Complex Dielectric Permittivity Spectra Research Articles

Effect of aluminium substitution on low energy electrodynamics of barium-lead M-type hexagonal ferrites

We present the first detailed study of the terahertz-infrared dielectric response of single crystalline lead-substituted M-type barium hexaferrites doped with Al3+. The broadband spectra of complex dielectric permittivity ε*(v)=ε’(v)+iε"(v) of Ba0.8Pb0.2AlxFe12-xO19 with concentrations of the dopant x(Al)=1.2, 3, 3.3 are obtained for two principle polarizations using Fourier-transform infrared spectroscopy and terahertz time-domain spectroscopy in the temperature range from 4 to 300 K and at frequencies from 10 cm−1 up to 8000 cm−1. We observe a rich set of excitations and assign them to the electronic transitions within the ground state 5E of the 4-fold coordinated divalent iron and to phonon resonances. Effect of Al3+ cation substitution on low energy (terahertz) dielectric response and infrared phonon spectra of barium-lead M-type hexaferrites is analysed and discussed.

Preparation, structural analysis, morphological investigation and electrical properties of gold nanoparticles filled polyvinyl alcohol/carboxymethyl cellulose blend

Polymer nanocomposite samples have been prepared through the solution casting method utilizing a polymer blend of polyvinyl alcohol and carboxymethyl cellulose (70/30wt.%) as organic host matrix and different concentrations of biosynthesized gold nanoparticles (Au NPs) by the leaf extract of green mint (Mentha Spicata L.) as inorganic nanofiller. The structural, optical and morphological properties of these samples have been through FT-IR, XRD, UV/Vis. and SEM techniques. The FT-IR spectra confirm the blend components are miscible by the formation of Hydrogen bond interaction and show the polymer-nanoparticle interactions. The XRD analyses depict the semicrystalline structure of these samples and the crystallinity degree decrease with increase of Au NPs content within the PVA/CMC structure. The TEM micrograph of biosynthesized Au NPs indicates that shapes of these NPs are spherical NPs and triangular/hexagonal nanoplates with average size range 5–29nm. The alternating electrical conductivity, electrical impedance, complex dielectric permittivity and electric modulus spectra of prepared samples have been investigated at 25°C in the frequency range (0.1Hz–20MHz). Thus, the variations in values of conductivity, dielectric permittivity and relaxation times indicate the feasibility of these materials as flexible nanodielectric of frequency tunable permittivity for radio/audio frequency operating microelectronic/conventional devices.

Impact of soil salinity, texture and measurement frequency on the relations between soil moisture and 20 MHz–3 GHz dielectric permittivity spectrum for soils of medium texture

Dielectric sensors are a popular choice for soil moisture determination. However, the output of many of these devices, especially those operating at frequencies in the MHz range, can be significantly affected by the influence of soil salinity and texture. The aim of this paper is to examine the impact of salinity, texture and measurement frequency on dielectric permittivity – soil moisture calibration curves for ten soils of medium texture in the frequency range from 20 MHz to 3 GHz based on the complex dielectric permittivity spectra measured with the use of a coaxial transmission line cell connected to a vector-network-analyzer. The use of laboratory-measured spectra ensures that at all frequencies dielectric permittivity is measured at the same conditions with no influence of factors such as different sensitivity zone or various installation conditions, as in the case of comparing individual sensors operating at various frequencies. The obtained relations were comparable to the calibration curves of several capacitance/impedance sensors operating at corresponding frequencies. Calibration curves for apparent permittivity, which were obtained with the use of simulations in the time domain based on the measured spectra, were also determined for the tested soils. Even though the tested soils did not include soils with high clay content, the impact of soil texture on the calibration curves was observed. Results confirmed that the influence of soil salinity and texture on dielectric permittivity was the most significant in the lower part of the frequency spectrum, while the smallest impact of these factors was observed at frequencies of several hundred MHz and above.

