Microwave Dielectric Measurements Research Articles

Highly Selective Nano‐Interface Engineering in Multishelled Nanocubes for Enhanced Broadband Electromagnetic Attenuation

AbstractWithin the nanoscale, methodically reconfiguring interface charges, and leveraging this newly structured interface to modify the energy‐momentum dynamics of heterojunction energy bands, hold profound implications for microwave electronics because of the intensified interaction between external microwaves and interfaces of materials. Mastering the orderly reconstruction of interface charges, contingent upon precise control over composition, orientation, and electronic structure remains a challenge at this scale. Herein, an in situ hierarchical assembly approach is used to successively deposit layers of Cu2S, C, and MoS2 on a hollow cubic framework with a thickness of 20 nm. Additionally, by harnessing the quasi‐graphitic characteristics and elevated work function of graphitized carbon in the middle layer, its inherent charge is steered toward both the outer and inner layers, establishing a structured configuration for the crafted Cu2S@C and C@MoS2 interfaces. Employing advanced off‐axis electron holography, microwave dielectric measurements, and first‐principle calculations, the dynamic reconstruction of interface charges and the resulting microwave response is ascertained. The synergistic effect revealed that the Cu2S@C@MoS2 materials exhibited exceptional microwave absorption, with an effective absorption band covering 7.03 GHz at 2.0 mm thickness. Furthermore, the orderly reconstruction of nano‐interfaces paves the way for research into novel electromagnetic protection materials and their unique electronic behaviors.

Microwave permittivity and permeability measurements on lunar simulants at low temperatures

Lunar simulants are used to approximate the behavior of the lunar regolith. This work focuses on materials responses relevant for microwave heating to inform in-situ resource utilization of lunar regolith for landing pads and building infrastructure. Microwave dielectric permittivity and magnetic permeability measurements have been made for the first time on several new highland lunar simulants (NU-LHT-4M, NUW-LHT-5M and CSM-LHT-1G). One mare lunar simulant (JSC-1A) is included in this work. We present these measurements in the low temperature range −185 °C to 250 °C and in the frequency range 50 MHz to 3 GHz. The dominant minerals in the simulants are the minerals bytownite, ortho- and clino-pyroxenes, olivine, and glass. Less complex rock feedstocks for highland simulants, anorthosite and pyroxenite, were also measured separately. The dielectric measurements were performed on samples having different densities. Differences in the dielectric responses were noted, however all simulants were weak microwave absorbers at the low temperatures. This data assists with planning for a hybrid approach to microwave sintering at the lunar south pole.

Liquid crystal microwave dielectric constant measurement sensor based on spoof localized surface plasmon

Liquid crystal microwave dielectric constant measurement sensor based on spoof localized surface plasmon

Structure and Microwave Dielectric Properties of Gillespite-Type ACuSi4O10 (A = Ca, Sr, Ba) Ceramics and Quantitative Prediction of the Q × f Value via Machine Learning.

Structure and dielectric properties of gillespite-type ceramics ACuSi4O10 (A = Ca, Sr, Ba) were investigated by crystal structure refinement, far-infrared reflectivity spectroscopy, and microwave dielectric measurements. A series of (CaxSr1-x)CuSi4O10 (0 < x < 1) ceramics with relative permittivities of 5.70-5.82, Q × f values of 20391-48794 GHz (@ ∼ 13.5 GHz), and τf of -46.3 to -38.9 ppm/°C were synthesized. By Ca2+ substitution for Sr2+ at the A-site, the rigid double-layered copper silicate framework remains stable, resulting in the nearly unchanged relative permittivity, while the [(Ca,Sr)O8] dodecahedron undergoes shrinkage and distortion, which is correlated to the changes in the Q × f and τf values. The normalized bond valence sums indicate that almost all ions are rattling, weakening the bond strengths and enlarging the molecular dielectric polarizability. The fitting of far-infrared reflectivity spectra reveals that the local structure changes suppress the intermediate and low-frequency vibrational modes significantly and improves the contribution from electronic polarization to permittivity. Symmetry breaking of the [(Ca,Sr)O8] dodecahedron conforms to the elevated restoring forces acting on the ions and improves the τf value. The large span in Q × f value may have intricate correlations to local structure changes and defects. Machine learning methods were introduced to explore the decisive structural factors for the Q × f value. A Q × f value prediction model correlated with the A-O2 bond length and the variance of A-O bond lengths was established. The Q × f values of isostructural (BaySr1-y)CuSi4O10 ceramics were predicted and verified by experiments.

