Polarization Conversion Ratio Research Articles

Vanadium dioxide and a graphene-based ultra-wideband absorption and polarization conversion switchable terahertz device

A multifunctional terahertz functional device based on vanadium dioxide (VO2) and graphene is proposed, which can realize ultra-wideband absorption and polarization conversion. When the VO2 is in the insulating state, the device can achieve the polarization conversion function to convert the incident wave into the corresponding cross-polarized wave. Polarization conversion ratios (PCRs) can exceed 90% in the 2.1–8 THz frequency range; in the 3–7.5 THz range, the PCR can be more than 95%. When VO2 is in the metallic state and the graphene Fermi energy is 0.9 eV, the device can realize a broadband absorption function. An absorption rate of more than 90% can be achieved over a wide frequency range of 3.3–7.7 THz. In addition, the polarization conversion device can maintain high performance in broadband polarization conversion at incident angles no greater than 40°. The absorber device also exhibits insensitivity to both incident and polarization angles. These advantages which make the proposed multifunctional terahertz functional device have a wide range of applications in the fields of terahertz imaging, sensing, communication, and so on.

Efficient polarization conversion metasurface for scattered beam control and RCS reduction

This study proposes and experimentally validates a multifunctional, ultra-wideband polarization conversion metasurface. The design integrates polarization conversion and electromagnetic scattering functions into a single structure, enabling applications in polarization conversion, beam control, and effective reduction of the radar cross-section (RCS). The metasurface achieves linear-to-circular polarization conversion with an axial ratio (AR) of less than 3 dB across dual-band ranges of 14.6–26.8 GHz and 31–33.5 GHz. Additionally, by adjusting metallic resonant rings within the unit structure, cross-polarization conversion with a polarization conversion ratio (PCR) greater than 0.9 is realized in the 13.6–29.8 GHz frequency range, maintaining excellent stability even at oblique incidence angles up to 50°. Leveraging the phase cancellation principle, various coding arrays are designed to precisely control the scattered beams, reducing the RCS by more than 10 dB. The comparison of simulation and experimental results further validates the wide application potential of this polarization converter in fields such as wireless communication, antenna engineering, and radar stealth.

Ultra-wide band and high efficient Polarization converting metasurface employing Bell-shaped unit cell for RCS reduction

Polarization is a dominant parameter regarding communication systems in recent times. The standard polarization techniques can be used only to a certain extent because of their huge size and limited bandwidth constraints. A design of bell-shaped polarization converting metasurface (PCMS) is presented in this paper which is highly efficient for Radar cross section (RCS reduction) and also operates in ultra-wideband. The designed PCMS attains a polarization conversion ratio of more than 90% by demonstrating the transformation of the linear polarization wave to its orthogonal counterpart. The PCMS is arranged in a triangular chessboard configuration to reduce the RCS. RCS reduction is obtained by achieving destructive interference, accomplished by two unit cells. The two unit cells, PCMS and its mirror will have a phase difference of 180 ± 37°. The phase cancellation is obtained by rotating and arranging the proposed PCMS at 90°, 180° and 270°. RCS reduction is obtained in a frequency range from 4 GHz to 24.8 GHz with 144% FBW. This PCMS is verified experimentally. A good agreement is found between the simulation and the experimental results.

Design of high efficiency and wideband dual-functional metasurface for polarization conversion and asymmetric transmission

A wideband and high-efficiency bi-functional metasurface for polarization conversion and asymmetric transmission (AT) based on the gratings/ polarization converter/gratings structure is proposed. The proposed metasurface structure consists of a two double-split ring structure array sandwiched by two orthogonal metallic sub-wavelength gratings. Using two orthogonal metallicsub-wavelength gratings, the proposed metasurface reveals excellent AT effect and nearly perfect polarization conversion performance for linearly polarized waves. The proposed metasurface achieves a polarization conversion ratio (PCR) of above 0.99 from 3.7 GHz to 20.2 GHz with a relative bandwidth (RBW) of 138% and an AT parameter of over 0.9 from 5.8 GHz to 17 GHz withan RBW of 99.5%. Moreover, the proposed metamaterial maintains high PCR and AT performance for a wide range of incident angles. Due to its excellent features, such as the wideband and high efficiency of both PCR and AT performances, the proposed bi-functional metasurface can be useful for promising applications such as polarization imaging. radar, radiometer, and transmission.array antennas.

