Improved Impedance Matching Research Articles

Adjustable electromagnetic response of ultralight 3D Ti3C2Tx composite via control of crystal defects

Microwave shielding materials and absorbers serve important roles in improving the reliability of smart devices and military equipment. In this work, three-dimensional (3D) Ti3C2Tx/Fe3O4 composites with adjustable electromagnetic responses are studied. Taking advantage of the negatively charged surface of the Ti3C2Tx, the cationic surfactant cetyltrimethylammonium bromide (CTAB) is used to precipitate the delaminated Ti3C2Tx sheets. The volatilization of CTAB during the annealing process inflates the Ti3C2Tx, and leads to the three-dimensional architecture of the composite. The results show that the free-standing 3D Ti3C2Tx/Fe3O4 composite film exhibits a high shielding efficiency of 60 dB in the X band. Owing to the traits of great flexibility, low apparent density, and thin thickness, the 3D Ti3C2Tx/Fe3O4 composite film achieves a high specific shielding efficiency of 3.5 × 105 dB/(g·cm−2). Furthermore, through the control of crystal defects in one-step annealing treatment, the shielding material can be transformed into a wideband microwave absorber. A high reflection loss up to −57 dB can be realized. And a 2-mm-thick absorber whose reflection loss is better than −10 dB in 11.2 ~ 18 GHz is also achieved. The experimental and first-principal studies on the evolution mechanism reveal that the destruction of the Ti-C bond mainly leads to the degradation of electrical conductivity and the improvement of impedance matching. Introduced crystal defects can help enhance the dielectric loss as well. The synergistic effects of ohmic loss, dielectric loss, and magnetic loss give birth to a broadband absorption of the composite.

Double dielectric modification of nickel foam-based microwave absorbers with improved impedance matching and absorption performances

Proper physical property and well-designed microscopic structures are significant in determining the electromagnetic energy conversion. In this work, nickel foam (NiF)-based rod-like absorbers with double dielectric regulation were achieved via continuous hydrothermal reaction and subsequent heating treatment. The NiF-based uniform integration of binary metal oxides not only maintain the inherent excellent dielectric property of NiF, but also introduce extra dipolar polarizations (caused by multiple covered dielectrics) and Maxwell-Wagner-Sillars effect (induced by large dielectric property differences at the interfaces), which all contribute to the excellent microwave absorption performance. In addition, derived from the high/low dielectric synergetic effect, a balance between the introduction and dissipation of the electromagnetic energy can be realized. Based on that, the maximum bandwidth of NiF-based binary absorber reaches 7.28 GHz at 2.4 mm. This work not only provides a facile and versatile strategy to fabricate NiF-based ternary microwave absorbers, but also demonstrates the significant role of dielectric synergetic effect in optimizing microwave absorption performance.

Modification of the particle swarm optimization method through the intervention technique and its application for antenna design

In this research, a modification of the particle swarm optimization method was proposed, which is based on an intervention technique for the design of antennas. The proposed method was tested through its application on typical benchmark functions. Moreover, it was applied to the optimal design of a narrow band antenna and two ultra-wideband antennas through shape and hybrid optimization. The objective function was based on minimizing the S11 magnitude in the desired frequency range to improve impedance matching. The modified method had a better performance than the original particle swarm optimization in the typical benchmark functions, and the best results were obtained for the antenna optimization process. Therefore, this method is a good alternative to be applied in these processes because it allows obtaining a better quality of solution and reducing the number of evaluations of the objective function.

Microwave induced in-situ formation of SiC nanowires on SiCNO ceramic aerogels with excellent electromagnetic wave absorption performance

Electromagnetic absorption (EMA) materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles. However, meeting these two requirements is always a great challenge, which excluded the most attractive lightweight candidates, such as carbon-based materials. In this study, SiCnw-reinforced SiCNO (SiCnw/SiCNO) composite aerogels were fabricated through the in-situ growth of SiCnw in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time. The phase composition, microstructure, and EMA property of the SiCnw/SiCNO composite aerogels were systematically investigated. The results indicated that the morphology and phase composition of SiCnw/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature. The composite aerogels show excellent EMA property with minimum reflection loss of −23.9 dB@13.8 GHz, −26.5 dB@10.9 GHz, and −20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz, 3.2 GHz, and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600 °C, 800 °C, and 1000 °C, respectively, which is much better than that of SiCN ceramic aerogels. The superior EMA performance is mainly attributed to the improved impedance matching, multi-reflection, multi-interfacial polarization, and micro current caused by migration of hopping electrons.

