Real Permittivity Research Articles

Structural, magnetic and high frequency (1–6 GHz) parameters of Sr-substituted BaFe2O4 monoferrites synthesized by sol–gel method

In this work, Sr-substituted samples of single-phase spinel monoferrites with chemical formula [Formula: see text] (x = 0.00, 0.33, 0.67, 1.00) were synthesized using sol–gel auto-combustion method. In order to confirm the single-phase formation of these samples, a sample (x = 0.00) was chosen for heat treatment at different temperatures (100, 300, 400, 600 and [Formula: see text]) for 4 h. The heat treated sample was then investigated by X-ray diffraction (XRD) analysis and results showed that a single-phase sample can be successfully synthesized at a temperature of [Formula: see text], which is much lower than that reported in earlier literature for synthesis of same structured samples. All the synthesized samples were then sintered at [Formula: see text] for 4 h to achieve better crystallinity. From XRD patterns, lattice parameters, cell volume and XRD density as a function of Sr-substitution were calculated. Scanning electron microscopy (SEM) results showed that the grain size increased as the temperature was increased. Fourier transform infrared spectroscopy (FTIR) results confirmed the single-phase spinel monoferrites at [Formula: see text]. From M–H loops (x = 0.0, 0.33, 0.67 and 1.00), different magnetic parameters such as saturation magnetization [Formula: see text], remanance [Formula: see text], coercivity [Formula: see text] and magnetic moment [Formula: see text] were calculated. Magnetocrystalline anisotropy constant and Y–K angles of Sr-doped Ba monoferrites were also calculated. In addition, the variation of different dielectric parameters (real permittivity, imaginary permittivity, real permeability, imaginary permeability, ac conductivity and loss tangent) as a function of frequency (1–6 GHz) has been discussed in this work. The results suggest that the synthesized materials have many advantages over previously reported single-phase spinel monoferrites.

Combustion-Synthesized Ni–Cd Ferrites and their Structural, Magnetic, and Microwave Absorbing Properties

Ni1 – xCdxFe2O4 ferrites (x = 0.2, 0.4, 0.6) were prepared by solution-combustion synthesis and characterized by XRD, SEM, FTIR spectra, hysteresis measurements, and voltage standing wave ratio (VSWR). The ferrite particles had a size of 20–30 nm. The saturation magnetization observed for x = 0.6 composition was about 56 emu/g. The real and complex permittivity in the frequency range 8–12 GHz was found to vary between 10 and 30. The Cd content of ferrites was found to increase the MW absorption. At x = 0.6, the MW absorbance attained a value of 0.958 at f = 9.5 GHz.

Enhanced Multiferroic Properties of YFeO3 by Doping with Bi3.

Tthe present work studied the cationic substitution of Y3+ by Bi3+ on the crystal structure of orthorhombic YFeO3 and its effect over magnetic, dielectric and electric properties of multiferroic yttrium orthoferrite. Stoichiometric mixtures of Y2O3, Fe2O3 and Bi2O3 were mixed and milled for 5 h using a ball to powder weight ratio of 10:1 by high-energy ball milling. The obtained powders were pressed at 1500 MPa and sintered at 700 °C for 2 h. The test samples were characterized at room temperature by X-ray diffraction (XRD), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and impedance spectroscopy (IS). The X-ray diffraction patterns disclosed a maximum solubility of 30 % mol. of Bi3+ into the orthorhombic YFeO3. For higher concentrations, a transformation from orthorhombic to garnet structure was produced, obtaining partially Y3Fe5O12 phase. The substitution of Bi3+ in Y3+ sites promoted a distortion into the orthorhombic structure and modified Fe-O-Fe angles and octahedral tilt. In addition, it promoted a ferromagnetic (FM) order, which was attributed to both the crystal distortion and Dzyaloshinskii-Moriya interaction. For doped samples, an increase in real permittivity values was observed, and reduced with the increase of frequency. This in good agreement with the Maxwell-Wagner effect.

Description of electric field-dependent dielectric permittivity in PMN ceramics

The temperature dependences of the linear and nonlinear components of the dielectric permittivity of PMN ceramics were determined as a function of bias electric fields. The influence of the applied bias electrical field, superimposed to the small signal oscillating electrical field, is investigated. A decrease in the real dielectric permittivity with increasing the applied bias electrical field was obtained for the investigated temperature range. The temperature dependence of the nonlinear dielectric response reveals an anomalous behavior, indicating a phase transition induced by the bias electric field. The present investigation revealed the influence of the bias electric field on the freezing temperature and activation energy. The results were discussed according to a spherical random bond–random field glassy model for relaxors.

