Microwave Properties Research Articles

Ultra-high quality factor of Mg6Ti5O16-based microwave dielectric ceramics with temperature stability

Mg6Ti5O16-based ceramics with ultra-high quality factor and temperature stability were prepared by a conventional solid-state reaction route. The effects of Ca2+ on phase composition, microstructure, and microwave dielectric properties of Mg6Ti5O16 ceramics were systematically investigated. X-ray diffraction (XRD) patterns and energy dispersive spectroscopy (EDS) analysis confirmed that the ceramics were composed of MgTiO3, MgTi2O4, and CaTiO3 with all Ca2+ contents. A kind of microwave dielectric ceramics based on Mg6Ti5O16 was developed, and the microwave properties of Mg6Ti5O16 ceramics can be effectively improved by doping of Ca2+. After sintering at 1360 °C for 4 h, Mg6Ti5O16 ceramics doped with x = 0.35 Ca2+ exhibited an ultra-high quality factor of 100432 GHz (at 9 GHz) and a dielectric constant of 19.87. The resonant frequency temperature coefficient was − 3.0 ppm/°C during the temperature range of 25–85 °C. It is a promising material in the field of microwave communication.

Effect of PEG and Mn on microwave properties of nano sized Ba4Co2Fe36O60 hexaferrite bulk

Investigations on the effect of the addition of polyethylene glycol and Mn doping on microwave properties of on Ba-M-Y(Ba4Co2Fe36O60) hexaferrite. Barium hexaferrite nanoparticles have been prepared by chemical co-precipitation method are reported. The powders were characterized by scanning electron microscope and X-ray diffraction methods. The mixed hexaferrite crystal structure was formed as the combination of M-type (BaFe12O19), Y-type (Ba 2 Co 2 Fe 12 O 22 ) hexaferrite phases. The addition of PEG and Mn doesn’t affect the crystal structure. The microwave properties of samples were measured by the waveguide reflectometer method. The complex permittivity and permeability of these samples measured by s VSWR slotted section techniques. TEM images of PEG added sample reveal the formation of nanoparticles. PEG added Ba-M-Y sample shows very high microwave absorbance in whole frequency band than that of without PEG sample and Mn doped sample while high miniaturization factor was achieved for Mn doped sample.

Synthesis and microwave properties of fluorinated terphenyl isothiocyanate liquid crystals

Synthesis and microwave properties of fluorinated terphenyl isothiocyanate liquid crystals

Molecular sieve catalyst compositions, catalytic composites, systems, and methods

FeNi films with the stripe domain (SD) pattern are prepared by electrodeposition and sputtering methods. The magnetic domain, static magnetic parameters, and quality factor, as well as dynamic properties of the two films, are respectively performed. The results show the magnetizations of the film were dependent on the direction of SD, and the rotation of the SD is lagging behind the magnetization reversal. The microwave properties of the SD emerge dynamic hysteresis before the saturation magnetic field. These microwave properties are selectively excited with acoustic mode, optical mode, and spin-wave mode. The frequency and intensity of different resonance modes of stripe domain are determined by the local magnetization. The magnetization variations and the rotation of SD of different modes are further illuminated by the micromagnetic simulation. The magnetic anisotropy and the resonance intensity of permeability of different modes were finally described by the modified resonance equations.

Nanoindentation characterization of polymer nanocomposites for elastic and viscoelastic properties: Experimental and mathematical approach

This work aims to determine the elastic and viscoelastic properties of microwave processed nanocomposites. Three different power rating has been used in microwave processing of polymer nanocomposite, i.e., 180 W, 360 W, and 540 W. Nanomechanical elastic properties of nanocomposites have been determined using the conventional nanoindentation method. Viscoelastic properties of nanocomposites have been determined by observing the increase in depth at maximum load (10 mN) during a small holding period (2 s). Polypropylene nanocomposites (PNT), high-density polyethylene nanocomposites (HNT), and low-density polyethylene nanocomposites (LNT) have shown an increase in modulus, hardness, and viscosity term with an increase in microwave power. The plasticity index has been obtained using the area under the loading and unloading curves. HNT and PNT samples have shown a plasticity index of 0.71 ± 0.02 and 0.62 ± 0.05, respectively. However, LNT samples have shown the same plasticity index 0.61 at all three-power ratings.