Studies on ionic liquid incorporated polymer blend electrolytes for energy storage applications

Solid polymer blend electrolytes (SPBEs) were prepared using poly(ethylene oxide) (PEO), poly(vinylidene fluoride-hexafluoro propylene) (P(VdF-HFP)) as polymer hosts, zinc triflate (ZnTr) as an electrolyte, and 1-butyl-3-methylimidazolium hexafluorophosphate (1B3MIHFP) as an ionic liquid (IL) via a conventional solvent casting technique. Various techniques like AC impedance spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA) respectively were carried out for the prepared samples. From AC impedance spectroscopic studies, maximum ionic conductivity of 95.72 × 10−4 S cm−1 was observed for the system with 20 wt% of 1B3MIHFP at room temperature. Further, the temperature-dependent ionic conductivity study seems to obey Arrhenius behavior. Complexation and increase in degree of amorphicity for IL incorporated system was confirmed through XRD analysis. Ionic transference number was calculated by Wagner’s polarization technique, and it was found to be 0.991 for the sample which possessed maximum ionic conductivity. This value suggested that the charge transport in the polymer blend electrolyte matrix is mainly due to the Zn2+ ions. The dielectric properties of the SBPEs were also studied using the complex dielectric permittivity spectra, complex electric modulus spectra, and loss tangent analysis. Significant morphological changes were observed from SEM micrographs. From the TG-DTA analysis, thermal stability of the sample was found to be 245 °C.

Verification of soil salinity index model based on 0.02–3 GHz complex dielectric permittivity spectrum measurements

Determination of electrical conductivity of soil pore-water from measurements of soil bulk electrical conductivity and volumetric water content or dielectric permittivity, requires theoretical or empirical models connecting these quantities. One such model is the salinity index model, which in the original formulation requires the measurement of soil bulk electrical conductivity and apparent dielectric permittivity determined with the time-domain-reflectometry (TDR) technique. Currently, many popular soil moisture sensors are operated at a single frequency, usually in the low-frequency part of the typical TDR bandwidth. Yet, no systematic verification of the salinity index model applied with the use of dielectric permittivity measured at specific frequencies in a broad frequency range has been performed. The aim of this paper is to evaluate the salinity index model with the use of dielectric spectra of 277 samples of 14 soils obtained in a 20 MHz–3 GHz frequency range with the use of a coaxial transmission-line cell vector-network-analyzer system. A three-pole Debye model was fitted to the spectra in order to determine bulk electrical conductivity and the real part of dielectric permittivity at chosen frequencies in order to diminish the influence of measurement errors. Then, the salinity index model was applied at each examined frequency and its soil-specific parameters were calculated. The performance of the model was evaluated with the use of the leave-one-out cross-validation scheme, and the frequencies at which the model performed best were found within 0.5–2 GHz range. Finally, the salinity index model parameters obtained at the optimal frequencies were correlated with other soil properties.

A Seven-Rod Dielectric Sensor for Determination of Soil Moisture in Well-Defined Sample Volumes.

This paper presents a novel seven-rod sensor used for time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR) measurements of soil water content in a well-defined sample volume. The probe directly measures the complex dielectric permittivity spectrum and for this purpose requires three calibration media: air, water, and ethanol. Firstly, electromagnetic simulations were used to study the influence of the diameter of a container on the sensitivity zone of the probe with respect to the measured calibration media and isopropanol as a verification liquid. Next, the probe was tested in three soils—sandy loam and two silt loams—with six water contents from air-dry to saturation. The conversion from parameters to complex dielectric permittivity from vector network analyzer (VNA) measurements was obtained using an open-ended liquid procedure. The simulation and measurement results for the real part of the isopropanol dielectric permittivity obtained from four containers with different diameters were in good agreement with literature data up to 200 MHz. The real part of the dielectric permittivity was extracted and related to the moisture of the tested soil samples. Relations between the volumetric water content and the real part of the dielectric permittivity (by FDR) and apparent dielectric permittivity (by TDR) were compared with Topp’s equation. It was concluded that the best fit to Topp’s equation was observed in the case of a sandy loam. Data calculated according to the equation proposed by Malicki, Plagge, and Roth gave results closer to Topp’s calibration. The obtained results indicated that the seven-rod probe can be used to accurately measure of the dielectric permittivity spectrum in a well-defined sample volume of about 8 cm3 in the frequency range from 20 MHz to 200 MHz.

