Surface Current Distribution Research Articles

Reflective one-to-multi-polarization conversion via separate control of phase and magnitude.

Polarization manipulation is a key issue in electromagnetic (EM) research. Research on 90° polarization rotators and circularly-polarized wave generators has been widely conducted. In this study, a polarization conversion metasurface that can shift one linearly-polarized EM wave into multi-polarization outgoing waves at certain frequencies is demonstrated, including co-, cross-, left-hand, and right-hand circular-polarization components. The surface was made of periodically arranged chiral meta-atoms. The polarization manipulation method is based on the independent control of phase and magnitude, in which the phase control is based on the Berry-phase theory of linearly-polarized EM waves, while the magnitude control is based on the cavity mode theory of the microstrip structure. Both eigenmode analysis (EMA) and characteristic mode analysis (CMA) were utilized for magnitude control, which was further verified by the surface current distribution. Finally, the metasurface was fabricated and measured, showing good agreement between the measured and simulated results. This research proposed what we believe to be a novel polarization method, which can be potentially applied in polarization manipulation, EM radiation, filters, wireless sensors, etc., over a frequency range from optics to microwave bands.

Broadband metamaterial absorber for stealth applications at K-band

This paper focuses on the design and analysis of a polarization-insensitive wide-angle broadband metamaterial absorber for stealth applications at the K band. The unit cell of the metamaterial absorber is comprised of a symmetrically arranged ladder shape geometry made of copper metal, which is imprinted on a metal-backed FR-4 substrate. The structure shows more than 91% absorptivity ranging from 21.2 to 28.2 GHz for both transverse electric (TE) and transverse magnetic (TM) polarized waves under normal incidence. The topology is four-fold symmetric and yields polarization-insensitive responses for different angles of polarization under both TE and TM polarized waves. The structure is also investigated under oblique incidence where the 80% absorptivity holds up to 45° incident angles for both TE and TM waves. The absorption mechanism is explained with the help of top and bottom surface current distribution, induced electric field, and parametric analysis. To verify the resonances in the structure, characteristic mode, and equivalent circuit analysis have been carried out and presented. A prototype of the absorber has been fabricated and simulated results are validated with measured results. The novelty of the proposed absorber lies in its unique metallic pattern on a λ0/8 thin FR-4 substrate while showing the wide absorption bandwidth to normal and oblique incidence. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction applications at the K band.

Mutual Coupling Reduction of a Multiple-Input Multiple-Output Antenna Using an Absorber Wall and a Combline Filter for V2X Communication.

This paper presents an MIMO antenna for vehicle-to-everything (V2X) communication, which adopts two ways of combline filters and absorption wall decoupling. A combline filter and an absorption wall are used, respectively, for internal and external decoupling. The combline filter is incorporated between the ground of the two adjacent antennas, which reduces the mutual coupling between them. Additionally, the mutual coupling of radiation between adjacent antennas is significantly reduced by the absorber wall. These combline filters and absorber walls use the method of electromagnetic field distribution to explain the reduction in the mutual coupling between the adjacent antennas. The transmission coefficient and surface current distribution explain the effectiveness of the decoupling structure. When the frequency is between 3.8 and 4.8 GHz, the simulation and measurement results show that S11 is less than -10 dB, the bandwidth is 25% and the peak gain is 7.8 dBi. In addition, the proposed MIMO antenna has a high isolation between antenna units (>37 dB), and the envelop correlation coefficient (ECC) is less than 0.005.

Eight-Port Tapered-Edged Antenna Array With Symmetrical Slots and Reduced Mutual-Coupling for Next-Generation Wireless and Internet of Things (IoT) Applications

