Split Square Research Articles

Compact dual-band dual sense circularly polarized flexible antenna with polarization rotation metasurface for off-body communications

ABSTRACT A dual-band dual circularly polarised flexible antenna, operating at 3.5 GHz for WiMAX and 5.8 GHz for industrial, scientific, and medical (ISM) bands, is proposed for wearable applications. The antenna design integrates a wideband comb-shaped slotted monopole antenna with a polarisation rotation metasurface (PRMF). The PRMF unit cell consists of a nested split square ring in the corner and a square ring in the centre, where the split square rings facilitate polarisation conversion and the centre square ring enhances the axial ratio. The PRMF integration helps achieve dual circular polarisation (CP) radiation, with left-handed CP in the WiMAX band and right-handed CP in the ISM band. The proposed monopole antenna and PRMF are printed on a conformal polyimide substrate, with a total footprint of 48 × 48 mm2 (0.31λo2). The proposed antenna has a 10 dB impedance bandwidth of 24.9% (3.2 to 4.2 GHz) and 18.9% (5.3 to 6.43 GHz), a 3-dB axial ratio bandwidth of 11.1% and 21.4%, and a peak gain of 6.4 and 6.7 dBic in both bands. Numerical and measured results demonstrate that the antenna performs well in the presence of human body and structural deformations. These attributes make the proposed design highly suitable for off-body wearable applications.

A Terahertz Programmable Digital Metasurface Based on Vanadium Dioxide

Metasurfaces can realize the flexible manipulation of electromagnetic waves, which have the advantages of a low profile and low loss. In particular, the coding metasurface can flexibly manipulate electromagnetic waves through controllable sequence encoding of the coding units to achieve different functions. In this paper, a three-layer active coding metasurface is designed based on vanadium dioxide (VO2), which has an excellent phase transition. For the designed unit cell, the top patterned layer is composed of two split square resonant rings (SSRRs), whose gaps are in opposite directions, and each SSRR is composed of gold and VO2. When VO2 changes from the dielectric state to the metal state, the resonant mode changes from microstrip resonance to LC resonance, correspondingly. According to the Pancharatnam-Berry (P-B) phase, the designed metasurface can actively control terahertz circularly polarized waves in the near field. The metasurface can manipulate the order of the generated orbital angular momentum (OAM) beams: when the dielectric VO2 changes to metal VO2, the order l of the OAM beams generated by the metasurface changes from −1 to −2, and the purity of the generated OAM beams is relatively high. It is expected to have important application values in terahertz wireless communication, radar, and other fields.

Permeability negative split square resonator for solid materials dielectric constant and aqueous solution pH sensing applications

Metamaterials (MTMs) offer unique electromagnetic properties with wide-ranging applications in microwave sensing. This work introduces a unique approach for non-invasive pH level measurement in aqueous solutions and dielectric properties sensing in solid materials. Mu Negative (MNG) Metamaterial with transmission line and rejection band shifting techniques are utilized for this sensing. The MTM unit cell comprises coupled split square resonators arranged in a 4 × 4 unit cell array with a transmission line underneath. The compact unit cell and array sizes are 0.3 λ × 0.3 λ × 0.06 λ and 1.6 λ × 1.6 λ × 0.06 λ, respectively. The sensor demonstrates impressive performance, with a narrow half-power bandwidth (HPBW) of 0.09 GHz and a high Q-factor of 135.22 for dielectric constant sensing of the solid material. It also achieves an HPBW of 0.38 GHz and a Q-factor of 37.3 for pH sensing. The proposed pH sensor achieves a high sensitivity of 6.15 (MHz/pH). Additionally, the MTM sensor boasts a substantial Figure of Merit (FoM) of 8.311 for solid materials and 16.2 for pH measurements. These promising results are validated through measurements, highlighting the potential of MTM sensors to revolutionize microwave sensing across various applications.