Characterization of the frequency dependence of the electrical properties of sandy soil with variable grain size and water content

The electrical properties of soil at low radio-frequencies are important for engineering applications. In this work the effects of excitation frequency (42 Hz-1 MHz) as well as soil characteristics and conditions on the electrical properties of soil are experimentally investigated using remolded soil samples. Several sandy soils were tested with variable water content (dry up to saturation) using guarded two-electrode arrangements. A method is proposed based on the Nyquist plot to estimate the critical frequency above which measurements of the electrical properties of wet soil are free from electrode polarization effects. The latter result in extremely high real permittivity values, which do not correspond to the response of soil. The critical frequency is higher for smaller grain size and higher water content and varies according to a power law with soil power-frequency conductivity. The real and (effective) imaginary relative permittivity decrease with increasing frequency whereas the effective conductivity increases; this is attributed to the distributed relaxation of the interfacial polarization mechanism associated with the particulate nature of soil. The values of soil electrical properties increase with increasing water content and decreasing grain size (increasing specific surface) as a consequence of enhanced polarization and conduction phenomena. The effective imaginary permittivity varies with frequency according to a power law with an exponent approximately −1; the multiplier coefficient of this law expresses losses and has been formulated as a function of the degree of saturation and soil specific surface.

Characterization of the frequency dependence of the electrical properties of sandy soil with variable grain size and water content

The electrical properties of soil at low radio-frequencies are important for engineering applications. In this work the effects of excitation frequency (42 Hz-1 MHz) as well as soil characteristics and conditions on the electrical properties of soil are experimentally investigated using remolded soil samples. Several sandy soils were tested with variable water content (dry up to saturation) using guarded two-electrode arrangements. A method is proposed based on the Nyquist plot to estimate the critical frequency above which measurements of the electrical properties of wet soil are free from electrode polarization effects. The latter result in extremely high real permittivity values, which do not correspond to the response of soil. The critical frequency is higher for smaller grain size and higher water content and varies according to a power law with soil power-frequency conductivity. The real and (effective) imaginary relative permittivity decrease with increasing frequency whereas the effective conductivity increases; this is attributed to the distributed relaxation of the interfacial polarization mechanism associated with the particulate nature of soil. The values of soil electrical properties increase with increasing water content and decreasing grain size (increasing specific surface) as a consequence of enhanced polarization and conduction phenomena. The effective imaginary permittivity varies with frequency according to a power law with an exponent approximately −1; the multiplier coefficient of this law expresses losses and has been formulated as a function of the degree of saturation and soil specific surface.

Optimizing design on the wide-band absorbing plasma using fluorescent lamps

The plasma was generated using the fluorescent lamp array and the generating principle was the glow discharge mode. The electron density and angular frequency of the plasma could be adjusted with the electronic ballast by changing the lamp input power. The microwave measurement system was built to get the transmission parameter as a function of the lamp input power and the frequency. The transmission parameter expression as functions of the plasma electron density and the electron collision frequency was deduced, and the optimized function could be established. Then the electron density and the electron collision frequency could be fit using a nonlinear least square interpolation method in the MATLAB software kit. The effective permittivity and permeability of the equivalent plasma absorber could be calculated, the real permittivity decreased and the imaginary permittivity increased as the lamp power increased. As the lamps filled with plasma were aligned with different duty ratio, the reflection and transmission parameter could be simulated in the Computer Simulation Technology (CST) software, and the equivalent permittivity was calculated. Finally, the genetic algorithm was used to optimize the structure of the plasma in two cases (lamps aligned adjacently or dispersed with space) as the reflection loss (RL) was set less than −10 dB in 1–8 GHz. The results showed that as the lamps were distributed adjacently, the lamp powers were of two kinds and the total layer number was 28, the minimum RL was −47.1 dB at 5.1 GHz. While as the lamp power was the same 25 W and the lamp layer alignment was different, the minimum RL was −38.2 dB at 5.7 GHz, the total layer number was only 9 and much smaller than that in the first case.

Effect of temperature on the dielectric properties of hydrofluoroethers and fluorinated ketone

The AC and DC dielectric properties of hydrofluoroethers (HFE) [C3F7 OCH3 ] and fluorinated ketone (FK) [C2F5 C(O)CF(CF3)2] have been characterised by dielectric spectroscopy and DC conductivity at different temperatures. Results show that DC conductivity and imaginary permittivity of both fluids are positively correlated with increasing temperature. However, the real permittivity decreases with increasing temperature. The breakdown voltages of HFE and FK at 295 K are∼10 kV mm−1 . Reducing temperature is an effective method to increase the breakdown voltage of the FK coolant, but the breakdown voltage of HFE is less temperature dependent. Finally, as expected repeated breakdown had no significant effect on the AC dielectric strength of both liquids.

