Complex Dielectric Permittivity Measurements Research Articles

Dielectric relaxation and hydrogen bonding interaction in xylitol–water mixtures using time domain reflectometry

The measurements of complex dielectric permittivity of xylitol–water mixtures have been carried out in the frequency range of 10 MHz–30 GHz using a time domain reflectometry technique. Measurements have been done at six temperatures from 0 to 25 °C and at different weight fractions of xylitol (0 < W X ≤ 0.7) in water. There are different models to explain the dielectric relaxation behaviour of binary mixtures, such as Debye, Cole–Cole or Cole–Davidson model. We have observed that the dielectric relaxation behaviour of binary mixtures of xylitol–water can be well described by Cole–Davidson model having an asymmetric distribution of relaxation times. The dielectric parameters such as static dielectric constant and relaxation time for the mixtures have been evaluated. The molecular interaction between xylitol and water molecules is discussed using the Kirkwood correlation factor (g eff ) and thermodynamic parameter.

Dielectric dispersion and hydrogen bonding interactions study of aqueous D-mannitol using time domain reflectometry

The measurement of complex dielectric permittivity of binary mixtures of D-mannitol and water have been carried out in the frequency range of 10 MHz to 30 GHz using time domain reflectometry (TDR) technique. Measurements were done at different temperatures ranging from 5°C to 25°C for different weight fractions of D-mannitol (0 < WM ≤ 0.18) in water. The dielectric relaxation behaviour of these mixtures is explained using Cole–Davidson model. The dielectric parameters such as static dielectric constant and relaxation time for the mixtures have been evaluated. The activation energy decreases with increased D-mannitol content in the mixture. The molecular interaction between D-mannitol and water molecules is discussed using the Kirkwood correlation factor and Thermodynamic parameters.

The Impact of Blue Inorganic Pigments on the Microwave Electrical Properties of Polymer Composites

We present the results of the measurement of complex dielectric permittivity, in the microwave frequency region, on glass reinforced polybutylene terephthalate (PBT) with blue inorganic pigments. The cavity resonant method had been used in order to measure the shift in the resonant frequency of the cavity, caused by the insertion of a sample, which can be related to the real part of the complex permittivity. Also, the quality factor of the cavity decreases with the insertion of a sample. The changes in the inverse of this quality factor give the imaginary part. In order to predict the dielectric behavior of this composite, we had developed a program of numerical simulation to calculate the complex permittivity of the inclusion. By using some of dielectric mixture laws (Maxwell-Wagner-Sillars, Hanai, Looyenga, inverse and direct Wiener, and Bruggemann), we can predict the dielectric behavior of the composite in a large range of volume fraction of inclusions.

Dielectric relaxation of dihydric alcohol–1,4-dioxane mixtures using time domain technique

Complex dielectric permittivity measurements of 1,2-propanediol–1,4-dioxane mixtures has been carried out at different concentration and in the frequency range of 10 MHz to 20 GHz using time domain reflectometry (TDR). The least squares fit method has been used to obtain the static dielectric constant, relaxation time, and Bruggeman factor for binary mixtures. The Kirkwood–Frohlich theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the 1,2-propanediol–dioxane mixtures. The excess parameters confirm that the heteromolecular hydrogen bonding interactions between 1,2-propanediol and dioxane molecules vary significantly in the mixture. The Bruggeman model for the nonlinear case has been fitted to the experimental dielectric data for mixtures. Keywords: dielectric relaxation, time domain reflectometry, alcohols

Complex permittivity measurements using cavity perturbation technique with substrate integrated waveguide cavities

Cavity perturbation technique is widely used in the measurements of complex dielectric permittivity of materials due to its accuracy and ease of configuration. This paper presents the theoretical formulas for the evaluation of complex permittivity of materials using cavity perturbation technique with substrate integrated cavity resonators. With the proposed formulas, the use of various planar cavities is possible by taking into account the dielectric characteristics of the substrate in which the cavity is implemented. Simulations and measurements are performed on various dielectric samples to validate the proposed theory. The maximum deviation in the measured dielectric permittivity values is below 6% compared to the literature values. The implemented substrate integrated cavity is then analyzed in terms of sensitivity, showing a good performance.

