Microwave Dielectric Constant Research Articles

Influence of V substitutions on sintering behaviors and microwave dielectric properties of Ba4LiNb3O12 ceramic

AbstractIn this study, a series of Ba4Li(Nb1‐xVx)3O12 (x = 0.05∼0.3) ceramics were synthesized using the solid‐state reaction method. X‐ray powder diffraction (XRD) analysis shows that the composite ceramics contain both Ba4LiNb3O12 and Ba3(VO4)2 phases, without any other phases present. The grains consist of Ba4LiNb3O12 and Ba3(VO4)2, as illustrated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Additionally, with the increase of V content, the grain size decreases, and the (microwave dielectric constant) decreases, the (resonant frequency temperature coefficient) value decreases, and the value increases (where = quality factor = 1 / dielectric loss, and = resonant frequency). The densest Ba4Li(Nb0.7V0.3)3O12, with a of 31.3, of + 70 ppm/°C, and high of 42 850 GHz, was obtained at a sintering temperature of 1350°C. Furthermore, the addition of 5 wt.% BaCu(B2O5) (BCB) into Ba4Li(Nb0.7V0.3)3O12 resulted in obtaining dense ceramics at a sintering temperature of 925°C, with a of 23.5, a high value of 14 370 GHz, and of + 88 ppm/°C. Further investigations have shown that Ba4Li(Nb1‐xVx)3O12 ceramics are chemically compatible with Ag, suggesting its potential use in low‐temperature cofired ceramics technology.

Dual nitrogen-sulfur-doping induce microwave absorption and EMI shielding in nanocomposites based on graphene

Graphene-oxide (GO) is one of the most commonly used carbon nanomaterials in advanced applications such as microwave absorption and EMI shielding, due to various advantages such as ease of synthesis and exfoliation, effective doping capability, and superior composite compatibility. In this study, we used the modified Hummer’s method to synthesize GO by exfoliating graphite powder, and a simple hydrothermal approach was employed for elemental doping and GO reduction. As nitrogen–sulfur (N, S) dual-doping precursors, thiourea and l-cysteine amino acids were utilized. The structural features and microporous network structure of GO aerogel foams were investigated. The microwave absorption capabilities of polyethersulfone-based nanocomposite films incorporating the as-produced nitrogen–sulfur enrich reduced GO (NS-rGO) are also explored. According to the physicochemical characterization, the existence of remarkable structural defects with a porous three-dimensional (3D) network was discovered due to heteroatom insertion and hydrothermal doping. Additionally, the dual-doped sample exhibited high Nitrogen and sulfur content of 8.93% and 13.19%, respectively. While NS-rGO possesses a higher conductivity of 174.7[Formula: see text][Formula: see text]S compared to 12.65[Formula: see text][Formula: see text]S for GO. The nanocomposites filled with NS-rGO foams demonstrated a high shielding efficiency (SE) of 45[Formula: see text]dB in the X-band with a filler loading of 0.5[Formula: see text]wt.%. This high SE arises from dopant heteroatoms and the heterogeneous interface, which induce interface polarization, thereby increasing microwave absorption and dielectric constant. It also results from multi-level reflections caused by the 3D porous structures. These findings offer valuable insights into the functionalization of carbon nanostructures and the development of 3D networks in GO-based functional materials, providing further guidance for engineering high-performance electromagnetic interference shielding materials.

Soil salinity estimation: Effects of microwave dielectric spectroscopy and important frequencies

AbstractThe microwave dielectric constant is a key bridge in establishing the relationship between microwave remote sensing and soil salinity (electrical conductivity, EC). However, the response between microwave dielectric spectrum type, frequency, and soil salinity is still unclear. The purpose of this study is to reveal the dielectric spectrum and frequency range closely related to soil salinity. In this study, 129 surface soil samples were collected, and soil EC and microwave dielectric spectrum (frequency range of 0.3–20 GHz) were measured. Four variable selection methods were used to select important spectral variables, and the relationship between these spectral variables and soil salt was constructed using a random forest model. The results showed that the combination of (real part) and (imaginary part) revealed the most implicit information related to soil salinity. Considering the important spectral variables, the model accuracy was generally improved to the full‐dielectric spectrum model (the ratios of the performance to the interquartile distance (RPIQ) improved by 0.11–0.40); furthermore, the variable iterative space shrinkage (VISSA) method could most effectively select important spectral variables (RPIQ = 2.32). The selected spectral‐RF models could provide important frequencies for estimating soil salinity; moreover, the low‐frequency range (0.3–4 GHz) and new important frequency ranges (e.g., 7 and 15 GHz) able to respond to soil salinity were identified. This study provides a new strategy for monitoring the soil salinization risk using multiple frequencies microwave remote sensing techniques.

