Numerical Simulation Of Electric Field Research Articles

80 Hz but not 40 Hz, transcranial alternating current stimulation of 80 Hz over right intraparietal sulcus increases visuospatial working memory capacity

Working memory (WM) is a complex cognitive function involved in the temporary storage and manipulation of information, which has been one of the target cognitive functions to be restored in neurorehabilitation. WM capacity is known to be proportional to the number of gamma cycles nested in a single theta cycle. Therefore, gamma-band transcranial alternating current stimulation (tACS) should be dependent of the stimulation frequency; however, the results of previous studies that employed 40 Hz tACS have not been consistent. The optimal locations and injection currents of multiple scalp electrodes were determined based on numerical simulations of electric field. Experiments were conducted with 20 healthy participants. The order of three stimulation conditions (40 Hz tACS, 80 Hz tACS, and sham stimulation) were randomized but counterbalanced. Visual hemifield-specific visual WM capacity was assessed using a delayed visual match to the sample task. High gamma tACS significantly increased WM capacity, while low gamma tACS had no significant effect. Notably, 80 Hz tACS increased WM capacity on both the left and right visual hemifields, while previous tACS studies only reported the effects of tACS on contralateral hemifields. This is the first study to investigate the frequency-dependent effect of gamma-band tACS on WM capacity. Our findings also suggest that high gamma tACS might influence not only WM capacity but also communication between interhemispheric cortical regions. It is expected that high gamma tACS could be a promising neurorehabilitation method to enhance higher-order cognitive functions with similar mechanisms.

Lightning Current Performance of Conventional and Enhanced Rod Ground Electrodes

The correct operation of surge arresters under lightning and switching transient conditions requires that grounding be effective at high frequencies as well as at power system frequency. Effective high frequency grounding also limits the electrocution risk to substation personnel due to transient ground potential rise. This article assesses the performance of high frequency electrodes at typical lightning impulse current magnitudes. The enhancement of such electrodes by addition of bonded horizontal arms in cross and star arrangement is also investigated. The effective impulse resistances for electrodes having lengths up to 4.8 m are calculated over a range of impulse current magnitudes at the same location. The results obtained indicate that, for low impulse current magnitudes, the preionization electrode's resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) falls with increasing rod length, a behavior reflected in the measured dc resistance. The presence of horizontal enhancement was found to reduce <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> in all cases. The occurrence of soil ionization in the immediate vicinity of the electrode resulted in a reduced postionization resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) at higher currents, tending toward a common asymptotic value independent of both the length of the rod and the presence of electrode enhancements. The observed behavior is supported by numerical simulation of electric field and current density distributions, indicating that the high current performance of a grounding rod is heavily influenced by soil ionization and breakdown in high-field regions at the electrode extremities.

Numerical simulation of electric field in cylindrical silo based on non-uniform electrostatic charge distribution caused by particle segregation

Size-induced particle segregation during the silo filling process greatly changes the electrostatic charge distribution, influencing the occurrence of the incendiary electrostatic discharge. However, few studies concern the electric field distribution in this condition. In this work, the non-uniform space charge density distribution obtained in DEM simulation of the particle segregation was used for simulating the electric field. A comparison between the electric fields of segregation and uniform cases was conducted. Results show that the electric field of the segregation case is similar to that of the uniform case in the monopolar charging system. While in the bipolar charging system, the electric field of the segregation case can become different from that of the uniform case due to the bipolar space charge density in particle layers. The neutralization of the charges carried on large and small particles can result in the decline of the electric field. In the case with low net charges, the probability of the electrostatic discharge can be more than three times higher than that in uniform cases once the particle segregation happens. Moreover, the enhancement effect of the particle segregation on the electrostatic discharge can be stronger when the volume fraction of small particles is less than 75%. Reducing the charging efficiency of particles and the repose angle and avoiding particle segregation are preferable approaches to lower the risk of the electrostatic discharge.