Broadband CPW-Fed Circularly Polarized Square Slot Antenna for Universal UHF RFID Handheld Reader

This paper presents a new coplanar waveguide (CPW)-fed circularly polarized square slot antenna (CPSSA). The proposed antenna uses an inverted Z-shaped feedline protruded from the signal line of the feeding CPW. Circularly polarized (CP) radiation can be achieved by adequately inserting the arc-shaped grounded strip into the upper right corner of the square slot. The widened vertical tuning stub on the L-shaped grounded strip can improve impedance matching and axial ratio (AR) performance. The measured results indicate that the 10 dB impedance bandwidth is 620 MHz (652-1272 MHz), and the 3 dB axial ratio bandwidth is 320 MHz (840-1160 MHz), which has a broadband characteristic. In the range of the universal UHF RFID band, the measured peak gain is about 4.4 dBi. The proposed CPSSA uses low-cost FR4 material as the dielectric substrate. The overall size of the antenna is 119 × 119 × 0.5 mm3. The proposed antenna has a simple structure, easy processing, good performance, wide operating bandwidth, and dual circular polarization characteristic. It can be applied to the universal UHF RFID handheld reader environment.

A Low-Profile, Wide-Scan, Cylindrically Conformal X-Band Phased Array

A low-profile, wide-scan antenna array operating in the 6-12 GHz band with planar and conformal variants is reported in this letter. The design comprises capacitively coupled dipoles, integrated with an artificial magnetic conductor layer to achieve a low profile (<; 0.2λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ). A patch with feed via is used as a conventional feed balun. In addition, a via fence is employed for resonance mitigation and improved impedance matching at the lower end of the frequency band. The array exhibits a wide-angle scan capability (±60°) in E-, H-, and D-plane for active voltage standing wave ratio (VSWR) <; 3. A 16 × 3 conformal array, axially mounted onto a cylindrical surface with a radius of 250 mm (10λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h</sub> ) and 8 × 8 planar array configurations, is simulated and analyzed. The measurement results of the conformal array prototype show good agreement with the simulations in terms of VSWR, radiation pattern, and realized gain. Therefore, the proposed design is an attractive candidate for planar and conformal wireless devices at C, X-band frequencies.

Novel bimetallic MOF derived hierarchical Co@C composites modified with carbon nanotubes and its excellent electromagnetic wave absorption properties

In the severe electromagnetic wave pollution situation, the absorbers must meet the requirements of lightweight, strong absorption, thin thickness and wide band. Under such a circumstance, it is of great significance to construct reasonable structure and composition for excellent electromagnetic wave absorption. Therefore, the Co/C composites anchored with carbon nanotubes (Co@CNTs) have been successfully prepared by rationally regulating the growth of bimetallic MOF and subsequent pyrolysis process. It is revealed that the conduction loss and polarization loss caused by the carbon nanotubes with different lengths and densities and the porosity of the composites are together responsible for the attenuation of electromagnetic wave. As expected, the hierarchical Co@CNTs composites showed a strong reflection loss of −76.6 dB and a broad effective absorption bandwidth of 6.2 GHz through the improvement of impedance matching and electromagnetic wave absorption ability. Herein, this work presents a strategy for the development of composites as promising electromagnetic wave absorbent.

Synergistic microstructure of sandwich-like NiFe2O4@SiO2@MXene nanocomposites for enhancement of microwave absorption in the whole Ku-band

Recently, thin, lightweight, wide and strong microwave absorption performance are the main targets for researchers to design high-performance absorbers. A new two-dimension MXene material has attracted significant attention because of its unique hierarchical structure, large specific surface area and special metallic features. However, its improperly high electrical conductivity of MXene causes the bad microwave absorption performance. To meet the needs of practical application, the sandwich-like NiFe2O4@SiO2@MXene nanocomposites were fabricated via multilayered MXene and core-shell NiFe2O4@SiO2 nanoparticles. By the synergistic effects from the SiO2 (transparent medium) improving impedance matching and the two-dimensional laminated MXene increasing conductive loss, the microwave absorption performance of NiFe2O4@SiO2@MXene can be effectively regulated and optimized. As a result, the minimum reflection loss of NiFe2O4@SiO2@MXene reaches −52.8 dB at 11.6 GHz with a thickness of 2 mm, and the maximum effective absorption bandwidth is 7.2 GHz (10.8–18 GHz) covering the whole Ku-band with only a 1.5 mm thickness. It has proved that microcosmic sandwich-like structure design is an efficient approach to achieving excellent microwave absorption performance. The multiple components and unique structure generate heterogeneous interfaces, multiple reflections, polarization features and well-matched impedance. This work provides an insight for rationally constructing hybrid materials with a complex structure in the application of microwave absorption field.

