Relative Permittivity Values Research Articles

Visible-light responsive BiVO4 nanocompositions: Enhanced photocatalytic, electrical and optical performance through Ni and Ni/Co doping

The pronounced light sensitivity of BiVO4 has garnered significant attention, establishing it as a visible light-responsive photocatalyst. This study was focused on enhancing the optical, dielectric constant properties, and photocatalytic activity of BiVO4 compositions. By employing a modified combustion method, pure BiVO4, Ni-mono-doped (BiNi0.02V0.98VO4), and Ni/Co-bi-doped (BiCo0.02Ni0.02V0.96VO4) were synthesized. X-ray diffraction (XRD) analysis validated the formation of a monoclinic BiVO4 phase. The incorporation of Ni2+ and Co2+ ions into the BiVO4 lattice was supported by variations in the lattice parameters, volume expansion and increased average crystallite size. Morphological investigation via scanning electron microscopy (SEM-EDAX) confirmed the purity of the synthesized nanocompositions and unveiled distinctive rod-like and needle-like particle shapes in BiNi0.02Co0.02V0.96VO4, with an aspect ratio of 0.07–0.1, indicating potential benefits for efficient charge separation in photocatalysis. Optical examination highlighted redshifts in band gap energy (2.36 eV) due to both Ni and (Co, Ni) co-doping, leading to direct band gaps of 2.34 eV and 2.32 eV, respectively. High refractive index values exceeding 2.5, conducive to optical applications, were observed across all samples. Through Ni and Ni/Co doping process, a notable enhancement in conductivity emerged, particularly within the low-frequency domain. The co-doping of Ni and Co demonstrated elevated relative permittivity (εʹ) values exclusively within the low-frequency span, up to 100 Hz. In contrast, the Ni-mono-doping interestingly disclosed an enhancement in (εʹ) across all frequency ranges. Photocatalytic results demonstrated heightened degradation activity in doped samples, with the BiNi0.02Co0.02V0.96VO4, sample exhibiting the highest rate, achieving 88 % degradation efficiency in 180 min. This exceptional performance can be attributed to its visible-light-responsive band gap, increased electron-hole trapping sites, and distinct morphology.

The Simulation of The Propagation of Electromagnetic Waves Through a Material with Various Thicknesses Using Finite Difference Time Domain (FDTD)

A finite difference time domain method in one dimension (1D-FDTD) is employed to study the properties of the propagation of electromagnetic waves across a medium with finite thicknesses. In this paper, we simulated the propagation of a Gaussian pulse. Since we simulated in one dimension, the absorbing boundary condition (ABC) can be applied to minimize undesirable reflection which generated at the numerical boundaries. We also implemented total field / scattering field (TF/SF) to ensure the source propagated in only one direction. The analysis performed by inserting the object with both relative permittivity and permeability values higher than one decreased the pulse’s amplitude.

Rock drilling performance of rotary ultrasonic tools incorporating PZT piezoceramic and Mn:PIN-PMN-PT piezocrystal

High performance Mn:PIN-PMN-PT piezocrystal material is investigated to understand if its extraordinary properties can replace the traditional hard piezoceramic material for space exploration applications. A bolted Langevin-style ultrasonic drill tool incorporating a pair of Mn:PIN-PMN-PT piezocrystal rings is built to compare with a same configuration ultrasonic drill tool actuated with a pair of hard piezoceramic rings, which are tuned to the first longitudinal mode (L1) at around 20 kHz. From the characterisation results, it is observed that the piezocrystal material presents significantly greater values of relative permittivity, electromechanical coupling coefficient, and piezoelectric charge coefficient than the hard piezoceramic material. Despite these outstanding properties, the piezocrystal driven ultrasonic drill tool shows similar displacement amplitudes to its counterpart. Nonetheless, the impedance magnitude of the piezocrystal driven ultrasonic drill tool at resonance is a magnitude lower than the piezoceramic actuated drill tool, due to the large piezoelectric charge coefficient d33. Ultrasonic rock drilling experiments suggest that the cutting force for sandstone and marble are greatly reduced, but limestone and tuff are less affected.In general, the piezocrystal driven ultrasonic drill tool demonstrates a marginally improved cutting performance than the piezoceramic actuated drill tool, in terms of lower cutting force and motor power consumption, however, the tool wear appears slightly poorer. The research outcome of this paper indicates that the thickness mode of the piezocrystal rings might not be the optimal form of excitation, which could be due to the piezoelectric losses at high excitation levels, so other excitation conditions and vibration modes will need to be explored to fully adopt the extraordinary material properties of the piezocrystal material.