High-performance ZnTiNb2O8 microwave dielectric ceramics produced from ZnNb2O6–TiO2 nano powders

Abstract Ixiolite-structured ZnTiNb2O8 (ZTN) ceramics were prepared by the simple but effective route of reaction sintering ZnNb2O6 and TiO2 nano powders. The effect of sintering temperature and soaking time on the densification behavior, microstructure evolution and microwave dielectric properties of the synthesized ZTN ceramics were systematically studied. Nano ZnNb2O6 and TiO2 raw materials were mixed, pressed and sintered directly into ceramic bodies without any calcination step involved. The sintered samples were characterized by Field-Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), and microwave dielectric measurements. Single-phase ZnTiNb2O8 ceramics with relative densities up to 97% theoretical density were achieved by sintering at 975–1075 °C. The ixiolite ZTN ceramics reaction sintered at 1050 °C for 3 h exhibited excellent microwave dielectric properties with a dielectric constant ( e r ) = 35.5, quality factor (Q × f0) = 52,500 GHz and a temperature coefficient of resonant frequency ( τ f ) = −60 ppm/°C. These results demonstrate that high-performance ZTN microwave dielectric ceramics can be successfully produced by the simple and efficient reaction-sintering method.

The Contribution of Storage Medium and Membranes in the Microwave Dielectric Response of Packed Red Blood Cells Suspension

During cold storage, packed red blood cells (PRBCs) undergo slow detrimental changes that are collectively termed storage lesion. The aging of the cells causes alterations in the composition of the storage-medium in the PRBC unit. In this paper, we present the comparison of the dielectric response of water in the primary (fresh) storage medium (citrate phosphate dextrose adenine solution, CPDA-1) versus the storage medium from three expired units of PRBCs. Dielectric response of the water molecules has been characterized by dielectric spectroscopy technique in the microwave frequency band (0.5–40 GHz). The dominant phenomenon is the significant increase of the dielectric strength and decrease the relaxation time τ for the samples of the stored medium in comparison with the fresh medium CPDA-1. Furthermore, we demonstrated that removing the ghosts from PRBC hemolysate did not cause the alteration of the dielectric spectrum of water. Thus, the contribution associated with water located near the cell membrane can be neglected in microwave dielectric measurements.

Moisture content investigation in the soil samples using microwave dielectric constant measurement method

The microwaves of typical frequency ranges of 3 GHz to 30 GHz have been in use for remote sensing applications which are progressing rapidly. The microwaves can sense existing moisture in any material that absorbs moisture such as soil or vegetation. In case of soils which may be comprised of variable mix proportionate of solids, liquids or gases and distinct textures subjected to the associated size and the arrangements of soil particles. Hence, the moisture absorption by a specific type of soil used to be different. The inherent physical and electrical properties such as color, texture, grains, dielectric constant, conductivity or permeability, etc. differentiate various soils. In this work, authors present soil moisture measurement by simple estimation of emissivity i.e. the ratio of energy radiated by an object to absorbing the body of same physical temperature. A strategic method of measuring dielectric constant using a microwave signal is used in this research work. The measurement of the dielectric constant of the soils collected from the specific regions and analysis of results has been reported. The proposed method is less complex and can further be used for the identification of soil moisture and agricultural applications.

