Surface Current Distribution Research Articles

A thin, wideband transmissive cross polarization converter.

This study presents a very thin wideband linear polarization converter in transmission mode with near-unity conversion efficiency. The suggested converter consists of a periodic array on a single-layer substrate, two metallic layers and six vias. Metallic vias connect the upper and lower layers of the construction. The radiated electromagnetic wave with linear polarization can be transformed into its orthogonal component in the transmission mode by the proposed converter. The suggested polarization converter operates well in the 9.53-13.35 GHz frequency band (36%). Additionally, The structure provides a larger than 90% Polarization Conversion Ratio (PCR) through the frequency range of 8.89-14.21 GHz. The conversion mechanism has been explained and confirmed through both surface current distribution, electric charge distribution and experimental tests. Over the whole frequency range, there is good agreement between the simulated and measured results.

An ultra-wideband thin metamaterial linear cross-polarization conversion

This article presents the design of a novel ultra-wideband, thin metamaterial linear cross-polarization converter (CPC) operating at microwave frequencies. The CPC consists of two concentric deformed rings on a dielectric substrate backed by a metallic surface. It demonstrates co-polarization and cross-polarization reflection coefficients below − 11 and above − 1.1 dB, respectively, over a wide frequency range of 8.75–17.75 GHz, achieving a 68% bandwidth. Within this range, the polarization conversion ratio exceeds 90%, with three prominent peaks at 9.3 GHz, 13 GHz, and 17.4 GHz, reaching 99.5%, 99.8%, and 99.3% respectively. The unit cell dimensions are compact at 6.3 × 6.3 × 2 mm3. The CPC’s performance was analyzed under varying polarization and oblique incidence angles, and the surface current distributions were studied to elucidate the polarization conversion mechanism. Simulations using CST and FEKO demonstrated substantial agreement, also equivalent circuit is determined and compared to CST software. The compact, thin, and ultra-wideband design makes this CPC a promising candidate for applications in advanced communication systems such as radar cross-section reduction and electromagnetic interference suppression. The results are validated further by experimental measurements of the fabricated CPC.

Numerical simulation of electromagnetically induced transparency in composite metamaterial

Abstract In high-refractive-index dielectric nanostructure, the Mie resonance become evident, and the destructive interference of the radiation fields from electric and toroidal dipole moments results in the excitation of anapole state, which has the unique optical properties of a dark state and can support the excitation of more diverse optical phenomena, such as the electromagnetically induced transparency (EIT) effect. In this study, we performed numerical simulations of a composite metamaterial consisting of Si nanocubes and gold nanorods. The Au-Si composite structure produces an electromagnetically induced transparency spectrum based on the coupling of the optical dark channel (i. e. anapole state) and bright channel (i. e. localized surface plasmon resonance). By tailoring the surface structure of the dielectric Si cube, the surface charge and current distributions can be modified, and finally, the nonradiative anapole state may be influenced and manipulated. The results show that the modified metal/dielectric metamaterial can realize an electromagnetically induced transparency effect with a transmission of up to 95% and a refractive index sensitivity of 170 nm RIU−1.

Compact complementary slot resonator antenna with L-Probe feed excitation for wireless communication

ABSTRACT This study presents a concise design of a complementary slot resonator antenna employing the L-probe feed excitation. The antenna features a compact size of 0.086λ0 × 0.086λ0 × 0.006λ0, unlike the wire-loaded miniaturised slot antenna, which has a greater height. The extensive electrical path length of the complementary slot resonator results in the proposed antenna resonating at 434 MHz, a frequency substantially lower than the wavelength (λ0). The work explores essential parameters, such as return loss, radiation patterns and efficiency, highlighting a consistent correlation between simulation and measurement results through a parametric study. In simulation, the antenna exhibits an efficiency of 92.19%, while in practical measurements, it maintains a high efficiency of 89.73%. In addition, the study incorporates simulated input impedance and surface current distribution data to enhance the comprehensive analysis of the antenna design. The antenna is fabricated using copper metal due to its excellent electrical conductivity properties and the achieved resonant frequency has applications in various wireless communication scenarios.