Electromagnetic dynamical characteristics of a surface plasmon-polariton

We consider an electromagnetic field near the interface between two media with arbitrary real frequency-dependent permittivities and permeabilities, under conditions supporting the surface plasmon-polariton (SPP) propagation. The dispersion of the electric and magnetic properties is taken into account based on the recent approach for description of the spin and momentum of electromagnetic field in complex media [Phys. Rev. Lett. 119, 073901 (2017); New J. Phys., 19, 123014 (2017)]. It involves the Minkowski momentum decomposition into spin and orbital parts with the dispersion-modified permittivities and permeabilities. Explicit expressions are derived for spatial densities of the energy, energy flow, spin and orbital momenta and angular momenta of the transverse-magnetic (TM) SPP field. The expressions are free from non-physical singularities; the only singular contribution describes a strictly localized surface part of the spin momentum that can be associated with the magnetization current in the conductive component of the SPP-supporting structure. On this ground, a phenomenological theory of the SPP-induced magnetization (predicted earlier based on the simplified microscopic approach) is outlined. Possible modifications and generalizations, including the transverse-electric (TE) SPP waves, are discussed.

Complex dielectric permittivity of metal and polymer modified montmorillonite

Owing to its high surface area and high surface charge density, clay, either contaminated with heavy metal ions or modified with organic additives as barrier materials, is difficult to assess and monitor. Complex dielectric permittivity (κ*) showed promising potential in tackling the above issues. In this study, the complex dielectric permittivity (κ*) of clays modified with a surfactant, four polymers, and four metal ions was measured at frequencies from 0.2-20 GHz. With the addition of polymer and metal ions, increasing frequency caused a slight decrement in real permittivity but a significant decrement in effective permittivity. A modified linearity polynomial equation, which considered the particle conductivity, was developed to fit the relationship between effective conductivity (σeff) and porosity ranging from 0.7 to 1.0. A three-dimensional Cole-Cole plot (κ'-κeff″-w) shows Cole-Cole circle expansion at higher water content. The resonance strength of modified clays was observed to increase with water content, which suggests that the number of water molecules in the diffuse layer of polymer or metal ions saturated clay increased. However, sorbed polymer and metal ions have an insignificant influence on the resonance time τs and stretching exponent 1-α. κ* can provide nondestructive characterization of metal or polymer modified clays.

Effect of tantalum on the temperature dependent electrical characteristics of NaNb1−xTaxO3 (0.0 [formula omitted] x [formula omitted] 0.3) ceramics between 400 and 560 °C

NaNb1−xTaxO3 (x = 0.0, 0.1, 0.2 and 0.3) (NT0, NT1, NT2 and NT3) ceramics are synthesized by conventional solid state reaction technique at high sintering temperature 1150 °C for 4 h. The crystallinity and surface morphology are studied by X - ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM) at room temperature, respectively. XRD analysis of Ta ion doped sodium niobate ceramics confirms the formation of single phase with orthorhombic symmetry. In FE - SEM analysis, the effect of tantalum (Ta) ion on the grain growth of NT ceramics is clearly noticeable. With increasing the amount of Ta ion in NT ceramics, size of grains get diminished. The dielectric and impedance behavior of NT material are studied as a function of frequency (100 Hz - 5 MHz) at selected temperature (400 °C - 560 °C). The maximum value of real permittivity (ε') is obtained in NT3 ceramics at 560 °C temperature. The impedance analysis of NT ceramics confirms that the relaxation peaks shift toward higher frequency with a rise in temperature. Such type of change in relaxation peak is attributed to the temperature dependent time relaxation phenomenon present in material.