A compact and low-cost eight-port (2x4 configuration) tapered-edged antenna array (TEAA) with symmetrical slots and reduced mutual-coupling is presented in this paper using the inset-feed technique. The 8-port TEAA is designed and simulated using CST microwave studio, fabricated using the flame-resistant (FR4) substrate having a dielectric constant (εr) = 4.3 and thickness (h) = 1.66mm and characterized using Keysight technologies vector network analyzer (VNA). The designed 8-port TEAA operates at the 5.05-5.2GHz frequency band. Various performance design parameters, like return-loss, bandwidth, gain, 2D/3D radiation patterns, surface current distributions, and isolation-loss, are briefly studied, and the results are summarized. The eight-port TEAA has featured the bandwidth/ gain characteristic of 195MHz/10.25dB, 3dB beam-width of 52.8o, and excellent mutual-coupling (high isolation-loss) of less than -20dB, respectively. The 8-port TEAA is proposed and characterized to work for next-generation high-throughput WLANs like IEEE 802.11ax (WiFi-6E), Internet-of-Things (IoT), and the upcoming 5G wireless communication systems.

Tri-band metasurface absorber based on square rotational symmetry

In this paper, a multi-band metasurface absorber is designed, measured and investigated. There are four centrosymmetric two-tangent copper trapezoids that make up its unit cell. The parameters of the unit cell have great influence on the frequency of absorption peaks, with optimized parameters leading to absorptivity of 99.4%, 93.9% and 99.7% at 4.80GHz, 8.68GHz and 10.92GHz, respectively. The physical mechanism of absorption is further analyzed based on the distributions of surface current, electric and magnetic field, as well as the impedance matching. Furthermore, the absorber exhibits characteristics of polarization insensitivity and incident sensitivity, which are demonstrated through experiment. In addition, the proposed absorber is able to monitor different environments that the sensitivities are 0.15 GHz/PIU, 0.50 GHz/PIU and 1.53 GHz/PIU at three absorption peaks. In addition, the FOM of the proposed sensors at corresponding resonant frequencies are 0.68, 1.61 and 4.78, respectively. The result reflects that the proposed metasurface shows effective sensing abilities. The designed metasurface absorber has potential applications in both military and civil fields.

Numerical study of a near-infrared to mid-infrared perfect absorber based on tunable GaAs metamaterial

An infrared perfect absorber structure is designed based on GaAs/Au/SiO2 metamaterial with numerical simulation, in which gold split ring resonators (SRR) embedded in the GaAs layer. The absorption exceeds 99% at 1360 nm under the plane wave excitation with its polarization perpendicular to the opening direction of the SRR. When the polarization of the plane wave is parallel to the opening direction, the absorption exceeds 97% and 56% at 970 and 2070 nm, respectively, which realize dual-band absorption. The absorption peaks are effectively modulated by controlling surface current density distribution and resonant electromagnetic response. In addition, the resonant wavelengths are further manipulated by optimizing the resonant ring structural parameters, which achieve ultrawide-band absorption ranging from near-infrared to mid-infrared region. The absorber remains absorption peaks above 96% under wide-angle plane wave incidence, and the resonant peak positions are independent of the incident angle. This work exhibits the promise of GaAs-based metamaterial in practical applications in energy harvesting and night vision imaging.

Absorptive/transmissive frequency selective surface with multiple transmission zeros for reduced transition bandwidth

An absorptive/transmissive frequency selective surface (ATFSS) with multiple transmission zeros is proposed, which consists of one lossy layer and two lossless layers separated by air space. As the key features, the slot-line loading and interlayer coupling technologies are adopted in the lossy layer and lossless layers, respectively, to introduce the infinite impedance points and four transmission zeros, thereby simultaneously achieving low insertion loss and high selectivity of the transmission band. Benefiting from the ohmic loss of the lumped resistance in the lossy layer, effective absorption can be readily implemented. A detailed qualitative analysis of the proposed structure is presented through the equivalent circuit theory, surface current, and power loss density distributions. Under normal incidence, the overall structure exhibits two discrete absorption bands over the frequency range of 6.34 to 13.40 GHz, whereas a transmission behavior is obtained from 9.34 to 11.40 GHz with a minimum insertion loss of only 0.14 dB. In particular, there are only 3.9% and 3% transition bandwidths between absorption and transmission functions. Then, a sample prototype is fabricated for demonstration, and the measured results are well consistent with the simulated one. As expected, the proposed ATFSS has the advantage of multiple transmission zeros, loss insertion loss, and narrow transition band, which is of great potential in the application of radar stealth radome.

