Relative Dielectric Permittivity Research Articles

Low-Power Energy Harvesting Voltage Doubler Using CTLs Based on Inverse Class-F Configuration Compatible with Fifth Generation

AbstractThis paper introduces a highly efficient and low-power inverse class-F voltage doubler (VD) designed for radio frequency (RF) energy harvesting systems. Specifically tailored for mid-band 5G technology, the VD is designed for operation within the 1240–1300 MHz satellite band. The innovative design employs an inverse class-F architecture, incorporating a $$\lambda /8$$ λ / 8 short-ended transmission line (TL) connected to the diode anode and a ($$\lambda /12$$ λ / 12 ) open-ended transmission line linked to the input of the voltage doubler. This configuration aims to reshape voltage and current waveforms, effectively reducing losses and series resistance in the diode. Dual-coupled transmission lines (CTLs) are utilized to provide passive voltage boosting at low-input power levels. The suggested voltage doubler is implemented using RO4003C substrate material with a dielectric relative permittivity ($${\upvarepsilon }_{r}$$ ε r ) of 3.38 and a thickness of 0.81 mm. Measured results demonstrate a minimum input return loss of − 29.3 dB at 1.25 GHz, operating seamlessly within a frequency band from 1.18 to 1.32 GHz. The measured conversion efficiency is 45.2% at an input power (Pin) of − 4dBm. Furthermore, the peak RF–DC efficiency reaches 50% at an input power of 0dBm. Simulated results predict a remarkable conversion efficiency of 60% and 68.7% at − 4dBm and 0 dBm, respectively. In addition to its exceptional performance, the suggested voltage doubler exhibits an experimental DC output voltage of 0.53 V at $$P_{{{\text{in}}}} = - 10{\text{dBm}}$$ P in = - 10 dBm and a saturated DC voltage of 3.4 V at an input power of 10dBm under a load terminal resistance of 8 KΩ. Finally, the dimensions of the proposed voltage doubler are $$25.3 \times 10.5 {\text{mm}}^{{2}}$$ 25.3 × 10.5 mm 2 .

Infrared relative dielectric permittivity and refractive index on the spherical CdSe/ZnS heteronanocrystals with self-consistent field

We deal with allowed-subband quantum states of two-electron in a semiconductor spherical core/shell quantum dot. Within framework of the infrared transitions, solving the Schrödinger-Poisson equation for repulsive interactions on the conduction-subbands, we obtain energy shifts in the absorption peaks of dielectric functions . The energy eigenvalues of the CdSe/ZnS nanocrystal have been computed as a function of the layer thicknesses through self-consistent field. The optical absorption transitions related to D − and D 0 donor states, have been plotted considering linear dielectric permittivity. The obtained values of dielectric constant for CdSe monolayers are compared with 3D simulation results. Refractive index and absorption coefficient under 3.0 nm CdSe core radius have been also presented as a function of infrared photon energies.

Electrochemical dielectric response of steel corrosion induced by chloride in simulated concrete pore solution

Electrochemical and dielectric properties of steel oxide films can have an impact on the corrosion process but are still poorly understood due to the unavailability of measurement methods. In this study, electrochemical impedance spectroscopy (EIS) was adopted to interpret steel corrosion induced by chloride in a simulated concrete pore solution. Particularly, validation of EIS data by Kramers–Kronig transforms was performed prior to further EIS interpretation. Relative dielectric permittivity of corroded steel/electrolyte interface was derived through theoretical induction and corrosion products were analyzed by X-ray photoelectron spectroscopy. Results indicated that measured EIS data in the present study depicted good causality and stability. Corrosion at the steel/electrolyte interface induced by increasing chloride led to high relative permittivity within the low frequency domain while marginal difference could be observed at the high frequency range. AC conductivity of corrosion products at steel/solution interfaces revealed a notable frequency dependence, based on which three distinct frequency regions were subdivided.

