Microwave Properties Research Articles

Medium-high K LiNb0.6Ti0.5-x(Zn1/3Nb2/3)xO3 microwave dielectric ceramics for miniaturized dielectric resonant antennas

High performance and miniaturization are becoming increasingly important for practical microwave electronics and high-density communication systems. Here, LiNb0.6Ti0.5-x(Zn1/3Nb2/3)xO3 (LNT-xZN, x = 0, 2, 4, 6, 8 mol%) ceramics have been successfully prepared by a solid-phase reaction. The relationship between the physical structure, microscopic morphology, Raman spectroscopy, and microwave properties is revealed. The better microwave dielectric properties of the LNT-4ZN ceramic sintered at 1075 °C are εr∼59.9, Q×f∼8261 GHz, and τf∼-7.4 ppm/°C. Using this ceramic, a miniaturized dielectric resonant antenna (DRA) is designed and demonstrated. The return loss, radiation efficiency, and realized gain of this device at the center frequency are −43.57 dB, 78.4 %, and 8.59 dB, respectively. The antenna, in addition to the good radiation performance, has a size advantage over similar devices (#Cylindrical sample, #R 3.1 mm × h 1.6 mm, @Square substrate, @a = b = 18 mm × h 3.1 mm). This work exemplifies the great potential of LNT-4ZN materials in communication devices and promotes the application of microwave dielectric ceramics in antenna fields.

The Impact of Structural Variations and Coating Techniques on the Microwave Properties of Woven Fabrics Coated with PEDOT:PSS Composition

Minimizing the impact of electromagnetic radiation (EMR) holds paramount importance in safeguarding individuals who frequently utilize electrical and electronic devices. Electrically conductive textiles, which possess specialized EMR shielding features, present a promising solution to mitigate the risks related to EMR. Furthermore, these textile-based shielding materials could find application as radar-absorbing materials in stealth technology, emphasizing the need for substantial absorption capabilities in shielding mechanisms. In this study, various textile-based materials with an electrically conductive coating that contain the conjugated polymer system poly(3,4-ethylene-dioxythiophene)-polystyrene sulfonate (PEDOT:PSS) were prepared and investigated. The influence of the textile substrate structural parameters, coating deposit, and coating method on their microwave properties—transmission, reflection, and absorption—was investigated. Reflection and transmission measurements were conducted within a frequency range of 2 to 18 GHz. These measurements revealed that, for the tested samples, the shielding properties are determined by the combined effect of reflection and absorption. However, the role of these two parameters varies across the tested frequency range. It was defined that for fabrics coated on one side, better reflection reduction is obtained when the shielding effectiveness (SE) is below |20| dB. It was found that by controlling the coating deposition on the fabric, it is possible to fine-tune the electrical properties to a certain extent, thereby influencing the microwave properties of the coated fabrics. The studies of prepared samples have shown that reflection and transmission parameters depend not only on the type and quantity of conductive paste applied to the fabric but also on the fabric’s construction parameters and the coating technique used. It was found that the denser the substrate used for coating, the more conductive paste solidifies on the surface, forming a thicker coat on the top. For conductive fabrics with the same substrate to achieve a particular SE value using the knife-over-roll coating technology, the required coating deposit amount is considerably lower as compared with the deposit necessary in the case of screen printing: for the knife-over-roll-coated sample to reach SE 15 dB, the required deposit is approximately 14 g/m2; meanwhile, for a sample coated via screen printing, this amount rises to 23 g/m2.

