Electric Current Density Distribution Research Articles

Significantly improved dielectric performances of nanocomposites via loading two-dimensional core-shell structure Bi2Te3@SiO2 nanosheets

Polymer/semiconductor-insulator nanocomposites can display high dielectric constants with a relatively low dissipation factor under low electric fields, and thus seem to promising for high energy density capacitors. Here, a novel nanocomposite films is developed by loading two-dimensional (2D) core-shell structure Bi2Te3@SiO2 nanosheets in the poly (vinylidene fluoride-hexafluoro propylene) (P(VDF-HFP)) polymer matrix. The 2D Bi2Te3 nanosheets were prepared through simple microwave-assisted method. The experimental results suggesting that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the dielectric constant, dielectric loss, AC conductivity, and breakdown strength of composites films. The composite films load with 10 vol.% 2D Bi2Te3@SiO2 nanosheets exhibits a high dielectric constant of 70.3 at 1 kHz and relatively low dielectric loss of 0.058 at 1 kHz. The finite element simulation of electric field and electric current density distribution revealed that the SiO2 shell layer between the fillers and polymer matrix could effectively improve the energy loss, local electric field strength, and breakdown strength of composite films. Therefore, this work will provide a promising route to achieve high-performance capacitors.

Enhancement of the electromagnetic energy in the asymmetric split rings with compensated microstructures

We study the terahertz transmission properties in mirrored asymmetric split ring metamaterials which were fabricated by using the method of microstructures compensation. Combined with the analysis of finite difference time domain, the distribution of terahertz electric field and current density are discussed in metamaterials structures. Our experiments show that the quality factor in compensated microstructures is 12.5 at the frequency of 0.92 THz which is higher than that of 8.29 in the uncompensated microstructures. The estimation of THz energy stored in the capacitor configuration indicate that the stored energy in compensated structures is 1.46 times that of in uncompensated structures, which resulted in the enhancement of quality factor about 50% in the compensated microstructures.

Fill factor controlled nanoimprinted ZnO nanowires based on atomic layer deposition

Enhanced diffraction by sub-wavelength nanostructures to convert incident electromagnetic radiation into waveguide modes has applications in anti-reflective coatings for optoelectronic devices. We propose a metal oxide (ZnO) nanowire grid polarizer as such a nanostructure, fabricated by ultraviolet nanoimprint lithography and whose fill factor (FF) is controlled by atomic layer deposition. Using finite difference time domain simulations, we investigated the polarization-dependent optical transmittance of the structures and calculated the polarizing efficiency. Optical profiles such as electric and magnetic field intensity and current density distributions of specific FF nanopatterns were determined for the transverse magnetic and transverse electric modes. The effects of geometrical parameters including the wire-grid period, fill ratio, and spacing between the wire-grid layers on diffraction wavelength were characterized. Respective FF-controlled ZnO nanowire structures were fabricated and their experimental optical transmittances were measured for nanowire grid polarizer applications.

Significantly Enhanced Dielectric Performances and High Thermal Conductivity in Poly(vinylidene fluoride)-Based Composites Enabled by SiC@SiO2 Core-Shell Whiskers Alignment.

Design of composites with ordered fillers arrangement results in anisotropic performances with greatly enhanced properties along a specific direction, which is a powerful tool to optimize physical properties of composites. Well-aligned core-shell SiC@SiO2 whiskers in poly(vinylidene fluoride) (PVDF) matrix has been achieved via a modified spinning approach. Because of the high aspect ratio of SiC whiskers, strong anisotropy and significant enhancement in dielectric constant were observed with permittivity 854 along the parallel direction versus 71 along the perpendicular direction at 20 vol % SiC@SiO2 loading, while little increase in dielectric loss was found due to the highly insulating SiO2 shell. The anisotropic dielectric behavior of the composite is perfectly understood macroscopically to have originated from anisotropic intensity of interfacial polarization based on an equivalent circuit model of two parallel RC circuits connected in series. Furthermore, finite element simulations on the three-dimensional distribution of local electric field, polarization, and leakage current density in oriented SiC@SiO2/PVDF composites under different applied electrical field directions unambiguously revealed that aligned core-shell SiC@SiO2 whiskers with a high aspect ratio significantly improved dielectric performances. Importantly, the thermal conductivity of the composite was synchronously enhanced over 7 times as compared to that of PVDF matrix along the parallel direction at 20 vol % SiC@SiO2 whiskers loading. This study highlights an effective strategy to achieve excellent comprehensive properties for high-k dielectrics.

