Electric Current Density Distribution Research Articles

Magnetic flux density measurement through phase decomposition using non‐interleaved scan in MREIT

Magnetic resonance electrical impedance tomography (MREIT) measures the z-component of magnetic flux density B = (Bx, By, Bz) induced by externally injected current through a pair of electrodes. MREIT visualises in-vivo electrical current density and/or conductivity distribution in a three-dimensional imaging object from the measured magnetic flux density Bz. MREIT techniques typically use the phase difference approach in an interleaved encoding scheme by the injection of positive and negative currents to cancel systematic phase artefacts. Developed is a method to measure Bz data using only a single scan by the injection of one current, avoiding the interleaved encoding scheme. The method separates measured multiple k-space lines into acquired k-space lines with and without injection currents and develops an algorithm to measure the magnetic flux density Bz using acquired k-space lines by the injecting current. Results from phantom experiments demonstrate that the method has potential to measure magnetic flux density using only a single scan by the injection of one current.

Proposal of ECM method for holes with complex internal features by controlling conductive area ratio along tool electrode

Holes with complex internal features are difficult to machine with traditional mechanical machining methods. In this paper, a novel electrochemical machining (ECM) method using a tool electrode with controlled conductive area ratio to shape the complex inner surface of the hole was presented. 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 the shape of inner surface of the hole. Simulation results showed that the proposed ECM method has the potential to create holes with various complex internal features. A prototype tool electrode with gradually decreased conductive area from its tip to the root was fabricated and used in the verification experiment. The machining result showed that a reverse-tapered hole was successfully shaped and the inner hole profile is in well accordance with the simulation result.

Modeling and simulation study of a metal free organic–inorganic aqueous flow battery with flow through electrode

A novel redox flow battery based on soluble organic redox active material is attracting increasing research attention, which employs a family of molecules known as quinones. A three dimensional numerical model of the novel flow battery with a flow through electrode has been developed. The electric current density and the ion current density along the electrode thickness under different specific areas and different electrode conductivities are analyzed, accounting for the electrode thickness effect on the cell performance. It can be concluded that six layers of carbon paper is the most appropriate electrode thickness. More than six layers of carbon paper provides more surface area at the expense of higher ohmic resistance, which is not appropriate. Less carbon paper cannot provide enough specific active area. The flow fields in the x direction and z direction are analyzed to account for the electric current density distribution. The high current density at the junction of the land and channel for the flow through electrode cell is related to the flow field in z direction. The simulation results are well-fitted for the experiment data. In addition, we improve the previously existing electrolyte conductivity calculation model and demonstrate that accurate electrolyte conductivity values are required for accurate modeling of the experiment. The model is validated using data obtained from combining a quinone/hydroquinone couple with a Br2/Br− redox couple flow battery system.

電流経路可視化技術

電流経路可視化技術

Simulation on Electrical Conductivity of CNTs/PE Composites

In order to investigate the electrical conductivity of carbon nanotubes (CNTs)/polyethylene (PE) composites, the relationship curves between the external electrical filed strength and the electrical conductivity of CNTs/PE composites with different microstructures were generated based on numerical simulation. The simulation models of CNTs/PE composites were designed through changing the content, aspect ratio and orientation degree of CNTs. After DC electrical field is applied between top and bottom surfaces of the composites, the distribution of electrical current density was calculated based on the finite element method by using the COMSOL simulating software, and then the electrical conductivity is obtained. Research results indicated the electrical conductivity of the composites increases significantly with the increase of aspect ratio of CNTs at the same CNT content and electrical field strength. As the orientation degree of CNTs along the applied electrical field increases, the electrical conductivity of the composites obviously increases. It can therefore be concluded that the changing of microstructures of CNTs/PE composites is effective to control the electrical conductivity of the composites.