Investigations on structural and electrical properties of conventional and microwave sintered BaTiO3 and Ba0.98Nd0.02TiO3 ceramics

In this article, BaTiO3 and Ba0.98Nd0.02TiO3 ceramics were prepared by high temperature conventional solid state reaction, followed by microwave sintering (MS) process separately. A comparative study on structural, morphological and electrical properties has been employed by powder X-ray diffraction (PXRD), Raman, scanning electron microscope and dielectric and ferroelectric measurements. PXRD and profile refinement analysis results revealed that tetragonal phase at room temperature. The Raman spectroscopy provided useful information on the presence of tetragonal symmetry. Surface morphology of the MS sample showed dramatic changes from scanning electron micrographs. Dielectric and ferroelectric behavior observed for MS sample.

Photocatalytic and antimicrobial properties of microwave synthesized mixed metal oxide nanocomposite

CdO-CuO-ZnO nanocomposite (CCZ NC) was prepared by a simplistic microwave-assisted route and inspected by utilizing diverse spectroscopic ways. The structural and morphological properties of CCZ NC were investigated via XRD, FTIR, and SEM with EDAX analysis. The XRD pattern reveals the crystal structure of cubic CdO, monoclinic CuO, and hexagonal ZnO with average crystallite size around 39 (CdO), 28 (CuO), 30 (ZnO) nm. The FTIR spectrum exposed distinctive vibration frequencies at 566, 630, and 451 cm−1 allocated to Cu-O, Cd-O, and Zn-O stretching vibrations, correspondingly. The flower-like structure was validated with SEM with EDAX investigation. The optical properties of CCZ NC were deliberated via UV–Visible and fluorescence spectroscopy. The optical bandgap of the synthesized CCZ NC is 2.8 eV. High-performance alizarin red S dye photocatalytic degradation (93% at 120 mins) was observed on the flower-like structure CCZ NC, under natural sunlight irradiation. Besides, the antibacterial activities of CCZ NC were investigated against foodborne microorganisms. CCZ NC showed a good zone of inhibition against Staphylococcus aureus (28 mm) and Salmonella typhi (22 mm). These results indicate that synergistic CCZ NC is a promising material for the functioning of bio-imaging, water purifying process, and pharmaceutical applications.

Electromagnetic Interference Shielding Properties of BaCo2Fe16O27 Nanoplatelets and RGO Reinforced PVDF Polymer Composite Flexible Films

AbstractThe electromagnetic Interference (EMI) shielding effectiveness of W‐Type barium hexaferrite (BaCo2Fe16O27) and reduced graphene oxide (RGO) nanofillers reinforced poly(vinylidenefluoride) (PVDF) polymer composite films are reported. Two different amounts of BaCo2Fe16O27 (10 wt% and 30 wt%) nanofillers and fixed amount of RGO (10 wt%) are loaded in PVDF matrix by solvent casting in order to fabricate the multifunctional PVDF/RGO/BaCo2Fe16O27 composite films. The synthesized samples are investigated using various instruments including X‐ray diffraction (XRD), Fourier‐transform infrared spectroscopy (FTIR), Raman spectroscopy, high resolution scanning electron microscopy (HRSEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analysis. The microwave properties of PVDF/RGO/BaCo2Fe16O27 composites are tested with vector network analyser (VNA) in 8–12 GHz frequency (X‐Band). The possible mechanism of EMI shielding is investigated from the analysis of complex permittivity and permeability.The resultant flexible films exhibit desirable EMI SE of 35.94 dB at 11.8 GHz for the 10 wt% of BaCo2Fe16O27 addition in PVDF composite for a very small thickness of 0.2 mm. The combination of high dielectric loss ( tanδε = 1.63) and magnetic loss (tanδμ = 0.26) contributes to high absorption of 29.85 dB (>99% attenuation) dominated over reflection. Thus, the simple and cost‐effective fabrication of ultrathin and flexible PVDF/RGO/BaCo2Fe16O27 composite film with low filler content has a great potential as suppresser in electromagnetic fields.