Dielectric Spectroscopy Using Dual Reflection Analysis of TDR Signals.

Time-domain reflectometry (TDR) has been a powerful tool for measuring soil dielectric properties. Initiating from apparent dielectric constant () measurement up until apparent and complex dielectric spectroscopies, the embedded information in the TDR signal can be extracted to inspire our understanding of the underlying dielectric behaviors. Multiple full waveform inversion techniques have been developed to extract complex dielectric permittivity (CDP) spectrum, but most of them involved prior knowledge of input function and tedious calibration. This rendered the field dielectric spectroscopy challenging and expensive to conduct. Dual reflection analysis (DRA) is proposed in this study to measure CDP spectrum from 10 MHz to 1 GHz. DRA is a simple, robust, model-free, and source-function free algorithm which requires minimal calibration effort. The theoretical framework of DRA is established and the necessary signal processing procedures are elaborated in this study. Eight materials with different dielectric characteristics are selected to evaluate DRA’s performance, by using both simulated and experimental signals. DRA is capable of measuring non-dispersive materials very well, whereas dispersive materials require the assistance of a long-time-window (LTW) extraction method to further extend the effective bandwidth. The DRA approach is suitable for field applications that can only record a limited amount of data points and in-situ dielectric spectroscopy.

Electromagnetic Properties and Absorption Evaluation of Processed Carbonyl Iron and MWCNT at PANI Nanocomposites in the <inline-formula> <tex-math notation="LaTeX">$X$ </tex-math> </inline-formula>-Band

Composites loaded with various carbonyl iron-based (CI) materials are fabricated and characterized with regards to their electromagnetic properties and absorption in the X-band (8–12 GHz). The combination of inclusion CI particles and multiwalled carbon nanotubes (MWCNT) is also explored. To this effect, CI micropowder has been successively processed to get the form of flaked, porous, and nanosized TiO2-coated particles, whereas MWCNT has been coated with polyaniline (PANI). The processed fillers were primarily characterized to verify their structural consistency and large variations in the microstructure. The static magnetic properties of the CI-based powders have been analyzed via the vibrating sample magnetometry. Finally, complex dielectric permittivity and magnetic permeability spectra along with the return loss (RL) maps of composites loaded with the powders under study have been extensively investigated. Among the studied samples, the multicomponent composite with core-shell-structured CI-TiO2 and MWCNT-PANI exhibits the maximum magnetic and dielectric losses, which yields high RL peaks (>20 dB) tuned within the X-band for layer thickness from 2.5 to 3.5 mm. Particularly for thickness from 2.85 to 3 mm, this quarter-wavelength absorber displays the broadband operation potential as RL values larger than 10 dB can be achieved throughout the X-band.

Multiple Reflection Analysis of TDR Signal for Complex Dielectric Spectroscopy

Most dielectric spectroscopy techniques require careful system calibration, tedious measurement, specially designed probes, precise input source, and some even involved complicated inversion models. This paper proposed a rapid, robust, and model-free multiple reflection analysis (MRA) of time-domain reflectometry (TDR) signals to measure the complex dielectric permittivity (CDP) spectrum. The key to MRA approach is to decompose the first top reflection and the subsequent multiple reflections from TDR signal and to compare their spectral ratio (MRA ratio). This ratio was theoretically derived from the transmission line theory and found to be independent of source function and impedance mismatches in the leading sections. Based on this theoretical formulation, the CDP spectrum can be uniquely inverted from the measured MRA ratio through optimization and an iterated initial guess method. Numerical evaluations and experimental verifications had proven that MRA is a reliable algorithm for measuring CDP spectrum covering 10 MHz–1 GHz. Factors influencing the reliable frequency region were discussed and recommendations on enhancing CDP measurement was proposed for highly dispersive materials. The MRA approach enables dielectric spectroscopy to be conveniently conducted in both laboratory and field, without complicated system setup and calibration.