Hybrid metasurface loaded tri‐port compact antenna with gain enhancement and pattern diversity

A tri-port compact antenna loaded on hybrid metasurface (MS) with gain enhancement and pattern diversity is proposed in this article. The antenna consists of three analytically designed contorted radiators (Ant-1, Ant-2, and Ant-3). A koch-fed fractal aperture ground plane is used to improve impedance matching and port isolation, thus eliminating supplementary decoupling networks. Ant-1 is 45° tilted, operating in wideband mode. Ant-2 is one-fourth, Ant-3 is one-half in electrical lengths with L-shaped metallic contortions to achieve good matching characteristics and asserts pattern diversity. A hybrid MS (combination of conventional customized MS's) structure is loaded for gain enhancement of ≈ 8.93 dBi. Ant-1 operates at (4.97-10.63) GHz with 72.56% frequency bandwidth (FBW), Ant-2 operates at (8.5-10.4) GHz with 20.1% (FBW) and Ant-3 operates at (7.2-9.6) GHz with 28.57% (FBW). The differentiation in antenna electrical size assists compactness, reduction in mutual coupling (>17 dB), has uncorrelated radiation patterns at each port delivering far-field diversity with low ECC < 0.1. A prototype antenna of size 28.6 mm × 28.6 mm is fabricated and experimented, which are in good agreements with EM simulation and equivalent circuit model response. The proposed tri-port antenna can be a promising candidate for MIMO diversity applications.

Post synthesis foaming of graphene-oxide/chitosan aerogel for efficient microwave absorbers via regulation of multiple reflections

Graphene-oxide (GO)/chitosan (CH) aerogels (GCA-1, GCA-2 & GCA-3) have been prepared through hydrothermal route by varying the GO:CH ratio (40:1, 50:1 & 60:1) and its microwave absorption mechanism is investigated. Owing to moderate electrical conductivity (~23 S/m) and high porosity (>99%), maximum attenuation (-16.5 dB) is observed for GCA-2, with 30% reflection and 68% absorption However, upon exposure to hydrazine hydrate vapor, absorption dominating attenuation of -16.3 dB is realized for GCHA-1 with reduction in reflection (SER = -0.42 dB, 8% reflection) and increment in absorption (SEA = -15.6 dB, 88% absorption), that can be attributed to trade-off between conductivity & porosity, leading to improved impedance matching and enhanced multiple internal reflections. This corresponds to absorbance per unit thickness per unit density value of 125 cm2/g and specific shielding effectiveness of ~-556 dBcm3/g in GCHA-1, which suggests its utility in making lightweight microwave absorbers for strategic applications.

Three-dimensional flower-like FeCoNi/reduced graphene oxide nanosheets with enhanced impedance matching for high-performance electromagnetic wave absorption

Nanostructured magnetic metal/reduced graphene oxide (rGO) composites, benefiting from well-performed losses including high dielectric/magnetic losses, have garnered considerable interest as advanced microwave absorbers (MAs) in recent years. Optional approaches of unique trimetallic/rGO nanostructures, however, are still limited to attain high electromagnetic (EM) absorption and broad bandwidth as well as improved impedance matching. Herein, porous flower-like FeCoNi/rGO nanosheets, synthesized via magnetic-field-assisted (MFA) reduction, presents facilitated microwave absorption performance. The zigzag-like attachments of neighbored nanosheets constitute the porous flower-like architecture; average thickness of the nanosheets is 5–20 nm. The reduction process, determined by appropriate GO dosage, plays a key role to tune geometry and distribution of the flower-like nanosheet structures. The optimal sample, owning a relatively high surface area (157.3 m2 g−1), achieves an impressive reflection loss (RL) intensity of − 75.95 dB and its maximum effective absorption bandwidth (RL ≤ −10 dB) is up to 4.69 GHz, along with improved impedance matching. This work provides a facile and alternative route for exploring other novel nanoalloy-based MAs.