Effect of secondary filler properties and geometry on the electrical, dielectric, and electromagnetic interference shielding properties of carbon nanotubes/polyvinylidene fluoride nanocomposites

AbstractHybrid polymer nanocomposites based on polyvinylidene fluoride (PVDF) as the matrix, carbon nanotubes (CNTs) as the primary conductive filler, and metal nanoparticles as secondary fillers were fabricated by melt mixing. Secondary nanofillers with different geometry and properties (nickel nanowire (NiNW), silver nanowire (AgNW), nickel nanoparticle (NiNP), and silver nanoparticle (AgNP) were selected to investigate the effect of geometry and properties of secondary filler on the hybrid polymer nanocomposites' properties. Electrical conductivity, electromagnetic interference (EMI) shielding effectiveness, and complex microwave properties of the fabricated hybrid nanocomposites were studied in X‐band frequency (8.2–12.4 GHz). The hybrid nanocomposites containing CNT/AgNW demonstrated superior conductivity and EMI shielding compared to individual fillers such as CNT, AgNW, NiNW, AgNP, NiNP, or hybrid system such as CNT/NiNW. The novelty of the present study lies in the unique synergy arising from the combination of nanofillers with similar geometry and high electrical conductivity, which resulted EMI shielding effectiveness as high as 27 dB for a shield with only 1.1 mm thickness. The EMI shielding mechanisms, including negative permittivity were studied and explained in details in the manuscript.

Crystal structure, Raman spectra, and microwave dielectric properties of high-Q Li2ZnTi3O8 systems with Nb2O5 addition

Li2ZnTi3O8(LZT)-xwt.%Nb2O5 (x = 0, 1, 2, 3, 4) microwave dielectric ceramics were synthesized by the conventional solid-phase sintering method. The effect of Nb2O5 addition on crystal structure, Raman spectra, and dielectric properties were studied. X-ray diffraction results indicated that the maximum crystallinity of LZT ceramics were obtained at 1075 °C, and that Nb5+ diffused into the LZT matrix completely to form a stable solid solution. XRD refinement results demonstrated that the substitution of Nb5+ for Ti4+ caused the cell volume to increase. The microscopic morphology of LZT-xwt.%Nb2O5 (x = 0, 1, 2, 3, 4) ceramics were further investigated by scanning electron microscopy, and results indicated that Nb2O5 could promote the grain growth and sintering of LZT ceramics. Extrinsic and intrinsic dielectric losses were studied through Raman and impedance spectroscopy. The highest value of quality factor × resonant frequency (Q × f) was attributed to the increase in relative density and reduced number of oxygen vacancies (VO••), as well as the decrease in damping behavior. Moreover, the dielectric constant (εr) showed the same trend as cell polarization and the temperature coefficient of resonant frequency (τf) was inversely proportional to cell volume. The LZT ceramics with 3 wt% Nb2O5 addition sintered at 1075 °C for 4 h exhibited the optimal microwave properties, i.e., εr = 26.52, Q × f = 66 304 GHz, and τf = - 14.2 ppm/°C.

Microwave Refractive Index in CoFe/Cu Superlattices with a Giant Magnetoresistive Effect

The microwave properties of magnetic metallic nanostructures with a giant magnetoresistive effect are studied in this work. The microwave refractive index is calculated; it is shown that its changes have two physical causes: the high-frequency giant magnetoresistive effect and the ferromagnetic resonance.

A novel ultra-low temperature sintered Li2CO3 doped Ba3V2O8 microwave ceramics

Novel Ba3V2O8 + x wt.% Li2CO3 (0 ≤ x ≤ 12) ceramics were synthesized at ultra-low sintering temperatures. The doping effect of Li2CO3 on microwave properties and the principle of ultra-low temperature sintering was investigated. The XRD refinement demonstrated that Q × f value showed a strong relationship with packing fraction, bond energy of V-O, and lattice energy as a function of Li2CO3 content. An appropriate amount of Li2CO3 dramatically reduced the sintering temperature of Ba3V2O8 ceramic from 1200 to 660 °C. Li2CO3 addition could modify the τf value of Ba3V2O8 to reach the near-zero value. The 8 wt% Li2CO3 doped Ba3V2O8 ceramic sintered at 660 °C displayed good microwave properties: εr = 13.07, Q × f = 33,000 GHz, and τf = 13.0 ppm/°C.

Preparation, structure and microwave dielectric properties of novel La2MgGeO6 ceramics with hexagonal structure and adjustment of its τf value

A novel La2MgGeO6 ceramic was synthesized through a solid-state reaction process within a sintering temperature range of 1450–1550 °C. By a combination of X-ray diffraction and Rietveld refinement analyses, the ceramics were found to have a pure hexagonal phase structure belonging to space group R3/146. The scanning electron microscopy images revealed that the ceramic grains were closely connected. The effects of internal (lattice energy, valence bond, and fraction packing) and external factors (density) on the microwave properties of ceramics were also studied. The ceramic exhibited excellent microwave dielectric performances, with a relative permittivity (Ɛr) of 21.2, a quality factor (Q × f) of 52 360 GHz, and a temperature coefficient of resonant frequency (τf) of −44.2 ppm/°C, when sintered at 1500 °C for 4 h. The τf value of the La2MgGeO6 ceramic doped with CaTiO3 could be adjusted to zero. Particularly, 0.2La2MgGeO6-0.8CaTiO3 ceramics have good microwave dielectric properties with τf = +2.1 ppm/°C, Q × f = 15 610 GHz, and Ɛr = 40.3.