Investigation of the microwave dielectric properties of the Li4x/3Zn2−2xTi1+2x/3O4 system by P–V–L theory and vibration spectroscopy

Li 4x/3 Zn 2–2x Ti 1+2x/3 O 4 microwave dielectric ceramics with a spinel phase were prepared via a high-temperature solid-phase method. P–V–L theory, vibration spectra, and XPS were utilized to establish the links between the intrinsic and extrinsic factors and the microwave dielectric properties. According to the characterization, the change in permittivity ( ε r ) was ascribed to the increase in the average bond ionicity of Ti–O( Af iTi-O ) and the polar mode of the lattice vibration; the change in quality factor( Q × f ) resulted from the change in the Ti–O lattice energy ( AU Ti-O ) and existence of oxygen vacancy; the increase in temperature coefficient of the resonance frequency ( τ f ) was triggered by the increase in the Ti–O bond energy. The Li 0.6 Zn 1.1 Ti 1.3 O 4 ceramics (x = 0.45) sintered at 1125 °C finally obtained optimal microwave dielectric constants of ε r = 17.3, Q × f = 76,318 GHz and τ f = -58 ppm/°C.

The Dielectric Constant of Ba6-3x(Sm1-yNdy)8+2xTi18O54 (x = 2/3) Ceramics for Microwave Communication by Linear Regression Analysis.

The electronics related to the fifth generation mobile communication technology (5G) are projected to possess significant market potential. High dielectric constant microwave ceramics used as filters and resonators in 5G have thus attracted great attention. The Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramic system has aroused people’s interest due to its underlying excellent microwave dielectric properties. In this paper, the relationships between the dielectric constant, Nd-doped content, sintering temperature and the density of Ba6−3x(Sm1−yNdy)8+2xTi18O54 (x = 2/3) ceramics were studied. The linear regression equation was established by statistical product and service solution (SPSS) data analysis software, and the factors affecting the dielectric constant have been analyzed by using the enter and stepwise methods, respectively. It is found that the model established by the stepwise method is practically significant with Y = −71.168 + 6.946x1 + 25.799x3, where Y, x1 and x3 represent the dielectric constant, Nd content and the density, respectively. According to this model, the influence of density on the dielectric constant is greater than that of Nd doping concentration. We bring the linear regression analysis method into the research field of microwave dielectric ceramics, hoping to provide an instructive for the optimization of ceramic technology.

Structural investigation and improvement of microwave dielectric properties in Ca(HfxTi1-x)O3 ceramics

Calcium hafnium titanate, Ca(HfxTi1-x)O3 (CHT) was prepared using the conventional solid state reaction route. The X-ray diffraction patterns were used for analyzing the phase compositions. The XRD patterns revealed the arrangement of a single phase perovskite structure and therefore the structure is transformed from non-centrosymmetric orthorhombic (Pbnm) to centrosymmetric cubic (Pm-3m) at 0.4 ≤ x. Lattice parameter, crystallite size, densities and porosity were calculated. The SEM morphology of CHT at various hafnium (x), which is comprises of round-rod shaped grains with small pores microstructure. The substitution of Hf4+ ions over Ti4+, the microwave dielectric constant (ε r) decreases from 145 to 52, while the quality factor (Qxf) increases from 8105 to 24305 GHz and temperature coefficient of resonant frequency tuned towards zero τ f ∼ 4.5 ppm °C−1. Good combination of microwave dielectric material properties was accomplished for the composition x = 0.8 (at 3 GHz).

