Polarization Conversion Metasurface Research Articles

Ultra-broadband and Wide-angle Reflective Terahertz Polarization Conversion Metasurface based on Topology Optimization

Abstract Terahertz polarization conversion devices have significant potential applications in various fields such as terahertz imaging and spectroscopy. In this paper, we utilize genetic algorithms to topologically optimize the metasurface unit cells and design a reflective linear polarization conversion metasurface, which has ultra-broadband and wide-angle characteristics. By partitioning the metallic pattern layer into quadrants, the encoding length is effectively reduced, resulting in shorter optimization time. The research results indicate that the converter possesses a polarization conversion efficiency ratio higher than 90% and a relative bandwidth ratio of 125% in a range from 0.231 THz to 0.995 THz. Meanwhile, it can maintain excellent polarization conversion properties when the incident angle of terahertz wave is less than 45° and the polarization angle is less than 15°, demonstrating excellent practicality. New insights are provided for the design of terahertz wide-angle ultra-wideband polarization conversion devices, and the proposed metasurfce has potential applications in terahertz polarization imaging, spectroscopy and communication fields.

An absorptive coding metasurface for ultra-wideband radar cross-section reduction

In this paper, an absorptive coding metasurface (ACM) is proposed for ultra-wideband radar cross section (RCS) reduction, the design process is presented in detail, in which a lossy polarization conversion metasurface (PCM) is proposed at first. The lossy PCM is an anisotropic resistive structure with both polarization conversion and absorption performances, so that its co-polarization reflection coefficients under u- and v-polarized incidences can be kept at less than − 10 dB in magnitude in the frequency range from 7.5 to 45.2 GHz. Though the magnitude of the cross-polarization reflection coefficient cannot be very small only due to the absorption, its phase will be changed by nearly 180° when the unit-cell structure of the lossy PCM is rotated by 90°. Thus, the lossy PCM can be used as one of the two types of lossy coding elements for an ACM when its unit-cell structure is rotated by 90° or not. Based on the lossy PCM, an ACM is proposed. The simulation and experimental results show that the ACM has an excellent RCS reduction performance under arbitrary polarized incidence, it can achieve effective RCS reduction under normal incidence in the ultra-wide frequency band from 7.4 to 45.5 GHz with a ratio bandwidth (fH/fL) of 6.15:1; moreover, an ultra-wideband RCS reduction can still be achieved when the incident angle is increased to 45°, which indicates that the ACM has good stealth performance under the detection of various radars working in X, Ku, K and Ka bands, it is very practical.

Optimal design of broadband linear-to-circular polarization conversion metasurface

Due to their inherent defects, circular polarization discrimination methods involving amplitude-phase or axial ratio are obstacles of the computer software-based optimal design of broadband linear-to-circular (LTC) polarization conversion metasurfaces. Therefore, based on the proposed circular polarization discrimination method relating to ellipticity angle β, this study exploits Python-programmed elitist preserving genetic algorithm to optimally design a reflective-type broadband LTC polarization conversion metasurface. The simulation results demonstrate that the final metasurface can realize the wideband LTC polarization conversion; the measured results are in excellent agreement with the simulations, thus validating the proposed design method. It provides an efficient alternative for broadband LTC polarization conversion metasurface designs, which drives the development of the design of LTC polarization conversion metasurfaces from manual methods towards automation. And this work can be applied in antenna designs, optical devices, and remote sensing.

Multifunctional Ultrathin Metasurface with a Low Radar Cross Section and Variable Infrared Emissivity.