Nanoscale dielectric properties of TiO2 in SiO2 nanocomposite deposited by hybrid PECVD method

In this paper, nanocomposites (TiO2 in SiO2) are produced by an advanced hybrid aerosol-PECVD method based on direct liquid injection of a non-commercial colloidal solution in an O2 / hexamethyldisiloxane (HMDSO) low-pressure plasma. Dielectric properties are investigated at nanoscale using techniques derived from Atomic Force Microcopy in terms of relative dielectric permittivity, charge injection and transport. Results show that a concentration in TiO2 up to 14% by volume makes it possible to increase the relative dielectric permittivity up to 4.8 while maintaining the insulating properties of the silica matrix. For a TiO2 concentration in the range 15%–37% by volume, the relative dielectric permittivity increases (up to 11 for 37% TiO2 by volume) and only few agglomerated nanoparticles lowering the insulating properties are observed. For TiO2 concentration above 40% by volume, the relative dielectric permittivity still increases but the quantity of agglomerated nanoparticles is very high, which greatly increases the charge transport dynamic and degrades the insulating properties. Finally, 37% of TiO2 by volume in the SiO2 matrix appears to be the best compromise, between high dielectric permittivity and low leakage current for the MIM applications aimed.

Magnetoelectric CoV2O6—Role of Fe inter-play in Co-based Ising spin chain interactions

CoV2O6, a Brannerite-type material, exists in both monoclinic (α) and triclinic (γ) forms. α- CoV2O6 exhibits quasi-1D ferromagnetic chains of octahedrally-coordinated Co2+ions in the higher spin state. Fe2+ doped α-CoV2O6 (3 mol%) single crystals were synthesized using high temperature melt method. The motivation is to investigate whether disruption of 1D Co2+ ferromagnetic chains by small Fe3+ substitution alters the antiferromagnetic ground state and lead to stronger spin-frustration. In this paper, we report the magnetic and magnetodielectric properties of Fe doped α-CoV2O6 in detail. The strongly anisotropic nature of magnetic and magnetodielectric characteristics were captured well in the data through orientation dependent measurements with H being parallel to a and c axes of the crystal. Relative dielectric permittivity (εr) exhibited sharp peaks coinciding with the plateau edges Hc1 ∼2.2 T and Hc2 ∼4.4 T in the magnetization curves (M-H) for applied H parallel to a-axis. For dielectric measurements under applied H parallel to c-axis, relative dielectric permittivity exhibited sharp peak around Hc2 ∼3.1 T, again coinciding with the M-H behavior. Such closely related magnetic field induced dielectric transitions reflected in both M(H) and εr(H) measurements is a rare phenomenon and representative of strong spin-lattice coupling in this phase.

Electromagnetic and microwave properties of single-layer thermoplastic natural rubber (TPNR)/yttrium iron garnet (Y3Fe5O12)/magnetite (Fe3O4) composites backed by a perfect conductor

The use of a single-layer material for microwave applications continues to attract many researchers due to materials’ homogeneity in an acceptable range of thickness. This study outlines the microwave electromagnetic characteristics and interpretation of results based on a single-layer material backed by a perfect conductor. Data from three different laboratory prepared thermoplastic natural rubber (TPNR)/yttrium iron garnet (Y3Fe5O12)/magnetite (Fe3O4) composites were presented. The microwave relative complex dielectric permittivity (ε r*) and magnetic permeability (µ r*) were measured using a microwave vector network analyser (MVNA) in the frequency range of 0.1846–10.0104 GHz. The specular material model backed by a perfect conductor was used to obtain the frequency-dependent reflection loss (R L) assuming a normal incident of electromagnetic (EM) wave. The real and imaginary components of ε r* (ε r′ and ε r″) and µ r* (µ r′ and µ r″) for the three samples show a similar trend of frequency dependent. TPNR/Y3Fe5O12 reflected the EM wave less when its thickness (t) equals a quarter of the propagating wavelength (λ m/4) inside the material. Interestingly, in the presence of Fe3O4, multiple minimal reflections occur at smaller thicknesses (e.g. t = λ m/32). For both cases, this is the condition where the reflected wave at the surface of the material is in a 180°-phase difference from the wave reflected earlier at the material-conductor interface. Destructive interference occurs when these two waves meet and is visualized as the dip on the reflection loss (R L) vs. frequency plot. The number of dips increases with thickness. The lowest frequency dip occurs at a lower frequency for a thicker material. For TPNR/Y3Fe5O12/Fe3O4 and TPNR/Fe3O4, as the material gets thicker, the high-frequency dips on the R L plot become smaller and the use of the material in microwave application is no longer practical due to the increase in its weight and a smaller reflection loss.