Green fabrication of unoxidized graphene by combination of frozen dispersion and multimode microwave thermal shock

Next-generation electronic materials must be produced and used sustainably. Nanocarbon materials have attracted much attention as next-generation materials because they have excellent properties and can be made from readily available and inexpensive raw materials. Among them, graphene is highly expected as a material that realizes high performance and energy saving in electric devices. It has excellent properties such as high electrical conductivity, high strength, and light weight. However, the current synthesis method for graphene requires the use of toxic chemicals such as strong oxidants and a large amount of energy consumption due to use of high vacuum and high temperature. Those requirements increases the environmental impact and cost. Therefore, a simple, environmentally friendly, inexpensive, and innovative process is required for the practical use of graphene. We have developed a novel process with a new mechanism using inexpensive and safe raw materials such as graphite, ice, and simple organic solvents and general equipment such as a microwave oven. The combination of the thermal expansion properties of graphite and the selective heating properties of microwaves created the new process. This paper shows that graphene synthesis can be achieved easily and cost-effectively using familiar equipment and materials by combining fundamental physical properties and phenomena.

Exploring the Preparation of Calcium-Doped Zinc Aluminate Ceramic Nanoparticles for Microstrip Patch Antenna Fabrication

Zinc aluminate (ZnAl2O4) dielectric materials have proven crucial in microwave applications, particularly in antenna miniaturization. This article presents the characteristics of sol-gel-prepared Ca-doped ZnAl2O4 (ZnAl2O4Ca) ceramic nanoparticles for their application in microstrip patch antenna (MPA). We examined the crystallinity, functional groups, morphology, and elemental properties of ZnAl2O4Ca ceramic nanoparticles using different techniques. Later, a prototype antenna was fabricated and evaluated, which demonstrated the return loss of -23.4 dB and -19.2 dB with voltage standing wave (VSWR) ratios of 1.1 and 1.2 at resonant frequency ( ) values 4.5 and 6.4 GHz, respectively. The presented work demonstrates that the prepared ceramic nanoparticles possess better microwave properties, enabling the fabrication of a patch antenna for c-band communication with two resonant peaks having reasonably good return loss.

Graphene induced carbon-based fibre composite as microwave absorber for X-band frequency application

Stealth performance for any microwave absorbing material (MAM) is primarily controlled by the intrinsic characteristic properties of the composition of the composite. The inbuilt property of graphene has enrich the interaction of electromagnetic waves (EMWs) when it is impregnated in its compatible components such as naturally occurring organic materials. The present research engraved with a natural fibre composite with graphene as a stuffing in a resin polymer environment. The powdered form of banana-coconut coir fibre dust with 50–50 wt.% of average particle size of 150 µm with graphene has been fabricated as a hybrid composite of Graphene/Banana-coconut (GN/BNN-CCNT). The surface morphology of the fabricated composite is significantly modified with the addition of graphene creating a sustainable and foam-like elastic skeletal structure for compatibility with EMW. The enhanced dielectric values with different microwave properties for stealth performance are computed. At a frequency of 10.63 GHz a significant −15.68 dB reflection loss is found which comprises of power loss of 97.5% showing the effectiveness of the GN/BNN-CCNT/Epoxy hybrid composite as a stealth material for different X band frequency applications.

Design and Fabrication of Wideband Dielectric Resonator Antenna Using Low Loss Ultra‐Low Sintering Temperature Li6B4O9 Microwave Dielectric Ceramic for Wireless Communication Applications

AbstractLow dielectric constant (ɛr), high quality‐factor (Q × f), and temperature stable microwave dielectric ceramics with ultra‐low sintering temperature are the preferred choice of researchers for the development of low‐cost and high‐performance dielectric resonator antenna (DRA), which have wide application prospects for wireless communication technology. In this work, wideband DRAs fabricated using ultra‐low sintering temperature, low‐loss, and high‐quality Li6B4O9 microwave dielectric ceramics are reported. Li6B4O9 ceramic synthesized via solid‐state reaction at sintering temperature of 620 °C demonstrates excellent microwave properties with optimum ɛr = 5.95, high Q × f = 38,700@12.4 GHz, and thermal coefficient of the resonant frequency (TCF ≈ −68.6ppm/○C). For the first time, performance comparison of two Li6B4O9‐based cylindrical DRAs with different ceramic aspect (radius to height) ratios excited by slot coupled microstrip line is realized. In the first DRA with ceramic aspect ratio of 0.864, DRA HE11δ mode is excited and bandwidth of 20.01% , 95% radiation efficiency, and 6.3 dBi maximum gain is attained. In the second DRA with ceramic aspect ratio of 2.367, slot and dielectric resonator resonances are merged to attain wide bandwidth of 38.15% over which antenna broadside radiation performance is preserved. The proposed DRAs can be utilized for high‐capacity, high‐speed wireless communication applications.