Dielectric relaxation and hydrogen bond interaction study of diol-water mixtures

Complex dielectric permittivity measurements in the frequency range 10MHz-20GHz have been carried out in diol-water mixtures over the entire concentration range using a time domain reflectometry (TDR) method at 25°C. A hydrogen bonded theory is applied to compute the dielectric constant for the mixtures. It adequately reproduces the experimental values of static dielectric constants for the diol-water mixtures. The dielectric parameters confirm that the intermolecular homogeneous and heterogeneous hydrogen bonding vary significantly with the increase in concentration of the constituents of the diol-water mixtures.

Correction to “Complex dielectric permittivity measurements from ground‐penetrating radar data to estimate snow liquid water content in the pendular regime”

Correction to “Complex dielectric permittivity measurements from ground‐penetrating radar data to estimate snow liquid water content in the pendular regime”

Complex dielectric permittivity measurements from ground‐penetrating radar data to estimate snow liquid water content in the pendular regime

Monitoring the snow water equivalent (SWE) is critical to effective management of water resources in many parts of the world that depend on the mountain snowpack for water storage. There are currently no methods to remotely sense SWE with accuracy over large lateral distances in the steep and often forested terrain of mountain basins. Previous studies have shown that measurements of ground‐penetrating radar (GPR) velocity can provide accurate estimates of SWE in dry snow. Introduction of liquid water into the snowpack results in a three‐phase system that cannot be accurately characterized with GPR velocity alone. We show that measuring the frequency‐dependent GPR signal attenuation and velocity provides a direct estimate of the complex dielectric permittivity. Because the imaginary component is a function only of liquid water content, we can utilize both the real and imaginary components of the permittivity to estimate liquid water content, snow density, and SWE using existing empirical relationships that are valid in the pendular regime. We tested this new method at two field sites and found that the estimates were accurate to within 12% of gravimetric methods in both a moist and a dry snowpack. GPR has the potential to provide SWE estimates across large lateral distances over a broad range of snow conditions.

Microwave propagation parameters in magnetic fluids

Complex dielectric permittivity and complex magnetic permeability measurements of two magnetic fluids (as microwave propagation media), in the approximate range 0.2-5 GHz were performed. The two samples consisted of magnetite nanoparticles, dispersed in kerosene and in water, respectively. Based on the dielectric and magnetic measurements, the frequency (f ) dependence of the attenuation parameter, [Formula: see text], the phase constant, [Formula: see text], the propagation constant, [Formula: see text], the intrinsic impedance, Z(m), the refractive index, n, the reflection coefficient, R, the wavelength, [Formula: see text] and the skin depth, [Formula: see text], of the investigated samples were determined.

Peculiarities of ionic transport of oxygen vacancy conducting superionic ceramics

The powder of Zr0:92Y0:08O2 (YSZ), Ce0:9Gd0:1O2i‐ (GDC) and Sm0:15Ce0:85O2i‐ (SDC) compounds from the company Fuel Cell Materials were used for sintering of ceramic samples in air at temperature T = 1673 K. The surface of the prepared ceramics was studied by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results of the performed XPS investigations revealed that cerium exists as Ce 3+ and Ce 4+ in both the Ce0:9Gd0:1O2i‐ and Sm0:15Ce0:85O2i‐ ceramics. XPS spectra of O 1s of all the investigated materials demonstrated two peaks corresponding to oxygen O(1) in crystal lattice and to adsorbed oxygen O(2). Measurements of complex impedance, electric conductivity, dielectric permittivity, and tan ‐ of dielectric losses were carried out in frequency range 10 6 n1.2¢10 9 Hz at temperatures ranging from 300 K to 700 K. Relaxation dispersion of the electric parameters has been found for all the compounds. The dispersion is caused by the oxygen vacancy (VO †† ) transport in grains of the ceramic samples.

Enhanced Microwave Absorption in Nickel-Filled Multiwall Carbon Nanotubes in the S Band

Nickel (Ni)-filled multiwall carbon nanotubes (MWCNTs) were synthesized by template-assisted electrochemical deposition of Ni in MWCNTs. Complex dielectric permittivity and magnetic permeability measurements of Ni nanowires (Ni NWs), MWCNTs, and Ni-filled MWCNTs were carried out in the S band. Ni-filled MWCNTs exhibited enhanced real (e 1 ) and imaginary (e 2 ) permittivity when compared to both Ni NWs and MWCNTs. This increase in e 1 and e 2 is attributed to the enhanced interfacial polarization, reduced eddy currents, and the presence of defects in MWCNTs. Ni-filled MWCNTs serve as an efficient microwave absorber in the S-band frequency regime.

