Decrease In Dielectric Permittivity Research Articles

Electromagnetic properties of coal using microstrip and an algorithm based on the Nicolson-Ross-Weir method

AbstractThe work implements an experimental methodology to find the dielectric parameters: electrical permittivity, effective permittivity, magnetic permeability, conductivity, absorption coefficient, impedance, and loss tangent of bituminous coal from the municipality of Morcá and Tópaga belonging to the Sogamoso-Jericó sub-basin of the Guaduas formation, one of the most important coal reserves in Colombia. The methodology, known for its efficiency, includes constructing a microstrip-type circuit, measuring scattering parameters or S-parameters at frequencies between 300 kHz and 1 GHz with a vector network analyzer, and extracting electromagnetic properties using the Nicolson-Ross-Weir algorithm. The implemented algorithm allowed us to see the behavior of the coal in a fraction of the ultra-high frequency band and to find quickly and easily the approximate values of the parameters as a function of frequency, which are very important for investigations in mathematical modeling and computational electromagnetics. The results show that the real and imaginary components of the relative dielectric permittivity decrease with increasing frequency, and the absorption coefficient and the loss tangent of the coal increase as a function of frequency, indicating that the coal behaves as a dissipative dielectric.

Role of mixed oxidant and controlled oxygen partial pressure heat treatment to regulate the dielectric properties and resistivity of SrTiO3-based CP ceramics

Sr0.99La0.01TiO3 (SLT10) colossal permittivity (CP) ceramic materials were synthesized using solid phase method and secondary heat treated using mixed oxidant 35%Bi2O3–10%Al2O3–20%MgO–25%CuO–10%SiO2 oxidant. The heat treatment atmospheres were chosen as O2, air, and Ar to correspond to different oxygen partial pressures. The dielectric properties of the Sr0.99La0.01TiO3-Percolated (SLT10-P) ceramics were investigated, and the contribution of the oxidant to the resistivity enhancement was verified by complex impedance spectroscopy and DC resistivity tests. Excellent dielectric properties were obtained for SLT10-P Air ceramic sample (16543 for dielectric permittivity and 0.016 for loss tangent), and the resistivity was increased from 2.13 × 108 Ω cm (SLT10) to 1.23 × 1011 Ω cm (SLT10-P Air). The resistance degradation mechanism of SLT10-P ceramics and oxygen vacancy migration in the process of resistance degradation were studied by using resistance monitoring device and thermally stimulated depolarization currents (TSDC) test. The introduction of oxidant optimizes the temperature stability and resistivity of SLT10 ceramics, but it will lead to the decrease of dielectric permittivity. The atmosphere of heat treatment changed the concentration of oxygen vacancy in ceramics. When SLT10-P O2 was treated in O2 atmosphere, the concentration of oxygen vacancy in ceramics decreased, which led to the decrease of dielectric permittivity and the increase of grain boundary resistance. For SLT10-P Ar ceramic, more oxygen vacancies and free electrons are induced by low oxygen partial pressure heat treatment, which enhances the dipole effect of electron pinning defects and leads to colossal dielectric permittivity, but high concentration of oxygen vacancies will affect the resistance decline. In SLT10-P Air ceramic, the coexistence of colossal permittivity and low loss tangent and high resistance is realized.

Influences of divalent ion substitution on the magnetic and dielectric properties of W-type barium ferrite

Abstract Saturation magnetization, magneto-crystalline anisotropy field and dielectric properties are closely related to microwave devices applied at different frequencies. For regulating the magnetic and dielectric properties of W-type barium ferrites, single-phase BaMe 2Fe16O27 (Me = Fe, Mn, Zn, Ni, Co) with different Me ions were synthesized by the high-temperature solid-state method. The saturation magnetization (M s) range from 47.77 emu/g to 95.34 emu/g and the magnetic anisotropy field (H a) range from 10700.60 Oe to 13739.57 Oe, depending on the type of cation substitution in the hexagonal lattice. The dielectric permittivity and dielectric loss decrease with increasing frequency of the AC electric field in the low-frequency region, while they almost remain constant in the high-frequency region. The characteristics of easy regulation and preparation make it a potential candidate for use in microwave device applications.