Electrical microstructures of CaTiO3-Bi0.5Na0.5TiO3 microwave ceramics with high permittivity (εrmax ∼487)

The (1-x)CaTiO3-xBi0.5Na0.5TiO3 [(1-x)CT-xBNT), x = 0.1–0.6] microwave ceramics were studied by traditional solid-state method. Crystal structures, microstructures, microwave dielectric properties and impedance analysis of the as-prepared ceramics were investigated systematically. Refinement of X-ray diffraction patterns from all of the samples were pure orthorhombic structure with Pbnm space group. The Raman spectra of (1-x)CT-xBNT were in accord with the previous reports except that some abnormal modes appeared in high-wavenumber of 1200 cm−1-3400 cm−1. The microstructures were dominated by even grains and the average sizes increased gradually with an increase in Bi0.5Na0.5TiO3 (BNT) content. The microwave dielectric constant, εr, improved from 184 to 487, and the quality factor, Q×f, decreased constantly from 6973 GHz to 157 GHz as the amount of BNT in (1-x)CT-xBNT increased. However, the temperature coefficient of resonant frequency, τf, was restricted to fluctuating from 680 ppm/°C to 820 ppm/°C due to that the oxygen octahedral was twisted. For analysis and modeling of impedance data of 0.7CT-0.3BNT ceramics, the most appropriate equivalent circuits were found to consist of a parallel resistor-capacitor-constant phase element (R-CPE-C). And the activation energy for grains, 1.8 eV, was different to that in the grain boundaries, 1.0 eV.

Structural, photophysical and microwave dielectric properties of α-ZnMoO4 phosphor

Solid state reaction synthesis was employed for the production of triclinic zinc molybdate (α-ZnMoO4) crystal. X-ray diffraction (XRD) pattern, Rietveld refinement analysis, Fourier-transform infrared (FT-IR) and Fourier-transform Raman (FT-Raman) spectroscopy confirmed that α-ZnMoO4 exhibit a triclinic structure without evidence of any impurity phase. FT-IR spectroscopy gives information about vibrational features of Mo–O in the [MoO4] clusters. The 13 active vibrational modes were observed in Raman spectra from 100 to 1000 cm−1. UV–Vis absorption spectroscopy was used for calculation of optical band gap. The band gap (Eg) of 4.12 eV was observed for a direct allowed transition. The photoluminescence (PL) spectrum of α-ZnMoO4 gives intense green emission. Microwave dielectric constant (εr), temperature coefficient at the resonant frequency (τf) and Q x f value were measured by Hakki-Coleman method and found to be 8.05, −121.81 ppm/oC and 48320 GHz respectively. These results suggested the applications of ZnMoO4 in LEDs, scintillating detectors and microwave device.

The modification of surface, size and shape of barium zirconate powder via salt flux

AbstractThe “top‐down” process via direct conversion of the micro (μm)‐to‐submicroscale (sub‐μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO3. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub‐μm‐BaZrO3 powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead‐free piezoelectric material in the 0.87BaTiO3–0.13BaZrO3–CaTiO3 (0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from >10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high‐purity with uniform sub‐micro/nanometer powder production in one step by using simple laboratory equipment and low‐cost raw materials.

Microwave Characterization of Metal-Decorated Carbon Nanopowders Using a Single Transmission Line

This paper presents a novel approach for the characterization of microwave properties of carbon-based nanopowders, decorated or not with magnetic nanoparticles. Their microwave parameters, dielectric constant, electrical conductivity, and complex magnetic permeability are extracted from measurements performed using a single transmission line acting as a test cell. Two geometries of transmission line were tested, and successful results were obtained with each one of them. The measurement results are assessed by a phenomenological model enabling to fit the measurement of the dielectric constant and conductivity, providing an insight on the compacity quality of the powder sample. Also, the extraction of the permeability is validated by the detection of a ferromagnetic resonance showing a linear dependence on external DC magnetic field.

Influence of laser fluence on structural, optical and microwave dielectric properties of pulsed laser deposited Ba0.6Sr0.4TiO3 thin films

Barium strontium titanate Ba0.6Sr0.4TiO3 (BST6) thin films are deposited by pulsed laser deposition method at different laser fluences keeping the oxygen pressure constant. X-ray diffraction analysis confirms the formation of single phase cubic BST6 thin films. The strain in the grown films have been investigated, and the results show that the strain is in increased under the application of varying laser fluences. It can be inferred that the laser fluence is an important parameter in tuning the dielectric/ferroelectric properties of the films under optimized conditions. The thin films microstructures have been studied using HRTEM, and the results shows the presence of (110) faceted planes of BST6 with dspacing ~ 2.72–2.79 A. The optical band gap of the BST6 thin films was calculated by applying the Tauc relation from the transmission spectra in the 190–2500 nm range. The BST6 thin films grown at 2 J cm−2 which shows the best microstructural and optical properties was selected for the microwave dielectric measurements by depositing a test circular patch capacitor. The microwave tunability and dielectric constant (er) of a well crystallized BST6 thin film were found to be ~ 56 and ~ 284%, respectively at 1 GHz making it suitable for applications in tunable microwave devices.