Enhancing subsurface contamination assessment via ensemble prediction of ground electrical property: A Colorado AMD-impacted wetland case study

Acid mine drainage (AMD) is recognized as a major environmental challenge in the Western United States, particularly in Colorado, leading to extreme subsurface contamination issue. Given Colorado's arid climate and dependence on groundwater, an accurate assessment of AMD-induced contamination is deemed crucial. While in past, machine learning (ML)-based inversion algorithms were used to reconstruct ground electrical properties (GEP) such as relative dielectric permittivity (RDP) from ground penetrating radar (GPR) data for contamination assessment, their inherent non-linear nature can introduce significant uncertainty and non-uniqueness into the reconstructed models. This is a challenge that traditional ML methods are not explicitly designed to address. In this study, a probabilistic hybrid technique has been introduced that combines the DeepLabv3+ architecture-based deep convolutional neural network (DCNN) with an ensemble prediction-based Monte Carlo (MC) dropout method. Different MC dropout rates (1%, 5%, and 10%) were initially evaluated using 1D and 2D synthetic GPR data for accurate and reliable RDP model prediction. The optimal rate was chosen based on minimal prediction uncertainty and the closest alignment of the mean or median model with the true RDP model. Notably, with the optimal MC dropout rate, prediction accuracy of over 95% for the 1D and 2D cases was achieved. Motivated by these results, the hybrid technique was applied to field GPR data collected over an AMD-impacted wetland near Silverton, Colorado. The field results underscored the hybrid technique's ability to predict an accurate subsurface RDP distribution for estimating the spatial extent of AMD-induced contamination. Notably, this technique not only provides a precise assessment of subsurface contamination but also ensures consistent interpretations of subsurface condition by different environmentalists examining the same GPR data. In conclusion, the hybrid technique presents a promising avenue for future environmental studies in regions affected by AMD or other contaminants that alter the natural distribution of GEP.

Determination of the maximum mechanical stresses in the insulating material around a defect with a high dielectric permittivity in an electrostatic field

Introduction. All insulating macrohomogeneous solid materials change shape under the influence of an electric field. Problem. The presence of minor defects changes the distribution of an electric field and causes a significant concentration of mechanical stresses in a given section of the material, which, under certain circumstances, can cause partial or complete destruction of this material. Goal. The purpose of the work is to determine maximum mechanical stresses according to the von Mises criterion in insulating materials around defects with ionized air and water in an electrostatic field. Also, to analyze the influence of the following parameters on the indicated stresses: the location of the defect, the orientation angle of the semi-major axis of the defect cross-section, the ratio of semi-major and semi-minor axes, elastic and dielectric properties of the insulating material and the defect. Methodology. The study is based on the interrelated equations of electrostatics and structural mechanics for an isotropic piecewise homogeneous medium. The solution of these equations is obtained by the finite element method. Results. Graphs of dependences of maximum mechanical stresses on the ratio of semi-major and semi-minor axes of the ellipsoidal cross-section of the defect have been obtained. The minimum ratio of the greatest stresses in the insulating materials around the surface cracks and pores for ionized air has been 9.3 times for the maximum ratio of major and minor semi-axes of the cross-section of the defect considered in the work, which is 10. For a water defect, the similar ratio has been 2...5.6 times, increasing when the relative dielectric permittivity of the insulating material changes from 7 to 2. When Young’s modulus of the insulating material increases from 1 MPa to 100 GPa, the angles of the inclination of the linearized dependences of maximum mechanical stresses around bounded pores with ionized air (water) to the axis of the ratio of major and minor semi-axes of the defect cross-section have been increased by 35.9° (58.0°) and 18.6° (20.1°) at orientations of major semi-axes at angles of 0° and 45°, respectively. Originality. The numerical-field mathematical two-dimensional model has been developed for the first time, which consists of sequentially solved equations of electrostatics and structural mechanics, for the determination of the distribution of mechanical stresses in an insulating material with a liquid or gaseous defect. It has been established for the first time that the ratio of the elastic properties of the insulating material and the defect determines the angle of the inclination of the linearized dependence of the maximum mechanical stress to the axis of the ratio of major and minor semi-axes of the defect cross-section. Practical value. The types of defects that contribute to the aging of insulation materials under the combined action of an electric field and a stress field to the greatest extent have been established.

