Microwave Dielectric Behavior Research Articles

Investigating a Cylindrical Dielectric Resonator Antenna Fabricated with Li3MgNbO5 Microwave Dielectric Ceramic

This work aims to fabricate a single-feed line Cylindrical Dielectric Resonator Antenna (CDRA) using low-temperature sintered Li3MgNbO5 microwave dielectric ceramic as a resonator, excited in HEM11δ mode. The ceramic synthesized using the conventional solid-state route resulted in a single-phase material exhibiting a cubic structure with an Fm-3m space group. The densely packed cylindrical disk of the ceramic was subsequently characterized for its microwave dielectric behaviour in TE01δ mode using the Hakki-Coleman method. The dielectric permittivity (ε r) measures 14.4, with a loss factor (tan δ) nearly equal to 4.01 × 10−4 and a temperature coefficient (τf) of −50.9 ppm °C−1. The antenna design was executed using the high-frequency structure simulator design software, utilizing the dielectric ceramic as the resonator, Cu strip as the feedline, and FR4 as the substrate. The maximum energy was coupled to the antenna when the resonator was placed at 11.75 mm on the substrate. The fabricated CDRA, using appropriate simulated parameters, resonated at 7.67 GHz, offering a return loss (S11) of −32.64 dB and an impedance bandwidth of 10.73%. Furthermore, the CDRA displayed a voltage standing wave ratio of 1.04, ensuring a nearby ideal impedance match and a bandwidth of 810 MHz to support high-speed data transmission.

Enhancement of temperature stability for magnesium niobite system by direct doping with titanium dioxide

Heterovalent ion doping has been playing a remarkably significant role in the microwave dielectric performances of columbite A2+Nb2O6 (A2+ = Zn, Ca, or transition metal). Here, the Q×f value of MgNb2O6 ceramics can be effectively enhanced from 32,893 GHz to 117,659 GHz by doping with 1 mol% (TiW)5+. Based on the high Q value of Mg(Nb0.98Ti0.01W0.01)2O6, TiO2 was selected to further adjust the τf value of the matrix material prepared by the conventional solid-state reaction method. The results show that the Mg(Nb0.98Ti0.01W0.01)2O6 ceramics undergo three phase zones with increasing TiO2 content: columbite (MgNb2O6) solid solution, a mixture of columbite and rutile (Ti0.5Mg0.167Nb0.333O2), and Ti0.5Mg0.167Nb0.333O2 solid solution. This variation in phase formation has an essential effect on the microwave dielectric behavior of Mg(Nb0.98Ti0.01W0.01)2O6@xTiO2 (0.03 ≤ x ≤ 0.25) ceramics. It is important to note that at x = 0.17, the specimen has excellent microwave dielectric performances, with εr = 34.79, Q×f = 24,103 GHz, and the τf of the specimen may be adjust to zero. It is anticipated that these materials will be utilised in contemporary microwave and telecommunication equipment.

An Overview of Microwave Dielectric Behaviour of Vegetable Based Soil: A Review

In this paper review of literature of dielectric behaviour of soil in Chhattisgarh, India,has been described from 2015 to 2021. In this literature the various parameters of dielectric behaviour of soil i.e. physical properties, chemical properties and geographical properties have been illustrated briefly. This paper helps those who are researching in the field of dielectric behaviour of soil.

Enhancement of microwave dielectric behavior by substitution of W6+ for Mo6+ in Li2Mg1.91Na0.18Mo3O12 ceramics

Microwave dielectric ceramics with low dielectric constants are widely used in the design and fabrication of microwave devices. Here, low-temperature sintered Li2Mg1.91Na0.18Mo3-x W x O12 (LMNMWO) (x takes values from 0 to 0.15) ceramics are prepared by the solid-phase reaction technology. XRD and BSE patterns indicated that W6+ is solidly dissolved into the lattice and exhibits an overall single phase. The dielectric properties of the ceramics are effectively enhanced by the substitution of Mo6+ for W6+. The trends of density and SEM microscopic morphology show that the trace W6+ substitution can effectively promote grain growth and enhance grain homogeneity. The results indicate that the Q×f values are related to the relative density and grain homogeneity. The EDS spectrum demonstrates that the ratio of elements is close to the chemical formula of Li2Mg1.91Na0.18Mo2.95W0.05O12. The trend of τf values is related to the lattice distortion generated when W6+ is irregularly solidified into the lattice. Specifically, dielectric properties of the substituted LMNMWO (x = 0.05) ceramics are determined as follows: εr = 8.3, Q×f = 48357 GHz, and τf = -59 ppm/°C.

