Uniform Current Density Research Articles

Deterministic Spin-Orbit Torque Switching by a Light-Metal Insertion.

Spin-orbit torque (SOT) switching of magnetization is a promising emerging technology for nonvolatile spintronic memory and logic applications. However, deterministic switching of perpendicular magnetization with SOTs requires an additional symmetry breaking, which is typically provided by an external magnetic field, making it impractical for applications. In this work, we disclose that by the insertion of a slightly asymmetric light-metal layer at the heavy metal-ferromagnet interface of SOT heterostructures, current-induced out-of-plane effective magnetic fields are introduced that enable deterministic switching without an external magnetic field. We obtain uniform perpendicular magnetic anisotropy and switching current density despite the asymmetry of the light-metal layer, and we show the scalability of our approach by studying device sizes that differ by 2 orders of magnitude. Our work provides a practical route for utilization of SOTs for magnetization switching on the wafer scale and paves the way for the practical application of SOT-based technology.

Effect of Screening Current Induced Field on Field Quality of an Air-Core HTS Quadrupole Magnet

An air-core high-temperature superconducting (HTS) quadrupole magnet has many advantages for heavy-ion accelerator applications due to the elimination of the iron-core of a conventional HTS quadrupole magnet. It is compact, lightweight, and free of hysteresis of a ferromagnetic material. In our previous study, an air-core HTS quadrupole magnet of 3.0 T/m field gradient was designed. It was composed of eight double-pancake racetrack coils, each wound using 4-mm wide HTS tapes. In the magnet design, a uniform current density was assumed in the HTS tapes. However, in the HTS racetrack coils, magnetization currents are induced by the magnetic field component perpendicular to the tapes, and the magnetization currents generate the so-called screening current induced field (SCIF). For the quadrupole magnet, the SCIF could be critical to the field quality of the magnet. In this study, the current density distribution was calculated considering the magnetization current. Furthermore, the effect of the SCIF on the field quality of the magnet is analyzed and discussed.

Factor analysis of the uniformity of the transfer current density in vanadium flow battery by an improved three-dimensional transient model

Vanadium flow battery has been regarded as one of the most promising candidates for large-scale energy storage, due to its attractive features of high safety, high performance-price ratio and environmental friendliness. The uniformity of transfer current density is one of the crucial factors affecting the performance of a vanadium flow battery. More uniform distribution of transfer current density will reduce the polarization and improve the battery reliability. In this work, a three-dimensional transient model in combination of the vanadium ions crossover through the separator has been developed. Based on the model, the effect of the applied current density, electrode porosity and electrolyte flow rate on the uniformity of transfer current density has been investigated. The result indicates that a lower applied current density, higher electrode porosity or higher electrolyte flow rate is beneficial to obtain a more uniform transfer current density and a reduced battery polarization. By comparison, the electrode porosity shows the most prominent effect on the uniformity of transfer current density, and a higher porosity is verified to be able to attain a better stability in several charge-discharge cycles. Finally, a preliminary study for an industrial scale battery designs has been performed based on an amplifying model.

Flat electrode contacts for vagus nerve stimulation.

The majority of available systems for vagus nerve stimulation use helical stimulation electrodes, which cover the majority of the circumference of the nerve and produce largely uniform current density within the nerve. Flat stimulation electrodes that contact only one side of the nerve may provide advantages, including ease of fabrication. However, it is possible that the flat configuration will yield inefficient fiber recruitment due to a less uniform current distribution within the nerve. Here we tested the hypothesis that flat electrodes will require higher current amplitude to activate all large-diameter fibers throughout the whole cross-section of a nerve than circumferential designs. Computational modeling and in vivo experiments were performed to evaluate fiber recruitment in different nerves and different species using a variety of electrode designs. Initial results demonstrated similar fiber recruitment in the rat vagus and sciatic nerves with a standard circumferential cuff electrode and a cuff electrode modified to approximate a flat configuration. Follow up experiments comparing true flat electrodes to circumferential electrodes on the rabbit sciatic nerve confirmed that fiber recruitment was equivalent between the two designs. These findings demonstrate that flat electrodes represent a viable design for nerve stimulation that may provide advantages over the current circumferential designs for applications in which the goal is uniform activation of all fascicles within the nerve.

The influence of flow direction variation on the performance of a single cell for an anode-substrate flat-panel solid oxide fuel cell

This study was performed for a computational investigation of a single cell for an anode-substrate flat-panel solid oxide fuel cell (SOFC) to scrutinize the performance related to thermodynamic potential and overpotentials according to three other flow configurations: parallel flow, countercurrent flow, and perpendicular flow. To understand the performance differences based on the typical three flow configurations, the contour plots of temperature, species, and current density were simulated, and the trends and the portions of the diverse overpotentials were analyzed. The calculated results demonstrated that the parallel flow configuration had a tendency to deliver the highest performance and the lowest overpotentials of the three configurations because the temperature and H2 concentration in the parallel flow configuration were changed countercurrently along the anode flow direction. These overpotentials were complemented by interacting with the more uniform current density and the total impedance induced by the opposite directional change for the temperature and H2 concentration.In designing the anode-substrate flat-panel SOFC, the uniformity of flow rate in each channel, which affects significantly to both performance and lifetime of the cell, has been checked. From this numerical analysis result, the design performance of single cell was satisfactorily verified by obtaining negligible flow deviation in each channel of the designed separator deviation, which was less than 3% of the average velocity.