Reconfigurable intelligent surface with high optical-transparency based on metalmesh

Reconfigurable intelligent surfaces (RISs) have aroused extensive attentions from academic and wireless communication communities due to their abilities to customize the electromagnetic (EM) characteristics of the propagation channels flexibly and rapidly. Recent advances in theoretical innovations and prototype systems have demonstrated the advantages of RISs in terms of low cost, low power consumption, and easy deployment. Meanwhile, the optically transparent RISs are demanded in some application scenarios. In this paper, we propose a 2-bit metalmesh-based RIS with high optical-transparency. By analyzing the surface current distributions on the element, we employ the metalmesh-grid patterns and metalmesh-stripe patterns on the top and ground layers respectively. The metalmesh patterns can help improve the optical transparency of RISs, while maintaining similar microwave characteristics. The RIS can reach the optical transparency of 79%, and the reflection amplitude is greater than −3.2 ​dB within the operating band. Finally, to verify the capability of the proposed RIS in wavefront controls, the far-field scattering patterns of the RIS with different coding sequences are investigated and the simulation results are in good agreement with the theoretical results.

An X-shaped triple split ring resonator-based metamaterial perfect absorber with quad-band incident and polarization angle insensitivity for C, X, and Ku band applications

In this study, an X-shaped triple split ring resonator-based metamaterial perfect absorber with quad-band incident and polarization angle insensitivity for C, X, and Ku band applications has been proposed. The metamaterial perfect absorber consists of a prearrangement with metallic patch, metal ground plane and a middle Rogers RT5870 dielectric substrate with 1.575 mm thickness. The numerical methods implemented using finite integration technology (FIT) demonstrate that the metamaterial perfect absorber (MPA) exhibits an absorption capacity exceeding 99% in all frequency bands, precisely matching the impedance of free space. These frequency bands are located at 4.37 GHz, 7.08 GHz, 9.38 GHz, and 10.65 GHz with the absorption levels of approximately 99.8%, 99.9%, 99.9%, and 99.9% respectively for both transverse electric (TE) and transverse magnetic (TM) modes. Additionally, the MPA demonstrates quality factors of 21.92, 7.2, 13.42, and 15 for both modes. The investigation of the electromagnetic (EM) field with surface current distribution has provided information about the mechanism of such quad-band absorbance. The numerical analysis reveals that the metamaterial perfect absorber (MPA) can achieve remarkable absorbance outcomes across a wide range of incident angles, up to 800s, while also being insensitive to polarization up to 300 for both modes. A comparable circuit analysis demonstrates the superior performance of the MPA, indicating its potential for excellent functionality within the advanced design system (ADS) software. Furthermore, the suggested structures, modelled using the high-frequency structure simulator (HFSS), closely align with the maximum absorbance observed at each resonance peak in the computer simulator technology (CST) simulator results. The proposed MPA possesses high-performance characteristics that enable its application in various domains such as satellite communications, raw satellite feeds, and radar systems.

Wideband and Low-Profile Multi-Polarization Reconfigurable Filtering Antenna Based on Nonuniform Metasurface

In this article, a wideband and low-profile multi-polarization reconfigurable filtering antenna based on metasurface (MS) is investigated. The proposed antenna consists of two layers, which are the feeding layer and the MS layer. The filtering function is achieved by utilizing a non-uniform MS and inserting a short via between the feedline and ground plane. Besides, by rotating the MS to change its surface current distribution, the antenna can switch among linear polarization (LP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). To demonstrate the simulated design, the proposed antenna is manufactured and measured. As the measured results show, when the antenna works in LP modes, it obtains an -10-dB overlapped impedance bandwidth of 22.4% and an in-band peak gain of 8.8 dBi. Furthermore, the antenna achieves 14-dB and 19-dB out-of-band radiation suppression levels for LP1 and LP2 modes, respectively. Whereas it operates in CP modes, the measured -10-dB overlapped impedance bandwidth and 3-dB axial ratio (AR) bandwidth of the antenna reach 26.5% and 22%, respectively. Meanwhile, its out-of-band radiation suppression level is more than 17.5 dB, with an in-band peak gain of 7.3 dBic. Hence, there illustrates a pretty good agreement between the simulated and measured results.