An Overview of Microwave Dielectric Behaviour of Vegetable based Soil

In this paper an attempt has been made to study overview of microwave dielectric behaviour of vegetable-based soil of Chhattisgarh. Soils are complex mixture of minerals, air, organic matter, and countless organisms. The properties of soil such as physical properties, chemical properties, geographical properties are really important in production of vegetables. Moisture content is very important parameters for the production of vegetable. Dielectric constant depends upon the percentage of moisture content in the soil. Humid climates sufficient for growing of vegetables crops. Optimum vegetables can produce in well-drained sandy loam soil.

Microwave absorption and dielectric behavior of lead sulfide – graphene composite nanostructure embedded polyvinylidinedilfuoride thin films

A lightweight and flexible microwave absorbing composite of polyvinyledine difluoride (PVDF) was fabricated by loading PbS nanocubes embedded Graphene hybrid nanostructures into the PVDF matrix. The PbS embedded graphene nanosheets (PbS/GNs) are synthesized by hydrothermal technique. The PXRD pattern of the PbS, GNS and PbS/GNS suggested face-centered cubic structured PbS loaded GNS nanosheets. FE-SEM images of the graphene-bound lead sulfide octahedral nanocubes are found to have a size of 100 nm and are unvaryingly distributed on the surface of graphene nanosheets. HRTEM image of graphene surface image showing sheet-like structure is embedded with PbS nanocrystals. The PbS/GNs in PVDF matrix were found to exhibit enhanced dielectric constant, reduction in resistivity, and electrical conductivity. The high dielectric constant was exhibited by the 4% GNs dispersed PVDF with a value of 3.7x105 and 6% GNs/PbS dispersed PVDF showed 3.5 x105 at 1 MHz. The composite PbS/GNs into PVDF exhibit the maximum reflection loss dips in frequency band X for the PbS/Gra/PVDF samples. It is apparent that there are three absorption peaks in the region of 9–12 GHz in which the absorption of −6.9 dB is observed at 10 GHz.

Investigation on the effect of in-situ growth of PPy on structural, thermal and dielectric properties of PVA-CMC blend films

ABSTRACT The intrinsic conducting polymer (ICP) Polypyrrole (PPy) was grown in situ in the matrix of polyvinyl alcohol (PVA)-Sodium carboxymethyl cellulose (CMC) using chemical oxidative polymerization method. The effect of in-situ growth of PPy on structural, morphological, thermal and dielectric properties of PVA-CMC blend films were investigated. Growth of PPy in the matrix of PVA-CMC was seen in SEM micrographs along with structural modifications which were confirmed by XRD and FT-IR analysis suggesting the amorphous nature of PVA-CMC-PPy blend films. Thermal analysis suggests good miscibility and compatibility of the polymers in the blend. The changes in the dielectric properties of in-situ-grown conducting polymer blend films of PVA-CMC-PPy were studied in detail at low frequency (100 Hz to 2 MHz) . Enhancement in the dielectric constant and ac conductivity values of PVA-CMC- PPy films were observed in this frequency range that is related to increased amorphousness and formation of conductive channels due to the presence of PPy. Further, the microwave absorption and dielectric behavior of PVA-CMC-PPy films in high-frequency region (200 MHz – 20 GHz) were specially studied to see the suitability of these films for EMI shielding application.

Anomalous microwave dielectric behaviour induced by the orthorhombic-tetragonal phase transition in CaLaGaO4 ceramics

In this work, orthorhombic (o-) and tetragonal (t-) phase CaLaGaO4 ceramics were synthesized using a conventional solid-state method. Phase evolution and crystal structure were investigated via XRD and TEM, and o-CaLaGaO4 phase with Pna21 space group can be obtained at a low temperature (<1260 °C). With the increase in sintering temperature, o-CaLaGaO4 and t-CaLaGaO4 phases (I4/mmm) coexisted when sintered in the range of 1280 °C – 1300 °C. The microwave dielectric properties of the o-CaLaGaO4 ceramic sintered at 1240 °C were εr = 11.2, Q × f = 63,900 GHz, and τf = −56.6 ppm/℃. By contrast, the phase transformation in the CaLaGaO4 ceramic led to a significantly increased εr (19.5) in t-CaLaGaO4 and a near-zero τf (+2.3 ppm/℃). The theoretical permittivity (εth) was calculated on the basis of the Clausius–Mossotti equation and P-V-L theory. Results indicate that in the low-symmetry-structure o-CaLaGaO4 ceramics, εth can be estimated accurately by the latter.