Room temperature fabrication and post-impregnation of LMO-ST composites: Engineering and modeling of dielectric properties

In this work, the effect of changing the Li2MoO4-SrTiO3 (LMO-ST) compositional proportion (1–100 wt%) on the microstructure, dielectric properties, and relative density of LMO-ST composites fabricated at room temperature was investigated. The results showed that increasing the LMO binder content resulted in a higher relative density (up to 93%), but a lower dielectric constant in the range of 75 to 5. Good agreement between the experimental results and the predicted values of relative permittivity was obtained using the Lichtenecker model, reformulated for a three-phase composite system. Modeling further explained the detrimental effects of porosity on the dielectric properties. To address this issue, impregnation with titanium (IV) isopropoxide (TTIP) was found to reduce overall porosity and improve relative permittivity from 72 to 99 at 1 MHz. The room temperature fabrication offers a wide range of relative permittivity for LMO-ST composites.

Valorization of ripe banana peels and cocoa pod husk hydrochars as green sustainable “low loss” dielectric materials

The banana and cocoa crops are relevant worldwide and tons of their residues do not enter the industrial value chain. With this in mind, it is imperative to find alternative uses for these residues that could lead to novel and sustainable applications in diverse fields, such as consumer electronics. Lignocellulosic residues can be hydrothermally carbonized to produce a solid fraction called hydrochar. In this work, the dielectric characteristics of ripe banana peels and cocoa pod husks hydrochars are explored. Hydrothermal carbonization (HTC) treatments were carried out at two temperatures (150 °C and 210 °C) and three HTC times (2 h, 4 h, and 6 h). The materials were characterized electrically using a Semiconductor Analyzer under frequency swepts of 1 KHz to 1 MHz. Cocoa pod husk hydrochars (CHH) showed less variability in relative permittivity values compared to ripe banana peel hydrochars (BPH). The relative permittivity values of CHH ranged between 9.83 and 10.29 (150 °C) and 8.25–9.39 (210 °C), while for BPH, these values ranged between 6.89 and 14.14 (150 °C) and 6.39–8.77 (210 °C). In addition, the loss tangent values of CHH varied from 0.034 to 0.041 (150 °C) and from 0.036 to 0.038 (210 °C), while in BPH, these values varied from 0.056 to 0.091 (150 °C) and from 0.046 to 0.051 (210 °C). In both cases, HTC produced highly stable materials with low loss tangent values, making them good candidates for insulation and possessing good dielectric properties that can be further processed for downstream applications in the electronics industry.

Magnetic and Electrical Characteristics of Nd3+ and Mn2+-Co-doped Calcium Molybdato-Tungstates Single Crystals.

Single crystals of Ca1-3x-yMny□xNd2x(MoO4)1-3x(WO4)3x molybdato-tungstates (□ denotes vacant sites) with a scheelite-type structure have been successfully grown by the Czochralski technique in an inert atmosphere. This paper presents the results of structural, optical, magnetic, and electrical properties, as well as the broadband dielectric spectroscopy measurements of single crystals with different Nd3+ ion concentrations, i.e., when x = 0.0050 or x = 0.0098, and with constant content of Mn2+ ions, i.e., when y = 0.0050. Our magnetic studies have shown that substitution of diamagnetic Ca2+ ions in the CaMoO4 matrix with paramagnetic Nd3+ ones with a content not exceeding 0.02 and having a screened 4f-shell revealed a significant effect of orbital diamagnetism and Van Vleck's paramagnetism. Both single crystals have revealed residual electrical conductivity without an intrinsic region and a change of sign of the Seebeck coefficient at ca. 230 K. Dielectric spectroscopy measurements have shown constant values of relative permittivity (εr ∼ 8) and loss tangent (tan δ ∼ 0.01) both up to 400 K and up to 1 MHz, as well as the Fermi energy (∼0.04 eV) and the Fermi temperature (∼500 K) determined for both crystals from the diffusion component of thermopower. These results suggest the presence of shallow acceptor and donor levels in the studied crystals.