Dielectric properties and modulus behavior of La0.67Sr0.16Ca0.17MnO3 ceramic prepared by solid state reaction

ABSTRACTWe have investigated the dielectric properties of La0.67Sr0.16Ca0.17MnO3 (LSCMO) perovskite synthesized by the solid-state reaction method. X-ray diffraction analysis revealed that this sample crystallizes in the distorted rhombohedral system with space group. Experimental results reveal that the real and imaginary dielectric permittivity ( and ), and dielectric loss tangent (tan ) parameters have strong frequency-dependence. The variation of dielectric permittivity and tangent loss (tan ) with frequency show a dispersive behavior at low frequencies and is explained on the basis of the Maxwell–Wagner model and Koop’s theory. It was found that LSCMO ceramics exhibited very high dielectric constant values compared to traditional ferroelectric materials. Electric modulus formalism has been employed to study the relaxation dynamics of charge carriers. The activation energy deduced from analysis of the imaginary part of electric modulus is found to be ∼46.33 meV. The apparent density of sintered pellets were determined using the Archimedes principle. Thus, the value of the density for this compound was 6.155 g.cm−3

Millimeter-Wave Dielectric Properties of Highly Refractive Single Crystals Characterized by Waveguide Cavity Resonance

This paper reports precision measurements of the electromagnetic permittivity of five highly refractive, single-crystal materials, SrTiO3, KTaO3, rutile TiO2, LiTaO3, and LiNbO3, using a single, well-controlled, frequency-scalable procedure over the frequency ranges 25–110 and 140–220 GHz. Real permittivity values were highly consistent for different samples measured across multiple frequency bands. For SrTiO3, KTaO3, and TiO2, real permittivities were more consistent with lower frequency values than typically reported in the millimeter-wave region of the spectrum. Real permittivities of LiTaO3 and LiNbO3 agreed with most reported data. The intrinsic dielectric loss of SrTiO3, KTaO3, and the extraordinary axis of rutile TiO2 was also characterized over the ranges 25–110 and 140–220 GHz, and intrinsic loss per unit frequency was found to be consistent with values measured at other frequencies by dielectric resonators and quasi-optical techniques.

Optical and Dielectric Properties of PMMA/α-Fe2O3–ZnO Nanocomposite Films

In this study, α-Fe2O3–ZnO mixed particles were incorporated into the poly methyl methacrylate (PMMA) matrix by using solvent casting process. In order to prepare a powder mixture, mechanical milling process was used. α-Fe2O3 synthesized by precipitation method and ZnO nanoparticles were mixed with same amount and milled with planetary type ball milling machine for 1 h. Morphological and structural examinations of the produced powders were conducted with scanning electron microscopy (SEM) and X-ray diffraction (XRD). Optical and dielectrical properties of composite materials produced with different amount of reinforcement (0.1 wt%, 0.5 wt% and 1.0 wt%) were examined by using UV–Vis spectrophotometry and vector network analyzer (VNA). It was observed that optical transmittance reduced with increasing reinforcement amount. Dielectric properties of produced pellet composites with 4 mm thickness were conducted between 70 and 110 GHz and the results showed that the real and complex permittivity and dielectric loss values of PMMA/α-Fe2O3 is higher than those of neat PMMA, PMMA/ZnO and PMMA/α-Fe2O3–ZnO.

Topological non-Hermitian origin of surface Maxwell waves

Maxwell electromagnetism, describing the wave properties of light, was formulated 150 years ago. More than 60 years ago it was shown that interfaces between optical media (including dielectrics, metals, negative-index materials) can support surface electromagnetic waves, which now play crucial roles in plasmonics, metamaterials, and nano-photonics. Here we show that surface Maxwell waves at interfaces between homogeneous isotropic media described by real permittivities and permeabilities have a topological origin explained by the bulk-boundary correspondence. Importantly, the topological classification is determined by the helicity operator, which is generically non-Hermitian even in lossless optical media. The corresponding topological invariant, which determines the number of surface modes, is a {Bbb Z}_4 number (or a pair of {Bbb Z}_2 numbers) describing the winding of the complex helicity spectrum across the interface. Our theory provides a new twist and insights for several areas of wave physics: Maxwell electromagnetism, topological quantum states, non-Hermitian wave physics, and metamaterials.

Effects of filler calcination on structure and dielectric properties of polyethylene/silica nanocomposites

This paper reports on an investigation of the effects of calcination on the structure and dielectric properties of polyethylene/silica (SiO 2 ) nanocomposites. Calcination temperatures of 600 and 900 °C have been used in order to modify the surface chemistry and surface structure of the SiO 2 . The results show that, after calcination, the concentration of surface hydroxyl groups and water molecules around SiO 2 and within resulting nanocomposites is reduced. The real permittivity of nanocomposites containing calcined SiO 2 decreases compared to nanocomposites based on uncalcined SiO 2 . The DC breakdown strength of nanocomposites containing calcined SiO 2 becomes higher than those containing uncalcined SiO 2 . In contrast, AC breakdown was found not to be significantly affected by addition of any of the silicas considered here. The use of calcined nanofillers can have positive effects akin to the use of chemically functionalized nanofillers in enhancing the dielectric properties of nanocomposites; both approaches remove polar surface hydroxyl groups.