A single layered high‐gain digital metasurface reflectarray antenna for millimeter wave applications

AbstractA high‐gain digital metasurface reflectarray antenna for 5G FR‐2 band is presented in this letter. The digital metasurface reflector is composed of single‐layered phase quantized meta‐bit unit cell elements. The metabit consists of a split square integrated with a circular ring. Two discretized phase states are obtained by varying the dimensions of the split square and the circular ring, which mimic the metabit‐0 and metabit‐1, respectively. A digital metasurface reflectarray having dimensions of 5.3 5.3 operating in the frequency range of 37–39 GHz is designed, fabricated, and characterized. A linearly polarized antipodal vivaldi antenna spatially feeds the digital metasurface reflectarray. A maximum measured gain of 19.1 dBi is obtained at 38 GHz, with an aperture efficiency of 23%.

A specialized partial discretized optimization algorithm for SLL suppression in FSS design

Side Lobe Level (SLL) suppression is a challenging but essential part of frequency selective surface (FSS) structural design. The SLL of the radiation pattern is a key parameter demonstrating the directional anti-interference ability and mainly depends on the geometry of the FSS. However, the correlation between SLL and FSS structural parameters is extremely complicated. A minor FSS structure change may result in a drastic diversion in the sidelobe’s direction or level, making the SLL the most difficult parameter to optimize. In this paper, an efficient optimization method specifically for SLL suppression is proposed. We discretized the edges of split square ring FSS structures by binary representation and generated new patterns based on the genetic algorithm. Optimization results showed that in the most optimal structure, the SLL was −23.41 dB, exhibiting a 5.17 dB reduction. Meanwhile, the center frequency variation was less than 2%. Moreover, the computation time cost was reduced by over 90% compared with that of the fully discretized pattern optimization method, showing that this novel method was truly effective in getting SLL suppressed FSS structures.

Low-Concentration Biological Sample Detection Using an Asymmetric Split Resonator Terahertz Metamaterial

A simple and efficient THz metamaterial based on an asymmetric double split square array resonator was designed and fabricated. The sensitivity and Q value of the metamaterial sensor were theoretically analyzed to be 278 GHz/RIU and 11, respectively. Three typical biological samples with different concentrations were measured to validate the sensitivity of the THz metamaterial. For the bovine serum albumin (BSA) protein solution, the lowest detectable concentration (LDC) can reach to 1 μM, which is comparable to most recent reports. For the Staphylococcus aureus bacteria, the LDC is 1 × 103 cells/mL, and for the K-citrate solution, the LDC is 0.1 mM. Our studies indicate that the THz metamaterial may be effectively applied in the low-concentration detection of biological samples.

Split square and split carpet as examples of non-metrizable IFS attractors

Split square and split carpet as examples of non-metrizable IFS attractors

Dual-Band Wide-Angle Reflective Circular Polarization Converter with Orthogonal Polarization Modes.

Herein a dual-band wide-angle reflective circular polarization converter, based on a metasurface was developed. The unit cell is composed of a split square ring and a nested square patch. The split square ring plays the role of creating polarization conversion. The square patch is useful for improving the quality of axial ratio. It was verified that the structure could transform the x-polarized incident wave into left-hand circular polarization in the lower frequency band, and to right-hand circular polarization in the higher frequency band. For y-polarized incidence, the transformation has orthogonal modes to that for x-polarized incidence. Moreover, the 3 dB axial ratio takes place in the ranges of 8.42-12.32 GHz and 18.74-29.73 GHz, corresponding to a relative bandwidth of 37.61%, and 45.35%, respectively. In addition, the polarization conversion efficiency is greater than 99% in the ranges of 8.65-11.83 GHz and 19.55-29.36 GHz. Furthermore, for oblique incidence, the axial ratio remains stable, even at 50° incidence, for the lower frequency band. Lastly, a prototype is fabricated and measured for experimental verification. The measured and simulated results were in good agreement. Compared with other designs in the literature, the proposed converter operates with good performance in dual-band, with high-efficiency, and with angular stability.