A new method for identifying TE&lt;sub&gt;01δ&lt;/sub&gt; mode during microwave dielectric measurements of low-loss materials

The metal resonant cavity method working with TE&lt;sub&gt;01δ&lt;/sub&gt; mode is a universal method for evaluating the microwave dielectric properties of low-loss materials. All the microwave dielectric resonators are multi-mode resonators, so the correct identification of TE&lt;sub&gt;01δ&lt;/sub&gt; mode is the basis for the microwave dielectric measurements. The TE&lt;sub&gt;01δ&lt;/sub&gt; mode can be identified by predicting the resonant frequency and its variation with resonator size, expelling the spurious modes according to the exciting conditions, etc., while these methods are relatively complex and sometimes unreliable. In the present work, a simple method for accurately identifying the TE&lt;sub&gt;01δ&lt;/sub&gt; mode is developed. A low-loss reference sample with known dielectric properties is introduced and placed in the cavity for the first step, and the to-be-measured sample is placed on the reference sample for the second step. The rough permittivity of the to-be-measured sample can be calculated from the TE&lt;sub&gt;01δ&lt;/sub&gt;-mode resonant frequencies in the two steps through the finite element analysis, and is used to predict the resonant frequency for TE&lt;sub&gt;01δ&lt;/sub&gt; mode when only the to-be-measured sample is placed in the cavity. The difference between the predicted and measured TE&lt;sub&gt;01δ&lt;/sub&gt;-mode resonant frequencies for the to-be-measured sample is less than 1%, so that the TE&lt;sub&gt;01δ&lt;/sub&gt; mode can be easily distinguished from the spurious modes and accurately identified.

Frequency spectrum analysis of lightweight foamed concrete using microwave dielectric measurement technique

AbstractThe dielectric characterization of concrete is a significant parameter to study the microwave signal transmission for the building materials. In this paper, a microwave measurement system has been developed using open ended coaxial sensor and vector network analyzer for frequency spectrum analysis of lightweight foamed concrete. The measurement setup is validated prior to make sure the system is working properly. The results of dielectric constant and loss factor of different densities lightweight concrete samples are measured and analyzed from 150 kHz to 8 GHz. From the analysis, the lightweight foamed concrete is a frequency spectrum friendly building material. In addition, the relationship between the dielectric constant and density of the lightweight foamed concrete is found to be interrelated. The empirical modeling of some selected frequencies has been formed. The models are useful for the future application on determining the dielectric constant and characteristic of lightweight concrete samples.

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.

Microwave Permittivity of Trace sp2 Carbon Impurities in Sub-Micron Diamond Powders.

Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.

Characterization of Co0.5(Ti1−xZrx)0.5NbO4 microwave dielectric ceramics based on structural refinement

Abstract Zr-substituted Co 0.5 Ti 0.5 NbO 4 microwave dielectric ceramics with low losses were prepared by the conventional solid-state method. To obtain dense ceramics, sintering temperatures from 1000 °C to 1280 °C were systematically investigated. The microstructure and the microwave dielectric properties of the Zr-substituted Co 0.5 Ti 0.5 NbO 4 ceramics were analyzed using different characterization techniques, including field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, Rietveld refinement and microwave dielectric measurements. Analyses showed that the dielectric properties are strongly dependent on the crystal structure, which causes densification of the microstructure of the ceramics. The structure of Zr-substituted Co 0.5 Ti 0.5 NbO 4 ceramics transformed from tetragonal to monoclinic as substitution increased. Additionally, the permittivity( ɛ r ) declined from 64.3 to 24.4 due to a change in the polarizability. However, the quality factor( Q × f ) increased considerably. The temperature coefficient of the resonant frequency( τ f ) was near zero due tothe compounding of tetragonal structure with a positive τ f and monoclinic structure with a negative τ f . Optimal microwave dielectric properties in Zr-substituted Co 0.5 Ti 0.5 NbO 4 included a ɛ r of 27.6, a Q × f of 40,132.8 GHz and a τ f of 5.8 ppm/℃.