The Impact of Concentration and Electric-Field Dependent Susceptibilities on Electrolyte Models

Electrolytes have a significant role in a range of scientific and technological fields such as fundamental electrochemistry, biochemical systems, semiconductors, and industrial devices. A widely used mathematical framework for describing electrolytes is based on Poisson-Nernst-Planck-type equations and their successors[1], but the Poisson equation assumes a constant dielectric susceptibility. However, recent research has developed a thermodynamically consistent model for the dielectric susceptibility that accounts for its dependence on both concentration and electric field [5,6]. This allows for the inclusion of the dependency of the susceptibility on salt concentration in liquid electrolytes, referred to as dielectric decrement[2,3,4], as well as the decline in susceptibility for large electric fields[8], known as dielectric saturation.The research findings highlight the importance of considering the variable dielectric susceptibility in electrolyte models, particularly in relation to the decrease in dielectric permittivity in front of a charged electrode surface[7]. The study demonstrates the impact of the concentration and electric-field-dependent susceptibility on the overall equation system for electrochemical double layers. By providing insights into the theoretical aspects of the approach, the researchers aim to contribute to the development of more accurate and comprehensive models of electrolytes that consider the complex interplay of various factors.

Enhancement of superior dielectric performance in ZnTiNb2O8 systems by multi‐layer architecture

AbstractZn0.995Cu0.005TiNb2O8@TiO2 mixed ceramics and Zn0.995Cu0.005TiNb2O8‐TiO2‐Zn0.995Cu0.005TiNb2O8 layered ceramics with different TiO2 contents were designed and manufactured to adjust the microwave dielectric performances of Zn0.995Cu0.005TiNb2O8/TiO2 composite ceramics. The effects of random distribution and laminated co‐firing processes on the microwave dielectric properties of the ZnTiNb2O8 systems were fully investigated and compared. During the random distribution process, the compound transforms from the original ZnTiNb2O8 phase to the Zn0.17Nb0.33Ti0.5O2 phase with the increase of TiO2 content. Its value can be adjusted to near zero, but its Q× f value decreases severely. For the laminated co‐firing process, the distinctive tri‐layer architecture allows the reaction between Zn0.995Cu0.005TiNb2O8 and TiO2 to be limited to a narrow region of about 20 µm width and can play a role similar to that of “glue” to connect the layers well. The process significantly minimizes the probability of Q× f values deteriorating. Compared with the random distribution Zn0.995Cu0.005TiNb2O8@TiO2, the Q× f value of the tri‐layer architecture ceramics is improved by about 85% with no significant decrease in dielectric permittivity while ensuring high‐temperature stability. When stacked with 0.04 wt% TiO2, the Zn0.995Cu0.005TiNb2O8‐TiO2‐Zn0.995Cu0.005TiNb2O8 tri‐layer architecture ceramic exhibits superior dielectric properties: = 39.96, Q× f = 51,987 GHz, and = ‐1.31 ppm/°C.

Dielectric spectrum of a ferrofluid layer exposed to a gradient magnetic field.

A low-frequency dielectric response of a ferrofluid based on transformer oil and MnZn ferrite nanoparticles is investigated in a gradient magnetic field. Four ferrofluid samples of various nanoparticle concentrations were introduced into planar micro-capacitors located over a magnetized tip. The dielectric spectra were measured in the frequency range from 0.1Hz to 200kHz and in the local magnetic field up to 100 mT. The spectra exhibit a dielectric relaxation ascribed to nanoparticle interfacial polarization. The low-frequency spectrum of each ferrofluid decreases upon application of the magnetic field up to 20 mT. The decrease in dielectric permittivity is caused by a magnetic force acting on larger nanoparticles in the gradient magnetic field. It is assumed that the interfaces of the concentrated nanoparticles in the gradient field do not contribute to the effective dielectric response. This reduces the effective relaxation time and shifts the relaxation toward higher frequencies. The dielectric spectra are well described by a relaxation fit function consisting of one Havriliak-Negami and a conductivity term. The fitting confirms that the only effect of the gradient magnetic field on the dielectric spectra is the shift of the dielectric relaxation and the decrease of the amplitude in the imaginary permittivity. This behavior is evident from a master plot, where all dielectric relaxations are superimposed on a single line. The knowledge of the presented behavior of the ferrofluid may be valuable when applying a ferrofluid to sharply magnetized parts of various electrical equipment (wires, tips, screws, nails, edges) as a liquid dielectric medium.