Tunable dynamic microwave properties of a magnetic skyrmion manipulated by strains

In this paper, we theoretically studied the tunable dynamic microwave properties of a magnetic skyrmion manipulated by strains through micromagnetic simulations. The strains are induced by voltage due to the converse piezoelectric effect and then applied to modulate the dynamic characteristics through the magneto-elastic coupling effect. The tunable dynamic microwave characteristics of a breathing mode and gyration modes are investigated. The resonant frequency of the breathing mode increases abruptly and then decreases slowly with the strain changing from compressive to tensile. A clockwise gyrotropic mode has been obtained, and the resonant frequency keeps increasing with the strain changing from compressive to tensile. In particular, strains can induce different gyrotropic trajectories of the skyrmion driven by an in-plane microwave field. Our results may contribute to the understanding of dynamic properties of skyrmions manipulated by voltage-induced strains and provide a method to realize tunable spintronic microwave devices based on skyrmion.

Mechanical strength and microwave dielectric properties of Al2O3 doped Li2MgTi3O8 ceramics with high temperature stability

A temperature stability microwave dielectric ceramic with composition of Li2MgTi3O8 (LMT) and Al2O3 with high flexural strength is synthesized by a conventional solid-state reaction method. The effects of Al2O3 (particles and whiskers) doping on the mechanical and dielectric properties of LMT ceramics are studied. A single spinel structure, without any secondary phases, is detected in the Al2O3 particles and Al2O3 whiskers doped LMT ceramics. The maximum flexural strengths of 152.5 MPa and 166.73 MPa are delivered in LMT +0.3 wt% Al2O3 (p) ceramics and LMT + 0.3 wt% Al2O3 (w) ceramics, respectively, which are enhanced by 53.21% and 67.52% over those of unmodified LMT ceramics. Pinning and grain refinement contribute to the enhanced flexural strength of the system. The intrinsic factors of Q × f change are analyzed by calculating the packing fraction and lattice energy. In addition, ceramics exhibit excellent comprehensive microwave properties at 1050 °C: (LMT + 0.2 wt% Al2O3 (p):Q × f = 67056 GHz, τf = −8.25 ppm/°C, εr = 24.34, σf = 133.3 MPa; LMT + 0.1 wt% Al2O3(w): Q × f = 68670 GHz, τf = −8.94 ppm/°C, εr = 24.32, σf = 122.7 MPa) The results indicate that Al2O3 particles and Al2O3 whiskers are decent reinforcing agents for LMT ceramics.

Structural characteristics and microwave properties of amorphous nanogranulated composites (Co41Fe39B20)x(SiO2)1-x

We presented results of experimental studies of the structure and microwave reflective, transmitting, and absorbing properties in the frequency ranges of 8–12 GHz and 25–36 GHz of amorphous nanogranular composites (Co41Fe39B20)x(SiO2)1−x, 32.79<x < 52.00 at. %) with a thickness of 1.60–2.54 μm deposited on a lavsan base with a thickness of about 20 μm. The spectra of the reflection and transmission coefficients as a function of frequency and the dependences of the reflection, transmission and absorption coefficients on the content of the ferromagnetic filler were obtained. Using the algorithm for calculating structural and conductive characteristics of amorphous nanogranular composites from the measured values of the microwave reflection coefficient, the conductivity of granules and the mean free path of electrons were estimated using the mechanisms of closed and open circuits of the model of intragranular currents. We showed that the electron mean free path corresponded to the gaps between the granules of the studied composites with weakly expressed conducting properties.