High efficient bi-functional metasurface with linear polarization conversion and asymmetric transmission for terahertz region

Abstract Polarization control is crucial in contemporary photonics, but achieving broad bandwidths and high efficiencies remains a significant challenge. Here, we propose a wideband and high-efficiency metasurface designed for linear polarization conversion and asymmetric transmission (AT) in the terahertz region based on a three-layer chiral structure. By integrating a double-split ring and strip resonator, the design can improve both wide bandwidth and high-efficiency cross-polarization conversion and AT capabilities for a linearly polarized wave. The operating band for AT is 0.73-3.01 THz with an efficiency above 0.8, while the polarization conversion ratio exceeds 0.99 across the 0.56-3.94 THz range. The underlying physical mechanism behind wideband transmission polarization conversion was fully elucidated through theoretical analysis and the characterization of surface current distribution. This designed structure can be used in terahertz imaging, sensing, and communication.

Flexible substrate based wideband polarization converter with extremely high polarization conversion ratio

In this article an anticipated reflection-mode cross-polarization converters (CPCs) are designed on a polydimethylsiloxane (PDMS) based flexible substrate operating in the GHz region. The proposed CPC metasurface comprises three layers where a flexible substrate is endwise between the resonating layer and ground layers. The converter can convert linear to circular and circular to cross-polarized waves at the frequency range of 5–8 GHz, as evidenced by the identical amplitude of Rxx and Ryx and a phase difference of 90°. More than 99 % of the polarization conversion ratio (PCR) was performed between the 6.75 and 9.07 GHz frequency range, while more than 80 % of the PCR was performed between the 6.0 and 10.73 GHz frequency range. The highest PCR values show nearly flawless energy conversion from an x-polarized incident wave to a y-polarized reflected wave. The PCR ratio of 80 % is achieved by this ultra-wideband linear-to-cross- and circular-to-cross-polarization converter. The anticipated converter's spectrum for all incidence angles between 0◦ and 60°. The PCR remained higher than 99 % over a wide incidence angle range to 60° without much performance degradation. The bending stability of the PDMS-based flexible substrate is also investigated up to 60°. The structure is fabricated on a flexible substrate, and the measured performance is compared with simulated results. Radar, antenna, and communications systems, as well as other cross-polarization converters, can utilize the transmitted wave's very high polarization purity result.

Single layer vanadium oxide assisted switchable metasurfaces for transmissive and reflective polarization conversion

Polarization control using metasurfaces is highly advantageous; however, most metasurfaces operate exclusively in either transmission or reflection mode. Additionally, achieving both wide bandwidth and high efficiency simultaneously in their design remains a significant challenge. Here, we design a high-efficiency and wideband switchable metasurface that can switch between transmissive and reflective polarization conversion modes by utilizing a single layer of I-shaped resonators and gold-vanadium dioxide (VO2) alternating gratings printed on a quartz substrate. When VO2 transitions to its metallic phase, the continuous metal layers of gold-VO2 eliminate transmission and the designed metasurface operates as a reflective cross-polarization converter with a polarization conversion ratio (PCR) exceeding 0.9 over a broad frequency range of 1.4–3.3 THz. Conversely, when VO2 is in its insulator phase, the THz incoming wave can transmit through the gratings, and the design behaves as a transmissive cross-polarization converter with a PCR above 0.99 in the 0.75-4.0 THz range for a forward y- polarized wave. The working mechanism for both transmissive and reflective polarization conversion modes is explained through theoretical analysis and surface current distributions. With the advantages of facile design, high performance, and dual functionality, our design is expected to be applied in the fields of imaging, sensing, and communication.