Preparation and Characterization of Silicate-1@Kaolin Clay Ceramic with Different Na+ Concentration

In order to explore the synthesis of silicate-1 membrane on kaolin clay ceramic and the effect of Na+ ion substitution on the dielectric properties of ceramic, silicate-1@kaolin clay ceramics containing different content of Na+ were successfully synthesized by combining sintering, sol-gel, and ion exchange method. Samples were analyzed by chemical composition (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), digital hardness tester, and microwave dielectric measurement system. SEM images exhibited that a layer of silicate-1 was successfully grown on the surface of the kaolin clay ceramic. The energy dispersive spectrometer (EDS) revealed that the content of Na+ in silicate-1 decreased with increase of ion exchange time. The content of Na+ in silicate-1@kaolin clay ceramic decreased from 1.46 to 0.29% when the silicate-1@kaolin clay ceramic was treated by the unsaturated solution of NH3 from zero to two times. In this process, the dielectric constant of the silicate-1@kaolin clay ceramic almost kept the same. But the dielectric loss of silicate-1@kaolin clay ceramic decreased from 0.474 to 0.131. Silicate-1@kaolin clay ceramic is expected to be used as sensor to detect some metal ions.

Polarization behavior of sol‐gel‐derived relaxor Ba(Zr, Ti)O3 films

AbstractFilms of the relaxor ferroelectric BaZr0.25Ti0.75O3 (0.25‐BZT) were synthesized via a sol‐gel route to investigate the effect of film thickness on the dielectric properties and for comparison with normal ferroelectric BaTiO3 (BT). The as‐prepared films on Nb‐doped SrTiO3 (Nb–ST) displayed a (100) orientation; thinner films had stronger (100) orientations. Microwave dielectric measurements up to a few GHz quantified the polarizations, that is, the dipole contribution, εdipole, the combination of the ionic and electronic polarizations, εionic+el., and the total contribution, εtotal. The εdipole in the relaxors at a film thickness of t=630 nm was 360, which was double that for the normal ferroelectric BT (εdipole=180) at t=735 nm. The larger apparent permittivity of the BZT therefore originated from the larger εdipole of the polar nanoregions (PNRs), while the nanograins of BT with few domain walls led to a comparably smaller εdipole. The volume ratio of the surface and film‐substrate interface lacking the dipole interactions increased with the reduction in the film thickness, leading to the significant depression in the permittivity for both specimens. The difference in the thickness dependence of the dielectric properties of the sol‐gel derived relaxor BZT and the normal ferroelectric BT films was attributed to the different origins of their dipole contribution, that is, the PNRs and ferroelectric domains, respectively.

Dynamic measurement of dielectric properties of food snack pellets during microwave expansion

The in situ dielectric properties of a starch-based food pellet have been measured during microwave expansion. A dual-mode cylindrical cavity allowed simultaneous microwave heating and dielectric measurements of a single pellet inside a quartz tube, ensuring uniform heating during microwave processing. The cavity included additional measurement devices to correlate the dielectric properties with the main parameters of the expansion process, such as temperature, expansion time, pellet volume and absorbed power.A commercially available snack food pellet was used as the test material for expansion experiments. Results indicated that dielectric constant (ε′) and loss factor (ε″) increased during heating, reaching a threshold value of ε’ = 12.5 and ε″ = 5.2, around a temperature of 115 °C when the material expanded and the dielectric properties dropped abruptly due to the loss of water content and the increase in size.This measurement procedure may provide useful material science information to improve the overall design of starch-based food pellets processed by microwaves.

A new method for the precise multiband microwave dielectric measurement using stepped impedance stub

This article presents a new method of wideband dielectric measurement at microwave frequencies. This method can be used to determine the complex dielectric properties of solid and semisolid materials from 0.9 GHz to 4.5 GHz, including the ISM bands of 915 MHz and 2450 MHz. The new method is based on the scattering parameter measurement of a stepped impedance open circuited micro-strip stub, partly loaded with dielectric test material. Current microwave wideband spectroscopy techniques generally measure dielectric materials over a wide range of frequencies but their accuracy is limited. In contrast, narrowband techniques generally measure dielectric properties to a high accuracy but only at a single frequency. This new technique is capable of measuring dielectric properties over a wide range of frequencies to a high accuracy. The technique has been verified by the empirical characterisation of the dielectric properties of Teflon and Duroid 5880 materials. Empirical results were in good agreement with values in the manufacturer’s Data Sheets. The complex permittivity data will be useful for further microwave processing of the materials.