Numerical simulations of electric potential field for alternating current potential drop associated with surface cracks in low-alloy steel nuclear material

Low-alloy steels used as structural materials in nuclear power plants are subjected to cyclic stresses during power plant operations. As a result, cracks may develop and propagate through the material. The alternating current potential drop technique is used to measure the lengths of cracks in metallic components. The depth of the penetration of the alternating current is assumed to be small compared to the crack length. This assumption allows the adoption of the unfolding technique to simplify the problem to a surface Laplacian field. The numerical modelling of the electric potential and current density distribution prediction model for a compact tension specimen and the unfolded crack model are presented in this paper. The goal of this work is to conduct numerical simulations to reduce deviations occurring in the crack length measurements. Numerical simulations were conducted on AISI 4340 low-alloy steel with different crack lengths to evaluate the electric potential distribution. From the simulated results, an optimised position for voltage measurements in the crack region was proposed.

Evaluation of flow behavior in copper electro-refining cell with different inlet arrangements

Abstract The arrangement of electrolyte inlet in the copper electro-refining (ER) cell has a great influence on the local flow field, which affects the distribution of electrical current density in consequence. In order to understand the complicated phenomena of electrolyte flow behavior in vertical counter electrodes in full-scale copper ER cell, the three-dimensional computational fluid dynamics (CFD) models with four different arrangements of electrolyte inlets, i.e., single inlet (SI), central bottom inlets (CBI), top side interlaced inlets (TII), and bottom side interlaced inlets (BII), were established to simulate the flow behavior. Simulation results have revealed that the parallel injection devices help to improve the electrolyte velocity between electrodes, and while the relative range of electrolyte velocity in CBI exceeds that of TII and BII, which is more than 4 times, indicating its severer unequal flow distribution. Meanwhile, the average velocity of electrolyte in BII is 4 times larger than that of SI due to its higher turbulence intensity. Generally, one of the efficient ways to supply fresh copper solution rapidly and uniformly into the inter-electrode space is to adapt the arrangement of BII. By utilizing such an arrangement, the electro-refining under high electrical current density is possible, and the productivity can be increased in sequence.

Enhanced the breakdown strength and energy density in flexible composite films via optimizing electric field distribution

High energy density flexible composite films have been used for the modern compact electronic devices and electric power systems. A novel nanocomposite film is developed by embedding polydopamine encapsulated Ba0.6Sr0.4TiO3 nanoparticles (BST NPs) in the polyvinylidene fluoride polymer matrix. The surface functionalization of BST NPs with polydopamine facilitates favorable interaction between the particle and polymer phase, enhancing nanoparticle dispersion. The elaborate functionalization of BST NPs with polydopamine has guaranteed both the increase of dielectric constant and the maintenance of breakdown strength, resulting in significantly enhanced energy storage capability. A finite element simulation of electric field and electric current density distribution suggested the functionalized BST NPs significantly enhanced the breakdown strength and energy density of the composite films. The nanocomposite with 2.5 vol% functionalized BST NPs displays a high energy density of 6.3 J cm−3 at the low field of 3500 kV m−1, which is larger than that of the biaxially oriented polypropylenes (BOPP) (1.2 J cm−3 at the field of 6400 kV m−1). Therefore, the proposed flexible composites films would also find their potential application prospects in electrical devices such as mobile electronic devices, hybrid electric vehicles and military.

An ultra-broadband metamaterial absorber based on the hybrid materials in the visible region

In this paper, an ultra-broadband metamaterial absorber is successfully designed in the visible region. The structure of the absorber is just obtained by the two-dimensional plane structure which rotate 90° along x-axis. Furthermore, the formation of the structure for the hybrid materials is based on the four U-shaped structure of the metal titanium is embedded in the semiconductor (indium antimonide). The simulated results show that the proposed metamaterial absorber can achieve an ultra-broadband absorption with greater than 90% from 252.2 to 822.3 THz, and the relative absorption bandwidth gets to 106.1%. Finally, the simulated electric field, surface current and power loss density distributions further illustrate the absorption mechanism of the metamaterial absorber. And we believe the metamaterial absorber will have many potential applications in energy harvesting and stealth devices.