A dynamically switchable and tunable metamaterial device based on vanadium dioxide and Dirac semimetal

In this paper, a dual-function metamaterial device based on vanadium dioxide (VO2) and Dirac semimetal (DS) operating in terahertz (THz) frequency range is designed. The reversible phase transition properties of VO2 are exploited to achieve the dynamic switch between the function of broadband absorption and broadband polarization conversion. It is demonstrated that when VO2 is in the metallic state and the Fermi energy level () of DS is set to 30 the broadband absorption in the operating frequency range of 1.42-3.40 THz can be achieved, and its absorbance exceeds 90% with a relative bandwidth of 82.16%. When VO2 is in the insulating state and the of DS is set at 180 , the high efficient broadband polarization conversion can be obtained in the operating frequency range of 2.08-4.88 THz and the polarization conversion ratio (PCR) is greater than 90% with a relative bandwidth of up to 80.46%. Therefore, the proposed switchable dual-functional THz device can be extensively utilized in absorption, polarization conversion and other potential fields.

Reconfigurable terahertz multifunctional wave plates with VO2/Ge hybrid metasurfaces.

Active control of polarization using metasurfaces is crucial in terahertz optics, offering promising advancements in sensing, imaging, and telecommunications. Here, we developed reconfigurable terahertz multifunctional wave plates by leveraging vanadium dioxide/germanium hybrid metasurfaces. This approach allows for mutual role changing of metasurface among quarter-wave plate, half-wave plate, and full-wave plate, facilitated by the introduction of continuous-wave and pulse lasers. The photoinduced phase change of vanadium dioxide, along with the bridging control of germanium, plays a key role in the transition of multifunctional wave plates. Also, the analysis of polarization conversion ratio, ellipticity, and underlying physics demonstrates the ability of multifunctional wave plates. These discoveries deliver valuable insight into advanced polarization control and demonstrate the potential for innovative active-control devices.

Broadband metamaterial linear polarization converter designed by a hybrid neural network with data augmentation

Deep learning techniques provide a new approach to the design and optimization of electromagnetic metamaterials. This study used a convolutional neural network and long short-term memory (CNN–LSTM) hybrid network to design and optimize a broadband metamaterial reflective linear polarization converter. The data augmentation method was also employed in few-shot learning to reduce optimization costs and improve model prediction performance. With the inverse prediction, a linear polarization converter that perfectly covers the Ku-band was obtained and fabricated with flexible printed circuit technology. Both simulation and experimental results indicate that this network can accurately predict the structural parameters. The polarization converter not only achieves remarkable broadband polarization conversion efficiency spanning the 2.2–18 GHz range but also maintains precise cross-polarization control across the entire Ku-band. The mean polarization conversion ratio in the Ku-band was calculated to be an impressive 99.69%. Finally, the mechanism of polarization conversion and the influence of each structural parameter on its performance further verify the optimality of the inverse design model. The use of CNN–LSTM deep learning methods significantly simplified the design process of electromagnetic metamaterials, reducing design costs while ensuring high design precision and excellent performance.

Reflective multi-layer metasurface based on half-wave plate structure for polarization control in the visible-near-infrared region

The precise control of the polarization of the electromagnetic field in the optical range is studied. A numerical simulation was performed, which corresponds to the optical devices operating in the 650–800 nm range and does not present any obstacles for fabrication. According to this, the three-layer system based on metasurfaces was developed, which operates as a half-wave plate consisting of a metal-dielectric-metal structure and takes very small dimensions, more than 3 times smaller than the observed wavelength. This half-wave plate is reflective and exhibits almost ideal behavior with a spectral width of about 10 nm within 735–745 nm. The losses are negligible, and the amplitude ratio of the directly reflected components in almost the entire studied spectrum exceeds 90%. With a spectrum of about 100 nm within 650–800 nm, it is 99%. Also, the system has an advantage characteristic of metasurfaces: regardless of the angle of the incident wave with the normal, it shows high efficiency, and even when the incident wave is below 45°, the polarization conversion ratio (PCR) remains greater than 80%. The system has optimal geometric dimensions, which works especially well, but even if the dimensions change (due to fabrication defects), its effectiveness does not weaken. The proposed system can become a very promising optical device and be used to control the state of electromagnetic waves in the optical range.