Studies on sodium nitrate based polyethylene oxide / polyvinyl pyrrolidone polymer blend electrolytes

Solid polymer electrolytes (SPEs) consisting of polyethylene oxide (PEO) /Polyvinyl pyrrolidone (PVP) complexed with sodium nitrate have been synthesized by solution casting technique. Structural studies were carried out using X-ray diffraction (XRD) measurements. The complex formation between the bonding of polymers and the salt were confirmed by Fourier Transform Infrared (FT-IR) spectral data. The ionic conductivity and dielectric response of the SPEs were studied within the frequency range of 42 Hz–1 MHz at the temperature range of 303–363 K. The maximum ionic conductivity was found to be 6.157 × 10−7 S/cm at 303 K for PEO (67 wt %) /PVP (27 wt %)/NaNO3 (6 wt%). The dielectric properties were also studied using the complex dielectric permittivity spectra of the SPE films. The higher dielectric permittivity was obtained due to accretion of ionic charges at lower frequencies. The surface morphology of the polymer blend electrolyte film complexed with sodium nitrate was studied using Scanning Electron Microscopy (SEM).

Analysis of Dielectric Spectra of Water with Conductive Impurities in a Wide Frequency Range

Experimental and theoretical studies of the electrophysical characteristics of water with different concentrations of conductive impurity, including the complex dielectric permittivity, complex conductivity, and complex impedance spectra are performed at frequencies in the range from 20 Hz to 40 GHz. It is demonstrated that the complex dielectric permittivity spectrum at frequencies in the range 500 MHz – 40 GHz is well described by the Debye model with a single relaxation time. In the low-frequency range, one more region of dispersion is observed caused by the phenomena occurring on the liquid-electrode interface. The characteristics of this dispersion region depend significantly on the dc electrical conductivity. It is demonstrated that in the examined frequency range, the influence of the interface phenomena on the complex impedance spectra of water with conductive impurity are well described by adding the impedance of an constant phase element. For the examined samples, the electrophysical characteristics and the parameters of the constant phase element are determined. The static dielectric permittivity and the parameters characterizing the double electric layer increase with the electrical conductivity.

A model delineating the dielectric spectra of a relaxor PLZT obtained by impedance analyzer

AbstractThe origin of the dielectric responses of relaxor ferroelectrics, featured by a signal dispersion according to the measurement frequency, were investigated systematically using a canonical relaxor Pb0.92La0.08(Zr0.65Ti0.35)0.98O3 (PLZT 8/65/35) ceramic. By scanning complex dielectric permittivity over a frequency range from 10 mHz to 10 MHz as a function of temperature from 0°C to 100°C, we revealed that the complex dielectric permittivity spectra obtained from an impedance analyzer are a consequence of a convolution of at least three distinct relaxation processes, featured by the unique relaxation time and distribution. The complex dielectric permittivity spectra at each measurement temperature were deconvoluted by the application of a series of Havriliak‐Negami relaxation models, resulting in three distinguished processes; namely, slow, intermediate, and fast process. We identified that the fast process is responsible for the overall magnitude of capacitance with little influence on the dielectric loss, the intermediate mainly for the thermal evolution of the capacitance, and the slow mainly for the thermal evolution of the loss. With this model, we successfully rationalized the characteristics of the relaxor behavior such as the frequency dispersion of the dielectric maxima, the disparity in peak positions of real and imaginary parts, and the unique feature during aging, so‐called a “dip.”