An optimization method for terahertz metamaterial absorber based on MOPSO

Metamaterials can freely control terahertz waves to obtain the desired electromagnetic characteristics by designing the geometry and direction of the unit structure, which is widely used in sensing, communication and stealth technology in radar. The traditional design of terahertz metamaterial absorber usually requires continuous structural adjustment and a large number of simulations to meet the expected requirements. The process is heavily dependent on the experience of researchers, and the physical modeling and simulation solution process is time-consuming and inefficient, which has greatly hindered the development of metamaterial absorbers. Therefore, deep learning has been used to predict the structural parameters or spectra of metamaterial absorbers due to its powerful learning ability. However, when designing a new structure, a large number of training samples need to be reprepared, which is time-consuming and not universal. Particle swarm optimization can quickly converge to the optimal solution through the sharing and cooperation of individual information in the group, without prior preparation. Therefore, this paper proposed a fast design method of terahertz metamaterial absorber based on multi-objective particle swarm optimization algorithm. Taking a new center symmetric absorber structure composed of four L as an example, the structure parameters are optimized to achieve fast automatic design of metamaterial absorber. The multi-objective particle swarm optimization takes the absorptivity and quality factor as independent targets to design the structure parameters of the absorber, realizes the dual-objective optimization of the absorber, and overcomes the shortcoming of the multi-objective conflict that PSO cannot solve. The optimally-designed absorber achieves perfect absorption at 1.613THz with a quality factor of up to 319.72 and a sensing sensitivity of 264.5GHz/RIU when used for refractive index sensing. In addition, the causes of absorption peaks are analyzed in detail using impedance matching, surface current, and electric field distribution. By studying the polarization characteristics of the absorber, it is found that it is not sensitive to polarization, which is more stable in practical application. In summary, the multi-objective particle swarm optimization algorithm can realize the design according to the demand, reduce the experience requirement of researchers in the design of metamaterial absorber, improve the design efficiency and performance, and have great application potential in the design of terahertz functional devices.

Petal-shaped Array Antenna with Slots for Improving Surface Current Distribution

Petal-shaped Array Antenna with Slots for Improving Surface Current Distribution

Dynamically switchable multifunctional device for terahertz application using vanadium dioxide and graphene-based metasurface

Abstract In this article, a dynamically switchable and multifunctional metasurface is realized using a combination of vanadium dioxide (VO2) and graphene-based structures. The device can be tuned using the temperature transition property of vanadium dioxide from a wideband linear-to-circular polarization converter (LTCPC) to a wideband linear-to-linear cross polarization converter (LTLPC) and a dual-band absorber. The unit cell is designed with a gold-backed lossy-silicon dioxide (SiO2) substrate with a permittivity of 3.9, and the top metasurface layer is designed with a graphene-based dual triangle loaded split ring (DTLSR) and two stripes of vanadium oxide to cover the split partially. The proposed device can be used as a wideband LTCPC at normal temperature (298 K) from 1.43 THz to 2.85 THz, i.e., 66.35% fractional bandwidth (FBW). At temperatures greater than 341 K, VO2 exhibits metallic properties, and the structure functions as LTLPC from 1.82 THz to 3.31 THz (PCR ≥ 80%), i.e., 58.08 % FBW and maximum polarization conversion ratio (PCR) reported as high as 99.65 %. Furthermore, at this metallic condition, two absorption peaks are obtained at 1.22 THz and 3.30 THz with absorptivity of 93.5% and 100%, respectively. The device offers incident angle invariability up to 40° for LTCPC and up to 50° for LTLPC operation. Further insight into the mechanism of operation is developed using the surface current density and electric field distribution analysis. The advantage of the proposed metasurface over other similar structures is assessed with respect to multifunctional behavior, bandwidth, and stability under oblique incidence.

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-layered chiral structure. By integrating a double-split ring resonator with a strip resonator, the proposed design can improve bandwidth and 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 is fully elucidated through theoretical analysis and the characterization of surface current distribution. The designed structure can be used in terahertz imaging, sensing, and communication.

Angle-insensitive broadband transparent microwave absorber with high shielding effectiveness.

In this work, a specially designed multilayer indium tin oxide (ITO) mesh structure metasurface was proposed as a microwave absorber, achieving both excellent angle-insensitive broadband absorption and high shielding effectiveness (SE). It features gradually changing surface resistance (Rs ), to expand the absorption bandwidth while maintaining high SE. Also, a folded square ring metasurface was designed to effectively suppress surface wave grating lobes, as well as to reduce the unit size of the metasurface and thus the absorber. What is more, an additional top dielectric layer was used to stabilize the absorption and SE under an oblique incidence condition (≤45°). As a result, an ultra-broadband miniaturized transparent absorber was realized, with an absorption of >80% in a 2.10-14.65 GHz frequency band (150% relative bandwidth) and a SE of >20 dB in 1-12 GHz at normal incident. The relative thickness of the absorber is only ∼0.117λ0, and the unit size of the metasurface is only 0.083λ0. The broadband absorption mechanism of the multilayer absorber was analyzed from the aspects of resonance frequency, surface current distribution, and equivalent circuit. In general, the proposed absorber showed angle-insensitive ultra-wideband absorption with high SE at the same time, implying a wide range of applications.