Deep neural network-enabled multifunctional switchable terahertz metamaterial devices

Under the support of deep neural networks (DNN), a multifunctional switchable terahertz metamaterial (THz MMs) device is designed and optimized. This device not only achieves ideal ultra-wideband (UWB) absorption in the THz frequency range but enables dual-functional polarization transformation over UWB. When vanadium dioxide (VO2) is in the metallic state, the device as a UWB absorber with an absorption rate exceeding 90% in the 2.43–10 THz range, with a relative bandwidth (RBW) of 145.2%, and its wideband absorption performance is insensitive to polarization. When VO2 is in the insulating state, the device can switch to a polarization converter, achieving conversions from linear to cross polarization and from linear to circular polarization in the ranges of 4.58–10 THz and 4.16–4.43 THz, respectively. Within the 4.58–10 THz range, the polarization conversion ratio approaches 100% with an RBW of 74.3%, the polarization rotation angle is near 90°. Within the 4.16–4.43 THz range, the RBW is 6.29% and the ellipticity ratio approaches 1, Moreover, the effects of incident angle and polarization angle on the operational characteristics are studied. This THz MMs due to its advantages of wide angle, broad bandwidth, and high efficiency, provides valuable references for the research of new multifunctional THz devices. It has great application potential in short-range wireless THz communication, ultrafast optical switches, high-temperature resistant switches, transient spectroscopy, and optical polarization control devices.

Graphene-Based Tunable Polarization Conversion Metasurface for Array Antenna Radar Cross-Section Reduction.

A graphene-based tunable polarization conversion metasurface (PCM) was designed and analyzed for the purpose of reducing the radar cross-section (RCS) of array antennas. The metasurface comprises periodic shuttle-shaped metal patches, square-patterned graphene, and inclined grating-patterned graphene. By adjusting the Fermi energy levels of the upper (μ1) and lower (μ2) graphene layers, different states were achieved. In State 1, with μ1 = 0 eV and μ2 = 0.5 eV, the polarization conversion ratio (PCR) exceeded 0.9 in the bandwidths of 1.65-2.19 THz and 2.29-2.45 THz. In State 2, with μ1 = μ2 = 0.5 eV, the PCR was greater than 0.9 in the 1.23-1.85 THz and 2.24-2.60 THz bands. In State 3, with μ1 = μ2 = 1 eV, the PCR exceeded 0.9 in the 2.56-2.75 THz and 3.73-4.05 THz bands. By integrating the PCM with the array antenna, tunable RCS reduction was obtained without affecting the basic radiation functionality of the antenna. In State 1, RCS reduction was greater than 10 dB in the 1.60-2.43 THz and 3.63-3.72 THz frequency ranges. In State 2, the RCS reduction exceeded 10 dB in the 2.07-2.53 THz, 2.78-2.98 THz, and 3.70-3.81 THz bands. In State 3, RCS reduction was greater than 10 dB in the 1.32-1.43 THz, 2.51-2.76 THz, and 3.76-4.13 THz frequency ranges. This polarization conversion metasurface shows significant potential for applications in switchable and tunable antenna RCS reduction.