Two methods of AC loss calculation in numerical modelling of superconducting coils

Numerical methods are widely utilised in the prediction of AC loss in superconducting coils. A commonly used approach is based on determination of the local dissipation calculated from the distributions of electrical field and current density throughout the winding, as well as its evolution over the AC cycle. This quantity reflects the heat release on a microscopic scale, and its integration throughout the coil winding over one AC cycle provides the value of loss per cycle in the coil. On the other hand, one can look at global quantities characterising the energy flow from a power supply to the coil: the electrical current supplied and the voltage on its terminals. Averaging, with respect to time, of the voltage times current product also gives the coil loss per cycle. Here we show that a comparison of results obtained with ‘local’ and ‘global’ methodologies can be useful in identifying the numerical errors caused by calculation techniques. However, this is possible only when the modelling method allows for determination of the essential physical quantities as independent variables. We illustrate this approach with an example utilising the A-φ and H-formulations for the AC loss evaluation in a ten-turn pancake coil wound from coated conductor tape.

Fabrication and simulation of semi-transparent and flexible PMMA/ATO conductive nanocomposites obtained by compression molding at different temperatures and pressures

This paper investigated the effect of temperature and pressure on the microstructure and electrical behavior of compression molded and mechanically blended polymer composites. Poly (methyl methacrylate) (PMMA) and antimony tin oxide (ATO) were used as the matrix and conductive filler respectively and the composition was varied from 0 to 1.75 ATO vol %. Mixtures of the two precursor materials were compression molded at temperatures ranging from 150 to 190 °C and pressures ranging from 12 to 50 MPa. It was found that a segregated network microstructure was formed in all cases but that the distribution of the conductive ATO fillers varied as a function of the compression molding temperature and pressure used. The thickness of the specimens, determined by the amount of precursor materials and pressure used during compression molding, was also found to affect the resulting microstructure and concomitant properties. The electrical conductivity of these polymer matrix composites can be increased by up to 2 orders of magnitude by decreasing the processing temperature, while maintaining the processing pressure and the filler concentration constant. On the other hand, the flexibility of PMCs can be improved by increasing the processing temperature. For the compositions evaluated, the maximum electrical conductivity obtained was 5 x 10-3 S/m (about three orders of magnitude lower than the conductivity of the filler). Finite element simulations were used to model this microstructure-driven phase segregated percolation behavior. COMSOL Multiphysics® was used to calculate the electric potential and current density distribution in a 3D geometry. There was good agreement between the experimental and simulation results.

Imaging of current flow in the human head during transcranial electrical therapy

BackgroundIt has been assumed that effects caused by tDCS or tACS neuromodulation are due to electric current flow within brain structures. However, to date, direct current density distributions in the brains of human subjects have not been measured. Instead computational models of tDCS or tACS have been used to predict electric current and field distributions for dosimetry and mechanism analysis purposes. Objective/HypothesisWe present the first in vivo images of electric current density distributions within the brain in four subjects undergoing transcranial electrical stimulation. MethodsMagnetic resonance electrical impedance tomography (MREIT) techniques encode current flow in phase images. In four human subjects, we used MREIT to measure magnetic flux density distributions caused by tACS currents, and then calculated current density distributions from these data. Computational models of magnetic flux and current distribution, constructed using contemporaneously collected T1-weighted structural MRI images, were co-registered to compare predicted and experimental results. ResultsWe found consistency between experimental and simulated magnetic flux and current density distributions using transtemporal (T7-T8) and anterior-posterior (Fpz-Oz) electrode montages, and also differences that may indicate a need to improve models to better interpret experimental results. While human subject data agreed with computational model predictions in overall scale, differences may result from factors such as effective electrode surface area and conductivities assumed in models. ConclusionsWe believe this method may be useful in improving reproducibility, assessing safety, and ultimately aiding understanding of mechanisms of action in electrical and magnetic neuromodulation modalities.

Ultrafast Discharge and Enhanced Energy Density of Polymer Nanocomposites Loaded with 0.5(Ba0.7Ca0.3)TiO3–0.5Ba(Zr0.2Ti0.8)O3 One-Dimensional Nanofibers

One-dimensional (1D) materials as fillers introduced into polymer matrixes have shown great potential in achieving high energy storage capacity because of their large dipole moments. In this article, 1D lead-free 0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Zr0.2Ti0.8)O3 nanofibers (BCZT NFs) were prepared via electrospinning, and their formation mechanism was systematically studied. Polypropylene acyl tetraethylene pentamine (PATP) grafted into the surface of BCZT NFs was embedded in the polymer matrixes, which effectively improved the distribution and compatibility of the fillers via chemical bonding and confined the movement of the charge carriers in the interface filler-matrix. The energy density at a relatively low electric field 380 MV m-1 was increased to 8.23 J cm-3 by small loading of fillers, far more than that of biaxially oriented polypropylene (BOPP) (≈ 1.2 J cm-3 at 640 MV m-1). Moreover, the nanocomposite loaded with 2.1 vol % BCZT@PATP NFs exhibits a superior discharge speed of ≈0.189 μs, which indicates the potential application in practice. The finite element simulation of electric potential and electric current density distribution revealed that the PATP grafted into the BCZT NFs surface could significantly improve the dielectric performances. This work could provide a new design strategy for high-performance dielectric polymer nanocomposite capacitors.