A drift‐diffusion based electrothermal model for organic thin‐film devices including electrical and thermal environment

AbstractWe derive and investigate a stationary model for the electrothermal behavior of organic thin‐film devices including their electrical and thermal environment. Whereas the electrodes are modeled by Ohm's law, the electronics of the organic device itself is described by a generalized van Roosbroeck system with temperature‐dependent mobilities and using Gauss–Fermi integrals for the statistical relation. The currents give rise to Joule heat which together with the heat generated by the generation/recombination of electrons and holes in the organic device occur as source terms in the heat flow equation that has to be considered on the whole domain. The crucial task is to establish that the quantities in the transfer conditions at the interfaces between electrodes and the organic semiconductor device have sufficient regularity. Therefore, we restrict the analytical treatment of the system to two spatial dimensions. We consider layered organic structures, where the physical parameters (total densities of transport states, reference energy levels , disorder parameter, basic mobilities, activation energies, relative dielectric permittivity, heat conductivity) are piecewise constant, and we work in a setting for some . We prove the existence of weak solutions using Schauder's fixed point theorem and a regularity result for strongly coupled systems with nonsmooth data and mixed boundary conditions that is verified by Caccioppoli estimates and a Gehring‐type lemma.

Improved antimicrobial and antibiofilm efficacy of adaptable BaTi2Fe4O11−(x)NiFe2O4 nanoceramics: investigating microstructural and spectroscopic analysis

In the pursuit of multifunctional applications, researchers face a crucial challenge in creating an efficient and economically viable perovskite-ferrite nanomaterial. In response to this challenge, multifunctional (1−x)BaTi2Fe4O11−(x)NiFe2O4 (BTF−xNFO) nanoceramics, where (x = 0.1–0.7), were successfully synthesized using the sol-gel method at a temperature of 550 °C. The XRD and FTIR were used to identify the crystal and chemical structure of the multifunctional nanocomposites. The XRD analysis confirms the emergence of a multiphase structure, with iron barium titanate adopting a hexagonal crystalline structure and nickel ferrite assuming a cubic crystalline arrangement. Moreover, the relative dielectric permittivity showcases frequency-dependent tendencies, showcasing a pronounced decline as the frequency increases. The obtained results highlighted the remarkable antimicrobial and antibiofilm potentials of BTF-7NF across all tested microbes. The study assessed the minimum inhibitory and biocidal concentrations of a specific nanocomposite. In terms of its antibiofilm properties, it was found that a concentration of 200 µg/ml of this nanocomposite (BTF-7NF) effectively eliminated biofilm formation.These findings strongly suggest BTF-7NF as a promising alternative antibacterial agent, capable of preventing harmful bacterial biofilm formation at exceptionally low concentrations.

Samarium-Doped Lead Magnesium Niobate-Lead Titanate Ceramics Fabricated by Sintering the Mixture of Two Different Crystalline Phases.