Ultra-Thin Metasurface Polarization Converter with Linear and Circular Polarization Features for RCS Applications

AbstractIn this study, an attractive ultra-thin metasurface (MS) converter is proposed for both K-band (18–27 GHz) and Ka-band (27–40 GHz) having the superior performance of the linear-to-linear polarization (LP-LP) conversion and the linear-to-circular polarization (LP-CP) conversion. Its operating bandwidth for the LP-LP conversion is approximately over 18.6–26.7 GHz (lower part of the K-band) with a conversion efficiency of more than 90% and over 19.55–24.8 GHz (upper part of the K-band) with a polarization conversion ratio (PCR) value of more than 99%. In addition, its operating bandwidth for the LP-CP conversion (a left-handed circular polarization (LHCP)) is nearly between 31.8 and 40.5 GHz (Ka-band) with a PCR value of more than 99%. The converter can achieve a PCR value greater than 90% for both the LP-LP and LP-CP conversions for an oblique incidence wave with an incidence angle up to $$ 40^\circ $$ 40 ∘ . The design also provides mono-static radar cross section for the 18.6–26.7 GHz frequency range, where the LP-LP conversion is provided. The proposed structure can be considered to be ultra-thin having a thickness of 1 mm corresponding to 0.075$$\lambda $$ λ in the LP-LP and 0.12$$\lambda $$ λ in the LP-CP cases concerning the center frequency. The cost-effective bandwidths (BWCEs) are 210 and 34 for the LP-LP and LP-CP conversions, respectively. Free-space experiments were carried out at X-band and Ku-band to validate our design.

Switchable Vanadium Dioxide Metasurface for Terahertz Ultra-Broadband Absorption and Reflective Polarization Conversion.

Based on the unique insulator-metal phase transition property of vanadium dioxide (VO2), we propose an integrated metasurface with a switchable mechanism between ultra-broadband absorption and polarization conversion, operating in the terahertz (THz) frequency range. The designed metasurface device is constructed using a stacked structure composed of VO2 quadruple rings, a dielectric layer, copper stripes, VO2 film, a dielectric layer, and a copper reflection layer. Our numerical simulations demonstrate that our proposed design, at high temperatures (above 358 K), exhibits an ultra-broadband absorption ranging from 4.95 to 18.39 THz, maintaining an absorptivity greater than 90%, and achieves a relative absorption bandwidth of up to 115%, significantly exceeding previous research records. At room temperature (298 K), leveraging VO2's insulating state, our proposed structure transitions into an effective polarization converter, without any alteration to its geometry. It enables efficient conversion between orthogonal linear polarizations across 3.51 to 10.26 THz, with cross-polarized reflection exceeding 90% and a polarization conversion ratio over 97%. More importantly, its relative bandwidth reaches up to 98%. These features highlight its wide-angle, extensive bandwidth, and high-efficiency advantages for both switching functionalities. Such an ultra-broadband convertible design offers potential applications in optical switching, temperature dependent optical sensors, and other tunable THz devices in various fields.

Resonator-based near perfect metamaterial absorber with high EMI shielding for Wi-Fi and 5G applications

This paper introduces a perfect metamaterial absorber (MMA) achieving exceptional electromagnetic signal absorption at application-oriented frequencies of 2.40 and 3.50 GHz in addition to 6.09 GHz. The MMA exhibits absorption rates of 99.85, 98.6, and 96.7%, with high shielding effectiveness (SE) of 36.44, 32.58, and 31.13 dB against electromagnetic interference (EMI) at those frequencies. The structure of the copper resonator on the FR4 substrate allows the on-design frequency switching from 3.43 to 3.70 and 5.65 to 6.55 GHz, respectively. The structural symmetry enables polarization and incidence angle independence up to 60° for both transverse electric and magnetic modes. The perfect absorption of the MMA is shown by the near-zero polarization conversion ratio. There is an adjacent correlation between the measurement and simulation results. The proposed MMA emerges as an efficient EMI shield for Wi-Fi and 5G signals, offering perfect absorption and extensive polarization characteristics.