A sustainable strategy to fabricate porous flower-like magnetic carbon composites for enhanced microwave absorption

The design and fabrication of biomass derived flower-like Co@Co3O4/carbon (Co@Co3O4/C) composites used for high-performance microwave absorbing materials are described. The porous carbon skeleton provides the electronic pathway and the nucleation locus for Co@Co3O4 nanoparticles. Meanwhile, the porous Co@Co3O4/C composites comprising dielectric and magnetic components could also improve impedance matching and be advantageous to electromagnetic energy conversion. Labeled with good impedance matching and strong attenuation characteristics, Co@Co3O4/C composites show excellent microwave response where the minimum reflection loss (RLmin) of −46.4 dB and the maximum effective absorption bandwidth of 11.0 GHz can be achieved. This work not only explores high-performance microwave absorbing materials but also demonstrates that shrimp shell derived materials can be regarded as unexceptionably sustainable resources.

Preparation and characterization of nanocomposites of MoS2 nanoflowers and palygorskite nanofibers as lightweight microwave absorbers

It is an effective strategy to use clay minerals (palygorskite) to prevent the aggregation of molybdenum disulfide (MoS2) nanosheets prepared with hydrothermal process. The palygorskite/molybdenum disulfide (Pal/MoS2) nanocomposites presented notable microwave absorption performances, which can be optimized by adjusting the content of Pal. The sample with optimized composition has a minimum reflection loss (RL) of -59.91 dB at 9.92 GHz at a thin thickness of 2.28 mm, owing to the enhanced interface polarization and improved impedance matching. It is believed that the 2D hierarchically structured Pal/MoS2 nanocomposites can serve as a potential microwave absorber for practical applications.

High-performance microwave absorption of MOF‐derived Co3O4@N-doped carbon anchored on carbon foam

Absorbing materials can convert electromagnetic wave (EMW) energy into heat and other energy and dissipate it. Carbon materials can attenuate EMW by generating large conduction losses due to their high conductivity. The introduction of low dielectric materials can improve impedance matching caused by high conductivity. However, the density of materials compounded with carbon materials is too large, which affects the overall density of composite materials. Therefore, this problem is solved by matching melamine foam with ZIF-67. As an ultra-light material, the melamine foam-based carbon material can significantly reduce the density of composite materials, and its developed three-dimensional structure can cause multiple scattering of EMW. The large specific surface area and evenly distributed metal oxides obtained after annealing of ZIF-67 can provide ultra-low-density carbon materials and abundant interfacial polarization to further attenuate EMW. So far, the methods of self-growing materials on the surface of melamine foam have not been reported. We prepared a 500 nm Co3O4 nanosheet/carbon foam (CF) composite material coated on the surface by a two-step method. The sample had a maximum reflection loss of −46.58 dB at 10.72 GHz, and an effective absorption bandwidth (EAB) of 5.4 GHz. This research provides a new idea for the growth of porous materials on the surface of melamine foam-based carbon materials.

Compact wideband hybrid fractal antenna loaded on AMC reflector with enhanced gain for hybrid wireless cellular networks

A wideband hybrid fractal monopole antenna loaded with artifical magnetic conductor (AMC) is proposed. Using a hybrid fractal generator, the monopole antenna achieves self-similarity compactness, reduced size and good wideband performances. The ground is semi-elliptic and has defected steps aiming to improve impedance matching and X-pol. reduction. The AMC reflector has 3× 3 array of cesaro shaped unit cells looped in a square metallic conductor. The AMC enhances radiation gain with back-lobe reduction. The AMC unit cell produce a 00 phase reflection at fAMC = 4.5 GHz and then loaded to optimize antenna performance. To validate the design, a prototype antenna is fabricated and measured. The antenna operates from (3.7–7.0) GHz with 61.68% impedance bandwidth, realized gain of (8.7–13.8) dBi, and radiation efficiency > 82.5%. The proposed antenna leverages on compactness, low-profile AMC height and good boresight radiation gain, which shows its potential for hybrid wireless cellular networks.

Investigation of e-textile dipole antenna performance based on embroidery parameters

E-textile antennas have the potential to be the premier on-body wearable sensor. Embroidery techniques, which can be applied to produce e-textile antennas, assist in large production volumes and fast production speeds. This paper focuses on the effects of three commonly used embroidery parameters, namely stitch type, conductive thread location, and stabilizer, on the performance of embroidered dipole antennas in order to determine the ideal embroidery combination for optimal antenna performance. Fifty-four dipole antenna samples were fabricated and measured at the industrial, scientific, and medical (ISM) frequency band of 2.45 GHz. The results of this study show that machine-embroidered antenna designs with satin stitches resonate at a lower frequency and exhibit a lower transmission gain compared with those made with contour stiches, and the conductive thread location in the bobbin location plus the use of a water-soluble stabilizer can help improve impedance matching.