The fabrication method plays a key role in the performance of lead magnesium niobate-lead titanate-based ceramics. (1 - w)[Pb(Mg1/3Nb2/3)0.67Ti0.33O3]-w[Pb1-1.5xSmx(Mg1/3Nb2/3)yTi1-yO3] piezoelectric ceramics were prepared by sintering the mixture of two different crystalline phases in which two pre-sintered precursor powders were mixed and co-fired at designated ratios (w = 0.3, 0.4, 0.5, 0.6). The X-ray diffraction results show that all the ceramics presented a pure perovskite structure. The grains were closely packed and the average size was ~5.18 μm based on observations from scanning electron microscopy images, making the ceramics have a high density that is 97.8% of the theoretical one. The piezoelectric, dielectric, and ferroelectric properties of the ceramics were investigated systematically. It was found that the properties of the ceramics were significantly enhanced when compared to the ceramics fabricated using the conventional one-step approach. An outstanding piezoelectric coefficient d33 of 1103 pC/N and relative dielectric permittivity ε33/ε0 of 9154 was achieved for the ceramics with w = 0.5.

Tuning the temperature coefficient of the resonant frequency of the AlPO4–BPO4–SiO2 ternaries with TiO2 addition and sintering atmosphere control

Microwave ceramics with low relative dielectric permittivities (εr), high-quality factors (Q×f values), and near-zero temperature coefficients of resonant frequency (τf) are strongly required for the 5 G and forthcoming 6 G wireless communication system. Effects of the TiO2 addition and atmosphere control on the microstructures and microwave dielectric properties of 0.05AlPO4-0.05BPO4-0.90SiO2 (5A5B90S) and 0.45AlPO4-0.45BPO4-0.10SiO2 (45A45B10S) ternaries were investigated in this paper to achieve the above objective. Adding TiO2 produced the TiP2O7 and/or (TiO)2P2O7 secondary phases in the 5A5B90S, and TiP2O7 in the 45A45B10S sintered bodies, respectively, which improved their sinterabilities. Near zero-τf value (τf∼ −2.0(8) ppm/°C) whilst retaining low εr (∼4.97(7)) and high Q×f value (54,000 ± 1619 GHz) could be attained for the 5A5B90S with the addition of 15 wt% TiO2. In contrast, both the Q×f and τf values deteriorated with the addition of TiO2 for the 45A45B10S. Sintering in the B2O3 protection atmosphere helps suppress the formation of TiP2O7 and/or (TiO)2P2O7 secondary phases for both samples, specifically in the surface layer of the sample, which increased the tunability of τf to be near zero. Combined good microwave dielectric properties with εr∼4.47(6)，Q×f ∼ 48000 ± 950 GHz，τf∼ − 2.1(8) ppm/°C; εr∼ 5.05(8)，Q×f ∼ 45,326 ± 900 GHz，τf∼ − 7.6 ± 1.2 ppm/°C could be attained for the 5A5B90S + 10 wt% TiO2 and 45A45B10S + 15 wt% TiO2 ceramics, respectively by sintering in B2O3 protection atmosphere.

Investigation of Dielectric Measurement Model for Coconut Fiber Water Content and the Associated Factors

Coconut fiber has excellent permeability and water retention properties, making it a popular choice as an organic substrate for cultivation in the field of facility agriculture. To investigate the dielectric properties of coconut fiber and develop an accurate measurement model for dielectric water content, a vector network analyzer was used to measure the relative dielectric permittivity of coconut fiber and study the dielectric properties of coconut fiber under different volumetric water contents, temperatures, and salinities. The results indicated that the relative dielectric permittivity of the coconut fiber increased with increasing volumetric water content. The optimal frequency range for measuring the water content of the coconut fiber was 200 MHz–3 GHz, with an optimal frequency of 210 MHz. The dielectric measurement model for the water content in the coconut fiber established at this frequency demonstrated good applicability, with an R2 of 0.9704 and RMSE of 0.0453 cm3/cm3. At the same moisture level (θV of approximately 30% and 50%), the error in the real part of the dielectric permittivity was less than 1.35 between 15 and 35 °C, and the error in the moisture content was less than 0.0339 cm3/cm3. The error due to the salinity was 0.0750 cm3/cm3. The experimental results showed that the modeling of the water content measurement of coconut fiber at 210 MHz can be applied to general greenhouse environmental conditions. This study serves as a valuable reference for calibrating the moisture monitoring sensors used in greenhouses for coir cultivation substrates, emphasizing the need for non-destructive, real-time monitoring of moisture content.