Instrumentation based material characterization of a split square ring metamaterial and its analytical study as cloak for microwave communication applications

The study of materials with flexibility, compressive strength, and outstanding resistance is in high demand in the domain of wireless technology. The aim of this study is to design a flexible substrate material that is suitable for cloaking in the microwave frequency range. To determine the characteristics of the materials, commercially obtainable analyzing techniques such as Scanning Electron Microscopy (SEM), x-ray Diffractometer (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) are used. The proposed structure is validated using an electromagnetic simulator, and the metamaterial characteristics are seen as a result. The metasurface is now wrapped around the cylindrical object that will be concealed. The power flow distributions are used to examine the cloaked cylindrical object. The cloak’s resonating frequencies are 4.17 GHz, 6.98 GHz, 9.79 GHz, 14.38 GHz, and 17.07 GHz. Finally, the cloak is measured in the near field using a horn antenna arrangement. The measured results agree perfectly with the simulated ones and are suitable for microwave applications in the X, C, and Ku bands.

Dual-band and dynamic regulated terahertz linear polarization converter based on graphene metasurface

In this paper, a highly efficient dual-band and dynamic regulated terahertz linear polarization converter is proposed. Based on the principle of electromagnetic (EM) wave polarization control, a periodic array metasurface composed of graphene split square ring and elliptical patches is designed to realize dual-band and high efficiency linear polarization conversion in terahertz band. The simulation results show that the polarization conversion ratio (PCR) is higher than 90% in the frequency range of 0.656–0.730 THz and 0.809–1.449 THz, and corresponding relative bandwidths are 10.7% and 56.7%, respectively. The dual-band performance is maintained within the incident angle of 50°. In addition, the dynamic regulation of dual-band terahertz linear polarization converter is obtained by modifying the Fermi level and relaxation time of graphene. The designed dual-band terahertz linear polarization converter has a broad application prospect in terahertz communication, sensing and spectrum.

A Miniaturized Triple-Band Antenna Based on Square Split Ring for IoT Applications

This article presents a miniaturized triple-band antenna for Internet of Things (IoT) applications. The miniaturization is achieved by using a split square ring resonator and half ring resonator. The antenna is fabricated on an FR4 substrate with dimensions of (33 × 22 × 1.6) mm3. The proposed antenna resonates at the frequencies 2.4 GHz, 3.7 GHz, and 5.8 GHz for WLAN and WiMax applications. The obtained −10 dB bandwidth for the three bands of the proposed antenna are 300 MHz, 360 MHz, and 900 MHz, respectively. The measured reflection coefficient values of the proposed antenna corresponding to each resonant frequency are equal to −14.772 dB, −20.971 dB, and −28.1755 dB, respectively. The measured gain values are 1.43 dBi, 0.89 dBi, and 1 dBi, respectively, at each resonant frequency. There is a good agreement between the measured and simulated results, and both show an omnidirectional radiation pattern at each of the antenna resonant frequencies that is suitable for IoT portable devices.

Polarization insensitive split square ring resonator based epsilon-negative and near zero refractive index metamaterial for S, C, and X frequency bands satellite and radar communications

This study has investigated the impact of inverse G-like shape resonators that exhibited epsilon negative (ENG) and near-zero refractive index (NZI) properties for multi-band wireless communications applications. The electrical measurement of structure is 0.118λ × 0.118λ × 0.021 λ, which is calculated at 3.94 GHz. FR-4 is used as a substrate layer, and the resonator is designed on it. This structure is manifested in the ENG and NZI characteristics within the frequency range of 3.8–4.17, 7.68–8.54, 10.67–11.36 GHz, and 4.07–4.15 and 8.29–8.37 GHz, respectively. This study also manifests the polarization insensitivity nature of 0°–90°, and the incident angle is investigated up to 60° for both TE and TM modes. The proposed structure achieves triple resonance at 3.94 GHz, 8.08 GHz, and 11.17 GHz, respectively, included in the S, C, and X frequency bands. The CST Microwave Studio 2019 software is conducted to design, develop, perform analysis, investigate electromagnetic properties, and extract effective medium parameters. The Advanced Design Software (ADS) is used to model the equivalent circuit of the unit cell. The simulated, measured, and ADS results verified the scattering parameter performance. The EMR value of the structure is 8.47, indicating the structure's compactness. The compact design with simplicity, ENG, and NZI properties make the proposed structure significant for microwave application, mainly to enhance the antenna bandwidth and gain filter design. ENG and NZI properties the operation frequency stability and efficiency for low earth orbit nanosatellite communications.