Global Solar Free Magnetic Energy and Electric Current Density Distribution of Carrington Rotation 2124

Solar eruptive phenomena, like flares and coronal mass ejections(CMEs) are governed by magnetic fields. To describe the structure of these phenomena one needs information on the magnetic flux density and the electric current density vector components in three dimensions throughout the atmosphere. However, current spectro-polarimetric measurements typically limit the determination of the vector magnetic field only to the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field for global solar atmosphere using a nonlinear force-free field(NLFFF) extrapolation codes implemented to a synoptic maps of photospheric vector magnetic field synthesized from Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) as boundary condition. Using the resulting three dimensional magnetic field, we calculate the three dimensional electric current density and free magnetic energy throughout the solar atmosphere for Carrington rotation 2124. We found that spatially, the low-lying, current-carrying core field demonstrates strong concentration of free energy in the AR core, from the photosphere to the lower corona; the coronal field becomes slightly more sheared in the lowest layer and it relaxes to the potential field configuration with height. The free energy density appears largely co-spatial with the electric current distribution.

Realization of magnetic resonance current density imaging at 3 tesla.

Magnetic Resonance Current Density Imaging (MRCDI) is an imaging modality, which reconstructs electrical current density distribution inside a material by using Magnetic Resonance Imaging (MRI) techniques. In this study, a current source with maximum current injection capability of 224.7mA, under 1kΩ resistive load is used. Experiments are performed with a 2D uniform phantom, in which a current steering insulator is inserted. Magnetic flux density distributions are measured, and current density images are reconstructed. The reconstructed images are in agreement with the reconstructions obtained with simulated measurements.

Calculation of Ionized Field of HVDC Transmission Lines by the Meshless Method

In this paper, the meshless method is used to calculate the ion flow field under the high-voltage direct current transmission lines for the first time. The meshless local Petorv-Galerkin method is employed to solve Poisson's equation, and the upwind meshless method is applied to solve the current continuity equation. After the validity of the method is tested, the distribution of electric field and ion current density at ground level with different temperature and altitude of the transmission lines are discussed. The results show that the electric field and the current density are greater when the temperature and altitude are higher.

Hybrid finite-element/boundary-element method to calculate Oersted fields

The article presents a general-purpose hybrid finite-element/boundary-element method (FEM/BEM) to calculate magnetostatic fields generated by stationary electric currents. The efficiency of this code lies in its ability to simulate Oersted fields in complex geometries with non-uniform current density distributions. As a precursor to the calculation of the Oersted field, an FEM algorithm is employed to calculate the electric current density distribution. The accuracy of the code is confirmed by comparison with analytic results. Two examples show how this method provides important numerical data that can be directly plugged into micromagnetic simulations: The current density distribution in a thin magnetic strip with a notch, and the Oersted field in a three-dimensional contact geometry; similar to the type commonly used in spin-torque driven nano-oscillators. It is argued that a precise calculation of both, the Oersted field and the current density distribution, is essential for a reliable simulation of current-driven micromagnetic processes.

Electromagnetophoresis of a Colloidal Sphere in a Spherical Cavity

The quasi-steady electromagnetophoretic motion of a spherical colloidal particle positioned at the center of a spherical cavity filled with a conducting fluid is analyzed at low Reynolds number. Under uniformly applied electric and magnetic fields, the electric current and magnetic flux density distributions are solved for the particle and fluid phases of arbitrary electric conductivities and magnetic permeabilities. Applying a generalized reciprocal theorem to the Stokes equations modified with the resulted Lorentz force density and considering the contribution of the magnetic Maxwell stress to the force exerted on the particle, which turns out to be important, we obtain a closed-form formula for the migration velocity of the particle valid for an arbitrary value of the particle-to-cavity radius ratio. The particle velocity in general decreases monotonically with an increase in this radius ratio, with an exception for the case of a particle with high electric conductivity and low magnetic permeability relative to the suspending fluid. The asymptotic behaviors of the boundary effect on the electromagnetophoretic force and mobility of the confined particle at small and large radius ratios are discussed.