Wideband Low-Loss Filter With Compact Size and Wide Stopband Based on Folded Planar Waveguide

In this letter, a hybrid, compact doubly slot-loaded folded ridged half-mode substrate-integrated waveguide (FRHMSIW) filter with wide bandwidth and high selectivity is presented and investigated. The low-pass and high-pass cutoff frequencies of the wideband filter can be independently controlled by adjusting the dimensions of the quasi-periodic slots and FRHMSIW sections, respectively. The dispersion curves, surface current distribution, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -field vector diagram of the proposed hybrid FRHMSIW bandpass unit are illustrated. Parametric study and loss analysis are also conducted. The footprint of the proposed filter is miniaturized due to the upper-side-slot-loaded FRHSIW transmission structure and meandered middle-layer slots. The stopband is further extended by etching I-shaped patterns on the ground layer. Finally, the filter is designed, simulated, and measured, with a wide passband between 3.86 and 8.3 GHz, a minimum insertion loss of 0.56 dB, a rejection level better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 20 dB from 8.6 to 20.8 GHz, and an electrical size of only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{g}^{2}$</tex-math> </inline-formula> at the center frequency.

Collective-Coupling Enhanced Ultrabroadband Linear Polarization Conversion on Zigzag-Split Metasurfaces

Polarization manipulation plays a pivotal role in integrated multifunctional devices. Various metasurface-based polarization converters successfully demonstrated high efficiency and broad bandwidth. However, new mechanisms to aggressively enhance performance are still in dire need. Herein, theoretical and experimental evidence corroborates an efficient ultra-wideband transmissive polarization converter based on a topological design method. The triple-layer meta-device consists of a layer of anisotropic zigzag-split resonator array amid two orthogonal wire-grating layers. By splitting double zigzag lines into compound 90°V-shaped resonators, the intra-unit cross-coupling extends to strong inter-unit cross-coupling, giving birth to the multi-resonances enhancement and significant bandwidth broadening. This polarization converter can efficiently convert linearly polarized incident waves into 90° cross-polarized transmitted waves, with a conversion efficiency above 80% over 3.98-22.71 GHz, reaching a fractional bandwidth of 140.4%. The proposed meta-device enables strong cross-coupling in mutual transition from intra-unit to inter-unit. From a physical viewpoint, the novel mechanism is elucidated by the surface current and electric field distributions upon constructive interferences stemming from V-shape-resonator combinations and the Fabry-Pérot-like cavity effect. With both spectrum and function extensions, the proposed polarization conversion strategy finds essential applications in polarization-related systematic scenarios, such as 6G communication, radar imaging, anti-interference, chiral sensing, etc.

Design and Analysis of the Hexagonal-Shaped Antenna with Multi-Band Feature for WLAN, WiMAX, and LTE Applications

Developing and researching antenna designs are analogous to excavating in an undiscovered mine. This paper proposes a multi-band antenna with a new hexagonal ring shape, theoretically designed, developed, and analyzed using a CST before being manufactured. The antenna has undergone six changes to provide the best performance. The results of the surface current distribution and the electric field distribution on the surface of the hexagonal patch were theoretically analyzed and studied. The sequential approach taken to determine the most effective design is logical, and prevents deviation from the work direction. After comparing the six theoretical results, the fifth model proved to be the best for making a prototype. Measured results represent that the proposed antenna can operate well in three bands with a return loss of -11.24 dB at 2.9 GHz, -25.99 dB at 4.9 GHz, and -21.26 dB at 5.4 GH. This type of antenna belongs to various wireless communication systems, including 2G, 3G, 4G, and 5G.