Structural and dielectric properties of (PEO–PMMA)–SnO2 nanocomposites

Abstract Polymer nanocomposite (PNC) films based on poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) blend as host polymer matrix dispersed with tin dioxide (SnO 2 ) nanoparticles have been prepared by the solution-cast method. X-ray diffraction measurements confirm that these films are semicrystalline and the degree of crystalline phase reduces with increase of SnO 2 contents in the polymer blend. The scanning electron microscopy reveals that the surface morphology of the PNC films is smooth with homogeneous distribution of the SnO 2 particles. Complex dielectric permittivity, electrical conductivity, electric modulus and impedance spectra of the PNC films have been investigated in the frequency range from 20 Hz to 1 MHz. The real part of the dielectric permittivity of these films has non-linear increase with the increase of SnO 2 nanoparticles contents in the PEO–PMMA blend over the audio frequency range, whereas it is found tunable with nanofiller concentration in the range from 2 to 3 at the radio frequencies. Dielectric loss tangent and the loss part of electric modulus spectra exhibit relaxation peaks which are ascribed to cooperative chain segmental dynamics of the PEO and PMMA macromolecules. It is observed that the polymers chain segmental dynamics becomes much faster when only 1 wt% SnO 2 nanoparticles are dispersed in the polymer blend matrix, which further enhances moderately with the increase of SnO 2 concentration up to 5 wt%. The dielectric relaxation time and electrical conductivity values of the PNC film are found Arrhenius in temperature of activation energies 0.15 eV and 0.43 eV, respectively.

Salinity index determination of porous materials using open-ended probes

The relations among soil water content, bulk electrical conductivity and electrical conductivity of soil solution can be described by a number of theoretical and empirical models. The aim of the paper is to examine the performance of open-ended coaxial probes with and without a short antenna in determination of complex dielectric permittivity spectra, moisture and salinity of porous materials using the salinity index approach. Glass beads of 0.26 and 1.24 mm average diameters moistened to various water contents with distilled water and KCl solutions were used to model the soil material. Due to the larger sensitivity zone, only the probe with the antenna enabled determination of bulk electrical conductivity and salinity index of the samples. The relations between bulk electrical conductivity and dielectric permittivity of the samples were highly linear, which was consistent with the salinity index model. The slope of the relation between salinity index and electrical conductivity of moistening solutions closely matched the value for sand presented in literature.

Soil Complex Dielectric Permittivity Spectra Determination Using Electrical Signal Reflections in Probes of Various Lengths

Core Ideas A new complex dielectric permittivity spectra determination method was developed. The method uses Fourier analysis of the reflected signals in two probes of different length. No assumptions on soil dielectric relaxation model are necessary. The complex dielectric permittivity (CDP) of soils is used in moisture and salinity measurements. We have developed a CDP spectra determination method based on Fourier analysis of electrical signals reflected in probes of various lengths. The S11 parameters of the probes placed in samples under test were measured using a vector network analyzer, and the results were transformed into the time domain using transient‐state analysis and a simulated needle pulse. The pulses reflected from the ends of the probes' rods were extracted using a windowing function and transformed into the frequency domain. The CDP was then calculated independently at each frequency using an analytical expression. In contrast to time‐domain spectroscopy techniques, knowledge of the incident signal in the soil sample is not needed. Also, no assumptions on a dielectric relaxation model of the tested materials are necessary. The method was tested on six reference materials and samples of two soils at various water contents. The accuracy of the obtained results was assessed and a rod length combination of 4 and 10 cm was selected for further use. The measurement errors for the tested reference media were determined. The method performed the best in the frequency range 0.2 to 1.0 GHz for the real part of the CDP and 0.20 to 0.85 GHz for the imaginary part. This approach may be adapted for use with a time domain reflectometry needle pulse device.

Quantum Effects Under Migratory Polarization in Nanometer Layers of Proton Semiconductors and Dielectrics at Ultralow Temperatures

Quantum mechanism of interlayer polarization in condensed media in an alternating electric field at low and ultralow temperatures is studied. The nonstationary Liouville equation is solved jointly with the stationary Schrodinger equation and operator Poisson equation without taking into account the proton-proton and proton-phonon interaction. The nonequilibrium density matrix is calculated for an ensemble of non-interacting protons moving in a one-dimensional multi-well potential relief of rectangular shape in an alternating polarizing field. With the help of the non-stationary density matrix, anomalous effects associated with the displacement of the low-temperature maximum of the angle of tangent of dielectric loss in the layered crystals to the temperature of liquid helium are investigated. The results of quantum-mechanical calculations of the complex dielectric permittivity spectra (SCDP) can be used to study the tunneling mechanism of spontaneous polarization in ferroelectrics (KDP, DKDP).