Validation of predictive model for galvanic corrosion under thin electrolyte layers: An application to aluminium 2024-CFRP material combination

An experimental setup was developed for the validation of a finite element model (FEM) for simulating galvanic corrosion occurring under very thin electrolyte for bi-material combination composed of aluminium AA2024 and carbon-fibre reinforced polymer (CFRP). The validation approach is explained and the results obtained are presented. The main outcomes of the model are electric current density and potential distribution on the electrode surface. Good agreement has been obtained between measured and modelled data. Further parameter studies are discussed to show the effect of different physical properties of the electrolyte on corrosion rates and total current changes in the materials involved.

Two different types of plasmoids in the plasma sheet: Cluster multisatellite analysis application

AbstractThe fine magnetic field structure of two successive plasmoids previously reported is investigated by magnetic rotation analysis using four Cluster satellite data. Between these two plasmoids, opposite trends of curvature radius (Rc) variations of the magnetic field lines from the boundary to the inner part are found. The different variations of Rc reflect that the two plasmoids have different magnetic configurations. The electric current density distributions for both plasmoids are found distinct. The By increase and abundant field‐aligned currents in the narrow core region of the first plasmoid indicate that a possible magnetic flux rope (MFR) core exists inside. The results indicate that the first observed plasmoid is of a magnetic loop (ML) type (with possible MFR core) and the second plasmoid is of a magnetic flux rope (MFR) type. The coexistence of ML and MFR in the near‐Earth plasma sheet may imply that multiple X line reconnection can occur by either an antiparallel or a component‐parallel way.

P 27. rTMS and eeg-investigations in healthy subjects

Question Depending on the frequency of rTMS protocols, previous combined EEG-rTMS-studies have shown different effects on the cortical excitability. Regarding conventional repetitive protocols, facilitation was observed after high frequency stimulation, whereas inhibition on cortical activity was shown after the application of low frequency protocols. Despite conclusions about the direction of rTMS effects, the after rTMS-effects where mainly observed in Event Related Potential (ERP)-studies. The results of oscillatory EEG studies are much more non-uniform, and still remain uncertainty about the nature of after rTMS effects on quantitative EEG measures, because of different rTMS protocols including high variability of experimental conditions such as investigated subjects (healthy probands versus patients), stimulation location, rTMS parameters and EEG-measure procedures. In this study we analyzed the frequency dependent effects of rTMS over the right dorsolateral prefrontal cortex (DLPFC) on the quantitative EEG in healthy female subjects. We preferred the right frontal stimulation regarding the prior findings in reduction of anxiety and depressive symptoms. Additionally we analyzed connectivity pattern in the default mode network (DMN). Our hypothesis was, that the right frontal low frequency rTMS inhibities cortical activity. Furthermore, we included behavioral measures to measure the interaction of rTMS with affective state. Methods Twenty out of 40 healthy female subjects received one session of 1 Hz rTMS on the right DLPFC, 20 subjects one session of 10 Hz rTMS. In a cross over design a placebo stimulation was applied two weeks later. Pre and post rTMS a 10 min resting state EEG was analyzed. After artefact control we used sLORETA (standardized low-resolution brain electromagnetic tomography), in order to analyse the three dimensional cortical distribution of electrical current density for the main EEG frequency bands. For behavioral measures we used the Beck Depression Inventar (BDI) questionaire as instrument for affective trait markers and the Multidimensional Mental State Measure Questionaire (German MDBF). Results After 1 Hz rTMS a reduction of temporal theta EEG activity ipsilaterally to the stimulation side was observed. In the DMN, after high frequency rTMS an increase of connectivity in alpha-band and after low frequency rTMS a decrease of beta activity, both between medial prefrontal cotex and left inferior parietal lobule, was found. Furthermore, an increase of frontal alpha-assymmetry towards left hemisphere after 1 Hz rTMS could be shown in participants with higher baseline BDI-scores. Clinically relevant changes of mood, however, were not present. Conclusions Both rTMS protocols have shown a modulating effect on the activity of the DMN in healthy females. In order to get more conclusions about translative rTMS effects on behavior, further analysis including more precise behavioral measures are necessary.