Novel Dielectric Nanogranular Materials with an Electrically Tunable Frequency Response

AbstractThe electrical modulation of the functionality of matter is of significant interest in physics and multifunctional tunable electronic device applications. Here, new dielectric materials with nanogranular structures comprised of nano‐sized Co granular metals dispersed in a Mg‐fluoride‐based dielectric matrix are explored. The dielectric relaxation frequency (fr), which represents a sharp decrease in dielectric permittivity in dielectrics, can be tuned by a DC electric field (E). As E increases, the position of fr first shifts to the low‐frequency side and then to the high‐frequency side, achieving a tunable fr in a certain frequency range. The ability to electrically modulate the relaxation frequency may help construct novel tunable frequency filters. The dielectric properties are theoretically examined based on the asymmetric electron tunnelling model that considers the size difference of granular pairs, offering an insightful understanding of the structure‐property relationship in disordered granular solids.

Effects of molecular structure on the dielectric relaxation of substituted cellulose derivatives

The paper discusses the temperature dependencies of the complex dielectric permittivity obtained at different frequencies for the substituted cellulose derivatives with various concentrations of the hydroxypropoxy group. The substituted cellulose derivatives are shown to undergo a low-temperature dielectric relaxation. The input of the dielectric relaxation into dielectric permittivity decreases when the OH groups in cellulose molecules are substituted by the methoxy groups. In contrast, when OH groups in cellulose molecules are substituted by hydroxypropoxy groups, the dielectric relaxation region shifts to higher temperatures, and its intensity increases. The dielectric spectroscopy method is shown to be a reliable method to estimate the degree of the substitutions of the hydroxyl groups with hydroxypropoxy groups in the cellulose derivatives, used in the pharmaceutical industry as drug carriers and drug delivery rate regulators.

Study of dielectric permittivity and electrical modulus of K2CrO4 doped PMMA

To understand the variations that occurs in electrical parameters on doping potassium chromate (K2CrO4) in Poly- Methyl-methacrylate (PMMA), the authors have developed composite films by doping 1 %, 2 %, 5 % and 10 % K2CrO4 in PMMA by solution cast technique at room temperature. These samples were analysed for structural properties using XRD and FTIR. The dielectric parameters like real part and imaginary part of dielectric constant (ε′ and ε′′), ac conductivity (σ) and real part and imaginary part of electric modulus (M'andM'') prepared of specimen have been evaluated from the electrical parameters obtained using Impedance analyzer WANN KERR. Both real and imaginary component of the dielectric permittivity decrease with increase in the frequency in the range 102 Hz to 105 Hz and increase on increasing the concentration of K2CrO4. AC conductivity shows an increase with increase in frequency and concentration of K2CrO4. M'andM'' the segmental movement of the polymer chain dominating the dielectric properties.

STRUCTURE AND ELECTROPHYSICAL PROPERTIES OF PVDF+PbS/CdS NANOCOMPOSITES

In the given paper were investigated structure and electrophysical properties of PVDF+PbS/CdS nanocomposites. Distribution and the size of PbS and CdS nanoparticles in the polymer matrix has been studied by scanning electron microscopy (JEOL JSM-7600 F). The structure of the nanocomposite samples was investigated by the X-ray diffraction spectroscopy. The dependence of dielectric permittivity at frequency and temperature was investigated. It was shown that the dielectric permittivity of PVDF+PbS/CdS nanocomposite samples was increase in small nanoparticles content. Further increase in the concentration of the filler leads to decrease in the dielectric permittivity. The subsequent decrease in dielectric permittivity at higher nanoparticles content can be explained by the increase in defects in the structure of the nanocomposite.

Characterization of microwave and terahertz dielectric properties of single crystal La2Ti2O7 along one single direction

New generation wireless communication systems require characterisations of dielectric permittivity and loss tangent at microwave and terahertz bands. La2Ti2O7 is a candidate material for microwave application. However, all the reported microwave dielectric data are average value from different directions of a single crystal, which could not reflect its anisotropic nature due to the layered crystal structure. Its dielectric properties at the microwave and terahertz bands in a single crystallographic direction have rarely been reported. In this work, a single crystal ferroelectric La2Ti2O7 was prepared by floating zone method and its dielectric properties were characterized from 1 kHz to 1 THz along one single direction. The decrease in dielectric permittivity with increasing frequency is related to dielectric relaxation from radio frequency to microwave then to terahertz band. The capability of characterizing anisotropic dielectric properties of a single crystal in this work opens the feasibility for its microwave and terahertz applications.