Toward sustainable electroplating of decorative silver for SMEs in Indonesia

Decorative silver electroplating has been a long time conducted by small and medium enterprises (SMEs) in Indonesia. Environmental pollution associated with the electroplating SMEs activities has created serious problems. For example SMEs of silver electroplating has contaminated groundwater which is no longer fit for domestic consumption due to its high level of cyanide contamination. Inefficient process and the use of high concentration of cyanide based electrolyte have been claimed to be the root cause. Therefore, the process of decorative silver electrodeposition in SMEs would be improved by developing an electrolyte with low cyanide concentration, determining onset potential and current densities, and modifying the process and the electrochemical cell so that the process would be more efficient and sustainable. A new electrolyte composed of AgNO3 and KCN with a ratio of 5:39 were chosen for the experimentation. For this electrolyte, silver would possibly be electrodeposited at potentials ranging from -2.2 V to -2.8 V. Corresponding current densities for silver electrodeposition would be between -2 and 7 mA/cm2. To improve the process, a new design of electrochemical reactor has been developed which ensure improvement of the observed electrochemical parameters i.e. the uniform current density distribution, the larger area of anode, and the stability of electrodes distance and position.

Maxwell duality and semiclassical analysis of the interaction of the magnetic quadrupole moment of a neutral particle with external fields

Based on the Maxwell duality, we consider nonuniform magnetic fields produced by nonuniform magnetic charge densities and nonuniform electric fields produced by uniform and nonuniform magnetic current densities. Then, we analyze the interaction of these fields with the magnetic quadrupole moment of a neutral particle from a semiclassical point of view by applying the Wentzel, Kramers, and Brillouin approximation.

Modeling of Industrial Electroplating Processes with Comsol Multiphysics in Order to Optimize Treatment of Complex Parts

Electroplating processes are widely used on several aeronautical applications to confer functional properties (electrical conductivity, tribological, anti-corrosion). In this industrial context, it is possible to keep the desired properties by respecting specifications such as thicknesses and coating composition for alloys. However, it is well-known that phenomena intrinsic to electrochemical processes create heterogeneities, especially on complex geometries like landing gears. Industrially, the treatment of these disparities is part of the know-how of the workshops, and they are balanced by complex auxiliary tools in order to obtain a more uniform local current densities distribution, and therefore coating thickness. The development of these specific anode shapes is time-consuming and depends strongly of an empirical know-how. The numerical simulation of electrochemical processes is developed at Safran Tech in collaboration with Institute Utinam to optimize the development of plating tools at industrial scale with ComsolÒ Multiphysic software. The global objective is to improve the reliability of the existing systems, and moreover to enhance the innovation by facilitating new coatings integration. This is crucial in the context of tightening of environmental REACH regulations, such as the substitution of cadmium by zinc-nickel. Modeling industrial electroplating processes by a secondary current distribution model is evaluated in terms of thickness prediction by a comparison with experimental results at a laboratory scale pilot. It has been emphasized that the main limitation are due to the failure to take full account of mass transport induced by convection. The study also participate to the development of good practice for auxiliary tools design, and the simulation demonstrate invaluable assistance in industrial operations. Figure 1

Model Identification for Adsorption Dynamics and Suppression Effect of Polyethylene Glycol Using Inverse Analysis Approach

Mathematical models of adsorption dynamics and suppression effect of Polyethylene Glycol (PEG) are identified using the inverse analysis approach. In contrast to the conventional assumptions of uniform concentration distribution and current density distribution, the models are identified in consideration of the concentration distribution and current density distributions on the electrode surface. Identified models are the polarization curve of copper deposition and the adsorption of PEG. The polarization curve is expressed by a piecewise linear function. The piecewise linear function is more flexible than the Butler-Volmer equation and improve model accuracy. Experiments are performed to verify the models. Numerical simulations are performed using the identified models under the same condition as the experiment.The calculated currents are compared with the experimental currents.The results show that the identified model reproduces the phenomenon.