Field distribution of epidural electrical stimulation

Epidural electrical stimulation has been applied in clinics for many years. However, there is still a concern about possible injury to spinal nerves. This study investigated electrical field and current density distribution during direct epidural electrical stimulation. Field distribution models were theoretically deduced, while the distribution of potentials and current were analyzed. The current density presented an increase of 70–80%, with one peak value ranging from −85° to 85° between the two stimulated poles. The effect of direct epidural electrical stimulation is mainly on local tissue surrounding the electrodes, concentrated around the two stimulated positions.

Magnetohydrodynamic motion of a colloidal sphere with self-electrochemical surface reactions in a spherical cavity

An analytical study is presented for the magnetic-field-induced motion of a colloidal sphere with spontaneous electrochemical reactions on its surface situated at the center of a spherical cavity filled with an electrolyte solution at the quasi-steady state. The zeta potential associated with the particle surface may have an arbitrary distribution, whereas the electric double layers adjoining the particle and cavity surfaces are taken to be thin relative to the particle size and the spacing between the solid surfaces. The electric current and magnetic flux density distributions are solved for the particle and fluid phases of arbitrary electric conductivities and magnetic permeabilities. Applying a generalized reciprocal theorem to the Stokes equations with a Lorentz force term resulting from these density distributions for the fluid motion, we obtain explicit formulas for the translational and angular velocities of the colloidal sphere valid for all values of the particle-to-cavity size ratio. The particle velocities decrease monotonically with an increase in this size ratio. For the limiting case of an infinitely large cavity, our result reduces to the relevant solution for an unconfined spherical particle. The boundary effect on the movement of the particle with interfacial self-electrochemical reactions induced by the magnetohydrodynamic force is equivalent to that in sedimentation and much stronger than that in general phoretic motions.

Current density distributions and sputter marks in electron cyclotron resonance ion sources

Most electron cyclotron resonance ion sources use hexapolar magnetic fields for the radial confinement of the plasma. The geometry of this magnetic structure is then--induced by charged particles--mapped onto the inner side of the plasma electrode via sputtering and deposition. The resulting structures usually show two different patterns: a sharp triangular one in the central region which in some cases is even sputtered deep into the material (referred to as thin groove or sharp structure), and a blurred but still triangular-like one in the surroundings (referred to as broad halo). Therefore, both patterns seem to have different sources. To investigate their origins we replaced the standard plasma electrode by a custom-built plasma electrode acting as a planar, multi-segment current-detector. For different biased disc voltages, detector positions, and source biases (referred to the detector) we measured the electrical current density distributions in the plane of the plasma electrode. The results show a strong and sharply confined electron population with triangular shape surrounded by less intense and spatially less confined ions. Observed sputter- and deposition marks are related to the analysis of the results. Our measurements suggest that the two different patterns (thin and broad) indeed originate from different particle populations. The thin structures seem to be caused by the hot electron population while the broad marks seem to stem from the medium to highly charged ions. In this paper we present our measurements together with theoretical considerations and substantiate the conclusions drawn above. The validity of these results is also discussed.

Three-Dimensional Simulation of Plasma Deformation During Contact Opening in a Circuit Breaker, Including the Analysis of Kink Instability and Sausage Instability

A three-dimensional (3-D) transient model has been developed to investigate plasma deformation driven by a magnetic field and its influence on arc stability in a circuit breaker. The 3-D distribution of electric current density is obtained from a current continuity equation along with the generalized Ohm's law; while the magnetic field induced by the current flowing through the arc column is calculated by the magnetic vector potential equation. When gas interacts with an arc column, fundamental factors, such as Ampere's law, Ohm's law, the turbulence model, transport equations of mass, momentum and energy of plasma flow, have to be coupled for analyzing the phenomenon. The coupled interactions between arc and plasma flow are described in the framework of time-dependent magnetohydrodynamic (MHD) equations in conjunction with a K-ε turbulence model. Simulations have been focused on sausage and kink instabilities in plasma (these phenomena are related to pinch effects and electromagnetic fields). The 3-D simulation reveals the relation between plasma deformation and instability phenomena, which affect arc stability during circuit breaker operation. Plasma deformation is the consequence of coupled interactions between the electromagnetic force and plasma flow described in simulations.