Development of EHD pump based on numerical simulation of electric field

Development of EHD pump based on numerical simulation of electric field

Numerical simulation and exploration of electrocoagulation process for arsenic and antimony removal: Electric field, flow field, and mass transfer studies

In order to intuitively and clearly evaluate the potential and current distribution, the fluid flow and mixing, as well as mass transfer involved in electrocoagulation process for As and Sb removal, numerical simulation of electric field, flow field and mass transfer were constructed by Comsol Multiphysics and verified by experiments. Results displayed that the primary current and potential distribution were improved by changing electrode distance or adding insulator in a batch reactor. When configuration 2 and 2 cm electrode distance were applied, a more uniform primary current distribution and higher electrode current efficiency were obtained. In a continuous flow reactor, the increase of flow rate resulted in the left shift of the peak in residence time distribution curve, gradual decrease of the tailing area, reduction of the stagnation zone, and more uniform mixing of the fluid. However, higher than 0.043 L/min was unfavorable to the formation of flocs and its effective combination with pollutants. According to the simulation of mass transfer, at the initial stage, the rate of electrolysis/hydrolysis was greater than that of mass transfer. Fe2+, OH−, and Fe(OH)2 were primarily concentrated on the anode, cathode, and between the two electrodes, respectively. Under the action of electromigration, diffusion and convection, the concentration distribution of Fe(OH)2 increased at the direction of streamline. The concentration of Fe2+ and OH− achieved the minimum value at the outlet. However, Fe(OH)+ concentration and distribution were hardly affected by the treatment time, and once generated, immediately proceed to the next hydrolysis reaction.

Effect of grading ring on ice characteristics and flashover performance of 220 kVcomposite insulators with different shed configurations

The energized icing tests for five kinds of 220 kV composite insulators with and without the grading ring (GR) at the high voltage (HV) end are performed in the artificial climate chamber. Combining with the numerical simulations of electric field (E-field), the differences between the influence of GR and shed configuration on the ice characteristics and flashover performance of composite insulators are compared and analyzed. Results indicate that GR can improve both the ice growths and E-field distributions near the HV end. The improvements of GR on the icing flashover voltages under light icing degree is relatively obvious, while with the increase of icing degree, these effects gradually become less apparent. For different insulators, the effects of icing degree on icing flashover voltages under the presence of GRs are all higher than that under the absence of GRs. Moreover, the influence law of icing degree among different insulators remains unchanged under the presence and absence of GRs. In general, the improvement of optimized shed configuration for the icing flashover performance is more obvious than that of GR, which can be considered as one main measure to improve insulation performance of composite insulators in ice regions.

600-V 27-mΩ normally off SiC junction field effect transistors for high-efficiency power supply

Normally-off SiC junction field effect transistors (JFETs) with high blocking voltage and low gate leakage current were developed by localized current-path doping (LCD). Numerical simulation of electric field revealed that LCD effectively decreases the on-resistance of SiC JFETs without degrading blocking voltage. On the basis of the obtained simulation results, 600-V 27-mΩ normally off SiC JFETs were fabricated by LDC. The gate leakage current of the fabricated JFETs was suppressed by surface oxynitridation. By applying in a server power supply, we found that these improved JFETs decreased power loss due to FETs by 66%.

Capacitor blocks for linear transformer driver stages

In the Linear Transformer Driver (LTD) technology, the low inductance energy storage components and switches are directly incorporated into the individual cavities (named stages) to generate a fast output voltage pulse, which is added along a vacuum coaxial line like in an inductive voltage adder. LTD stages with air insulation were recently developed, where air is used both as insulation in a primary side of the stages and as working gas in the LTD spark gap switches. A custom designed unit, referred to as a capacitor block, was developed for use as a main structural element of the transformer stages. The capacitor block incorporates two capacitors GA 35426 (40 nF, 100 kV) and multichannel multigap gas switch. Several modifications of the capacitor blocks were developed and tested on the life time and self breakdown probability. Blocks were tested both as separate units and in an assembly of capacitive module, consisting of five capacitor blocks. This paper presents detailed design of capacitor blocks, description of operation regimes, numerical simulation of electric field in the switches, and test results.

Numerical simulation of electric field in complex geometries for different electrode arrangements using meshless local MQ-DQ method

Abstract In this paper the meshless Local Multi Quadrics-based Differential Quadrature (MQ-DQ) method is applied to obtain the electric field distribution for different applicable irregular geometries. This method is the combination of Differential Quadrature approximation of derivatives and function approximation of MQ-Radial Basis Function (RBF). Three different geometries with irregular boundaries are considered and the obtained results are compared with those gained by Finite Element (FE) solutions achieved by COMSOL commercial code. Outcomes prove that current technique is in very good agreement with FEM and this fact that MQ-DQ method is an accurate and flexible method in solution of electrostatic equations.