Relationship between Rattling Mg2+ ions and anomalous microwave dielectric behavior in Ca3-xMg1+xLiV3O12 ceramics with garnet structure

Ca3-xMg1+xLiV3O12 (0 ≤ x ≤ 1) ceramics with cubic-garnet-structure were synthesized by the solid-phase reaction. The replacement of Ca2+ with the smaller Mg2+ exerted an increasingly strong “rattling” effect at the A-site of Ca3-xMg1+xLiV3O12. With increased Mg2+, εr increased from 10.5 ± 0.1 to 15.4 ± 0.1 and εcorr increased from 11.0 ± 0.1 to 16.0 ± 0.1, whereas the theoretical εth decreased from 12.0 ± 0.1 to 10.5 ± 0.1. εcorr was higher than εth due to the “rattling” effect. The enhanced “rattling” effect caused τf to increase rapidly from –64.1 ± 1.0 ppm/°C to +267.2 ± 1.0 ppm/°C. With increased x, Q × f decreased from 74,700 ± 500 GHz to 15,370 ± 500 GHz, due to the decreased packing fraction, increased FWHM of the A1g modes, and enhanced “rattling” effect. Additionally, the chemical compatibility between Ca2.75Mg1.25LiV3O12 and Ag electrodes was confirmed, indicating this material’s potential for LTCC.

1D-3D mixed-dimensional MnO2@nanoporous carbon composites derived from Mn-metal organic framework with full-band ultra-strong microwave absorption response

Nano-porous carbon (NPC) composites derived from metal-organic frameworks (MOFs) possess effective microwave absorption (MA) properties. However, the fabrication of MOF-derived NPC composites with full-band MA performance is challenging. In this work, the effect of the bandgap on the microwave dielectric behavior of Mn-MOF derivatives was investigated. The results demonstrated that a narrower MnO2 bandgap resulted in higher conductivity and a larger dielectric constant of the corresponding materials. The three-dimensional (3D) [email protected] composites achieved excellent low-frequency MA ability. The maximum reflection loss (RL) of [email protected] carbonized at 800 °C reached −54.38 dB at 5.12 GHz. The 1D-3D mixed-dimensional MnO2@NPC composites with the ultra-strong MA response in the full band were obtained by oxidizing [email protected] to MnO2@NPC. MnO2@NPC-800 showed superior MA capacity with the maximum RL value equal to −63.21 dB at 12.48 GHz and 2.05 mm thickness. The maximum RL values in S, C, X, Ku bands also exceeded −50 dB. Such an outstanding MA performance of MnO2@NPC-800 composite was attributed to the MnO2 presence and its multi-dimensional structure. This work provides the foundation for the fabrication of MOF-derived materials capable of full-band MA.

Microwave dielectric spectroscopy of renal calculi: A large scale study on dielectric properties from 500 MHz to 18 GHz

Inherent dielectric property discrepancy between biological anomalies and healthy tissue enables the microwave diagnostic and therapeutic technologies. To reveal this discrepancy, microwave dielectric properties of many different biological tissues are tabulated. Although the dielectric properties of biological tissues are well documented in the literature, the knowledge on microwave dielectric property behavior of the renal calculi is limited. This work presents ultra wideband dielectric properties of three renal calculi types between 500 MHz to 18 GHz to pave the way for possible application of microwave technologies for diagnosis, treatment, and prevention of urolithiasis. Microwave dielectric spectroscopy is performed on a total of 66 natural stone samples with open-ended coaxial probe technique. The samples belong to three commonly diagnosed renal calculi categories namely calcium oxalate, cystine, struvite. Analysis of variance (ANOVA) test is performed on fitted Cole-Cole parameters and it was concluded that there is a statistically significant difference between the dielectric properties of the renal calculi types. A patient-to-patient statistical test is also performed and it was concluded that there is no statistical difference between the samples belonging to the same renal calculi category. To this end, based on the relative permittivity discrepancy between the renal calculi types, the category of renal calculi can be identified by measuring the dielectric properties of renal calculi with open-ended coaxial probe technique.