Millimeter-Wave Transmittance Measurements on Ferrites Near Ferromagnetic Resonance

This paper presents complex dielectric permittivity and magnetic permeability measurements of pure and diluted barium ferrites in the millimeter-wave frequency range. A broadband quasi-optical millimeter-wave spectroscopy with backward-wave oscillators as high-power tunable sources of coherent radiation has been utilized. The real and imaginary parts of the dielectric permittivity and magnetic permeability as functions of frequency are computed from the transmittance spectra. A magneto-optical approach in millimeter waves has been successfully employed for the separation of the dielectric and magnetic effects and the simultaneous determination of the magnetic and dielectric parameters of barium ferrite materials near ferromagnetic resonance.

Synthesis of Micrometer-Scale ZnO Rods and Its Electromagnetic Performance in Microwave Band

The micrometer-scale ZnO rods are synthesized from ZnO nano-powder with microwave heating technique. Its Scanning Electronic Microscope (SEM) image shows that the section of ZnO micrometer-scale rods is in hexagonal shape with smooth surface. The measurements of complex dielectric permittivity and permeability for ZnO micrometer-scale rods synthesized were taken with the Model Agilent N5230A net vector analyzer. The measurements show that these ZnO micrometer-scale rods are also microwave absorption materials.

Dielectric properties of PbNb2O6 ferroelectric ceramics at cryogenic temperatures

Complex dielectric permittivity measurements in PbNb2O6 ceramics were performed in a frequency and temperature range of 1kHz–1MHz and from 15to900K, respectively. The results revealed two dielectric anomalies showing typical characteristics of relaxor ferroelectric materials at cryogenic temperatures. Comparison with other tetragonal tungsten bronze (TTB) structure-type materials suggests the existence of successive phase transitions, which until now were not reported. The observed low temperature dielectric behaviors seem to be due to intrinsic physical characteristics related to the TTB structure.

Electrical and petrophysical modeling of Ferron Sandstone data

As part of the 3D characterization of a fluvial reservoir analog site in the Ferron Sandstone in east-central Utah, new lab measurements of porosity, permeability, water content, and complex dielectric permittivity are collected and analyzed. Petrographic analysis of thin sections extracted from the same samples produced data on bulk, macro- and microporosity, lithology, and cementation. Thus, we have an unusually comprehensive data base for analysis. Debye models of complex dielectric permittivities are fitted using three frequency-dependent Debye relaxation mechanisms. Most ambient and dry samples are dominated by low-frequency relaxation mechanisms. The average dielectric constant and electrical conductivity at the typical ground-penetrating radar (GPR) frequency of [Formula: see text] are directly related to volumetric water content and are 3.86 and [Formula: see text] for oven-dried samples, 4.50 and [Formula: see text] for ambient saturated sam-ples, and 15.42 and [Formula: see text] for fully saturated samples. Electrical conductivity is poorly estimated from the oven-dried samples (for all clay content) because ion mobility is significantly reduced; thus, the dry conductivity is less useful for estimating petrophysical variations. Multivariate regressions with the petrophysical parameters estimate the electrical properties at [Formula: see text] and [Formula: see text] with average correlation coefficients of [Formula: see text] and [Formula: see text], respectively. Empirically derived predictions of dielectric constant as a function of water content will always provide better fits to the observed values than either generic models (such as the CRIM model) or fits to other data sets (such as the Topp formula, which was derived for soils). The Topp model consistently underestimates the dielectric constant, while the CRIM model generally overestimates it, at both 75 and [Formula: see text]. The overall regression procedures can be applied to data from other sites and potentially used as the basis of inversion of petrophysical properties from measurements of electric and dielectric properties.