Polarization insensitive multiband metasurface absorber for L, C, and X band applications

An ultrathin, multiband, polarization insensitive with wide angle stability metasurface absorber having unitcell dimension is proposed ( is the free space wavelength at 1.6 GHz). The four-fold symmetry of the unitcell makes it insensitive to TE and TM polarizations. This metasurface follows the sub-quarter wavelength thickness including an air gap of 2.5 mm and metal backing. The proposed unitcell of the metamaterial absorber (MMA) is designed by parametric optimization and has absorption peaks in L, C, and X bands. This absorber is suitable for applications like radar cross section reduction, isolation, and stealth technologies. The lumped SMD resistors are used to enhance absorption peaks simultaneously in all bands mentioned above. This metasurface has absorptivity of 95%, 99%, 97% & 94% at 1.6 GHz, 5 GHz, 7.5 GHz and 10.2 GHz respectively. This is a polarization-insensitive absorber showing stable absorption for different incidence angles between and at the above-given frequencies. The absorption effect has been studied by investigating the filter effect from the equivalent circuit modeling using surface current distribution and normalized impedance. The proposed structure has been fabricated and its measurement results agree well with the simulated one.

Design and analysis of compact flower-shaped wideband slotted monopole antenna for RFID reader applications

This article introduces the design and analysis of a compact, high gain, and wide bandwidth flower-shaped slotted monopole antenna for RFID reader antenna applications. The proposed antenna comprises a flower-shaped radiator with six arc-shaped slots and a partial ground plane. The measurement results indicate a wide operating band in the frequency range of 2.4 GHz–7.6 GHz. The proposed antenna is designed to operate at 5.8 GHz ISM band for RFID reader applications with a peak measured gain of 3.9 dBi. The structure has an overall dimension of 0.78λ× 0.58λ× 0.03λ at an operating frequency of 5.8 GHz and is found compact in comparison to some related designs. The monopole antenna shows an omnidirectional radiation pattern in the operating band and indicates a maximum realized gain value of 4.2 dBi. The study provides a detailed mathematical analysis of the operating principle with surface current distribution plots. The design indicates a reading range of 2.56 cm at 5.8 GHz and the satisfaction of the propagation-test makes the compact, wideband, and high-performance design suitable for different short-range RFID reader applications.

Wideband reflective half- and quarter-wave plate metasurface based on multi-plasmon resonances

In this article, a single-layer reflective anisotropic metasurface (MS) is proposed, which presents both half- and quarter-wave plate operation in different microwave frequency regimes. The unit cell of the proposed metasurface consists of a tilted rectangular plane with triangular ends accompanied by an equidistant-filled triangle on both sides. The unit cell is printed on a dielectric substrate backed by a metallic plane. The proposed meta-plate transforms horizontal polarization into vertical and vice versa in two wide frequency bands, 7.1-15.3 GHz and 19.8-21.7 GHz. Similarly, a linearly polarized (LP) wave is transformed into a circularly polarized (CP) wave and vice versa at 7.9 GHz and 21.8 GHz. The wide bandwidth is acquired through three plasmonic resonances occurring at 8.2 GHz, 12.7 GHz and 20.8 GHz, where the cross-polarization conversion ratio reaches almost 100%. Moreover, quarter and half-wave plate operations occurring at 7.9 GHz and 7.1-15.3 GHz, respectively, are robust to changes in oblique incidence angle (up to 45°) both for transverse-electric (TE) and transverse-magnetic (TM) polarizations. The physical mechanism behind polarization conversion is also explained through surface current distribution. The proposed meta-plate structure is fabricated and validated through experimental measurements. The wide bandwidth, high efficiency, angular stability, and simple structure make the proposed metastructure incredible for numerous microwave applications such as antennas, radars, and satellite communication.

Multiband polarization insensitive metamaterial absorber for radar cross-section reduction