Structures and microwave dielectric behavior of Sr0.1Ca0.9TiO3–Bi0.1Na0.1Li0.4Sm0.4TiO3 ceramic system

Microwave dielectric ceramics with xSr0.1Ca0.9TiO3–(1−x)Bi0.1Na0.1Li0.4Sm0.4TiO3 (xSCT–BNLST) compositions were prepared through the conventional oxide-state reaction. X-ray diffraction results showed that the symmetry in xSCT–BNLST system were improved with the increase of x. Based on the calculation results, the deviation of observed dielectric polarizabilities from theoretical values could be ascribed to the increase of A-site ionic polarizability and B-site bond valence. The decreased temperature coefficient of resonant frequency, τf, was dependent on the B-site bond valence in the tilted region. With the increase of temperature, the samples changed their main conductive carrier, from first ionization of oxygen vacancies to second ionization of oxygen vacancies. Optimum microwave dielectric properties were achieved, for 0.09SCT–BNLST ceramic with relative permittivity, er = 111, quality factor, Q × f = 3819 GHz and τf ~ 0 ppm/°C. The system has the potential for use in dielectrically loaded antennas and C0G high-frequency filter applications.

Review of Literature on Microwave Remote Sensing and Dielectric Behaviour of Soil in India

Review of Literature on Microwave Remote Sensing and Dielectric Behaviour of Soil in India

Microwave dielectric properties and thermally stimulated depolarization of Al‐doped Ba4(Sm,Nd)9.33Ti18O54 ceramics

AbstractBa4(Sm0.15Nd0.85)9.33Ti18‐zAl3z/4O54 (BSNT‐zAl, 0.0 ≤ z ≤ 2.5) ceramics were prepared via a solid‐state reaction, and the effects of Al doping on the microwave dielectric properties and defect behavior of the title compound were studied. X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) photographs suggested that Al ions successfully entered the lattice to form tungsten‐bronze‐like solid solutions. With a small amount of Al substitution, the relative dielectric constant (εr), and the temperature coefficient of resonant frequency (τf) values decreased, whereas the quality factor (Q × f) substantially increased by approximately 50%. The defect‐related extrinsic dielectric loss was clarified via the thermally stimulated depolarization current (TSDC) technique. With Al doping, the TSDC relaxation of across‐grain‐boundary oxygen vacancies () vanished, whereas that of defect dipoles () appeared at relatively low temperatures. Therefore, in the BSNT‐zAl ceramics, oxygen vacancies were more inclined to interconnect with to form defect dipoles. This could reduce the activity of and account for the notable improvement in the Q × f values. In particular, the excellent characteristics of εr = 67.33, Q × f = 16 530 GHz, and τf = +0.87 ppm/°C were achieved in the specimens with z = 1.5 sintered at 1350°C for 4 hours.

Structure and microwave dielectric behaviour of low-temperature-fired Li2Zn1−xCoxTi3O8 (x = 0–0.07) ceramics for low temperature co-fired ceramic applications

Low-temperature-fired Li2Zn1−xCoxTi3O8 (x = 0, 0.03, 0.04, 0.05, 0.06, 0.07) ceramics with 1.5 wt% Li2O–B2O3–SiO2–CaO–Al2O3 (LBSCA) glass as sintering aid were attained through a traditional solid-state-reaction method, and the relationship between their structures and microwave dielectric properties were thoroughly investigated. X-ray diffraction patterns revealed that the solid solutions composed of Li2ZnTi3O8 and Li2CoTi3O8 were produced. The main peaks were identified with the cubic spinel phase of the Li2(Zn,Co)Ti3O8. Co substitution successfully lowered the sintering temperature of Li2ZnTi3O8 to approximately 900 °C and accelerated its densification when LBSCA glass was used as the sintering aid. The cobalt content considerably influenced grain homogeneity, grain size and dielectric polarizability, as well as the variation in relative permittivity (er) and quality factor (Q × f). When x = 0.04, Li2Zn0.96Co0.04Ti3O8 ceramic sintered at 900 °C had the most uniform grain size and exhibited optimum microwave dielectric properties, having a relative permittivity of 21.61, Q × f of 79,100 GHz and temperature coefficient of resonance frequency (τf) of − 12.3 ppm/°C. Thus, it showed potential for low temperature co-fired ceramic applications.