3d current density in tumors and surrounding healthy tissues generated by a system of straight electrode arrays

The knowledge of the adequate current density distribution to apply when using different electrode arrays in tumor tissue and the healthy surrounding tissue is one of the most significant challenges to improve the effectiveness of electrochemical treatment. This paper proposes a mathematical approach to obtain a three-dimensional analytical expression for the current density generated by multi-needle electrodes. Such array of electrodes can be allocated in an arbitrary shape and inserted anywhere in the tumor. Calculations of the electrical potential and electric current density distributions based on a three-dimensional model for different straight multi-needle electrode configurations are carried out by solving the Laplace equation. The results show that appropriate positioning, insertion depth and electrodes polarity are essential for tumor treatment with direct current and multiple needle electrodes, arranged in concentric circumferences, concentrate a higher electric current density in the tumor. This configuration of multiple straight needle electrodes inserted along the tumor improves the effectiveness of electrochemical treatment because the current density covers the entire volume of the tumor, unlike those configurations that are inserted in the tumor base and only partially cover its volume.

High-Energy-Density Polymer Nanocomposites Composed of Newly Structured One-Dimensional BaTiO3@Al2O3 Nanofibers

Flexible electrostatic capacitors are potentially applicable in modern electrical and electric power systems. In this study, flexible nanocomposites containing newly structured one-dimensional (1D) BaTiO3@Al2O3 nanofibers (BT@AO NFs) and the ferroelectric polymer poly(vinylidene fluoride) (PVDF) matrix were prepared and systematically studied. The 1D BT@AO NFs, where BaTiO3 nanoparticles (BT NPs) were embedded and homogeneously dispersed into the AO nanofibers, were successfully synthesized via an improved electrospinning technique. The additional AO layer, which has moderating dielectric constant, was introduced between BT NPs and PVDF matrixes. To improve the compatibility and distributional homogeneity of the nanofiller/matrix, dopamine was coated onto the nanofiller. The results show that the energy density due to high dielectric polarization is about 10.58 J cm-3 at 420 MV m-1 and the fast charge-discharge time is 0.126 μs of 3.6 vol % BT@AO-DA NFs/PVDF nanocomposite. A finite element simulation of the electric-field and electric current density distribution revealed that the novel-structured 1D BT@AO-DA NFs significantly improved the dielectric performance of the nanocomposites. The large extractable energy density and high dielectric breakdown strength suggest the potential applications of the BT@AO-DA NFs/PVDF nanocomposite films in electrostatic capacitors and embedded devices.

A parallel solution for the numerical study of transcranial magnetic stimulation using the scalar potential finite differences method

Introduction In transcranial magnetic stimulation (TMS) coils are used for the stimulation of human brain cortex. Numerous coil designs have been proposed and tested for different applications, both diagnostic and therapeutic. Purpose The objective of the current study is the fast and accurate calculation of the induced electric field and current density distribution inside the human head, in order to allow for the design of coils fulfilling specific treatment requirements. Materials and methods In order to avoid the intense computation of finite and boundary element meshes we developed a parallel in-house code, which implements a finite difference method. It calculates the magnetic scalar potential inside a human head model, given the electric conductivity distribution and the magnetic vector potential from 3D thin-wire coils. Tissue conductivity values can be derived either from volumetric data of realistic, voxelized human models, or from DICOM data segmentation. The numerical code was validated using analytical solutions of induced electric field in homogeneous conductive spherical models. Results The simulation gives information on focality, depth of stimulus, peak value and orientation of the induced electric field for different coil topologies. These characteristics of the TMS are different for various areas of the brain cortex. Furthermore, they show not only intra- but also inter-subject changes that can easily be quantified. Conclusion Our code can calculate the induced electric fields from TMS coils in the tissues of a human head model. The results can be derived within reasonable computational times and, therefore, the code can be used in the future to design coils with given specifications. Disclosure Authors declare that they have no competing interests.