Rectangular ring resonator-based symmetrically engineered metamaterial absorber for electromagnetic interference shielding in the S and C bands

Abstract This research aims to investigate the use of metamaterial (MM) structures in S and C bands for efficient EMI shielding. The designed MM absorber consists of four rectangular ring resonators (RRR) made of copper separated by a 1.3 mm thick FR-4 dielectric layer with dimensions of 15 mm × 15 mm and a ground layer of annealed copper with a thickness of 0.035 mm. The simulated results demonstrate two absorption peaks at 4.1 GHz and 6.8 GHz, with absorption values of 99.9% and 96%, respectively. The properties of the reflection coefficient are investigated using a circuit model of the MM absorber, and the electromagnetic wave absorption mechanism is further studied by examining the surface current, H-field, and E-field distributions at absorption peaks. The metamaterial (MM) absorber exhibits almost perfect absorption across a significant angle of incidence and polarisation angle up to 60 degrees. The suggested MM design provides dual-band shielding characteristics with a -10 dB reflection coefficient (S11) at 4.0-4.14 GHz and 6.83-6.89 GHz. Furthermore, the Metamaterial (MM) absorber offers a shielding efficiency of > 20 dB in all bands, according to the theoretical analysis. The MM’s 99% absorption and shielding capability makes it suitable for a wide range of high-potential applications.

Wideband star-shaped antenna based on artificial magnetic conductor surface for unidirectional radiation

Gathering the advantages of low profile, high gain, high efficiency, and wideband operation in a planar antenna is a challenging objective for the antenna designer. Low profile wideband antennas are usually characterized by low gain. An antenna of wideband impedance matching usually suffers continuous variations of the gain over such a wideband due to the variation of the radiation mechanisms and surface current distributions over the frequency band of impedance matching. Therefore, the motivation of the present work is to provide both impedance matching and stabilized high gain by the aid of wideband artificial magnetic conductor (AMC) with a design of the unit cell that is suitable to the antenna structure and the desired frequency band. The present work, proposes the utilization of low-size wideband AMS surface (AMCS) to be placed behind a wideband omnidirectional antenna to enhance the gain over the frequency band of operation. In this way, the radiating structure combines high gain and wideband operation in the same design. A wideband planar monopole printed antenna is designed to operate as omnidirectional antenna with perfect impedance matching and radiation efficiency over the frequency band 3.6-7.2GHz when placed in free space. The gain of the free-standing antenna varies from 2dBi to 4.5dBi over the frequency band. A wideband AMCS is designed to enhance the antenna gain over frequency band of operation. The designed AMCS is composed of only 3×3 unit cells and overall dimensions of 10×10cm. This surface is placed parallel to the planar antenna at a distance 1.7cm behind it. The enhanced gain of the radiating structure of the AMCS-backed antenna reaches 8.5dBi without affecting the bandwidth over which the input impedance is matched to the feeding line. The radiation efficiency of the AMCS-backed antenna is maintained above 98% over the frequency band of operation (3.7-7.2GHz). The wideband antenna and the AMCS are fabricated for practical evaluation of the overall AMCS-backed antenna performance including the measurements of impedance matching, gain and radiation efficiency. The measurements and simulation results are in good consent.

Reconfigurable frequency selective surface based absorber realized using interlocking blocks

Abstract A reconfigurable frequency selective surface (FSS) based absorber structure has been designed using a novel, cost-effective, simple to operate and easy to fabricate 3D printed interlocking blocks. Four different topologies have been investigated and validated through simulation and experimental studies. The basic geometry comprises a 3D printed mounting board, on which different blocks can be attached using interlocking studs. The frequency reconfigurability has been obtained by mechanically changing various resonating blocks on the board, which results in four distinct absorption frequencies at 4.89 GHz, 4.02 GHz, 2.92 GHz and 2.25 GHz achieving the absorptivities of 98.92 %, 96.52 %, 99.3 % and 99.5 % respectively in S and C bands. The absorption characteristics are further justified by evaluating the surface current distribution and impedance responses. The prototypes have been fabricated and tested, and they have attained a good agreement with the simulated responses. The absorption characteristics and operational frequencies remain the same, for all four cases during variations in the polarization angle for oblique incidence for both TE and TM polarizations up to 45°, as studied in the simulation. These have been experimentally verified up to 30° for TE polarization, thereby demonstrating the polarization-independent and angularly stable responses.