A high gain antenna utilizing Mu-near-zero metasurface structures for 5G applications

AbstractA high gain antenna with Mu-near-zero metasurface (MNZ-MS) is introduced in this work. The proposed antenna can be utilized for future 5G applications. The patch antenna is designed on the upper face of the square substrate with a ground plane at the bottom face. To improve the antenna gain, a layer of MNZ-MS unit cells is placed above the antenna substrate with 0.48λ0 air space between the two layers, where λ0 is the wavelength in free space at the resonance frequency of 26.3 GHz. The MNZ-MS layer consists of four double-sided split square resonators. The overall thickness of the proposed antenna is 0.66λ0. To approve the execution of the proposed antenna, a prototype model is manufactured and tested. The outcomes fulfill a reflection coefficient lower than −10 dB over the frequency spectrum of 26–28 GHz. A gain improvement better than 5 dB is obtained compared to the gain of the reference patch at the center frequency of 26.3 GHz.

Deflected beam pattern through reconfigurable metamaterial structure at 3.5 GHz for 5G applications

In this paper, the reconfigurable metamaterial is proposed to deflect the radiated beam of the bow-tie antenna at a 5G band of 3.5 GHz. The split square resonator (SSR) is designed at a sub-6 GHz band and reconfigured to produce different refractive indices. For obtaining the desired deflection angles, 3 × 7 SSR unit cells with ON and OFF configurations are printed into the antenna substrate. This arrangement creates two metamaterial configurations with different refractive indices in the closeness of the radiating elements, thereby deflecting the main beam to the direction of high refractive index metamaterial. In the passive beam deflection antenna, the reconfigurable SSRs deflect the radiation beam of the antenna by angles of ±39° in E-plane at 3.5 GHz. Furthermore, the embedding of SSRs helps improve the gain by 2.4 and 2.3 dB for the positive and negative deflection angles, respectively. On the other hand, in the active beam deflection antenna, the reconfigurable SSRs based on real PIN diodes can deflect the antenna radiated beam by angles of ±36° in the E-plane. These reconfigurable antennas have the potential to be used in 5G beam deflection applications. Both passive and active metamaterial antennas are fabricated, and their performances are measured.

Electromagnetic induction-like transparency in dual-band with dual-bright mode coupling

In this paper, a metamaterial structure with a double-layer split square ring and a double C-shaped structure is designed, which has dual-band electromagnetically induced transparency effects in the terahertz band. This structure has transmission peaks at 1.438 THz and 1.699 THz. Through the analysis of the surface current distribution, the reasons for the dual-band electromagnetically induced transparency are discussed. The effect of the designed metamaterial on the transmission window is studied when the opening size of the open square ring and the distance of the double C-shaped structure and the incident angle are changed. At an incident angle, the transmission spectrum of the designed material changes greatly, implying that it is highly sensitive to angle. The research results show that the structure has potential applications in sensors and angle filters.

Tunable Frequency Selective Surface With Angular Stability

In this letter, a paradigm for designing tunable frequency selective surfaces (FSSs) with angular stability is presented. The tunable FSS is implemented by nonresonant subwavelength unit cells loaded with varactor diodes, which can be applied in a dynamic and efficient compensation mechanism. The red shifts introduced by varactor diodes are used to compensate the deviation under oblique incident angles. The proposed tunable FSS is a two-layer structure composed of an array of wire grid and an array of split square ring loaded two varactor diodes. The periodicity of one split square ring is same with that of 2 × 2 wire grids. The equivalent circuit based synthesis method is analyzed to investigate the underlying principle of the proposed FSS. The experimental measurement is carried out in C-band frequency, which demonstrates the feasibility of this method. The measured results are in good agreement with the simulations, manifesting the angular stability at 4.25 GHz.