Improvement in microwave dielectric properties of Sr2TiO4 ceramics through post-annealing treatment

Sr2TiO4 ceramics were synthesized via the conventional solid-state reaction process, and the effects of post-annealing treatment in air on the microwave dielectric properties and defect behavior of title compound were investigated systematically. The Q × f values could be effectively improved from 107,000 GHz to 120,300 GHz for the specimens treated at 1450 °C for 16 h. The thermally stimulated depolarization currents (TSDC) revealed two kinds of defect dipoles [ $$ \left({\mathrm{Ti}}_{\mathrm{Ti}}^{\hbox{'}}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ and $$ \left({V}_{\mathrm{Sr}}^{"}-{V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ ] and oxygen vacancies $$ \left({V}_{\mathrm{O}}^{\bullet \bullet}\right) $$ were considered the main defects in Sr2TiO4. Under a post-annealing treatment in air, the concentrations of such defects in the ceramics decreased. Meanwhile, the impedance spectrum revealed the activation energy of the grain boundaries increased. These evidences could account for the improvement of Q × f values. Accompanied with a high er of 40.4 and a large τf of 126 ppm/°C, the enhanced high-Q Sr2TiO4 ceramics can be good candidates for applications in wireless passive temperature sensing.

Microwave Dielectric Behavior of �Silk Based Soil� in India with Reference to Chhattisgarh

Microwave Dielectric Behavior of �Silk Based Soil� in India with Reference to Chhattisgarh

Highly-efficient electromagnetic interference shielding and microwave dielectric behavior of a (Bi2O3 + B2O3)-doped MWCNT/BaTiO3 ceramic nanocomposite

Microwave dielectric properties along with electromagnetic interference shielding effectiveness (EMI SE) of a multi-walled carbon nanotube (MWCNT)/barium titanate (BaTiO3) nanocomposite are investigated in this paper. Appropriate amount of sintering additive (Bi2O3 + B2O3) was doped into some nanocomposites to reduce the sintering temperatures. The dielectric properties of the nanocomposites with various MWCNT and sintering additive contents were evaluated at different microwave frequency ranges. It was found that the incorporation of optimized amount of (Bi2O3 + B2O3) can give rise to significantly good dielectric properties. Results also indicated that incorporation of 6 wt% (Bi2O3 + B2O3) into 1.5 mm-thick nanocomposite containing 8 wt% MWCNT led to an EMI SE greater than 28 dB, suggesting this novel nanocomposite as a promising candidate for microwave absorption and electromagnetic interference applications.

Peaked dielectric responses in Ti3C2 MXene nanosheets enabled composites with efficient microwave absorption

The microwave dielectric behavior of sandwich-like Ti3C2 MXene nanosheets with efficient microwave absorption was investigated by a combination of experiments and simulations. The obvious frequency dispersion effect and the double-peaked feature of dielectric spectra in Ti3C2 MXene nanosheets could be observed over the frequency range of 2–18 GHz, giving rise to superior microwave attenuation capability. Furthermore, a revised Drude-Lorentz model was proposed to explain the peaked feature of permittivity, and simulated results were demonstrated to agree well with the experimental measurements. It was concluded that the hopping migration between Ti3C2 MXene nanosheets with longer relaxation time than “micro-dipole” relaxation within nanosheets makes a superior contribution to overall absorbing performance.

Effects of lanthanides on structural and dielectric properties of NdNbO4-LnNbO4 ceramics

Recently, lanthanide niobates have attracted significant attentions in multi-functional materials. Herein a series of fergusonite structure-related (1-x)NdNbO4-xLnNbO4 (Ln = Yb, Er, Ho, Dy, Gd and Ce; 0.02 ≤ x ≤ 0.08) ceramics were prepared via conventional solid-state reaction method and the microwave dielectric properties were systematically discussed. The X-ray diffraction, Raman spectra were employed to investigate the crystal structure. Obtained results indicate that the ceramic samples present single monoclinic phase belong to the space group of I2/a. Microwave dielectric behaviors shown that the permittivity (εr) and the quality factor (Q × f) were influenced by the relative density, and the temperature coefficients of resonant frequency (τƒ) value kept the same variation tendency with the Nb-site bond valence. Furthermore, Far-IR and bond energy study evidenced the Ln-O oscillations dominated the main dielectric polarization and system stability. Good microwave dielectric properties, with εr ~ 20.88, Q × f ~ 66,510GHz (at 8.60GHz) and τf ~ − 36.59ppm/°C, were obtained in 0.94NdNbO4–0.06YbNbO4 ceramics when sintered at 1250°C for 4h. The (Nd0.94Yb0.06)NbO4 might be potential candidate for the applications of modern microwave devices.