Intricacies of designing metallic patch antennas in the optical band: Enhancements of the effects of the secondary physical parameters

This study considers the modifying effects of the patch antenna thickness and complex dielectric constant of the (real metal) patch on its radiation characteristics in the optical band, in comparison to the conventional microwave patch antenna. Patch thickness aware full wave simulation is used, for the first time, to find resonant length of the back cavity of the optical patch considering its Surface Plasmon Polariton modes and cavity height expansion due to wave penetration into the bottom and top (patch) metal layers. Verification of the results are based on a Fabry Perot cavity model based semi-analytic method, without earlier precedent. It is seen that in the analysis of a patch in the optical band, in contrast to the microwave case, patch thickness and dielectric constant of metal, which was secondary parameters, should be considered. Results of this study is a good base to design optical patch radiators and related flat optical devices.

Synthesis, Characterization, and Microwave Dielectric Properties of MgTiNb2O8 Ceramics Produced Through the Solid State Reaction Method

In the present work, a higher dielectric constant microwave dielectric ceramic Ni0.5Ti0.5NbO4 was prepared by the solid state method. The ceramic powders were calcined at 1050 °C for 2 h and then sintered at various temperatures. The ceramic have been investigated using the X-ray powder diffraction, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) and network analyzer. Singlephase Ni0.5Ti0.5NbO4 was obtained at the sintering temperature range of 1050-1200 °C. Dielectric constant, quality factor and temperature coefficient of resonant frequency of Ni0.5Ti0.5NbO4 ceramics were studied depending on sintering temperatures. The excellent microwave properties of Ni0.5Ti0.5NbO4 ceramic was found at 1100 °C with r=62.37, Q· f =10,630 GHz, f =88.30 ppm/°C.

Dielectric constant calculation based on mixture equations of binary composites at microwave frequency

Abstract The effective microwave dielectric constants of binary composites are examined through mixture equations in this paper. The ratios of dielectric constant of filler material to that of matrix material are studied from 0.77 to 24.55 and 0.21 to 9.53 in small and large volume fractions of filler material, respectively. The most adequate mixture equation for predicting the dielectric constants of binary composites is suggested. It was found that all mixture equations could give reasonably good predictions under similar dielectric constant between filler and matrix material situation and in the small volume fraction region. The effective medium theory model matched well for all volume fractions and a small amount secondary phase existence. Moreover, precision can be improved by the porosity corrected relative permittivity of composites.

Low Temperature Sintering and Characterization of MgO-B2O3-SiO2 Glass-Ceramics for LTCC Substrate Applications

ABSTRACTMgO-B2O3-SiO2 (MBS) glass-ceramics, with and without TiO2 as additive, has been prepared by sintering at 900oC and their structural, thermal and dielectric properties have been studied. The XRD and SEM studies show that the crystallization increases with addition of nucleating agent TiO2. The per cent thermal expansion decreases as TiO2 content increases. The value of dielectric constant increases with increasing wt% of TiO2 in MHz and GHz frequency range. The dielectric constant values lie in between 3 and 5 in the frequency range of 13.5–18 GHz and in between 9 and 11 at 1 MHz frequency. The microwave dielectric constants of the specimen have been found to be strongly dependent on TiO2 content. Due to low dielectric constant and low sintering temperature, this glass-ceramics is an attractive material for low temperature co-fired ceramics (LTCC) application.

The microstructure, dielectric abnormalities, polar order and microwave dielectric properties of Ag(Nb1−xTax)O3 (x = 0–0.8) ceramics

Ag(Nb1−xTax)O3 (x=0–0.8) ceramics were prepared using a solid-state reaction method, and a single-phase perovskite was identified using XRD for dense ceramics with x=0–0.65. However, small Ag precipitates and microstructural inhomogeneities were observed using BSE-SEM and EDS. There are four kinds of dielectric abnormalities at RF frequencies, including a new abnormality that has a strong relaxation in the dielectric loss. A ferrielectric-like dielectric tunability was observed at 20–80°C for x=0 and 0.2, while the ceramic with x=0.5 exhibited an antiferroelectric-like dielectric tunability. Furthermore, a transition behaviour was observed for x=0.35, indicating that the ferrielectric–antiferroelectric transition does not correspond to the M1–M2 phase transition. The microwave dielectric constant of Ag(Nb1−xTax)O3 ceramics reaches its maximum value at x=0.35, while the Qf value and the temperature coefficient of resonant frequency increase monotonously with the value of x.