RCS reduction of microstrip antenna using split square loop thin absorber

This study proposes an electrically thin frequency-selective surface-based microwave absorber without using resistive surface and lumped resistors to make it simple and inexpensive. The ground plane of the microstrip antenna (MSA) serves as the metallic back of the absorber. The top two layers of the proposed absorber are printed on both sides of the top FR4 sheet in a square annular ring form to encircle the square patch. Both simulations and measurements are carried out to obtain the scattering parameters, which are used to retrieve the absorption coefficient, relative permittivity (ɛ r), and relative permeability (μ r). An equivalent circuit model for the proposed absorber is constructed and validated. The absorption performance is insensitive to the angle of incidence (θ) up to 50°. The absorption mechanisms are studied based on the surface current distribution, electric field distribution, and constitutive parameters. The absorber is then integrated with an MSA operating at 4.2 GHz, which gives a maximum monostatic radar cross-section (RCS) reduction of 15 dB. Numerical and experimental results of the radiation performance and the RCS of the absorber integrated antenna structure have been presented. A very good agreement between simulation and measurement results is observed.

Compact dual mode X-band SIW bandpass filter with wide spurious suppression using split square ring slot resonator

PurposeThis paper aims to design a dual mode X-band substrate integrated waveguide (SIW) bandpass filter in the conventional SIW structure. A pair of back-to-back square and split ring resonator is introduced in the single-layer SIW bandpass filter. The various coupling configurations of SIW bandpass filter using split square ring slot resonator is designed to obtain dual resonant mode in the passband. It is shown that the measured results agree with the simulated results to meet compact size, lower the transmission coefficient, better reflection coefficient, sharp sideband rejection and minimal group delay.Design/methodology/approachA spurious suppression of wideband response is suppressed using an open stub in the transmission line. The width and length of the stub are tuned to suppress the wideband spurs in the stopband. The measured 3 dB bandwidth is from 8.76 to 14.24 GHz with a fractional bandwidth of 48.04% at a center frequency of 11.63 GHz, 12.59 GHz. The structure is analyzed using the equivalent circuit model, and the simulated analysis is based on an advanced design system software.FindingsThis paper discusses the characteristics of resonator below the waveguide cut-off frequency with their working principles and applications. Considering the difficulties in combining the resonators with a metallic waveguide, a new guided wave structure – the SIW is designed, which is synthesized on a planar substrate with linear periodic arrays of metallized via based on the printed circuit board.Originality/valueThis study has investigated the wave propagation problem of the SIW loaded by square ring slot-loaded resonator. The electric dipole nature of the resonator has been used to achieve a forward passband in a waveguide environment. The proposed filters have numerous advantages such as high-quality factor, low insertion loss, easy to integrate with the other planar circuits and, most importantly, compact size.

Multi-wavelength carpet cloaking based on an ultrathin single layer metamaterial microstructure

Ultrathin metasurfaces provide a completely new route to achieve an invisibility cloak through local phase compensation. However, conventional carpet cloaking only works at a single frequency. Here, we propose a dual-wavelength carpet cloaking based on a single layer metasurface. Based on the electromagnetic coupling effect between the outside split square loop and inner metal structure array, the independent phase compensation and reconstruction of the reflected wavefront can be realized. The cloaking can effectively suppress the unexpected scattering and hide an object with arbitrary shape. This ultrathin metasurface cloaking can be applied in illusion optics, radars and antenna systems.

Design of a 16‐beam pattern‐reconfigurable antenna for vehicular environment

This article presents the design of a multipattern antenna with pattern switching for vehicular communications. The proposed antenna has four triangular patches integrated onto a split square ring (SR) resonator to operate at two distinct frequencies, viz. 2.4 and 3.5 GHz. The proposed antenna is designed with a view to enhancing the link reliability of Wireless Local Area Network (WLAN), WiMax, and vehicle to vehicle communication frequencies. Each triangular patch is separately excited using a microstrip line feed to enable beam steering. The ground plane of the antenna is embedded with two SR slots to improve the bandwidth and radiation performance. Further gain enhancement is achieved by loading the antenna with a plane reflector located at a distance of 20 mm from the antenna's ground surface. In reality, this reflector is realized using the vehicle's roof which provides gain enhancement up to 5.2 dBi at 2.4 GHz and 4 dBi at 3.5 GHz. By exciting single to multiple ports sequentially 16 different radiation patterns are obtained, which provides high-gain omnidirectional coverage. The prototype antenna is fabricated and the simulation results are verified using experimental measurements. From the results, it is evident that the proposed antenna is suitable for vehicular communication applications.