Design of band reconfigurable Koch fractal antenna for wideband applications

In this communication, a band reconfigurable fractal antenna with modified partial ground is proposed for wireless applications. Four switches using PIN diodes supported by the antenna biasing circuit provide frequency reconfigurability, while star-shaped fractal geometry is used to achieve both miniaturisation and wideband functioning in the proposed antenna. The surface current distribution of the radiating patch is altered by the ON and OFF states of the PIN diode, which leads to the multiband resonance and reconfiguration features of the designed structure. The designhas an overall electrical size of 70 × 45 × 1.6 mm3 and is made on a commonly available FR4 substrate with a thickness of 1.6 mm and a dielectric constant of 4.4. The three operational bands are as follows: case I, which covers 3.7–5 GHz (30 %); case II, which covers 1.7–3.5 GHz (71 %); and case III, which covers 1.4–4 GHz (96 %). Two distinct bands are obtained in cases I and II; and case III nearly covers the frequency band of cases I and II. Therefore, the impedance bandwidth (IBW)offers continuous wideband frequency coverage from 1.4 to 5 GHz (110 %). To sense the full band and then modify its bandwidth to choose the appropriate sub-band and prefilter out the others, the proposed antenna may switch between a wide operational band of 1.4–5 GHz with three distinct subbands. The antenna could potentially be useful for wireless communication systemsin the future due to its frequency-selective feature and stable radiation patterns.

Polarization insensitive eye-shape enclosed split ring resonator-based multi-band metamaterial absorber/sensor for S, C, X, Ku, and K-band microwave applications

This article proposes an eye-shape enclosed split ring resonator (ESE-SRR) based metamaterial absorber for multi-band microwave applications with high absorption levels. Four-fold rotational symmetric eye-shaped electrical resonators form the structure of the proposed metamaterial absorber (MMA) to achieve polarisation-insensitive characteristics. Eight near-unity absorption peaks between S, C, X, Ku, and K-band are achieved, where peak absorptions are attained at 3.349 GHz, 5.06 GHz, 6.829 GHz, 9.178 GHz, 14.54 GHz, 17.96 GHz, 18.89 GHz, and 20.4 GHz with absorption levels of 99.8%, 99.7%, 92.9%, 99.1%, 96.4%, 93.3%, 91.3%, and 99.35%, respectively. The electrical dimension of the unit cell is 0.112λmin × 0.112λmin × 0.018λmin, making it a subwavelength compact structure for oblique incident angle stable absorption behaviour. The absorption characteristics are also investigated with metamaterial properties, surface current, and electromagnetic field distributions. The designed MMA is validated by prototype fabrication and measurement, which shows good agreement with simulation results. Finally, the proposed MMA shows an electrically compact structure with eight near-unity absorption peaks and polarisation insensitivity, which makes it an attractive candidate for absorption, sensing, radar cross-section reduction, etc.

Electric and magnetic resonances inducing triple-stopband terahertz metamaterial filter

A polarization insensitive triple-stopband terahertz metamaterial filter is proposed. This filter consists of a flexible polyimide substrate and periodically arranged copper structures on its top. The shape of the metal unit is a “田” inside a square ring. The simulation results show that the resonant frequencies of the filter are 0.107, 0.23, and 0.271 THz; the stopband depths are −35.56 dB, −42.7 dB, and −37.485 dB; the 3 dB bandwidths are 34, 53, and 32 GHz; and the relative bandwidths are 31.78%, 23%, and 11.8%, respectively. Effective parameter analysis demonstrates that the first resonance originates from the negative effective permittivity and positive effective permeability, but the reason for the latter two resonances is opposite to the first. The surface current distributions indicate that the first resonance is electric type, while the latter two resonances are the lower and higher orders magnetic resonances, respectively. Then, we verify the triple-stopband characteristic of the filter based on the equivalent circuit. Finally, the analysis reveals that the performance of the filter is independent of the incident polarization angle. This filter has the characteristics of multi-frequency, broadband, deep stopband, polarization insensitivity, and simple structure, which can be used in terahertz communication, detection, and other fields.

Design of Band Stop Filter Using Epsilon-Negative Frequency Selective Surface

This paper focuses on designing a band stop filter based on epsilon-negative frequency-selective surface (FSS). The unit cell has an electrical length of 0.104λ0 × 0.104λ0 which offers a bandwidth of 2.53 GHz from 1.24 GHz to 3.77 GHz. It has a center frequency of 2.44 GHz and the obtained fractional bandwidth is above 100%. Additionally, the behavior of the presented FSS is explained by the equivalent circuit model and surface current distribution. Within the entire bandwidth, it offers a negative permittivity. The refractive index of BSF is almost zero for 2.45−3.98 GHz range of frequency. The proposed FSS structure exhibits polarization-independent properties and offers a stable frequency response for normal and oblique angles under both TE and TM polarization. Good agreement between the simulated and measured results is obtained for the designed prototype.