The development of stealth devices that are compatible with both infrared (IR) and radar systems remains a significant challenge, as the material properties required for effective IR and radar stealth are often contradictory. In this work, based on an IR electrochromic device (IR-ECD), concepts of metamaterial manipulating electromagnetic waves are applied to develop a multifunctional ultrathin metasurface with a low radar cross section (RCS) and variable infrared emissivity. This paper presents a linear-to-linear polarization conversion metasurface (PCM) designed by hollowing the IR-ECD. In this way, the IR-ECD based on polyaniline (PANI) can also modulate the reflection waves in the microwave band without affecting its features in the infrared region. Thus, the proposed metasurface integrates both microwave stealth and variable infrared emissivity through a single layer. The measured results show that a 10 dB RCS reduction is achieved in the band of 8.46-9.5 GHz, and the infrared emissivity can be adjusted from 0.870 to 0.513 in the infrared stealth band of 8-14 μm. Due to the ultrathin thickness (only 0.081λ0 at 9 GHz), low RCS in the X-band, and variable infrared emissivity, the designed multifunctional stealth metasurface has promising applications on military platforms with various surrounding environments.

Multifunction and switchable hybrid metasurface based on graphene and gold

This paper presents the design and numerical investigation of a graphene-based switchable terahertz (THz) metasurface for ultrawideband absorption and multiband cross polarization conversion. The device’s operational mode can be altered to absorption or reflection by using the electrostatic capabilities exhibited by graphene. The numerical calculations yield results indicating that in absorption mode, it maintains a bandwidth ratio of 152% within the frequency range of 1.04–7.74 THz. In polarization conversion mode, the design demonstrates the ability to convert linearly polarized and circularly polarized waves to their respective cross-polarization states within the frequency ranges of 1.8–2.5 THz, 3.5–4.1 THz, and 5.6 THz. Moreover, calculated results indicate that linear-to-circular conversion can be realized at 2.64, 3.45, and 5.4 THz frequencies. In addition, the absorption and polarization conversion ratio parameters were analyzed using the multiple reflection theory, which demonstrated significant agreement with the simulation results. The designed metasurface exhibits significant potential in the field of terahertz devices, including stealth technology, smart switches, and other related applications.

Design, optimization, and comparative analysis of wide-band polarization conversion along with dual coding sequences for RCS reduction

In this paper, a wideband polarization conversion metasurface is designed. Additionally, coding and chessboard metasurfaces are specifically tailored for radar cross-section reduction (RCS). Initially, a compact unit cell demonstrating exceptional polarization conversion performance is introduced, achieving a polarization conversion ratio (PCR) exceeding 90%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\%$$\\end{document} across frequencies ranging from 7.9 to 22.7 GHz. The PCR remains effective even when oblique incidence angles of up to 30∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document} are utilized across this frequency band. Roger RT5880, with a thickness of 0.254 mm, serves as the substrate. An airgap is introduced between the substrate and the ground plane to enhance the polarization conversion bandwidth. This unit cell serves as the fundamental building block for subsequent metasurface configurations. To assess the scalability and effectiveness, a 36 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 36 unit array is assembled, confirming efficient polarization conversion capabilities extending to larger structures. Moreover, a 1-bit coding unit “0” and “1” are formed by the Pancharatnam-Berry phase based on the same-sized meta-atom with 90∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document} orientations. The robustness and practicality of the design are demonstrated by creating 12 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 12 lattices and evaluating their RCS reduction potential under two distinct scenarios: a chessboard pattern and a coding-based scheme. Notably, its results indicate substantial RCS reduction across a broad frequency spectrum (7.9 to 22.7 GHz) for both configurations. This study demonstrates the wide-ranging applicability of metasurface design, making it a valuable contribution to the fields of microwave engineering, polarization control, and radar stealth technology. Owing to its simplicity, bandwidth, and versatility, this approach offers innovative solutions for diverse real-world applications.

