Analysis of the temperature-frequency effect on dielectric losses in a grain medium

The aim of the study is to determine the influence of the thermal effect on dielectric losses in grain mass subject to bruising during drying and storage on the example of wheat across a wide external electric field frequency range. The study of the electrophysical characteristics of a dispersed medium comprising mechanically activated wheat grains takes into account the effect of the degree of breakage on the dielectric parameters of the studied medium. The studies were carried out on experimental samples having different degrees of mechanical activation of particles, which ranged in size from from 50 to 1000 μm. Variations in the dielectric loss tangent were studied using the dielectric method across a wide temperature-frequency range. Studies of variations in dielectric properties were carried out for wheat sam-ples subjected to grinding according to the mechanical activation method at temperatures varying from 20°C to 255°C with a constant heating rate of 0.7 deg / min. During the course of the experiment, the frequency of the external electric field was varied from 25 Hz to 1∙106 Hz. Dielectric constant and dielectric loss tangent calculations were carried out using data on electrical capacity and conductivity obtained using an E7-20 immittance meter and a measuring cell in the form of a flat capacitor. An analysis of variations in these dielectric characteristics was also performed. The obtained stable correlation of the dielectric loss tangent with the frequency of external electric impact and the degree of heating of the samples was most pronounced for finely dispersed samples (particle size 50 μm). Variations in dielectric characteristics are most significant when the frequency decreases to 100 Hz and below. The study of variations in the main dielectric parameters can be used to prevent self-heating and ignition of the grain mass during storage, as well as for selecting the most efficient energy-saving drying mode.

Electrophysical properties of mixtures of mineral oil and synthetic ester dielectric liquid

Power transformers are key equipment in power generation, transmission, and distribution systems. The reliability of power transformers is based on the performance of the insulation system, which includes solid cellulose insulation and a liquid dielectric. Modern power engineering requires liquid insulation to have excellent insulating properties, high fire resistance, and biodegradability. Mineral oil that has been in use for over 100 years does not meet certain requirements. Therefore, various methods of enhancing the insulating properties of the oil are currently being considered, including mixing it with other liquid dielectrics, which have excellent properties. Synthetic and natural esters are considered as alternative fluids.This article discusses the possibility of enhancing the insulating characteristics of mineral oil with a high content of aromatic hydrocarbons (for example, T-750 oil) by mixing it with synthetic ester Midel 7131. Assessment is given of insulating parameters of the resulting mixtures with an ester fraction in mineral oil from 0% to fifty%. The main characteristics of the mixtures are described, such as density, kinematic viscosity, flash point, dielectric loss tangent, relative dielectric permittivity, breakdown voltage, and moisture content. It is shown that with an increase in the proportion of ester, some parameters of the obtained insulating liquid improve (flash point, dielectric constant, breakdown voltage), while values of other parameters (density, kinematic viscosity, dielectric loss tangent) with an ester content of more than 10% in the mixture do not meet the requirements for mineral oils.

UGCPW Structure-Based Embedded Resonator with High Quality Factor for Microwave Substrate Characterization

In this paper, an ungrounded coplanar waveguide-based embedded resonator method for microwave substrate characterization was presented. The effective dielectric constant of the structure and the dielectric constant of microwave substrates can be calculated by the measured resonant frequency. The measured insertion losses at resonant frequencies and the 3 dB bandwidth can be used to determine the loaded and unloaded quality factors, including the dielectric quality factor which is related to dielectric loss tangent. The radiation loss and the extra length due to fringing effect caused by the open-end structure were taken into account to improve the extraction accuracy. The experimental unloaded quality factor of the proposed resonator at resonance order 1 reaches 211.3. The extracted dielectric constant and dielectric loss tangent of Taconic TLY at resonance order 1 are, respectively, 2.218 and 9.286×10−4, which are only 0.018 (relatively 0.82%) and 0.286×10−4 (relatively 3.18%) deviations from the datasheet values, respectively. The proposed resonator method is especially suitable for dielectric characterization of newly developed materials with the difficulty of realizing metal via holes, in which case substrate-integrated-waveguide (SIW) resonator methods are not applicable. When comparing with microstrip resonator methods, the proposed method is of higher quality factor, and it is more reliable and economical as well.