Wideband monostatic and bistatic radar cross‐section reductions using polarization conversion metasurface

AbstractA high‐efficiency polarization conversion metasurface (PCM) is proposed and applied to radar cross section (RCS) reduction. The PCM can achieve cross‐polarization conversion with a polarization conversion ratio of over 97% from 13.9 to 30.3 GHz, covering K‐band. The low‐RCS antenna is designed from a circularly polarized patch antenna loading with the PCM. The antennas with and without PCM are fabricated and measured. The results show that the radiation performance is well preserved and the scattering performance is greatly improved. The average monostatic RCS reduction value reaches 14.6 dB in an ultra‐wideband from 12.2 to 30.2 GHz under normal incidence. What's more important, bistatic RCS is researched in detail and evident RCS reduction is achieved at different incidence angles. This research has potential applications in the field of stealth platform.

Tunable terahertz polarization conversion and absorption devices based on metamaterials

Metamaterials, as novel materials, have electromagnetic behaviors that can be realized by rationally designing the unit structure. It plays an important role in the research of terahertz functional devices. Switchable terahertz devices are constructed by flexibly combining the excellent properties of graphene and vanadium dioxide (VO2) with the application potential of terahertz technology. When the VO2 is in the metallic state and the graphene Fermi energy level is 0 eV, the device behaves as a broadband polarization switching device. It can realize cross-polarization conversion for the incident electromagnetic wave in the range of 2–4.2 THz. When the VO2 is in the insulating state and the graphene Fermi energy level is 0.9 eV, the device is an absorption device. The absorption rate can reach more than 99% at 4 THz. In addition, the polarization conversion ratio (PCR) as well as the absorption rate of the device can be tuned independently. This actively tunable switchable terahertz device provides ideas for dynamically controlling terahertz, bringing more possibilities for various applications such as terahertz imaging, stealth, and communication.

WITHDRAWN: Cross polarization converter with high transmittance and near unity polarization conversion efficiency for visible light based on bilayer all-dielectric metasurface

It is highly desired to achieve high efficiency polarization converters in visible wavelength region for ultra-compact optical systems which have shown potential applications in optical sensing, communication and imaging. Due to the intrinsic property of low loss, all dielectric metasurfaces are more competitive candidates to be utilized for fabrication of polarization converters than the counterparts based on metals. In this paper, we design a bilayer all dielectric metasurface polarization converter composed of a Si double-rod resonator placed on the top of a glass block with a polymer substrate for linearly polarized visible light. The proposed bilayer metasurface structure can convert linearly polarized light to the cross-polarized light efficiently within the visible region from 542 nm to 563 nm in the transmission mode with high transmittance and near unity polarization conversion efficiency. The transmittance is larger than 0.8 in the mentioned wavelength range with a maximum transmission of 0.86 at 556 nm and polarization conversion ratio is larger than 90% in the same wavelength range with a maximum polarization conversion ratio of 99.01% at 556 nm. The underline physical mechanisms of high conversion efficiency and high transmittance are analyzed in detail with simulated distributions of surface current, electrical field distributions and the calculated multipole decompositions of the scattering power.

Dual-Polarization Conversion and Coding Metasurface for Wideband Radar Cross-Section Reduction

Modern stealth application systems require integrated meta-devices to operate effectively and have gained significant attention recently. This research paper proposes a 1-bit coding metasurface (CM) design. The fundamental component of the proposed CM is integrated to convert linearly polarized incoming electromagnetic waves into their orthogonal counterpart within frequency bands of 12.37–13.03 GHz and 18.96–32.37 GHz, achieving a polarization conversion ratio exceeding 99%. Furthermore, it enables linear-to-circular polarization conversion from 11.80 to 12.29, 13.17 to 18.44, and 33.33 to 40.35 GHz. A second element is produced by rotating a fundamental component by 90°, introducing a phase difference of π (pi) between them. Both elements are arranged in an array using a random aperiodic coding sequence to create a 1-bit CM for reducing the radar cross-section (RCS). The planar structure achieved over 10 dB RCS reduction for polarized waves in the frequency bands of 13.1–13.8 GHz and 20.4–30.9 GHz. A prototype was fabricated and tested, with the experimental results showing a good agreement with the simulated outcomes. The proposed design holds potential applications in radar systems, reflector antennas, stealth technologies, and satellite communication.