Reconfigurable transmissive metasurface with a combination of scissor and rotation actuators for independently controlling beam scanning and polarization conversion

Polarization conversion and beam scanning metasurfaces are commonly used to reduce polarization mismatch and direct electromagnetic waves in a specific direction to improve the strength of a wireless signal. However, identifying suitable active and mechanically reconfigurable metasurfaces for polarization conversion and beam scanning is a considerable challenge, and the reported metasurfaces have narrow scanning ranges, are expensive, and cannot be independently controlled. In this paper, we propose a reconfigurable transmissive metasurface combined with a scissor and rotation actuator for independently controlling beam scanning and polarization conversion functions. The metasurface is constructed with rotatable unit cells (UCs) that can switch the polarization state between right-handed (RHCP) and left-handed circular polarization (LHCP) by flipping the UCs to reverse their phase variation. Moreover, independent beam scanning is achieved using the scissor actuator to linearly change the distance between the UCs. Numerical and experimental results confirm that the proposed metasurface can perform beam scanning in the range of 28° for both the positive and negative regions of a radiation pattern (RHCP and LHCP beams) at an operational frequency of 10.5 GHz.

A Multiband and Multifunctional Metasurface for Linear and Circular Polarization Conversion in Reflection Modes

Multifunctional integrated meta-devices are the demand of modern communication systems and are given a lot of attention nowadays. Most of the research has focused on either cross-polarization conversion (CPC) or linear-to-circular (LP–CP) conversion. However, simultaneously realizing multiple bands with good conversion efficiency remains crucial. This paper proposes a multiband and multifunctional dual reflective polarization converter surface capable of converting a linearly polarized (LP) wave into a circularly polarized (CP) wave, in frequency bands of 12.29–12.63 GHz, 16.08–24.16 GHz, 27.82–32.21 GHz, 33.75–38.74 GHz, and 39.70–39.79 GHz, with 3 dB axial ratio bandwidths of 2.7%, 40.15%, 14.6%, 13.76%, and 0.2%, respectively. Moreover, the converter is capable of achieving CPC with a polarization conversion ratio (PCR) that exceeds 95%, within the frequency ranges of 13.10–14.72 GHz, 25.43–26.00, 32.46–32.56 GHz, and 39.14–39.59 GHz. In addition, to identify the fundamental cause of the CPC and LP–CP conversion, a comprehensive theoretical investigation is provided. Furthermore, the surface current distribution patterns at different frequencies are investigated to analyze the conversion phenomena. A sample prototype consisting of 20 × 20 unit cells was fabricated and measured, verifying our design and the simulated results. The proposed structure has potential applications in satellite communications, radar, stealth technologies, and reflector antennas.

Broadband Spin-Decoupled Meta-Devices Enabled by a Polarization Conversion Metasurface

Broadband Spin-Decoupled Meta-Devices Enabled by a Polarization Conversion Metasurface

Miura origami based reconfigurable polarization converter for multifunctional control of electromagnetic waves

Polarization is one of the basic characteristics of electromagnetic (EM) waves, and its flexible control is very important in many practical applications. At present, most of the multifunction polarization metasurfaces are electrically tunable based on PIN and varactor diodes, which are easy to operate and have strong real-time performance. However, there are still some problems in them, such as few degrees of freedom of planar structure control, complex circuit, bulky sample, and high cost. In view of these shortcomings, this paper proposes a Miura origami based reconfigurable polarization conversion metasurface for multifunctional control of EM waves. The interaction between the electric dipoles is changed by adjusting the folding angle θ, thereby tuning the operating frequency of the polarization conversion and the polarization state of the reflected wave. This mechanical control method brings more degrees of freedom to manipulate EM waves. And the processed sample is with lightweight and low cost. To verify the performance of the proposed origami polarization converter, a Miura origami structure loaded with metal split rings is designed and fabricated. The operating frequency of the structure can be tuned in different folding states. In addition, by controlling the folding angle θ, linear-to-linear and linear-to-circular polarization converters can be realized at different folding states. The proposed Miura origami polarization conversion metasurface provides a new idea for reconfigurable linear polarization conversion and multifunctional devices.