Two Element Magneto-Dielectric Resonator Antenna for Angle Diversity

Abstract In the present work two element magneto-dielectric resonator antenna configuration, designed using two different magneto-dielectric (MD) materials, separated by a distance of quarter wavelength (λ/4) and half wavelength (λ/2) has proposed. These materials have been designed such that their temperature coefficient value approaches to zero. The microwave dielectric constant (εr) and permeability (μr) of both materials are calculated by Nicholson-Ross-Weir conversion technique and found to be 8.02, 1.64 and 10.47, 1.52, respectively. For the inter element separation of λ/4 and λ/2, the first resonant frequencies of proposed antenna are 5.75 GHz and 5.78 GHz and showing penta-directional and tri-directional radiation patterns characteristics respectively. This property can be utilized for the diversity scheme to mitigate the problem of fading.

Synthesis and microwave dielectric behavior of (Bi1−xPbx)NbO4ceramics

Ceramic samples of (Bi[Formula: see text]Pbx)NbO4([Formula: see text], 0.025, 0.05, 0.10, 0.15, 0.20) with 0.75[Formula: see text]wt.% V2O5addition sintered at 920[Formula: see text]C, 940[Formula: see text]C and 960[Formula: see text]C are investigated. Pb is selected as a substitute for Bi[Formula: see text] in BiNbO4ceramics as it exists in two stable valence states of [Formula: see text]2 and [Formula: see text]4 and the average valency matches to that of Bi[Formula: see text]. The average Shannon radius (for octahedral coordination) of Pb[Formula: see text] (1.19[Formula: see text]Å) and Pb[Formula: see text](0.775[Formula: see text]Å) cations is 0.9825[Formula: see text]Å, which is similar to that of Bi[Formula: see text] ion (1.03[Formula: see text]Å). The dense ([Formula: see text]%) polycrystalline (Bi[Formula: see text]Pbx)NbO4samples fabricated mostly reveal orthorhombic (Pnna) phase ([Formula: see text]-BiNbO4, Sp. Gp. 52) by powder XRD. Presence of satellite Pb2Nb2O7phase, the amount of which is increasing with increase in Pb content, is also noticed. The microwave dielectric constant ([Formula: see text]) values of the niobates are found to increase from 42 to 71, whereas the quality factor (Qu.f) values are found to decrease from 5400 to 550 GHz with increasing substitution of Pb. The compositions so synthesized are important as hardly there are any microwave dielectric ceramics available with [Formula: see text].

A CPW-fed quad-directional stacked magneto-dielectric resonator antenna for angle diversity application

This article presents quad-directional magneto-dielectric (MD) resonator antenna configuration, designed using two different MD materials with stack configuration. These materials have been designed such that their temperature coefficient is approximately zero. The microwave dielectric constant (εr) and permeability (μr) of both materials are calculated by Nicholson–Ross–Weir conversion technique and found to be 8.02, 1.64 and 10.47, 1.52, respectively. The designed antenna can radiates in four directions simultaneously at the resonant frequency of 5.84 GHz. The beam shaping has been achieved using single feed and this property can be utilized for the angle diversity. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:62–64, 2016

Low-temperature1/fnoise in microwave dielectric constant of amorphous dielectrics in Josephson qubits

The accurate analytical solution for the low temperature $1/f$ noise in a microwave dielectric constant of amorphous films containing tunneling two-level systems (TLSs) is derived within the standard tunneling model including the weak dipolar or elastic TLS-TLS interactions. The results are consistent with the recent experimental investigations of $1/f$ noise in Josephson junction qubits including the power law increase of the noise amplitude with decreasing temperature at low temperatures $T<0.1$K. The long time correlations needed for $1/f$ noise are provided by the logarithmic broadening of TLS absorption resonances with time due to their interaction with neighboring TLSs. The noise behavior at higher temperatures $T>0.1$K and its possible sensitivity to quasi-particle excitations are discussed.