Effect of LiF addition on sintering behavior and dielectric breakdown mechanism of MgO-based microwave dielectric ceramics

Glass-free MgO-based microwave dielectric ceramics (1-x) wt% (0.98 MgO-0.02 Al2O3)-x wt% LiF (x = 0.5, 1, 2, 3, 4) were synthesized where LiF and Al2O3 were utilized as sintering additive and reinforcement phase in MgO matrix respectively. It was found that ion substitution is apt to occur between LiF and MgO, leading to the formation of oxygen vacancies and MgF2. Nevertheless, different from ordinary liquid-phase sintering, morphologies of ceramics were distinctly altered with grains changing from polyhedron to sphere-like shape and densities underwent obvious decrease when excessive amount of LiF was introduced and we call it excessive liquid-phase sintering. Grain boundary weakening caused by this circumstance would exert an adverse effect on physical properties. Moreover, LiF addition dramatically reduced dielectric breakdown strength and altered the dielectric breakdown behavior of MgO-based ceramics, which is dominated by electrical breakdown mechanism. Combination of good properties were achieved in 1 wt% LiF modified MgO-based ceramics sintered at 950 °C which exhibited superior microwave properties (εr = 9.56, tanδ = 9.2 × 10−5, Qf = 124,600 GHz), high flexural strength (184.5 MPa), high thermal conductivity (21.3 W/(m⋅K)), high coefficient of thermal expansion (∼12 ppm/°C) and moderate electrical properties (Eb = 35.9 kV/mm, ρ = 4.9 × 1012 Ω cm).

Effects of boron on microstructure and properties of microwave sintered FeCoNi1.5CuY0.2 high-entropy alloy

The mechanical properties of high-entropy alloys (HEAs) containing rare earth are improved by adding boron element. Under the condition that the content of rare-earth is fixed, FeCoNi1.5CuY0.2Bx high-entropy alloy with different boron atom ratios (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) is prepared by advanced microwave sintering process. The effect of boron addition with different atomic ratios on the phase evolution, microstructure, compressive mechanical properties and magnetic properties of the FeCoNi1.5CuY0.2 high-entropy alloy is emphatically studied. The results show that the phase transformation temperature decreases with the increase of boron content, which is conducive to the rapid sintering at low temperature. When boron content is less than 0.4 atomic ratio, the alloy is dominated by FCC base phase and BYO3, eliminating the oxidation phase of Y2O3. When boron adding amount as x = 0.4, it has the largest maximum compression ratio. When the amount of boron exceeds 0.4 atomic ratio, boride precipitates in the alloy, which increases the strength and hardness and at the cost of plasticity and soft magnetism. When the amount of boron is x = 1, the hardness arrives at utmost, and the compressive strength, yield strength and hardness are 1546 MPa, 1112 MPa and 367.1HV, respectively, which are 150%, 129% and 29.03% higher than those of boron-free sample. The improvement of mechanical properties is due to the fact that boron with small atomic size is easy to solute into the FCC base phase, forming interstitial solid solution, which results in lattice distortion and solid solution strengthening effect. And BY12 particles precipitated in BYO3 have dispersion strengthening effect on the alloy.

Investigation of Microwave Characteristics of a Composite Based on Copper-Substituted Nickel-Zinc Ferrite

The results of ferrite synthesis and composite preparation and investigation are presented. The Cu substituted Ni-Zn ferrite was prepared in single phase form. The morphology and chemical composition were obtained. The composites on the base of experimental Ni0.28Zn0.62Cu0.1Fe2O4 and commercially available one were prepared. The microwave properties of all samples were investigated. It was checked that the used synthesis method (temperature and time range) can be used for ferrite producing for industry. The microwave properties of composites made of synthesized ferrites are very close to those of composites based on commercially available one. All samples exhibit broad magnetic loss peaks associated with a natural ferrimagnetic resonance.

Functional Sr0.5Ba0.5Sm0.02Fe11.98O4/x(Ni0.8Zn0.2Fe2O4) Hard-Soft Ferrite Nanocomposites: Structure, Magnetic and Microwave Properties.