The characteristics of microwave-treated insoluble and soluble dietary fibers from grape and their effects on bread quality.

This study investigated the morphological and hydration properties of untreated and microwave (MW)-treated isolate forms of soluble (SDF) and insoluble dietary fibers (IDF) obtained from grapes. Then, the rheological, textural, and other physical effects of the fibers (5% flour basis) were evaluated on bread quality. For this purpose, grape pomace was valorized as the juice extraction waste. MW significantly improved hydration properties of SDF and IDF by modifying their microstructures (p < .05). SDF had a clean-cut morphology whereas IDF had an indented microstructure with a wrinkled surface. After MW treatment, deep grooves and holes were observed. These variations in the IDF structure were more extensive. DF additions influenced water absorption, mixing tolerance index, dough development time, dough stability, resistance to extension, extensibility, energy of the dough and hardness, cohesiveness, springiness, chewiness, weight loss, specific volume, crust color difference of the bread in comparison with the properties of control samples significantly (p < .05). IDF had especially pronounced effects on the dough and bread characteristics. SDF enrichment provided more comparable results with the control bread than IDF. The originality of this work is to characterize isolated (100% purity) SDFs and IDFs, then discuss their effects on semi (dough) and final (bread) product quality.

Impact of Sc3+/In3+ ions co-substitution on structural, magnetic, and microwave features of SrFe12O19 hexaferrites

ScIn→Sr NHFs have been synthesized via the sol-gel combustion method. The phase and morphonology were analyzed via XRD, SEM, TEM, and HR-TEM. XRD measurements confirmed the purity of all products having the crystallite size (DXRD) of 31–77 nm obtained via Rietveld refinement. The agglomeration of products was observed in SEM and HR-TEM images due to their magnetic character. SEM images revealed the hexagonal-shaped nanoparticles. Mössbauer spectra showed that In3+ and Sc3+ ions are located at generally octahedral (Oh) 4 f2 site. The electron density s of iron ions of 4 f2 and 2a sublattices is affected by doping content. The obtained M-H curves (field-dependence of magnetization) demonstrated ferrimagnetic hysteresis loops at both 300 and 10 K. The analysis of M-H curves also showed that the saturation magnetization (Ms) first declined until x = 0.03, then grew up to x = 0.05, and returned to decrease thereafter. The coercivity (Hc) decreased sharply with Sc-In substitution, transforming the magnetic character of samples from hard to soft. Microwave (MW) properties were measured and analyzed between 33 and 50 GHz. It was demonstrated that the increase of the Sc3+/In3+ concentration led to modifications in amplitude-frequency characteristics of the electromagnetic absorption process. It was shown that Sc3+/In3+ substituted Sr NHFs can be used for developing radioelectronic coatings and providing electromagnetic compatibility.

Electric field control of the ferromagnetic resonance linewidth in synthetic antiferromagnetic heterostructure

In this study, we present a novel approach to control the microwave properties of a Co/Ru/FeNi film, characterized by strong antiferromagnetic coupling and in plane uniaxial anisotropy. The film is fabricated on a Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) ferroelectric substrate using the magnetron oblique sputtering. Our experimental results demonstrate a remarkable non-volatile mediation of the ferromagnetic resonance (FMR) field and linewidth by applying the perpendicular-bias electric field. The observed asymmetric butterfly curve indicates the existence of electric mediation dominated by strain effect. Moreover, we investigate the angular dependence of FMR under different electric field, which reveals changes in magnetic anisotropy including FMR field. Notably, the FMR linewidth exhibits a distinctive four-fold anisotropy. Through microstructure analysis of the film surface, we identify that the origin of this FMR linewidth anisotropy is attributed to the two-magnon scattering induced by the oblique sputtering.