Impact of radial external magnetic field on plasma deformation during contact opening in SF6 circuit breakers

A three-dimensional (3D) transient model is developed to investigate plasma current deformation driven by internal and external magnetic fields and their influences on arc stability in a circuit breaker. The 3D distribution of electric current density is obtained by solving the current continuity equation along with the generalized Ohm's law in the presence of an external magnetic field, while the magnetic field induced by the current flowing through the arc column is calculated by the magnetic vector potential equation. The applied external field imposes a rotational electromagnetic force on the arc and influences the plasma current deformation, which is discussed in this paper. In SF6 circuit breakers when gas interacts with the arc column, the fundamental equations such as Ampere's law, Ohm's law, turbulence model, transport equations of mass, momentum, and energy of plasma flow have to be coupled for analysing the phenomenon. The coupled interactions between the arc and the plasma flow are described within the framework of magnetohydrodynamic equations in conjunction with a K–ε turbulence model. Simulations are focused on sausage and kink instabilities in the plasma (these phenomena are related to the electromagnetic field distribution and define the plasma deformations). The 3D simulation reveals the relation between plasma current deformation and instability phenomena, which affects the arc stability during the operation. Plasma current deformation is a consequence of coupling between electromagnetic forces (resulting from internal and radial external magnetic fields) and the plasma flow that are described in the simulations.

Analysis of the temperature field near a corner composed of dissimilar metals subjected to a current flow

The 2D electro-thermal problem near a corner composed of two dissimilar materials in an angled metal line is analyzed. The line is assumed to be of uniform width and subjected to a steady direct current flow. We show the development work leading to the formulation of the current density and temperature distributions. The parameters affecting the singularities concerning the electro-thermal problem are also discussed. The electrical potential and current density distributions near a corner in an arbitrary angled line are determined, and the temperature field in a point symmetric line which is commonly met in metal interconnection structures is analyzed. In addition, we show that the temperature field solution is also valid for a symmetric line and a right angled line.

Impact of External Magnetic Field on Plasma Current Layer Deformation During Contact Opening in Medium-Voltage Puffer $\hbox{SF}_{6}$ Circuit Breaker

A 3-D transient model has been developed to investigate plasma current deformation driven by internal and external magnetic fields and their influences on arc stability in a circuit breaker. The 3-D distribution of electric current density is obtained by solving the current continuity equation along with the generalized Ohm's law in the presence of an external magnetic field, while a magnetic field induced by a current flowing through an arc column is calculated by a magnetic-vector-potential equation. The applied external field imposes a rotational electromagnetic force to the arc and influences plasma current deformation which is discussed in this paper. In SF6 circuit breakers, when gas interacts with the arc column, fundamental equations such as Ampere's law, Ohm's law, turbulence model, transport equations of mass, momentum, and energy of plasma flow have to be coupled for analyzing the phenomenon. The coupled interactions between arc and plasma flow are described in the framework of magnetohydrodynamic equations in conjunction with a K - e turbulence model. Simulations have been focused on sausage and kink instabilities in plasma (these phenomena are related to Bennett relation and electromagnetic fields and define plasma deformations). The 3-D simulation reveals relations between plasma current deformation and instability phenomena, which affect arc stability during operation. Plasma current deformation is the consequence of coupling between electromagnetic forces (resulting from internal and external magnetic fields) and plasma flow that are described in simulations.