Microwave and millimeter wave dielectric permittivity and magnetic permeability of epsilon-gallium-iron-oxide nano-powders

In millimeter wave frequency range, hexagonal ferrites with high uniaxial anisotropic magnetic fields are used as absorbers. These ferrites include M-type barium ferrite (BaFe12O19) and strontium ferrite (SrFe12O19), which have natural ferromagnetic resonant frequency range from 40 GHz to 60 GHz. However, the higher frequency range lacks suitable materials that support the higher frequency ferromagnetic resonance. A series of gallium-substituted ε-iron oxides (ε-GaxFe2−xO3) are synthesized, which have ferromagnetic resonant frequencies appearing over the frequency range of 30 GHz to 150 GHz. The ε-GaxFe2−xO3 is synthesized by the sol-gel method. The particle sizes are observed to be smaller than 100 nm. In this paper, in-waveguide transmission and reflection method and the free space magneto-optical approach have been employed to study these newly developed ε-GaxFe2−xO3 particles in millimeter waves. These techniques enable to obtain precise transmission spectra to determine the dielectric and magnetic properties of both isotropic and anisotropic ferrites in the microwave and millimeter wave frequency range from single set of direct measurements. The complex dielectric permittivity and magnetic permeability spectra of ε-GaxFe2−xO3 are shown in this paper. Strong ferromagnetic resonances at different frequencies determined by the x parameter are found.

Quantum Properties of Dielectric Losses Spectra in Lamellar Crystals at Extra-low Temperatures

Quantum mechanism of interlayer polarization in condensed mediums in alternating electric field in the limits of low and extra-low temperatures is studied. Unbalanced density matrix is calculated for the ensemble of noninteracting protons, moving in one-dimension multipit potential image of rectangular shape in variable polarizing field. With the help of unbalanced density matrix, anomalous effects are studied, connected with the move of low-temperature maximum loss tangent of dielectric in lamellar crystals towards the temperatures of liquid helium. Results of quantummechanical calculation of spectra of complex dielectric permittivity (SCDP) may be used in the study of tunnel mechanism of spontaneous polarization of ferrielectrics (KDP, DKDP). Key – words: hydrogen – bonded crystals (HBC); interlayer polarization; proton relaxation; unbalanced proton density matrix; quantum statistic for the ensemble of non - interacting protons; spectra of complex dielectric permittivity (SCDP); anomalous effects during the proton relaxation

Electrodynamic properties of lead Zirconate-Titanate thin films in the terahertz frequency range

The transmission/reflection spectra of bilayer structures consisting of thin amorphous and polycrystalline Pb(Zr0.52Ti0.48)O3 ferroelectric films deposited on dielectric substrates of magnesium oxide MgO and sapphire α-Al2O3 were measured in the frequency range of 5–4000 cm−1. Based on these spectra and using the dispersion analysis method, the spectra of complex dielectric permittivity ɛ*(ν) and dynamic conductivity σ′(ν) of the films were simulated, the electrodynamic parameters of the films were determined, and the dielectric dispersion responsible for the formation of static permittivity was found.

Temperature-dependent dielectric relaxation study of polyhydric alcohols (propane-1,3 and 1,2-diol) using a TDR technique

The complex dielectric permittivity spectra of 1,2-propanediol, 1,3-propanediol and its binary mixtures with water have been studied as a function of frequency (10 MHz–30 GHz) and temperature. The dielectric relaxation parameters i.e. static dielectric constant and relaxation time were obtained by using non-linear least square fit method. The static dielectric constant of 1,3-propanediol is larger than the corresponding value for 1,2-propanediol. The intermolecular hydrogen bonding of 1,2-propanediol–water and 1,3-propanediol–water has been discussed using Kirkwood correlation factor and thermodynamic parameters. The activation energy decreases with increased water content in the mixture as expected from the Arrhenius behaviour. The dielectric constant for mixture has been fitted to Bruggeman mixture formula in non-linear case.