The working bandwidth of LPC changes by adjusting the chemical potential of the graphene. The LPC structure has more than 99% polarization conversion ratio in the frequency range of 0.83-0.92 THz, even by changing the angle of incident wave up to 45°, the results are still acceptable. The LTC-PC has less than 3dB axial ratio (AR) in the frequency range of 0.6-0.67 THz for left-handed circularly polarized (LHCP) waves and 0.72-0.97 THz for right-handed circularly polarized (RHCP) waves. To verify the simulation results, an equivalent circuit model based on the structure performance is proposed. Equivalent circuit model results agree very well with the simulation results. Due to the fabrication feasibility, ultra-thin thickness, incident angle insensitive, and high efficiency, our structure has great potential in state-of-the-art technologies such as imaging, sensing, communication, and other optical applications.

Ultra-broadband and high-efficiency reflective polarization rotator based on fractal metasurface with multiple plasmon resonances

A fractal metasurface-based ultra-broadband and high conversion efficiency reflective polarization rotator (PR) is proposed. The linearly y-/x-polarized (LP) incident electromagnetic (EM) wave can be rotated over 90ºafter reflection by the proposed metasurface. The unit cell of the proposed PR is designed based on the fractal cut-wire resonator. Compared with a typical cut-wire resonator exciting three resonances, the fractal one can generate an extra resonant frequency. An ultra-broad bandwidth with a polarization conversion ratio greater than 0.9 (PCR>0.90) can be obtained from 8.00 to 23.00 GHz (a fractional bandwidth of 96.8%) at normal incidence, which is realized by the combination of the four resonances. The physical working mechanism and the polarization conversion performance of the metasurface are analyzed by surface current and E-field distributions, simulations and explained based on numerical calculations and plasmon resonance modes. Good agreement between the experiments and simulations is obtained. Compared with traditional PRs and other published metasurface-based PRs, the proposed metasurface can achieve an ultra-broad band and a high efficiency with a sub-wavelength size of the unit cell. The use of fractal topologies provides a novel and efficient method to further upgrade resonance characteristics in the design of PR, and the scalable geometry of the design shows its potential applications at optical, terahertz, and microwave frequencies.

Ultra-wideband and high-efficiency reflective polarization converter for both linear and circular polarized waves

In this work, an ultra-wideband and high-efficiency reflective polarization converter is proposed based on an orthotropic anisotropic metasurface for both linear and circular polarized waves, which is a symmetric structure with a pair of mutually perpendicular symmetric axes. Both the simulated and measured results show that the polarization converter can realize linear polarization conversion at x- and y-polarized incidences in the frequency range from 8.77 to 24.71 GHz, which is corresponding to a 95.2% relative bandwidth; moreover, it can keep the handedness of the reflected wave the same as that of the incident wave in this band and realize reflection-type circular polarization conversion at circular polarized (CP) incidence. We have explained the root cause of these polarization conversions, and made it clear that it is just the symmetry of the metasurface structure which makes the magnitude of co-polarized reflection coefficient at CP incidence equal to that of the cross-polarized reflection coefficient at x- and y-polarized incidences, thus it is shown that the previously proposed various reflective linear polarization converters based on orthotropic anisotropic metasurfaces can all realize reflection-type circular polarization conversion.

Wideband and High-Efficiency Reflective Polarization Conversion Metasurface Based on Anisotropic Metamaterials

In this paper, we propose a wideband and high-efficiency reflective polarization conversion metasurface (PCM) based on anisotropic metamaterials. The PCM has a period of sub-wavelength and simple design with a double-meander-line-shaped resonator printed on a metallic copper plate backed dielectric substrate. Owing to strong anisotropic properties and multiple plasmon resonances at neighboring frequencies, the PCM has a simulated fractional bandwidth of 82.3% from 8.40 GHz to 20.15 GHz with a polarization conversion ratio over 0.9. Numerical analysis and experimental validation are carried out to study the polarization conversion characteristics of the PCM. In addition, the mechanisms are analyzed in detail on the basis of multiple plasmon resonances and surface magnetic field distributions, respectively. The measured and simulated results obtained are in good agreement, which validates the effectiveness of the simulations and analysis.

Wideband and high efficiency reflective polarization rotator based on metasurface

A wideband and high efficiency reflective polarization rotator (PR) based on metasurface is presented. The unit cell of the PR consisting of two oblique symmetry triangle split rings and simulated results show the PR has more than 90% polarization conversion efficiency from 9.24 to 17.64 GHz (a relative bandwidth of 62.50%) under normal incidence. The broad polarization conversion bandwidth and high efficiency results from multiple plasmon resonances and nearly 100% polarization conversion is obtained at three plasmon resonances. The mechanism of the proposed PR is analyzed by surface current distributions. Electric and magnetic resonances generate broad polarization conversion bandwidth and high polarization conversion ratio within the operating band. In addition, we analyze the polarization states of the PR unit numerically based on the reflected fields, which serves as theoretical predictions of polarization conversion. To verify the simulation results and analysis, a sample was fabricated and measured. The measured results are in good agreement with simulated results and numerical analysis.

Design of a wideband reflective linear polarization converter based on the ladder-shaped structure metasurface

In this paper, a ladder-shaped structure metasurface is proposed and investigated theoretically and experimentally, which can efficiently convert a linear polarized electromagnetic (EM) wave to its orthogonal component in a wideband range. The wideband reflective polarization convertibility is resulted from three resonance modes generated by the ladder-shaped structure MM for the normal incident waves. The mechanism of high-efficiency reflective polarization conversion is illustrated by surface current distribution and the destructive interference theory. The experimental measurement results show that the average polarization conversion ratio (PCR) is greater than 90% from 6.9 to 15.4GHz, which are in good agreement with the numerical simulations and theoretical predictions. The designed metasurface possesses the merits of wideband and high-efficiency, and thus has great application values in novel polarization-control devices.