Model of Electrical Stimulation of Back Muscles in the Treatment of Scoliosis

The article presents a three-dimensional model of the tissues of the human back in the ZBrush and SolidWorks software packages. Modeling of the spinal column with a bend, muscles, adipose tissue and skin was performed. Using the COMSOL Multiphysics environment, the effects of electrical stimulation on biological objects are modeled, and characteristics are determined. When modeling, in the properties of each biological tissue, the values of electrical conductivity and relative permittivity were set, the electrodes were adjusted, a grid was created to divide the models into smaller parts and elements, and the required frequency was adjusted. To verify the simulation results, a study was carried out on the patient, the calculation and analysis of the results obtained. The developed models can be used in clinical medicine to determine the strength of the stimulating current and set the parameters of electrical stimulation. When building a model, one can change the thickness of adipose tissue, skin, muscle and bone sizes, change the size of the electrodes, and thereby select the most optimal parameters for electrical stimulation. Models can be used in the development of the most effective method of electrical stimulation and the scheme for applying electrodes for a certain type of scoliosis.

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.

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."

Ground penetrating radar detection of buried depth of pavement internal crack in asphalt surface: A study based on multiphase heterogeneous model

Sample identification method and virtual generation method were put forward to construct the multiphase heterogeneous asphalt surface models of the pavement for electromagnetic differential simulation, which reproduces the actual phase distribution better compared with the homogeneous models and the random heterogeneous models applied in the current studies. For the electromagnetic wave with different frequency which transmitted by the ground penetrating radar (GPR), the generation mechanism of the heterogeneity interference wave and the reflection wave from the top or bottom of layer was discussed, and their influences on the identification of internal crack with different relative permittivity values were analyzed. The heterogenous dielectric distribution in the asphalt surface layer was studied by combining simulation and laboratory test, and the double-way travel time method for detecting the buried depth was optimized on this basis, and an additional term reflecting the heterogeneity interference was introduced into the buried depth detection results.

Analysis and characterization of structural, dielectric and magnetic properties of MgxCo(0.90−x)Zn0.10Fe2O4 nanoparticles based flexible metamaterial absorber for wireless communication

The anisotropic flexible metamaterial absorber (FMA) structure comprises a resonating layer, a ferrite-based flexible substrate layer, and a back layer. The sol-gel method is used to prepare the ferrite-based nanomaterial for enhancing absorbability. The solution prepared material is according to the formula of MgxCo(0.90−x)Zn0.10Fe2O4 and specified as X25, X50, X75 for X = 25%, 50%, and 75%, respectively. Then the proposed ferrites materials are characterized by XRD, and FESEM, respectively. Moreover, the magnetic and dielectric properties of the proposed MgxCo(0.90−x)Zn0.10Fe2O4 ferrites samples were explored for microwave applications. The dielectric constants and loss tangents of the fabricated, flexible substrates are measured at a frequency range of 3–7 GHz using the DAK 3.5. The computed relative permittivity values are 2.95 for X25, 3.55 for X50, and 4.05 for X75, respectively, while the loss tangents values are 0.00295 for X25, 0.00495 for X50, and 0.00695 for X75. Whereas the permeability and magnetic loss tangent values varied from 0.875 to 1.00 and 0.00225–0.00585, respectively. Finally, the resonators of the absorber consist of a Y-style shape, square-shaped metallic plate resonator, square ring resonator (SRR), and cross-liked shape. The proposed flexible metamaterial absorber (FMA) structure is developed on MgxCo(0.90−x)Zn0.10Fe2O4 nanomaterial-based flexible substrate with dimensions of 0.110λ x 0.110λ x 0.017λ to validate the design experimentally. The electrical dimension is calculated at a 5.5 GHz resonance frequency. The simulated results from the CST Microwave Studio simulator reveal that absorption peaks at 5.5 GHz with a 99.99% absorption that includes the C band frequency that can be used in satellite applications. The proposed FMA structure achieved a 60° incident angle response for TE and TM modes. The structure has superiority with compact dimensions, lightweight, and flexibility and can be used for C band wireless communications.