This paper reports the correlation between the composition of the functional Sr0.5Ba0.5Sm0.02Fe11.98O19/x(Ni0.8Zn0.2Fe2O4) hard–soft nanocomposites (SrBaSmFe/x(NiZnFe) NCs), where 0.0 ≤ x ≤ 3.0, and their structural features, magnetic, and microwave properties. SrBaSmFe/x(NiZnFe) hard/soft ferrite NCs are produced using the one-pot citrate combustion method. According to the XRD analysis, all samples showed the co-existence of both SrBaSmFe and NiZnFe phases in different ratios. Magnetic properties are measured in a wide range of magnetic fields and temperatures (10 and 300 K) and correlated well with the composition of the investigated samples. The microwave properties (frequency dispersions of the magnetic permeability, and electrical permittivity) are discussed by using the co-axial method in the frequency range of 0.7–18 GHz. Non-linear dependences of the main microwave features were observed with varying of composition. The microwave behavior correlated well with the composite theory. These results could be used in practice for developing antenna materials.

Microwave Foaming of Materials: An Emerging Field.

In the last two decades, the application of microwave heating to the processing of materials has to become increasingly widespread. Microwave-assisted foaming processes show promise for industrial commercialization due to the potential advantages that microwaves have shown compared to conventional methods. These include reducing process time, improved energy efficiency, solvent-free foaming, reduced processing steps, and improved product quality. However, the interaction of microwave energy with foaming materials, the effects of critical processing factors on microwave foaming behavior, and the foamed product’s final properties are still not well-explored. This article reviews the mechanism and principles of microwave foaming of different materials. The article critically evaluates the impact of influential foaming parameters such as blowing agent, viscosity, precursor properties, microwave conditions, additives, and filler on the interaction of microwave, foaming material, physical (expansion, cellular structure, and density), mechanical, and thermal properties of the resultant foamed product. Finally, the key challenges and opportunities for developing industrial microwave foaming processes are identified, and areas for potential future research works are highlighted.

Microstructure and microwave dielectric properties of 3D printed low loss Bi2Mo2O9 ceramics for LTCC applications

Low sintering temperature, ultra-low loss microwave ceramics are envisaged as future dielectrics for fabricating low temperature co-fired ceramic (LTCC) components for 5G applications. Low sintering temperature bismuth molybdate β-Bi2Mo2O9 ceramic powders have been synthesised using a solid-state reaction method. Their additive manufacture and resulting microwave properties are reported for the first time. Optimum densification occurred for 3D printed samples sintered 4 hours at 670°C which resulted in a maximum relative density (ρr) of 92%, relative permittivity (εr) of 34, dielectric loss (tanδ) of 0.0007, giving a microwave quality factor (Qxf) of 10,050 GHz, properties attractive for LTCC applications.

Regulation of Microstructure, Static, and Microwave Magnetic Performance of NiFe/FeMn/NiFe Heterogeneous Multilayer Films Based on Thickness of FeMn Films

Ferromagnetic (FM)/antiferromagnetic (AFM) heterogeneous multilayer films have triggered tremendous interests for application in microwave/mm devices and components. However, with the development trend of miniaturization, high frequency, and lightweight of devices, the FM/AFM heterogeneous multilayers are desired to possess high saturation magnetization (4πMs), low coercivity (Hc), and low ferromagnetic resonance (FMR) linewidth (∆H). Herein, the Ni81Fe19 (50 nm)/Fe50Mn50 (t nm)/Ni81Fe19 (50 nm) films were fabricated by DC magnetron sputtering, and the effects of thickness of the Fe50Mn50 on the microstructure, static, and microwave properties were investigated in detail. With increasing the FeMn film thickness, the saturation magnetization firstly increased and then decreased from 7947 to 9448 Gs. The in-plane coercivity firstly decreased and then increased from 28.58 to 0.6115 Oe, and the out-of-plane exchange bias field undergoes a transition from a negative exchange bias to a positive exchange bias. Besides, the ferromagnetic resonance linewidth firstly decreased and then increased from 142 to 87 Oe. Remarkably, with a 15-nm Fe50Mn50 film, the heterogeneous multilayer films achieved optimum performance with high saturation magnetization (9448 Gs), low coercivity (1.02 Oe), and low FMR linewidth (94 Oe). The outstanding Ni81Fe19/Fe50Mn50/Ni81Fe19 heterogeneous multilayer films exhibit great potentials in radar remote sensing, communication, and electronic countermeasure fields.