Retrieving the Intrinsic Microwave Permittivity and Permeability of Ni-Zn Ferrites

Mixing rules may be extremely useful for predicting the properties of composite materials and coatings. The paper is devoted to the study of the applicability of the mixing rules to permittivity and permeability and the possibility of retrieving the intrinsic properties of inclusions. Magnetically soft Ni-Zn ferrites are chosen as the object of the study due to their low permittivity and the negligible influence of the skin effect. Due to this, the microwave properties of bulk ferrites may be measured by standard techniques. It is suggested to perform the analysis of the microwave properties of composites filled with Ni-Zn ferrite powder in terms of the normalized inverse susceptibility defined as the volume fraction of inclusions divided by the effective dielectric or magnetic susceptibility of the composite. The measured properties of the bulk ferrite are compared with those obtained by mixing rules from composite materials. The experimental evidence for difference between the mixing rules for permittivity and permeability of a composite, which was previously predicted only theoretically, is obtained. The reason for the difference is considered to be the effect of non-ideal electrical contacts between neighboring inclusions. It is also experimentally shown that the measured permeability of the bulk material may differ from the retrieved one. The measured static permeability is 1400 and the retrieved one is 12. The reason for the discrepancy is the difference between the domain structures and demagnetizing fields of particles and bulk ferrite.

Micromagnetic simulation of electrochemically deposited Co nanowire arrays for wideband microwave applications

We study the magnetic properties of arrays of Co nanowires which exhibit zero bias-field ferromagnetic resonance absorptions in a 0–30 GHz range. Columnar arrays of Co nanowires with lengths of 8–15 µm were electrochemically grown using ∼20 µm thick anodic alumina membranes with 50 nm pore diameters. Microstructural, static magnetic, and microwave properties of five different nanowire arrays were characterized. The studied Co nanowires present different crystal structure textures and magnetic properties. The static magnetic loop shapes and the ferromagnetic resonance frequencies of the nanowire arrays were correctly reproduced using the Mumax3 micromagnetic software. For each sample input parameters dependent on the x-ray diffraction and microstructural data, were fine-tuned to allow the best fit of the experimental hysteresis loops and the related microwave spectra. Using this method, it was possible to analyze the rather complex interplay between geometry and magneto-structural features of the different arrays, defining which parameters play a key role in the development of nano-systems with specific microwave properties.

Ultralow-loss Sr1+xMgGe2O6+x ceramics: Sintering behavior, microstructure, covalence, lattice vibration, and dielectric properties

Sr1+xMgGe2O6+x ceramics were prepared by the solid-state reaction method (SSR). The effects of Sr2+ non-stoichiometry on phase composition, sintering characteristics, microstructure, and microwave properties were analyzed. XRD detected a slight excess of strontium to produce the secondary phase Sr2MgGe2O7. Rietveld refinement obtained the structural parameters, and the crystal structure was studied. SEM revealed that excessive strontium promoted grains' growth and increased ceramics' density. Raman spectrum indicates that the FWHM is closely related to microwave properties. The change of Q × f was explained by analyzing the packing fraction and average covalence. The distortion of the GeO4 tetrahedron and bond energy revealed the relationship between τf and crystal structure. Sr1.03MgGe2O6.03 ceramics sintered at 1250 °C have the best microwave properties of εr = 8.69, Q × f = 77660 GHz, τf = −74 ppm/°C.