Structural, optical and giant dielectric constant properties of pure ktenasite and schulenbergite/CuO minerals

In this study, schulenbergite [(Cu,Zn)7(SO4)2(OH)10·3H2O)]/CuO and pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] minerals were simply synthesized via addition of sodium sulfide (Na2S) to a mixture of nanosized CuO powder dispersed into Zn(NO3)2·6H2O solution. The X-ray diffraction patterns illustrate the formation of schulenbergite/CuO mineral with ratio of 69:31% and 87/13% owing to additions of 0.1 and 0.2 mol L−1 Na2S, respectively. The addition of 0.4 mol L−1 Na2S substance lead to formation of pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral. The absorption vibration modes based on Fourier-transform infrared (FTIR) analysis verified the formation of schulenbergite/CuO and pure ktenasite compositions. The scanning electron microscope micrographs of schulenbergite/CuO and pure ktenasite samples reveal the formation of mixed grains with needle, sheets, cotton and wool shapes. The selected area electron diffraction images of the synthesized powders show strong dot-rings, indicating polycrystalline nature. Optically, all samples possess a high absorption ability for infrared-visible light wavelengths. At lower frequencies, the pellet of pure ktenasite sample exhibits giant dielectric constant characteristics. Exactly, pure ktenasite sample reveals a dielectric constant value of ~ 1.3 × 106 at frequency of 42 Hz. For schulenbergite/CuO (87/13%) sample, a large dielectric constant value of ~ 5311 was measured at frequency of 42 Hz. The colossal and variable relative permittivity values make the pure ktenasite [(Cu,Zn)5(SO4)2(OH)6·6H2O)] mineral is a suggested material for energy storage applications.

Giant dielectric constant and ac electrical conductivity: Cu and Cu/W incorporated perovskite BaTiO3

Gigantic relative permittivity and ac electrical conductivity characteristics were realized in BaTiO3 through incorporation of Cu2+ and Cu2+/W4+ ions. The XRD results evidenced that pure BaTiO3 powder has a single phase with tetragonal structure. In Cu doped and (Cu, W) codoped samples, α-Ba2TiO4 phase with ratio of 17–25% was formed into BaTiO3 powder. The crystal analysis proved that the formed α-Ba2TiO4 phase naturally decay with time or heating at high temperature. The SEM micrographs illustrated the formation of elongated connected network particles in Cu doped and (Cu, 1%W) codoped BaTiO3 while cauliflower-like grains were seen for (Cu, 3% W) codoped BaTiO3 sample. Pure BaTiO3 powder reveals an ultraviolet (UV) absorption edge, corresponding to band gap energy of 3.25 eV. Owing to Cu2+ doping and (Cu2+, W4+) codoping, the absorption edge of BaTiO3 structure was powerfully red shifted and displayed oblique lines, matching to band gap energies within 3.06–2.68 eV. Pure BaTiO3 reveals a relative permittivity value of 811 (42 Hz) which transferred to gigantic values of (7.01572 × 105), (9.54016 × 105) and (3.00234 × 105) after insertion of Cu2+ and (Cu2+, W4+) ions. For Cu doped and (Cu, 1% W) codoped BaTiO3, the giant relative permittivity was considerably increased with temperature up to 125 °C and until 150 °C for (Cu, 3% W) codoped BaTiO3 sample. After decomposition of α-Ba2TiO4 phase (α-Ba2TiO4 → BaTiO3 + BaO), the dielectric constant still reveals stable colossal values equal to (7.5300 × 104), (3.66431 × 105) and (1.2277 × 104) at frequency of 42 Hz for Cu doped, (Cu, 1% W) and (Cu, 3% W) codoped BaTiO3, respectively.