Switchable bi-functional metasurface for absorption and broadband polarization conversion in terahertz band using vanadium dioxide and photosensitive silicon

We proposed a bi-functional switchable metasurface based on vanadium dioxide (VO2) and photosensitive silicon. The metasurface functions as a transmissive polarization converter in its insulating state with asymmetric transmission characteristics. It attains a remarkable polarization conversion rate (PCR) surpassing 90% and a notable maximum asymmetric transmission (AT) parameter value of 0.73. This performance is observed within the frequency range from 4.31 to 7.86 THz. Dynamic regulation of PCR and AT can be achieved by adjusting the conductivity of photosensitive silicon. To illustrate the underlying factor behind the broadband polarization conversion, the surface current distribution is analyzed at 5.96 THz and 6.08 THz. On the other hand, when VO2 is in the metallic state, the metasurface transforms into a bidirectional absorber with near-perfect absorption in both illumination directions. Under forward incidence of terahertz waves, the absorption rates for the transverse electric and transverse magnetic waves are 99.3% at 3.54 THz and 93% at 3.56 THz, respectively. The physical mechanism of near-perfect absorption is explained using impedance matching theory and the electric field distribution. This research expands the applications of transmissive polarization converters within multifunctional metasurfaces, providing new avenues for their practical implementation.

Wideband and wide-angle reflective metasurface for efficient linear and circular polarization conversion in X, Ku, and K bands

A single-layer wideband and wide-angle reflective metasurface exhibiting linear to cross-polarization conversion (CPC) and linear-to-circular polarization (LP-to-CP) conversion in the X, Ku, and K bands is presented in this research. The devised metasurface serves as a multifunctional platform, achieving CPC over a substantial fractional bandwidth of 64.34% (9.75–19 GHz) with remarkable efficiency exceeding 90% within the 9.75–16 GHz range, reaching a remarkable 100% at resonant frequencies of 11 GHz and 14.6 GHz. Additionally, linear-to-circular polarization conversion is achieved over a significant bandwidth of 9.54 GHz. Notably, the carefully optimized unit cell structure ensures robust polarization transformation, maintaining stability against variations in the incidence angle of up to 45° for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. The proposed metasurface, characterized by its simplicity, compactness, angular stability, and multifunctionality, demonstrates the considerable potential for various microwave communications, antenna design, radar invisibility, and remote sensing device applications.

Ultra-Wideband Low-RCS Circularly Polarized Antennas Realized by Bilayer Polarization Conversion Metasurfaces and Novel Feeding Networks

Ultra-Wideband Low-RCS Circularly Polarized Antennas Realized by Bilayer Polarization Conversion Metasurfaces and Novel Feeding Networks

Multiband dual polarization conversion metasurface based on three-quarter circular-shape in the terahertz regime

Multifunctional THz meta-devices are the demand of modern communication systems and have received a lot of attention recently. Most studies have concentrated on either linear-to-linear or linear-to-circular polarization conversion. However, to simultaneously achieve both in a wide bandwidth with high conversion efficiency remains a key factor. This paper introduces a reflective-type metasurface that operates in the THz frequency range and is capable of wideband dual-polarization conversion in multi-band. The basic component of the suggested converter consists of a three-quarter circular structure with an embedded X-shape. It has the ability to convert linearly polarized (LP) electromagnetic (EM) waves into circularly polarized (CP) waves with axial ratio less than 3 dB at frequencies of 1.83–2.93 THz (RHCP), 3.56–3.68 THz (LHCP), and 3.90–3.93 THz (LHCP), with fractional bandwidth (FBW) of 46.21 %, 3.31 %, and 0.76 %, respectively. The reflected waves exhibit a phase difference of approximately ±90° and ±270° between their cross- and co-coefficients. Besides, the converter is capable of achieving cross-polarization conversion (CPC) with a polarization conversion efficiency (PCE) that exceeds 97 % within the frequency ranges of 3.18–3.42 THz and 3.96–3.97 THz. The fractional bandwidth (FBW) for these ranges is 7.27 % and 0.25 % respectively. Furthermore, the investigation of surface current distribution patterns at different frequencies is conducted to analyze the conversion phenomena. The proposed polarizer has applications in electromagnetic measuring, THz sensing, antennas, imaging, and stealth technologies.