An adaptive assisted method based on MOPSO for THz MMA effective designing

Abstract To address the high time cost and low efficiency of traditional terahertz metamaterial absorber design, an adaptive method based on multi-objective particle swarm optimization was proposed. First, we presented a symmetric absorber of a four-split-ring resonator with a cross-shaped top layer. The structural parameters were optimized by the particle swarm optimization and multi-objective particle swarm optimization algorithms. The simulation results indicated that the multi-objective particle swarm optimization rapidly obtained geometric parameters that balance the high absorptivity and high quality factors. This method quickly identified a symmetric structure with absorptivity greater than 99% and quality factor of 377.45 at 1.584 THz. Additionally, the asymmetric structure achieved near-perfect absorption at 1.585 THz with a Q value of 281.32. By studying the electric field distribution and the surface current distribution, the physical mechanism of the absorber designed has been explained. This adaptive assisted method based on multi-objective particle swarm optimization can efficiently design metamaterial absorbers and offer an artificial intelligence strategy for terahertz functional device design.

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.

Halvorsen chaotic system based microwave absorber modelling for fighter jet stealth technologies

This study focuses on the development and detailed analysis of a broadband microwave absorber utilizing Halvorsen chaotic dynamics, that focuses at enhancing stealth capabilities for fighter jets. The investigation begins by exploring the mathematical formulation of the Halvorsen chaotic system and conducting a parametric sweep of its control parameters to generate distinct two-dimensional and three-dimensional chaotic attractor plots. These plots are then post-processed using Julia set theory to develop intricate fractal patterns, which serve as the foundation for the absorber design. Image processing techniques, including filtering and thresholding, are employed to refine the patterns by removing artifacts and noise, ensuring they are suitable for practical implementation. The refined fractal patterns are then imported into a computational electromagnetic simulation environment where they are patterned onto a 0.035 mm thick copper sheet. Moreover, the Magtrex 555 substrate with a thickness of 1.52 mm, is selected for its high permittivity and low-loss characteristics. A comprehensive series of parametric studies are conducted to evaluate the influence of various design parameters such as side length, unit cell geometry, and substrate thickness on the absorber’s electromagnetic performance. Important parameters include the effects of chaotic control parameter optimization and the electromagnetic boundary conditions applied during the simulations. Extensive simulations are performed across the 2–20 GHz frequency range to evaluate absorption efficiency, focusing on key metrics like absorptivity, surface current distribution, and electric field distribution. The final design achieves over 90 % absorption efficiency within the target frequency band when the chaotic control parameters are optimized. Finally, comparative analysis using different commercially available substrates, including FR-4 and Rogers RO3003, reveals that Magtrex 555 offers superior absorption performance. The study concludes with a detailed presentation of the final absorber design, alongside an indepth discussion of the frequency range, parametric variations, and the impact of chaotic system dynamics on the absorption properties. This research provides crucial insights into the design and optimization of chaotic-system-based microwave absorbers, that advances the development of stealth technology in military applications.

Wide angle wide band polarization insensitive metamaterial absorber for C, X and Ku band application with hexagonal packaging

Abstract In this paper wide angle wide band polarization insensitive Metamaterial absorber (MA) has been proposed. The proposed unit cell structure consists of hexagonal concentric ring along with hexagonal packing. The structure is fabricated on FR4 substrate. The advantage of hexagonal packing is that it covers less area as compared to square packing. The unit cell structure is scaled w.r.t hexagonal ring and resistance of the substrate. The absorptivity achieved range from 6.54 to 14.85 GHz having Bandwidth (BW) of 8.31 GHz. The metamaterial behaviour of the structure is proven by plotting real and imaginary pat of permittivity and permeability. Absorption mechanism is shown by plotting surface current distribution at the top and bottom of the surface. The proposed MA structure is analysed for normal and oblique incidence. From the normal incidence it was found that structure has wide angle polarization insensitive. The absorptivity of the fabricated structure is measured inside the anechoic chamber. The simulated and measured plot is compared and found that both the results are very close to each other. At last, the proposed and already reported MAs are compared and from the observation it was found that proposed unit cell have larger BW compact in size, polarization insensitive and have hexagonal packing. The proposed MA covers partial C band, full X band and partial Ku band. The Proposed MA found practical applications for satellite communication, Wi-Fi devices, cordless telephone, military, air traffic control, defence tracking, vehicle speed detection.