Volumetric water content estimation of concrete by particle swarm optimization of GPR data

This study investigates the Volumetric Water Content (VWC) of concrete block by inversion of Ground-penetrating radar (GPR) traces by Particle Swarm Optimization (PSO) method. PSO method was applied to GPR data set, which contains 24 days of data. PSO was used as a tool to estimate relative dielectric permittivity, relative magnetic permeability and electrical conductivity values of concrete. The relative dielectric permittivity has a direct relationship with the water content. Generally, the relative dielectric permittivity value is estimated from velocity estimation by picking reflections on radargrams. However, the picking of reflection may be erroneous and subjective. In this case, this study was aimed on PSO method as an inversion tool to estimate relative dielectric permittivity to calculate VWC of concrete instead of velocity calculation approach to avoid man-made error during first arrivals picking. Firstly, PSO application on the 3rd day data of the fresh concrete was introduced in detail. Afterwards, PSO results on all data set were presented. In order to show the accuracy of PSO calculations, the percentages of relative error (%RE) values, which indicate the fit between observed and calculated GPR traces, were estimated. %RE values were varied between 3.11% and 6.05%. After the PSO process, estimated dielectric permittivity values were used to calculate the VWC. So, the PSO application was utilized to monitor water content change of concrete. Nevertheless, besides the traditional methods, the information on the water content can be obtained with the proposed method non-destructively.

Carbon-Dot-Containing Poly(methyl methacrylate) for Highly Dielectric Nanomaterials

In this paper, we report a massive enhancement of the relative permittivity of PMMA-based nanodielectrics in the presence of carbon dots (CDs) and neodymium-doped carbon dots (Nd-CDs). Different weight percentages (0.5, 5, and 10 wt %) of CDs and Nd-CDs were composited with PMMA to form PMMA@CD and PMMA@Nd-CD nanocomposite films, and films were characterized by different techniques. The dielectric response study indicates the significant enhancement of the relative permittivity of PMMA in the presence of CDs (∼15 times), and this value is increased further in the presence of Nd-CDs (∼153 times). The presence of many interfaces inside the PMMA@CD composites due to nanofillers is the cause of this significant enhancement in dielectric permittivity, which is further increased in the presence of Nd-CDs. As the temperature increases, the effective dipolar polarization of the composites increases, which in turn helps enhance relative permittivity. Nevertheless, at 75 °C and 100 Hz, the relative permittivity value for PMMA@Nd-CD composites reaches nearly 1242 (234 times), the highest reported for PMMA composites to date. Moreover, the AC conductivity for PMMA@Nd-CD is higher than that for PMMA@CD, possibly as a result of more charge conduction from the valence band to the conduction band for PMMA@Nd-CD. The conductivity is also increased as a function of temperatures for all composites as a result of the decrement of electronic resistance inside semiconductor nanofillers. In this study, a unique and sensitive change in dielectric and electrical properties of PMMA-based nanodielectrics was observed, which is helpful in the commercial use of PMMA nanodielectrics inside capacitors.

Influence of the intermediate oxidation layer on the characteristics of lead zirconate titanate thin films with aluminium substrate

This paper presents a flexible piezoelectric device that has been realized by depositing lead zirconate titanate (PZT) thin films by chemical solution deposition (CSD) on a commercial aluminum foil as a substrate. The thermal treatment required for the crystallization of the PZT thin films leads to the oxidation of the substrate and a parasitic intermediate layer of alumina (Al2O3) is formed between the substrate and the first PZT layer. The comparison with and without the use of a conductive ruthenium dioxide (RuO2) interlayer, which can shunt the insulating alumina layer, showed the influence of the latter on the different characteristics of the material. The thickness of the alumina layer on the surface of the aluminum substrate after deposition of the PZT film (≈ 39 nm) was determined by calculation and confirmed by transmission electron microscopy (TEM). Dielectric characterization of the sample without considering this layer gives the permittivity of the Al2O3/PZT bilayer and not the active material alone (PZT). A relative permittivity value of 313 is measured against 558 for the single PZT layer if the alumina layer is taken into account, which means a decrease of 44%. The piezoelectric characterization is also influenced by the alumina layer, the piezoelectric coefficient is 14 pC/N while it is 26 pC/N when this layer is taken into account. This study evidences and quantitatively evaluates the influence of the oxidation layer (Al2O3) on the dielectric and piezoelectric characteristics and mechanical energy harvesting performances.