In this paper, a polarization-insensitive, metamaterial absorber with more than 91 % absorptivity is investigated numerically and experimentally for radar cross-section reduction at X, Ku, and K bands. The unit cell structure of the absorber is comprised of a symmetrically arranged defective L-shaped patch made of copper metal, which is imprinted on a metal-backed FR-4 lossy dielectric substrate. The proposed absorber yields multiband absorption response at distinct absorption peaks at 11.1, 15.5, and 16.3 GHz along with the broadband response of 4.8 GHz from 18.6 to 23.4 GHz (absorption peaks at 18.9, 20, 21.9, and 23 GHz) in the absorption spectra. The Characteristic mode analysis has been carried out and presented to verify the modes and resonance in the structure. The physical absorption phenomenon is clarified by presenting the induced electric field, top and bottom surface current distribution, and various retrieved constitutive electromagnetic parameters. The structure is studied for various polarization angles for both transverse electric (TE) and transverse magnetic (TM) waves at normal incidence which shows strict insensitivity to the direction of arrival of electromagnetic(EM) signal. The structure is also investigated under oblique incidence for both TE and TM waves where the response holds good up to 50° incident angles in both cases. The novelty of the proposed absorber lies in its multiband response at X, Ku, and K bands through a unique metallic pattern on a thin FR-4 substrate along with characteristics of broadband, polarization insensitiveness, wide incidence angle independence, and compactness incorporated in a single and simple design without using external components. A prototype of the absorber has been fabricated and simulated results are validated with measured results. All the above-mentioned attributes in a simple design make it commercially suitable for radar cross-section (RCS) reduction and energy harvesting applications at X, Ku, and K bands.

Dual-mode bidirectional multifunctional chiral metamaterial based on self-complementary resonators

In this paper, we propose an intrinsic chiral metamaterial (ICM) consisting of two metal self-complementary resonators, dielectric layer, and an embedded continuous vanadium dioxide (VO2) layer, which can operate in reflection and transmission modes and tailor different polarization manipulations for circular and linear polarized waves in opposite incident directions. When VO2 is in metallic state, the ICM can achieve broadband and narrowband circular polarization conversions at 1.52–2.50 THz and 2.93 THz for opposite propagating directions, respectively; when VO2 is in an insulating state, it shows a strong asymmetric transmission (AT) effect at 2.43 and 3.19 THz for forward and backward linear polarized waves. In addition, the physical mechanisms of different polarization operations are explained by analyzing the surface current and electric field distributions, multiple interference model, and near-field distributions in detail, and the circuit models are introduced to verify the simulated results. Furthermore, we investigate the influence of structural parameters on performance. The proposed ICM has important implications for the development of polarization detectors, frequency selectors, etc.

Bifunctional Terahertz Metasurface for Transmissive Broadband Linear-to-Circular and Linear Polarization Conversion

In this work, we experimentally demonstrate a bifunctional terahertz (THz) metasurface that can achieve broadband linear-to-circular polarization conversion (LCPC) and linear polarization conversion (LPC) in two different bands, respectively. The measured 3-dB axial ratio relative bandwidth is 34.2% for the LCPC in the lower band from 0.34 THz to 0.48 THz, and the measured polarization conversion ratio is over 80% for the LPC in the higher band from 0.53 THz to 0.85 THz. The physical mechanism of the LCPC and LPC is explained by the surface current distribution and is further discussed by employing the multiple interference model. This bifunctional THz metasurface polarization converter has promising applications in THz systems, communications, spectroscopy, etc., and the design strategy can also be extended to microwave and millimeter bands.

Triple band terahertz metamaterial absorber within (0.4-0.46thz) frequency range

An ultrathin Terahertz Triple-band ideal meta material absorber with a brand-new design that is straightforward has been presented. The suggested terahertz meta material absorber has a unit cell that is made up of two D-shaped resonators with slots and a ground metallic plane. These elements are separated from one another by a polyimide dielectric substrate that has a thickness of 500 micrometers. The absorber construction that has been presented provides three distinct absorption peaks within the narrow frequency range of (0.4-0.46 THz) without producing any interference. In order to get a deeper comprehension of the mechanism behind the absorption process, an investigation into the electric field, the magnetic field, the surface current distribution, and the independence of the polarization angle has been carried out. It is anticipated that the configuration of the terahertz absorber that has been described would find use in applications relating to the lowering of radar cross-section, detection, imaging, and sensing. One of the contributions of this study is the description of a downsized and compact triple-band terahertz meta material absorber. In order to generate the unit cell of a terahertz absorber, an identical I-typed resonator, which is represented by a rectangular patch with two very small notches, is first deposited on top of a dielectric sheet and then a metallic mirror. The terahertz regime reveals three distinct frequency spots, and the design of the very small structure allows for virtually full absorption of all of them.