Microwave Properties of Ba-Substituted Pb(Zr0.52Ti0.48)O3 after Chemical Mechanical Polishing

We have studied the effect of chemical-mechanical polishing (CMP) on the ferroelectric, piezoelectric, and microwave dielectric properties of Ba-substituted PZT (BPZT), deposited by pulsed laser deposition. CMP allowed for the reduction of the root mean square surface roughness of 600 nm thick BPZT films from 12.1 ± 0.1 nm to 0.79 ± 0.15 nm. Ammonium peroxide (SC-1) cleaning was effective to remove Si CMP residuals. Measurements of the ferroelectric hysteresis after CMP indicated that the ferroelectric properties of BPZT were only weakly affected by CMP, while the piezoelectric d33 coefficient and the microwave permittivity were reduced slightly by 10%. This can be attributed to the formation of a thin dead layer at the BPZT surface. Moreover, the intrinsic dielectric permittivity at microwave frequencies between 1 and 25 GHz was not influenced by CMP, whereas the dead layer series capacitance decreased by 10%. The results indicate that the CMP process can be used to smoothen the BPZT surface without affecting the film properties strongly.

Modeling the frequency characteristics of the waveguide structure of a heterodyne receiver with sideband division for the range 211...275 GHz

The microwave properties of the components of the waveguide structure of a heterodyne receiver in the 211...275 GHz range with sideband separation based on a pair of superconductor–insulator–superconductor (SIS) tunnel junctions are described. The following elements of the waveguide were studied structures: hybrid four-port splitter, directional coupler, T-shaped splitter body and waveguide absorber. S parameters were calculated for all elements. For hybrid divider additionally shows a phase balance with deviations of less than 0.4 degrees, and an amplitude balance within 1 dB. The expected level of quality of band separation in a band separation receiver using the studied waveguide elements is analyzed; its value is more than –25 dB. The waveguide elements are designed taking into account the fact that the block will be manufactured using precision milling; the minimum dimensions of the waveguide structure are limited by the diameter of the cutter used; in our case, 100 μm was chosen. All numerical calculations were performed using the finite interval method in the HFSS package.

Face-centered cubic packing model for microwave properties of polymer composites with segregated conductive network

Face-centered cubic packing model for microwave properties of polymer composites with segregated conductive network

Barium and Yttrium Co-doping in Bismuth Ferrite Nanoparticles to Enhance Microwave Properties

The microwave properties of multiferroic Bismuth Ferrite have been widely studied and focus has been placed on the improvement of microwave absorption, impedance matching, effective bandwidth through doping with suitable elements, and formation of nanostructures. In this work, Barium and Yttrium co-doping at the Bi site of BiFeO3 nanoparticles (BayBi1-x-yYxFeO3) were observed to be effective in enhancing the dielectric and magnetic properties of the sample with x = 0.03 and y = 0.1. A minimum reflection loss of −61.7 dB was achieved in the sample for a composite absorber length of 7.5 mm attributed to the best balance observed between dielectric loss (tanδ ε ) and magnetic loss (tanδ μ ) based on the match equation, tanδ ε = tanδ μ . The best impedance matching observed in this sample also supports the observed high microwave absorption required for practical application as microwave absorption material.

An investigation on tribological properties of advanced microwave synthesized molybdenum disulfide as anti-friction additives in commercially available lubricating oils

The frictional stress between opposing contact surfaces will damage the mechanical parts of a machine. An appropriate lubricant can significantly reduce this. Blending nanoadditives with base oil is claimed to be an effective technique to increase the anti-friction qualities of lubricants using nanotechnology. Advanced microwave synthesized molybdenum disulfide (MoS2) anti-friction nanoadditive was employed in various lubricating oils namely fully synthetic, semi-synthetic, mineral, and hydraulic oil to formulate the nanolubricant. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), and a physical stability observation test were used to study the nanoadditives (MoS2) physicochemical characteristics. The tribological analysis of the MoS2 nanolubricant was measured using the four-ball tribotester. The coefficient of friction (COF) and average wear scar diameter (WSD) of the anti-friction additives were analyzed. The experimental results revealed improvements in COF and WSD in the range of 7.47–15.81% and 6.57–16.07% after the addition of MoS2 nanoparticles in the various lubricating oils. This study discovered that engine oil with advanced microwave-synthesized MoS2 nanoparticles has a significantly lower COF and WSD than engine oil that is not added with the anti-friction additives.