Adsorption of a Polyelectrolyte Chain at Dielectric Surfaces: Effects of Surface Charge Distribution and Relative Dielectric Permittivity

Adsorption of a Polyelectrolyte Chain at Dielectric Surfaces: Effects of Surface Charge Distribution and Relative Dielectric Permittivity

Improved piezoelectric properties of 2–2 piezoelectric single crystal composites for acoustic transducer applications via alternating current polarization

Piezoelectric single-crystal composites with 2–2 type (2–2 PSCCs) have attracted widespread attention in acoustic transducer applications due to the higher hydroacoustic piezoelectricity and electromechanical coupling performance compared to traditional ceramic piezoelectric composites. At present, alternating current polarization (ACP) has been proven as an effective method to improve the performance of piezoelectric materials. Here, to optimize the conditions of ACP, the influence of ACP on the properties of 2–2 PSCCs with different amplitudes, frequencies, and polarization cycles of the electric field was investigated. Compared to direct current polarized (DCP) samples, the piezoelectric coefficient (d33), the relative free dielectric permittivity (ε33T/ε0), and the thickness electromechanical coupling factor (kt) of ACP samples were improved by 36%, 60%, and 3.5% respectively. Furtherly, the domain structure of DCP and ACP samples was compared, and the result demonstrates that the improvement in piezoelectric and dielectric properties is related to the grown domain size in single crystals. This work shows a simple and effective method to improve the performance of 2–2 PSCCs.

Primary standard for complex units of permittivity at frequency range 0.1–178.4 GHz GET 110-2023

The article is dedicated to research in the fi eld of measuring the dielectric parameters of materials. The aim of the research is to study promising methods for measuring the complex dielectric permittivity of weakly absorbing materials in the decimeter wavelength range, as well as the non-resonant method for measuring the dielectric parameters of materials with high dielectric losses. In order to achieve the set goal of improving the state primary standard of complex dielectric permittivity in the frequency range from 1 to 178.4 GHz, tasks were set to expand the frequency range to 0.1 GHz and the range of reproducible values of the dielectric loss tangent to 10–1. As a result of the improvement, new equipment was introduced into the composition of the standard, and new measurement methods were developed. To measure the complex dielectric permittivity of weakly absorbing materials in the decimeter wavelength range, a resonant measurement method in a coaxial resonator with a shortening capacitive gap and a measurement method in a bulk H011-resonator with dielectric fi lling were developed. To measure elevated dielectric losses up to 10–2–10–1, a measurement method using a non-resonant measuring transducer based on a shielded dielectric waveguide with a measured dielectric sample as such a waveguide has been developed. The developed methods are applied in the Primary standard of complex dielectric permittivity in the frequency range from 0.1 to 178.4 GHz, GET 110-2023. The frequency range of the standard is 0.1–178.4 GHz, the range of reproducible values of relative dielectric permittivity is 1.2–500, dielectric loss tangent 10–8–10–1. The scope of application of GET 110-2023 is metrological support of dielectric control in production of radio frequency cables, telecommunication equipment, electronic components, etc.

Wearable Capacitive Tactile Sensor Based on Porous Dielectric Composite of Polyurethane and Silver Nanowire.