Composite Feedstock Filaments for Fused Deposition Modeling (FDM) of Microwave Interconnects

Improved manufacturing methodology of ceramic-thermoplastic composite feedstock filaments using solvent assisted dispersion is presented with one of the highest reported ceramic particle filler volume concentration of 50%. Relative permittivity values up to 12.35 along with a low loss tangent of 0.003 have been achieved for newly developed feedstock filaments. They have been employed for fuse deposition modelling (FDM) of test specimens for characterization of complex permittivity, which exhibited dielectric loss tangent in the range of 0.001-0.007 at frequencies ranging from 4 GHz to 12 GHz. This is on par with that of the best microwave laminates. Also, surfactant-assisted ball milling was used to downsize ceramic fillers, while simultaneously applying a surface treatment by a strategically chosen surfactant to improve the interfaces between organic matrix and inorganic particles. The effect of the surfactant surface treatment on the dielectric and loss properties of the composite feedstock materials has been explored, which is compared with analytical model predictions. Two 40 mm-long dielectric rod waveguides (DWG’s) were 3D printed by using an in-house developed composite filament and a commercial counterpart. The former exhibited a much lower attenuation of 0.012 dB/mm as compared to 0.038 dB/mm shown by the latter. Measurements were compared to 3D EM simulation results to extract effective permittivity of DWG fabricated by FDM printing using in-house developed composite feedstock filament, which agrees very well with measured permittivity values.

Electrical Aging Effect on PD Characteristics of Cellulose Pressboard Modified by Nano-TiO2

Cellulose pressboard has been widely used as internal insulation in oil-immersed transformers. Partial discharge (PD) is the main cause of the degradation of the insulation properties for electrical equipment. Nano-modification is one of the methods to improve the electrical properties of the oil–paper insulation. In this article, the effects of the oil-immersed pressboards modified by nano-TiO2 particles on PD characteristics were studied. The pressboards modified by different mass fractions of nano-TiO2 (10-nm particle size) were prepared. The electrical aging experiment was carried out on the oil-immersed pressboard. Experimental platforms for partial discharge inception voltage (PDIV) and relative permittivity were established to measure the dielectric performance of the pressboard. Phase-resolved partial discharge (PRPD) spectrograms and PD current pulses of the samples under different electrical aging states were obtained for different PD time. The surface morphology of the pressboards was observed by scanning electron microscope (SEM) to verify the effects of nano-TiO2 particles. The results showed that the values of electric field strength for the samples were 4.58 and 3.6 kV/mm, respectively, when the PD occurred in the samples modified by nano-TiO2 with 3 wt% and the unmodified ones. Compared with the unmodified pressboard, the modified one had a lower value of relative permittivity. The pulse current of the pressboard modified by 3 wt% nano-TiO2 particles under different electrical aging states was smaller than that of the other samples. The addition of 3 wt% nanoparticles was the optimum ratio to suppress the PD of the samples in the ac electrical field.

Time Domain Reflectometry Waveform Interpretation With Convolutional Neural Networks

AbstractInterpreting time domain reflectometry (TDR) waveforms obtained in soils with non‐uniform water content is an open question. We design a new TDR waveform interpretation model based on convolutional neural networks (CNNs) that can reveal the spatial variations of soil relative permittivity and water content along a TDR sensor. The proposed model, namely TDR‐CNN, is constructed with three modules. First, the geometrical features of the TDR waveforms are extracted with a simplified version of VGG16 network. Second, the reflection positions in a TDR waveform are traced using a 1D version of the region proposal network. Finally, the soil relative permittivity values are estimated via a CNN regression network. The three modules are developed in Python using Google TensorFlow and Keras API, and then stacked together to formulate the TDR‐CNN architecture. Each module is trained separately, and data transfer among the modules can be facilitated automatically. TDR‐CNN is evaluated using simulated TDR waveforms with varying relative permittivity but under a relatively stable soil electrical conductivity, and the accuracy and stability of the TDR‐CNN are shown. TDR measurements from a water infiltration study provide an application for TDR‐CNN and a comparison between TDR‐CNN and an inverse model. The proposed TDR‐CNN model is simple to implement, and modules in TDR‐CNN can be updated or fine‐tuned individually with new data sets. In conclusion, TDR‐CNN presents a model architecture that can be used to interpret TDR waveforms obtained in soil with a heterogeneous water content distribution.