A polarization conversion metasurface for reducing radar cross section and enhancing radiation performance of circularly polarized array antennas

In this paper, we present a metasurface for ultra-wideband polarization conversion. The unit structure of the PCM consists of a metallic pattern layer, an air layer, and a grounded dielectric layer, which can achieve a polarization conversion bandwidth (PCR) from 6.17 GHz to 19.5 GHz (103.9%). According to the phase cancellation principle, the PCM cells and their mirror cells are arranged in a checkerboard fashion to form a metasurface. Applying it to a circularly polarized patch array antenna for RCS reduction. With the addition of PCM, the impedance matching (S11) bandwidth of the antenna is broadened from 7.2 to 8.3 GHz (14.2%) to 6.2–8.4 GHz (30.1%), the axial ratio (AR) bandwidth is broadened from 6.9 to 8.25 GHz (17.8%) to 6.75–8.32 GHz (20.1%), the peak gain to 11.1 dBi and the antenna's monostatic RCS achieves more than 5 dB reduction from 6.4 to 18.6 GHz (97.6%) under x- and y-polarized plane wave irradiation.The current distribution of the antenna is used to explain the gain improvement. Finally, we fabricated and tested a prototype of the proposed metasurface antenna.

Liquid metal based metasurface for cross-band and ultra-wideband polarization conversion

Liquid metal based metasurface for cross-band and ultra-wideband polarization conversion

Deep-learning-assisted Design of Polarization Conversion Metasurface with On-demand Frequency Response and Ultra-broadband Electromagnetic Scattering Reduction

Deep-learning-assisted Design of Polarization Conversion Metasurface with On-demand Frequency Response and Ultra-broadband Electromagnetic Scattering Reduction

Ultrawideband Polarization Conversion Metasurface with Wide Incidence Angle Suitable to Reduce RCS of Planar and Curved Surfaces

Ultrawideband Polarization Conversion Metasurface with Wide Incidence Angle Suitable to Reduce RCS of Planar and Curved Surfaces

Using characteristic mode theory to design and analyze an X-band polarization conversion metasurface

This paper proposes a new framework based on the characteristic modes analysis (CMA) to design polarization conversion metasurfaces (PCMs). This approach relies on the information inferred from the characteristic currents of the dominant modes (DMs). To demonstrate the advantages of this strategy, a multi-functional PCM is designed for the X-band frequencies. Besides, this paper expands and develops the characteristic mode rotation (CMR) method to investigate the intrinsic behavior of PCMs. Based on the extended CMR method, the physical concepts behind polarization conversion purity and angular stability at the resonance frequencies are revealed in a new manner. Finally, a prototype of the designed polarizer is fabricated and its reflection coefficients are measured. A great agreement between simulation and measurement results is obtained.

Dual-band transmission polarization conversion metasurface and its reconfigurable-phase design

Although abundant transmission polarization conversion metasurfaces (T-PCMs) have been reported, a dual-band T-PCM has only received little attention. Moreover, a reconfigurable-phase design of the T-PCMs is limited to a single-frequency band operation. There is hardly any literature to integrate dual-band and reconfigurable-phase features into a T-PCM. Herein, a dual-band T-PCM is presented based on the Fabry-Pérot-like resonant cavity. Particularly, the T-PCM meta-atom contains dual anisotropic patches distributed in different layers, and the novel dual-patch structure introduces multiple current modes to implement dual-band operation. Further, a reconfigurable-phase design of the dual-band meta-atom is performed, and four PIN diodes are embedded in each meta-atom to realize a 1-bit reconfigurable phase. In this way, the T-PCM meta-atom can simultaneously achieve high-efficiency 90° polarization rotation and 1-bit dynamic phase manipulation in 2.3–3.0 GHz and 4.4–7.5 GHz. By changing the encoding of the T-PCM, both cross-polarized transmission and beam manipulation are demonstrated in two divided bands. A sample is fabricated and measured to validate our design, and the results confirm the simulations. With the advantages of ingenious design and a clear operation mechanism, the novel dual-patch structure can be extended to the terahertz and optics regimes.