Effect of transfer roller surface profile on discharge mark

In this report, we discuss the reason why transfer roller surface profile affects the discharge mark, and propose a new roller model for numerical simulation. Our observation has revealed that the discharge mark depends on the surface profile of transfer rollers, the conventional foam roller, smooth roller which has a smooth surface made of high polymer materials upon a foam roller, and the rough sanding roller which has the sanded surface of smooth roller. To make its dependence clear, we experimented with the electric charge distribution at transfer nip area focusing on the surface profile of the roller. Then, we build &#x201C;Surface layer model&#x201D; consisting of base-layer and surface-layer. The numerical simulation of electric field using this model made it clear that roller surface profile affects the discharge mark.

Application of functionally graded material for reducing electric field on electrode and spacer interface

For the size reduction and the enhancing reliability of electric power equipment, the electric field stress around solid insulators should be considered enough. For the relaxation of the field stress, the application of FGM (Functionally Graded Materials) with spatial distribution of dielectric permittivity (?-FGM) can be an effective solution. In this paper, we investigated the applicability of ?-FGM for reducing the electric field stress on the electrode surface with contact to the solid dielectrics, which was one of the important factors dominating a long-term reliability of the insulating spacer. Firstly, we carried out numerical simulation of electric field to confirm the reduction of the electric stress by U-shape permittivity distribution. Secondly, we investigated the fabrication feasibility of ?-FGM with the U-shape distribution. Thirdly, we estimated the longterm electrical insulation performance of the ?-FGM. Finally, we verified the applicability and the fabrication technique of the ?-FGM to solid dielectrics for improvement of the electric stress and the long-term insulation performance in electric power equipment.

Role of substrate potential on filling the gap between two planar parallel electrodes in electrophoretic deposition

Here we investigated low frequency AC electrophoretic deposition of TiO 2 nano-particles suspended in acetone by experiment and simulation. Deposition is done under influence of a non-uniform 1 Hz AC electric field. The non-uniform electric field is generated by two parallel planar gold electrodes coated on a glass substrate. Experiment shows that during deposition, TiO 2 nano-particles fill the gap between electrodes. Numerical simulation of electric field reveals the role of glass substrate on gap filling. Our model shows that existence of surface charge on the substrate between two electrodes is the reason why the TiO 2 nano-particles move to the gap between two electrodes and deposit there.

Numerical simulation of the electric field and zonal current in the Earth’s ionosphere: The dynamo field and equatorial electrojet

The work is devoted to the numerical simulation of the dynamo electric field and its effects in the Earth’s ionosphere within the scope of the thermosphere-ionosphere-protonosphere global self-consistent model developed at WD IZMIRAN. The new electric field calculation block, which was used to obtain results of the self-consistent calculations of the electric field potential generated by the dynamo effect of the thermospheric winds (the dynamo field) and the equatorial electrojet for March 22, 1987, is briefly described in this work. A comparison of the obtained results with the experimental data showed a satisfactory agreement. Moreover, the proposed model was used to calculate the diurnal variations in the ionospheric parameters for Jicamarca equatorial station under the same conditions with the help of the new block of the electric field. The results of these calculations are also presented and discussed in this work. It has been indicated that the new model satisfactorily describes the specific features of electric field distribution at the geomagnetic equator and the well-known phenomenon of equatorial electrojet.

Numerical simulation of electric field with open boundary using intelligent optimum charge simulation method

For improving the calculation precision of the electric field, a novel combination of genetic algorithms (GA) and charge simulation method (CSM) is proposed. In which, the allocations and quantities of the optimized charges can be obtained using GA, and higher calculation precision can be achieved. The combined CSM and the hybrid conventional and optimized CSM were applied for computing the electric field of the demonstration examples. The comparison of the relative error between the conventional and optimized CSM has been obtained. The feasibility, practicability and validity of the proposed optimized CSM have been verified