Miniaturized Wideband Loop Antenna Using a Multiple Half-Circular-Ring-Based Loop Structure and Horizontal Slits for Terrestrial DTV and UHD TV Applications.

A miniaturized wideband loop antenna for terrestrial digital television (DTV) and ultra-high definition (UHD) TV applications is proposed. The original wideband loop antenna consists of a square loop, two circular sectors to connect the loop with central feed points, and a 75 ohm coplanar waveguide (CPW) feed line inserted in the lower circular sector. The straight side of the square loop is replaced with a multiple half-circular-ring-based loop structure. Horizontal slits are appended to the two circular sectors in order to further reduce the antenna size. A tapered CPW feed line is also employed in order to improve impedance matching. The experiment results show that the proposed miniaturized loop antenna operates in the 460.7–806.2 MHz frequency band for a voltage standing wave ratio less than two, which fully covers the DTV and UHD TV bands (470–771 MHz). The proposed miniaturized wideband loop antenna has a length reduction of 21.43%, compared to the original loop antenna.

Design of Broadband Dual-Polarized Rectenna Array for WPT Applications

A broadband dual-polarized microstrip array antenna designed is proposed. To achieve wide 10 dB bandwidth for broadband operation, the technique of applying a ladder-shaped monopole antenna type with a rectangular slot insertion in the ground plane is implemented. The proposed design showed wide impedance bandwidth of the 1702-2755 MHz (47.2%). In addition, adding an open slot into the rectangular radiating element with an asymmetric ground plane was used and resulted in a slightly displacement of the radiation pattern. The 1 × 2 array type for two ladder-shaped patch array elements are arranged in symmetric feed network. By meticulously arrangement the two array antennas’ positions to achieved good ports isolation, with 10 dB bandwidth for the operating bands in free-space can be achieved. This antenna is used as a rectenna (rectifying antenna), which receives the RF energy of vertical and horizontal polarization wave in free space for 2.4 GHz wireless power transmission. The rectifier circuit setup using two zero biased rectifier and voltage doubler circuit. A matching network designed with small size chip components have a significant improvement in impedance matching and eliminate high order harmonics between the antenna and rectifying circuit. The proposed dual-polarized rectenna provided the RF-to-DC conversion efficiency as high as 78.8% when 14 dBm microwave power was received at 2.4 GHz with a 1 KΩ load.

Dispersed spherical shell-shaped palygorskite/carbon/polyaniline composites with advanced microwave absorption performances

Palygorskite was coated with a thin layer of carbon by using a hydrothermal process with glucose, in order to form palygorskite/carbon (Pal/C) composites, which were then used as a template to load polyaniline through in-situ polymerization, thus obtaining dispersed spherical shell-shaped palygorskite/carbon/polyaniline (Pal/C/PANI) ternary composites. The Pal/C/PANI composites exhibit promising electromagnetic absorption performances, which can be optimized by adjusting the content of Pal/C. In this case, palygorskite acts as a skeleton and dispersion agent, which effectively prevents the agglomeration of carbon and polyaniline. Due to the improved impedance matching and increased dielectric loss, the Pal/C/PANI composites display an optimal reflection loss of −74 dB at 6.24 GHz, with a maximum effective absorption bandwidth of 4.96 GHz. Such composites could be candidates as high performance microwave absorbers.

High-efficiency microwave absorber based on carbon Fiber@La0.7Sr0.3MnO@NiO composite for X-band applications

Carbon fiber (CF) as a multifunctional material with superb performance in aviation industry has serious drawback such as impedance mismatch which restricted the capability of using it as microwave absorber materials. In this research, a novel hierarchical carbon fiber@La0.7Sr0.3MnO@NiO (CF/LS/N) composite was facilely and successfully synthesized via sol-gel and subsequent hydrothermal reactions. The structural, morphological, magnetic and electromagnetic behavior of the composite were precisely evaluated via XRD, FESEM, XPS, VSM and VNA analysis. According to the systematic evaluation results, the synergistic positive effect of adding NiO nanoparticles is revealed in improving the microwave absorption performance of CF@La0.7Sr0.3MnO composite. Literally, dielectric features of the prepared composite enhanced by introducing NiO nanoparticles. Due to improvement in impedance matching, dipole polarization, multiple reflection/scattering, eddy current, interfacial polarization and magnetic resonance phenomenon the minimal reflection loss of the obtained hybrid composite reach to -26 dB with 2.6 mm thickness at filler content of 20 wt%. CF/LS/N composite is predictable to be suitable candidate for military purposes because of the lightweight, low cost and outstanding absorbing properties.