An air core pulse transformer with a linearly integrated primary capacitor bank to achieve ultrafast charging

An air core transformer that linearly integrates a capacitor bank as well as a selfclosing switch into the primary winding (LIP) was designed to achieve ultrafast charging. Limiting stray inductance and maximizing the uncoupled dual resonance of the primary and secondary windings were the primary design criteria. To show this concept, two transformers with an uncoupled resonant frequency of approximately 8 MHz were designed for a low voltage output (several kV) and a high voltage output (>100 kV). The design was simulated in a Multisim discrete circuit model and a CST hybrid model which includes the transformer's 3-D structure as well as discrete circuit components. The discrete output (voltage and current) as well as the distributed parameters (electric field distribution and surface current density distribution) for the transformer were obtained. These designs were validated by experimental results. We show that their respective resonance characteristic and voltage gain are accurately predicted by the simulated values, demonstrating the design procedure is valid for both low voltage and high voltage applications. For the high voltage transformer, it has a voltage gain of 3-4. The maximum output voltage was tested up to 120 kV. A charging pulse with a rise time of less than 100 ns was obtained.

Observation and micro-electrochemical characterisation for micro-droplets in initial marine atmospheric corrosion

Micro-droplets formed around NaCl droplet on carbon steel surface were observed with a confocal laser scanning microscope. Micro-electrochemical characterisation of the micro-droplets zone was also performed by a scanning Kelvin probe (SKP) and the scanning vibrating electrode technique (SVET). Results show that the electric current density and potential distribution of carbon steel under the NaCl droplet are asymmetrical; the peripheral regions of the droplet are cathodic, whilst its centre is anodic. The potential difference between the anode and cathode is 0.36 V, and the cathodic current density reaches 2.02 μA cm−2. This kind of asymmetrical distribution of electrochemical characterisation results in cathodic polarisation at the fringe of the NaCl droplet, thus inducing the formation of OH–, which could promote water adsorption and subsequent formation of micro-droplets around the NaCl droplet. The electrochemical potential difference of the oxygen concentration cell formed between the central and peripheral regions of the NaCl droplet is the main driving force for micro-droplet formation on metal surfaces.

Simulation of the Electric Current Flow in Amorphous-Crystalline Ti<sub>2</sub>NiCu Alloy with Shape Memory Effect

A new technique for the production of nanograined alloys from rapidly quenched amorphous ribbons by serial electric pulses has been proposed recently [1]. The present work involves a theoretical study of electric current flow in a nonhomogeneous Ti2NiCu alloy consisting of an amorphous matrix with a crystalline phase of spherical morphology embedded in it. The electric current density distribution was calculated in the vicinity of a spherical nucleus, which has an electrical resistance that is only 0.4 times that of the amorphous matrix. The calculation of Joule heat density was done in the nucleus and in the amorphous volume surrounding it. It was shown that during the current pulse the Joule heat evolution in nucleus exceeds one in equatorial region in matrix, but less than near the poles. The dependence of relative resistivity of nonhomogeneous amorphous-crystalline alloy on volume fraction of spherical crystalline nuclei was calculated

Simulation of Micro ECM for Complex-shaped Holes

A novel electrochemical machining (ECM) method using tool electrodes with controlled conductive area ratio to shape the complex inner surface of holes was discussed. The machining process was modeled to investigate the electric potential and current density distribution on the electrodes’ surface and in the electrolyte, and the evolution of shape of inner surface of the hole. The effect of current efficiency was taken into account when determining the machining velocity of target hole. The relationship between conductive area ratio and the machining depth was also discussed. Simulation results showed that this method is capable of creating reverse-tapered micro holes and holes with various complex internal features with relatively simple control system.

Numerical Simulation of the Electroslag Casting With Liquid Metal for Producing Composite Roll

The electroslag casting with liquid metal (ESC LM) is a new technology for producing composite roll of high quality based on electroslag metallurgy. In the present work, a two‐dimensional quasi‐steady state mathematical model of just one half of the ESC LM facility is developed due to the axial symmetry. Influences of operating voltage and pouring temperature on the heat transfer of the composite roll system have been studied. The Lorentz forces and Joule heat are combined with the turbulent flow and energy equations via additional source terms in these equations by the user‐defined functions (UDF) based on Fluent software. Simulation results indicate that the distributions of electric potential, current density, Lorentz forces, and Joule heat are concentrated on the upper area of slag bath and a much shallower molten steel pool is obtained. By using the current carrying mold, the heat transfer from slag bath and superheat of the molten steel pool are lower than the conventional ESR process, which is beneficial to a vertical crystallization and an excellent bonding interface between the roll core and working layer of the composite roll. The study of this paper gives us a better understanding of the ESC LM process.