Complex-Permittivity Measurement and Modeling of Moso Bamboo From 0.5 to 18 GHz

Accurate measurement of the complex permittivity of plant is essential for remote-sensing applications. The complex dielectric properties of moso bamboo (Phyllostachys heterocycla) were measured from 0.5 to 18 GHz based on the coaxial transmission/reflection method. A high-precision numerically controlled machine was used to process the bamboo samples. Based on the measured data, the complex permittivity can be better modeled as a second-order polynomial about the moisture content than the traditional exponential function. The real parts of the relative dielectric permittivity decrease with the increase in the frequency, while the imaginary parts decline first and then rise. The dielectric permittivity of the longitudinal direction is larger than that of the cross-sectional direction due to the anisotropic fibrocyte structure of moso bamboo.

Conductivity and dielectric properties of lithium-ion biopolymer blend electrolyte based film

In the present work, the effect of lithium salt contents on the ionic conduction of blend biopolymer electrolyte (BBE) comprising chitosan (CS) and methylcellulose (MC) complexed with lithium iodide (LiI) has been explored. The maximum ionic conductivity (6.26 × 10−6 S/cm) was achieved at room temperature upon incorporating 40 wt% of LiI. The frequency-dependent ac conductivity of the BBE follows the Jonscher power law, and the analysis confirmed that the Li-ion conduction mechanism is correlated barrier hopping (CBH) type. The temperature-dependent dc conductivity follows the Arrhenius relation in the investigated temperature ranges. The highest Li-ion conducting sample has minimum activation energy. The dielectric permittivity and dielectric loss decrease regularly with an increase in the frequency of the applied field. The asymmetric and broadening of imaginary modulus peak suggesting a non-Debye type dielectric relaxation.

Structural and dielectric studies of three-phase composite containing multiwalled carbon nanotubes, nanodispersed silica and KDP

ABSTRACT The study provides experimental results for clarifying the influence of a conductive filler of multiwalled carbon nanotubes (MWCNT) and a dielectric inclusion of nanodispersed silica (nSiO2) on dielectric properties of a classical ferroelectric of KH2PO4 (KDP) in composites containing these substances. Wits increasing nSiO2 content, the phase transition point of KDP was shifted toward higher temperatures along with a decrease in dielectric permittivity. Meanwhile, MWCNT composition did not affect phase transition, but enhanced dielectric permittivity that reached highest values at MWCNT:nSiO2:KDP mass ratio of 0.096:1:1. The thrshod of MWCNT in the composite was also determined. The conductive nature of MWCNT and the interaction between nSiO2 with KDP in the presence of residual water was figured out as the main reason for these anomalies.

Dielectric properties of polymer/clay nanocomposites

Intercalated and exfoliated nanocomposites of insulating polymers poly methyl methacrylate and acrylonitrile butadiene styrene with organically modified montmorillonite (OMMT) was prepared by solution casting method. Formation of polymer nanocomposites was confirmed by X-Ray Diffraction. Fourier transform infrared spectroscopy confirmed the interaction between polymers and cations on the surface of OMMT layers. Dielectric properties of these nanocomposites were examined at room temperature in the frequency range of 100 Hz–1 MHz. The findings of dielectric measurements exhibited higher real and imaginary dielectric permittivity values for exfoliated nanocomposites and lesser real and imaginary dielectric permittivity values for intercalated nanocomposites as compared with pure polymers in the same frequency range. The increase in the permittivity values is attributed to Maxwell Wagner polarization in exfoliated nanocomposites because of increased interfacial area between polymer and the clay layers. Decrease in dielectric permittivity in intercalated polymer nanocomposites is attributed to restricted mobility of polymer chains due to nanoscopic confinement of the polymer with the silicate layers.

Lead-free Na0.4K0.1Bi0.5TiO3 ceramic: Poling effect and enhancement in electromechanical and piezoelectric voltage coefficient

The effect of electric poling on the piezoelectric properties of the sintered Na0.4K0.1Bi0.5TiO3 is studied with varying poling field and temperature. An optimized poling condition (EP =50 kVcm, TP =110 °C) exhibited a high piezoelectric voltage (g33∼ 85 mV m/N) and charge coefficients (d33∼193pC/N). A combination of electric field induced irreversible transformation from polar nano regions embedded in a non-polar relaxor state to a long-range ordered ferroelectric state and increase in the structural ordering are responsible for the observed high piezoelectric properties. A mechanism is discussed to reveal the origin of high voltage coefficient due to poling, where the decrease of dielectric permittivity can facilitate high g33. This investigation provides an approach for designing the high performance Na0.4K0.1Bi0.5TiO3based materials suitable for sensors and energy harvesting applications.