Preparation and dielectric properties of SiO2/silicate-1 ceramics

For exploring the using of silicate-1 zeolite in dielectric ceramic, SiO2@silicate-1 ceramics were fabricated by combining oxidation-bonding, sol–gel directional infiltration and sintering methods. The resulting samples were analyzed by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, digital hardness tester and microwave dielectric measurement system. It can be found that silicate-1 particles are well bond by silica sol. And the pores of perform are partially filled with silica. The sintering temperature has great effect on microstructure and properties of SiO2@silicate-1 ceramics. When the ceramic is sintered at 400 and 600 °C, it keeps the MFI-type structure and almost has the same low-dielectric-constant (5.71 and 5.62, respectively). When the ceramic is sintered at 800 and 1000 °C, its MFI-type structure is broken down and its dielectric constant is 7.38 and 6.75, respectively.

Elbow- and hinge-bending motions of IgG: Dielectric response and dynamic feature.

Immunoglobulin G (IgG) is a Y-shaped globular protein consisting of two Fab segments connecting to an Fc segment with a flexible hinge region, in which the Fab segments show secondary flexibility at an "elbow" region. In the present work, the hinge-bending and elbow-bending motions of aqueous solutions of IgG by microwave dielectric measurements below the freezing point of bulk water was observed. The presence of unfreezable water around the macromolecules reduced the effects of steric hindrance normally generated by ice and enabled the intramolecular motions of IgG. At the same time, the overall IgG molecule rotation was restricted by ice. Papain digestion and reduction of the disulfide linkage at the hinge region was used to generate Fab and Fc fragments. In solutions of these fragments, the dielectric relaxation process of the hinge-bending motion was absent, although the elbow-bending motion remained. Three relaxation processes were observed for papain-digested IgG. The high, middle, and low frequency processes were attributed to unfrozen water, local peptide motions cooperating with bound water, and the elbow-bending motion, respectively. In the case of the intact IgG, an additional relaxation process due to the hinge-bending motion was observed at frequencies lower than that of the elbow-bending motion. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 626-632, 2016.

Microwave dielectric properties measurements of sodium and potassium water glasses

Dielectric properties of alkali silicates ((Na,K)2(SiO2)nO) or ‘water glasses’ are a critical input into the electromagnetic modeling of these materials, which have a broad range of applications. Recent increased interest in understanding geopolymerization of aluminosilicates with water glasses and the potential to improve understanding of the role of moisture in damage due to alkali–silica reaction (ASR) in concrete (where water glass is a suitable analogue for ASR gel) motivates this research. This investigation presents the results of microwave dielectric property measurement of twelve laboratory-produced (synthetic) water glass samples at X-band (8.2–12.4GHz). Results show an exponential decay of loss factor as a function of increasing silica-to-alkali ratio, suggesting a correlation with increase in bound water in the samples and a decrease in the fluid ionic concentration. The results provide an insight into the temporal changes of the dielectric properties of ASR-affected materials, as well as geopolymers.

Sintering behavior and microwave dielectric characteristics of ZnTiNb2O8 ceramics achieved by reaction sintering of ZnO–TiO2–Nb2O5 nanosized powders

Sintering behavior, microstructure and microwave dielectric properties of ZnTiNb2O8 (ZTN) ceramics prepared by reaction-sintering method were investigated. The prepared ceramic samples were characterized by field emission scanning electron microscopy, X-ray diffraction, and microwave dielectric measurements. All samples prepared at sintering temperatures ranging from 1025 to 1125°C exhibit a single ixiolite phase and their relative densities range from ~86.5 % to ~99 %. The variation trend of permittivity and Q×f value was in accordance with variation trend of relative density. Pure ixiolite ZTN ceramic sintered at 1075°C for 5h exhibits good microwave dielectric properties with a permittivity about 36.7, Q×f value about 54,000GHz, and temperature coefficient of resonant frequency about −70.4ppm/°C. The obtained results demonstrated that the reaction-sintering process is a simple and effective method to prepare the ZnTiNb2O8 ceramics for passive microwave dielectric devises.