In recent years, the implementation of wearable and biocompatible tactile sensing elements with sufficient response into healthcare, medical detection, and electronic skin/amputee prosthetics has been an intriguing but challenging quest. Here, we propose a flexible all-polyurethane capacitive tactile sensor that utilizes a salt crystal-templated porous elastomeric framework filling with silver nanowire as the composite dielectric material, sandwiched by a set of polyurethane films covering silver nanowire networks as electrodes. With the aids of these cubic air pores and conducting nanowires, the fabricated capacitive tactile sensor provides pronounced enhancement of both sensor compressibility and effective relative dielectric permittivity across a broad pressure regime (from a few Pa to tens of thousands of Pa). The fabricated silver nanowire-porous polyurethane sensor presents a sensitivity improvement of up to 4-60 times as compared to a flat polyurethane device. An ultrasmall external stimulus as light as 3 mg, equivalent to an applied pressure of ∼0.3 Pa, can also be clearly recognized. Our all-polyurethane capacitive tactile sensor based on a porous dielectric framework hybrid with conducting nanowire reveals versatile potential applications in physiological activity detection, arterial pulse monitoring, and spatial pressure distribution, paving the way for wearable electronics and artificial skin.

Electron-beam synthesis of thin magneto-dielectric coatings with mixed nickel-iron and upper alumina layers

We have synthesized magneto-dielectric coatings with thicknesses 290, 550, 5460 and 6063 nm with an upper protective and electrically insulating layer of alumina ceramic and a lower magnetic iron-nickel layer. The coatings were formed in a helium atmosphere at forevacuum pressures (from 1.5 to 15 Pa) by electron-beam evaporation of a mixture of iron and nickel fragments, and of a solid alumina ceramic target placed in a separate crucible. Magnetic properties of the coatings have been studied by a ferromagnetic resonance technique with estimation of the effective saturation magnetization together with evaluation of the signal-to-noise ratio and relative broadening of the resonance lines. Owing to the layer of alumina ceramic, the values of relative dielectric permittivity (5.6) and electrical conductivity (0.78–3.00 mS/m) remain typical for thin-film dielectrics.

Magnetically active composites with relatively giant dielectric permittivity

"Magnetically active composites based on silicone rubber, silicone oil, carbonyl microparticles, graphene nanopallets and fabric, as a reinforcing element, are manufactured. For a constant amount of carbonyl iron microparticles and silicone oil, and for different ratios between the amounts of silicone rubber and graphene nanopalets, three composite samples are prepared. Using the plane capacitor method, the relative permittivity of the composites is determined. It is shown that by using graphene nanopallets, composites with giant values of relative dielectric permittivity can be obtained and that the relative dielectric permittivity values are sensitive to the magnetic force induced by the static magnetic field superimposed on the medium-frequency electric field. Using the model of the dipolar magnetic approximation and elements of the theory of dielectrics in medium frequency electric fields, the mechanisms participating in the obtained effects are described."

Condition Assessment of Natural Ester-Mineral Oil Mixture Due to Transformer Retrofilling via Sensing Dielectric Properties.

Mineral oil (MO) is the most popular insulating liquid that is used as an insulating and cooling medium in electrical power transformers. Indeed, for green energy and environmental protection requirements, many researchers introduced other oil types to study the various characteristics of alternative insulating oils using advanced diagnostic tools. In this regard, natural ester oil (NEO) can be considered an attractive substitute for MO. Although NEO has a high viscosity and high dielectric loss, it presents fire safety and environmental advantages over mineral oil. Therefore, the retrofilling of aged MO with fresh NEO is highly recommended for power transformers from an environmental viewpoint. In this study, two accelerated aging processes were applied to MO for 6 and 12 days to simulate MO in service for 6 and 12 years. Moreover, these aged oils were mixed with 80% and 90% fresh NEO. The dielectric strength, relative permittivity, and dissipation factor were sensed using a LCR meter and oil tester devices for all prepared samples to support the condition assessment performance of the oil mixtures. In addition, the electric field distribution was analyzed for a power transformer using the oil mixtures. Furthermore, the dynamic viscosity was measured for all insulating oil samples at different temperatures. From the obtained results, the sample obtained by mixing 90% natural ester oil with 10% mineral oil aged for 6 days is considered superior and achieves an improvement in dielectric strength and relative permittivity by approximately 43% and 48%, respectively, compared to fresh mineral oil. However, the dissipation factor was increased by approximately 20% but was at an acceptable limit. On the other hand, for the same oil sample, due to the higher molecular weight of the NEO, the viscosities of all mixtures were at a higher level than the mineral oil.