Dielectric anomaly at the orbital order–disorder transition inLaMnO3+δ

We report a novel dielectric anomaly around the Jahn–Teller orbital order–disorder transition temperatureTJT inLaMnO3+δ. The transition has been characterized by resistivity(ρ) versustemperature (T), calorimetry, and temperature dependent x-ray diffraction studies. Measurements of complex dielectricpermittivity ε* (= ε′−iε′′) over a low-frequency range (1 Hz–10 MHz) acrossTJT reveal a distinct anomaly. This observation, and the reported relatively high static dielectric constantat T = 0 (ε0∼18–20),possibly indicate that the orbital order gives rise to intrinsic polarization that undergoes transitionat TJT. The frequency dispersion of the dielectric response at any given temperature,however, reveals that the dielectric response consists of Maxwell–Wagnercomponent, due to interfaces, within such a low frequency range. TheTJT and the natureof the anomaly in ε′(ω,T),ε′′(ω,T) at TJT, ofcourse, vary—from a sharp upward feature to a smeared plateau and then a downward trend—dependingon the Mn4+ concentration of the sample. The observation of an intrinsic dielectric response due to long-range orbitalorder in LaMnO3—where no ferroelectric order is possible due to the absence of off-centre distortion inMnO6 octahedra—may throw a new light onto these classes of materials vis-à-vis multiferroicmaterials.

Complex permittivity and permeability of strontium ferrites at millimeter waves

Magneto-optical approach for the measurements of complex dielectric permittivity and magnetic permeability of solid and powdered strontium ferrite materials has been performed in the Q-, V-, and W-band frequency ranges. Free-space quasioptical millimeter-wave spectrometer equipped with a backward-wave oscillator as a tunable source of coherent radiation provides the transmittance spectra in transverse magnetic field up to 7.5kOe. Frequency dependences of dielectric and magnetic parameters of strontium ferrites have been calculated by matching theoretical curves to the experimental transmittance spectra. Shifting of the ferromagnetic resonance to higher frequencies and broadening of the zone of strong absorption in magnetic field for solid ferrite materials have been observed.

Microwave dielectric properties of glass-reinforced polymers

AbstractThe well-balanced combination of properties of some polymers makes them good materials for industrial microwave applications, such as telecommunications or microwave ovens. Particular electrical properties are usually needed and can be controlled by additives. In this work, we present the results of complex dielectric permittivity measurements, ε* = ε’ - iε’’, in the microwave frequency region (2.7 and 12.8 GHz), at constant temperature 300 K, on different glass-reinforced and pigmented plastics (poly(butylene terephthalate), polypropylene and acrylonitrile- butadiene-styrene), using the resonant cavity method. We measured the shift in the resonant frequency of the cavity, Δf, caused by the insertion of the sample, which can be related to the real part of complex permittivity, ε’, while the change in the inverse of the quality factor of the cavity, Δ(1/Q), gives the imaginary part, ε’’.

Acoustic and dielectric properties of propionic acid + amine mixtures

Acoustical attenuation measurements between 100kHz and 2 GHz, complex (dielectric) permittivity measurements between 1 MHz and 40 GHz, as well as various auxiliary measurements (density, viscosity, heat of mixing, optical refractive index) of propionic acid mixtures with amines are reported. The data reveal a complex coupled reaction scheme, involving a variety of hydrogen bonded structures, of proton transfer complexes, and of completely dissociated species. The combined consideration of the data indicates the complexation of an acid molecule with another one or with a propionic acid-amine complex to be likely reflected by a high frequency relaxation term in the acoustical spectra of the mixtures. The additionally existing low frequency acoustical relaxation term is assigned to the formation of a complex from a molecule of base and an acid dimer.

Collective dielectric relaxation in smectic A and smectic C⋆ phases near transition temperature of electroclinic liquid crystals

The collective dielectric relaxation processes of electroclinic liquid-crystal materials have been investigated in a thin (3.5μm) planar cell in the frequency range of 1 Hz–10 MHz. Measurement of complex dielectric permittivity versus temperature has been taken on aligned samples filled with different electroclinic liquid-crystal materials. The dielectric data were collected by using the measuring electric field perpendicular to the smectic layer planes. The behavior of the collective dielectric modes has been studied in smectic C*(SmC*) and smectic A(SmA) phases. However, near the transition temperature of SmC*-SmA phase, the dielectric permittivity due to the Goldstone mode and soft mode could not be separated. It has also been observed that the dielectric permittivity increases with temperature before the transition temperature of SmC*-SmA phase under bias field. Temperature dependence of dielectric increments before the transition temperature under bias field and relaxation frequency suggests that the electroclinic liquid crystal shows transitional behavior over a wide temperature range and does not obey the Curie–Weiss law near the transition temperature like in other ferroelectric liquid-crystal materials.