Measurement of the real dielectric permittivity ϵr of glacial ice

Owing to their small interaction cross-section, neutrinos are unparalleled astronomical tracers. Ultra-high energy (UHE; E > 10 PeV) neutrinos probe the most distant, most explosive sources in the Universe, often obscured to optical telescopes. Radio-frequency (RF) detection of Askaryan radiation in cold polar ice is currently regarded as the best experimental measurement technique for UHE neutrinos, provided the RF properties of the ice target can be well-understood. To that end, the Askaryan Radio Array (ARA) experiment at the South Pole has used long-baseline RF propagation to extract information on the index-of-refraction (n=ϵr) in South Polar ice. Owing to the increasing ice density over the upper 150–200 m, rays are measured along two, nearly parallel paths, one of which refracts through an inflection point, with differences in both arrival time and arrival angle that can be used to constrain the neutrino properties. We also observe (first) indications for RF ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary birefringent axes, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Qualitatively, these effects offer the possibility of redundantly measuring the range from receiver to a neutrino interaction in Antarctic ice, if receiver antennas are deployed at shallow (z ∼ −25 m) depths. Such range information is essential in determining both the neutrino energy, as well as the incident neutrino direction.

Effect of boron doping on waterproof and dielectric properties of polyborosiloxane coating on SiO2f/SiO2 composites

A hydrophobic coating of the silica fiber reinforced silica composites (SiO2f/SiO2) was synthesized by sol-gel method using methyltriethoxy-silane (MTES) and boric acid (B(OH)3) as raw materials. The relationship among boron doping, chemical structure of precursors and durability of hydrophobic coatings was discussed. The Si-O-B and methyl groups were successfully introduced in the gel precursors according to the FT-IR and XPS results. The resins were filled in the internal and surface holes of the SiO2f/SiO2 composites partially or completely, which is beneficial to reduce the physical adsorption of the moisture. In addition, hydroxyl groups of the SiO2f/SiO2 composites reacted with the resins and hydrophobic methyl groups were introduced, leading to the reduction of the chemical adsorption of water. Also, the boron doping was beneficial to enhancing the physical cross-linking between the coating and the SiO2f/SiO2 composites, and improved the adhesion of the coating to the substrate. The results show that the optimal hydrophobic coating with contact angle 130.33°, moisture absorption 0.33% and adhesion level 1 is obtained when the molar ratio of MTES to B(OH)3 is 10:4. The real permittivity of M10B4 is constant in the range of 2.32–2.51 and the dielectric tangent loss is constant in the range of 5.5 × 10−4–8.7 × 10−3. The hydrophobic coating has excellent dielectric properties.

The Influence of ZnO nanoparticles in the epoxy resin on the complex permittivity and dissipation factor

Abstract Epoxy resins are used as electro-insulating materials because they have great electro-insulation properties, adhesion, chemical resistance, and minimal shrinkage during curing. Epoxy nanocomposites have gained much interest in the area of nanotechnology, because of the ease of manufacture and the significant gain in properties. The influence of the various concentration of ZnO nanoparticles in epoxy resin Vukol 022 on the changes of the complex permittivity and dissipation factor has been measured at the temperature range from 20 °C to 120 °C. Frequency dependences of these parameters were measured within the frequency ranges from 1 mHz to 1 MHz by a capacitance method. The 0,5 wt.% nanoparticles caused a decrease of the real part of the complex relative permittivity. The higher concentration of nanoparticles for frequencies above 10 Hz had higher real relative permittivity as pure epoxy resin. At the study of the influence of temperature on dissipation factor, α-relaxation process and its shift to lower frequencies with ZnO fillers were observed.

Magnetic and Dielectric Properties of Low Temperature co-fired Na-Ta co-doped M-type Barium Ferrites

Na-Ta ions co-doped M-type barium ferrites, BaFe12-2x(NaTa)xO19, were synthesized at low temperature by the solid-state method. Na-Ta ion could occupy crystalline sites but not change the phase formation of barium ferrite. SEM images showed that samples had the regular and hexangular shape with 1-2 μm size. With the increase of Na-Ta, saturation magnetization (Ms) obviously decreased from 57.5 emu/g to 37.6 emu/g, and the coercivity (Hc) decreased from 4156 Oe to 2069 Oe. For dielectric properties, the real part permittivity (ε