Studies on Metal Oxide Nanoparticle Doped PVP Polymer Nanocomposites

Magnesium Oxide (MgO) nanoparticles have been synthesized by solution combustion technique using stoichiometric composition of magnesium nitrate as oxidizer and urea as fuel. Structure of the MgO was studied with the X-ray diffraction (XRD) using Cu-Kα radiation. MgO/polyvinylpyrrolidone (PVP) nanocomposites have been prepared by blending MgO nanoparticles with the polyvinylpyrrolidone. MgO/PVP nanocomposites were characterized by Fourier transform infrared (FTIR) spectroscopy. Frequency dependence of dielectric constant (ε′), dielectric loss tangent (tanδ) and AC conductivity studies have been undertaken on the MgO/PVP nanocomposites in the frequency range 50Hz-5MHz at room temperature. Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tanδ) are found to decrease with the increase in the frequency. Further, AC conductivity of MgO/PVP nanocomposites was found to increase with an increase in the frequency. Observed variation in the a. c. conductivity with the frequency has been understood on the basis of electron hopping model.

The effect of modification diamond nanopowders detonation synthesis to change their electrokinetic and electrophysical characteristics

Development of methods for controlling the change in the functional cover and the energy composition of the surface of detonation synthesis diamond nanopowders is necessary to create stable suspensions and materials from them. The aim of this work is to study changes in the electrokinetic and electrophysical characteristics of the powder as a result of the modification of detonation synthesis diamond nanopowders using a liquid-phase thermochemical treatment. Diamond nanopowders of grades ASUD-75 - ASUD-99 with different sp2-hybridization carbon content, manufactured at the V.I. Bakul National Academy of Sciences of Ukraine from the product of detonation synthesis of diamond from the company "ALIT" (Zhytomyr) investigated. Diamond nanopowders of ASUD-90 grade after their modification by means of liquid-phase thermochemical treatment using: a melt of alkalis, a mixture of nitric and sulfuric acids, a mixture of chromic and sulfuric acids were investigated by electrophoresis using a device "Dzeta-potential-analizer" company "Mikromeritiks". Electrokinetic characteristics of diamond nanopowders: the magnitude and sign of the electrokinetic potential, electrophoretic mobility are determined. The methods were used to study the physicochemical characteristics of nanopowders: electrical resistivity, carbon content of sp2-hybridization, mass fraction of impurities in the form of an incombustible residue, and specific surface area. In this work, it was established by electrophoresis that the value of the electrokinetic potential and electrophoretic mobility of the powder decrease by 2-10 times with a decrease in the mass fraction of sp2-hybridization carbon from 23.6 to 0 wt%. Using the ASUD-90 nanopowder as an example, it is shown that the modification of the nanopowder by the liquid-phase method using thermochemical treatment with mixtures of oxidants leads to a decrease in the values ​​of electrophoretic mobility by 1.1-7.5 times and electrokinetic potential by 1.1-7.3 times. It was found by dielectric measurement that the tangent of the dielectric loss angle of diamond nanopowders of grades ASUD-90 - ASUD-99 is in the range 0.3046 - 0.3146. Modification of the ASUD-90 grade nanopowder using a liquid-phase thermochemical treatment leads to a change in the interval of the dielectric loss tangent, namely 0.2450-0.3249. According to the degree of increase in the ratio of the dielectric loss tangent from 0% humidity to 100% humidity, the methods for modifying nanopowders can be arranged as follows: modifying using a melt of alkalis (ASUD-90-1 sample, S = 12.8%) <mixture of chromic and sulfuric acids (sample ASUD-90-3, S = 13.8%) <mixture of nitric and sulfuric acids (sample ASUD-90-2, S = 20.8 %).

Analisis Parameter Antena Mikrostrip dengan Metode Split Ring Resonator pada Frekuensi L-Band

Pada penelitian ini dilakukan perancangan antena mikrostrip dengan menggunakan metode split ring resonator (SRR) untuk aplikasi pada frekuensi L-Band. Antena ini mempunyai dimensi substrat 90 mm x 50 mm dengan panjang patch 60 mm dan lebar patch 44 mm. Desain antena menggunakan material FR4-Epoxy dengan spesifikasi konstanta dielektrik 4,6 dengan ketebalan 1,6 mm dan dielectric loss tangent 0,02. Pada penelitian ini, parameter yang mengalami perubahan signifikan adalah lebar patch SRR, gap SRR, dan posisi SRR pada ground plane. Desain patch SRR dengan nilai sepertiga panjang gelombang pada frekuensi 1,5 GHz memenuhi karakteristik dari frekuensi L-Band. Berdasarkan hasil simulasi, antena menghasilkan bandwidth (< -10 dB) sebesar 1,2466 GHz dengan rentang frekuensi 988,25 MHz sampai 2,2349 GHz. Nilai return loss simulasi adalah -36,89 dB. Pada rentang 1 GHz sampai 2 GHz, gain tertinggi berada pada frekuensi 2 GHz dengan nilai 3,5 dBi. Sedangkan gain terendah adalah 1,21 dBi, yaitu pada frekuensi 1,050 GHz. Secara keseluruhan, desain antena ini telah mencapai performa kinerja yang lebih baik melalui modifikasi pada patch SRR.