Dispersion characteristics of terahertz transverse electric mode in a smooth-wall cylindrical waveguide with a degenerate plasma layer

The propagation of transverse electric mode in a cylindrical metallic smooth-wall waveguide contains a dielectric rod and a cold collisionless unmagnetized degenerate plasma layer is analytically investigated in the terahertz frequency region. The dispersion relations of fast and slow waves for this mode are derived and solved numerically. The effects of geometrical and physical parameters such as dielectric, plasma and metal radii, and dielectric permittivity on the dispersion characteristics of terahertz transverse electric mode and its frequency spectrum are studied. It is shown that the decrease of dielectric permittivity and metal radius, and the increase of degenerate plasma radius leads to higher frequency fast waves. It is also indicated that an increase in the dielectric radius results in a decrease in the frequency of fast waves. In addition, it is found that by reducing the dielectric rod radius and with increasing metal radius, the frequency is increased in the slow waves. Finally, it is shown that the increase in dielectric permittivity causes a decrease in the frequency of both fast and slow waves.

Role of ionic contribution in dielectric behaviour of a nematic liquid crystal with variable cell thickness

In this research article, we have investigated the dielectric properties of a nematic liquid crystal (NLC), namely 4 cyano-4′- pentylbiphenyl (which is commonly known as 5CB), in sample cells of variable thickness. The dielectric behaviour has been studied through a LCR meter in the frequency ranging from 20 Hz to 1 MHz. It was observed that the real part of complex dielectric permittivity (ε') decreases and the peak value of the energy dissipated per unit cycle (ε′′) increases on increasing the cell thickness. It has also been noticed that the relaxation frequency of LC material under investigation shifts towards the lower side with the increment in the sample cell thickness. The observed dielectric behaviour has been attributed to the contribution of the ionic species available in the NLC used. The mobilized ions have a significant contribution in influencing the dielectric studies of 5CB in thin cells. Further, all the above mentioned physical attributes of 5CB will play an important role in fabricating a device which is not only cost effective but also has higher transmittance and negligible power consumption.

Time-Domain Reflectometry (TDR) Monitoring at a Lab Scale of Aerobic Biological Processes in a Soil Contaminated by Diesel Oil

This study aims to monitor the biological processes ongoing in a hydrocarbon polluted soil. The experiments were carried out at a laboratory scale by measuring the evolution of its geophysical electromagnetic parameters. Time-domain reflectometry (TDR) probes were used to measure dielectric permittivity and electrical conductivity in columns of sandy soil artificially contaminated with diesel oil (Voil/Vtot = 0.19). To provide aerobic conditions suitable for the growth of microorganisms, they were hydrated with Mineral Salt Medium for Bacteria. One mesocosm was aerated by injecting air from the bottom of the column, while the other had only natural aeration due to diffusion of air through the soil itself. The monitoring lasted 105 days. Geophysical measurements were supported by microbiological, gas chromatographic analyses, and scanning electron microscope (SEM) images. Air injection heavily influenced the TDR monitoring, probably due to the generation of air bubbles around the probe that interfered with the probe–soil coupling. Therefore, the measurement accuracy of geophysical properties was dramatically reduced in the aerated system, although biological analyses showed that aeration strongly supports microbial activity. In the non-aerated system, a slight (2%) linear decrease of dielectric permittivity was observed over time. Meanwhile, the electrical conductivity initially decreased, then increased from day 20 to day 45, then decreased again by about 30%. We compared these results with other researches in recent literature to explain the complex biological phenomena that can induce variations in electrical parameters in a contaminated soil matrix, from salt depletion to pore clogging.

Dielectric and ferroelectric properties of BTFCO thin films

Single phase Bi3.25La0.75Ti2.5Nb0.25Fe0.125Co0.125O12 (BTFCO) thin films were deposited on Pt/TiO2/SiO2/Si substrates by RF-magnetron sputtering. Ferroelectric domain switching, including 180° and non-180° domains walls, was observed in polarization- electrical field hysteresis loops. The coercive field Ec of the materials, linking with zero polarization, is near 100 kV/cm. Dielectric permittivity changing with DC electric field shows one permittivity peak near 50 kV/cm, which suggests that field induced switching of 180° domains is completed at 50 kV/cm. Further increasing the DC field causes the decrease of dielectric permittivity, which can be attributed to the decrease of density of 90° domain walls. The difference between the Ec and the field for permittivity peak show that the switching field of 180° domain is lower than that of 90° domains in BTFCO ferroelectric films.