Proceedings #63: Low-Profile 3D Microelectrodes with Near-Uniform Current Density for High-Resolution Neural Stimulation

Background: Uniform current density electrodes can reduce the risk of electrode corrosion and tissue damage, but existing geometries do not suit thin planar leads. Objectives: This study examines current density distribution (CDD) on lowprofile electrode designs and proposes an approach to obtain optimal geometries with near-uniform CDD requiring reduced recession depths. Methods: The electrodes are defined as parametric curves, analyzed using the quasi-static approach, and optimized using the downhill simplex method. Results: Obtained electrode designs with near-uniform CDD remain low profile and require twice as less recession depths comparing to reference designs. Conclusion: These electrode shapes are suitable for miniature high-resolution planar DBS leads

Closed‐form solutions for a circular inhomogeneity in nonlinearly coupled thermoelectric materials

AbstractThermoelectricity is a class of material possessing the ability of interconverting heat and electricity. For the sake of high conversion efficiency, inclusions/fibers are usually introduced into thermoelectric materials. However, the discontinuity of material property and geometry brought by inclusions/fibers might result in severe stress concentration and thus greatly affect the mechanical properties of thermoelectric material in its engineering service. This paper introduces a nonlinear coupled thermal–electrical–mechanical formulation for the plane problem of a circular inhomogeneity embedded in a thermoelectric medium under a combined uniform electric current density and energy flux. A special attention is directed towards the induced thermal stress field which has often neglected in the literature. Using methods based on Cauchy integrals, the complex potentials of the electric field, temperature field and associated stress field are derived explicitly in both the inhomogeneity and the surrounding matrix. The analysis shows that the electrically and thermally induced stress has a linear relationship with the energy flux applied at infinity, but has a nonlinear relationship with the remote electric current density. Numerical simulations are also performed to examine how the inhomogeneity influences the electrically induced thermal stress concentration on the interface. The presented results can be directly used for reliability consideration in design and optimization of thermoelectric composites with circular fibers/inclusions.

A Split Triple-Gate Power LDMOS With Improved Static-State and Switching Performance

A novel split triple-gate (STG) LDMOS is proposed to improve static-state and switching performances. The proposed structure features a triple-gate and split gates (SGs). The triple-gate consists of planar part and trench part, and the SGs are embedded into the drift region and isolated with slanted oxide. The triple-gate enlarges the channel width. Furthermore, the trench part of triple-gate and trench drain–source contributes to a uniform on-state current density distribution from the surface to the bottom of the drift region, resulting in a high average current density. Consequently, the specific ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON},\textsf {sp}}$ ) and the transconductance are improved. In the off-state, the SGs act as a slanted field plate to not only modulate the electric field distribution, but also assist in depleting the drift region to increase the optimal doping concentration, which further decreases the ${R}_{ \mathrm{\scriptscriptstyle ON},\textsf {sp}}$ and maintains a high BV. Moreover, the SG is introduced to reduce the gate–drain capacitance and switching power dissipation. Compared with the triple-gate LDMOS (TG LDMOS), the STG LDMOS not only reduces the ${R}_{ \mathrm{\scriptscriptstyle ON},\textsf {sp}}$ by 66%, but also decreases the gate–drain charge by 41%.

Effect of aging process on the microstructure, corrosion resistance and mechanical properties of stainless steel AISI 204

In this study, the microstructure thermostability, corrosion resistance, and mechanical properties of AISI204 stainless steel after aging were investigated. The microstructural analysis showed precipitation of M23C6 carbide along grain boundaries and its amount tends to increase with increasing aging time and temperature. Little effect of carbide precipitation on tensile strength where the maximum drop was at temperature 850 °C and aging time 48 h by 5.09%. At the same aging conditions, precipitation severely affected yield strength, ductility, and the microhardness. The yield strength decreased by 46% and microhardness to 210 HV. On the other hand, the ductility increased to 21% in terms of percent reduction in area. Weight loss as a result of uniform corrosion and corrosion current density were strongly dependent on aging time and temperature. Furthermore, Passivation current density showed independent behavior as the temperature increase.

Computational analysis of heat transfer in a PEM fuel cell with metal foam as a flow field

Thermal management of proton-exchange membrane (PEM) fuel cell has an important effect on the overall cell performance. In this paper, metal foams as flow field are used to render more uniform temperature, gaseous reactants and current density distribution and also to reduce the mass and the cost of machining of flow-field channels and to enhance the performance of the PEM fuel cell. A 3-D model is considered and a set of equations including continuity, momentum, species, energy, and charge together with electrochemical kinetics are developed and numerically solved. A comparison is made between the PEM cell with metal foam and parallel channel as flow-field gas distributor. The results show that utilization of metal foam as flow field leads to increase in the reactant gas transfer and current density, and the current density distribution improves. The maximum temperature in the cell with metal foam is lower than conventional cell, and temperature distribution is more uniform within the cell. At low and middle current densities, the cell with metal foam has better performance than conventional channel due to lower temperature and lower ohmic resistance and this cell is more efficient at high current density due to lower mass transport losses. Furthermore, metal foam with high permeability provides a more uniform distribution of reactant gases with low pressure loss.

Incorporation of spatially-resolved current density measurements with photoluminescence for advanced parameter imaging of solar cells

The spatial distribution of device performance parameters of solar cells provides important insight into their operation, including the type and magnitude of conversion losses and potential areas of improvement. In most of the procedures used to create these parameter images, a uniform (i.e., global) short-circuit current density (JSC) is usually assumed. However, JSC is known to vary over the surface of a solar cell, especially in polycrystalline absorber materials like multicrystalline silicon. In this work, a high speed quantum efficiency measurement rastered over the surface of a solar cell is used to obtain images of JSC. These JSC images are then used to calculate images of series resistance, dark saturation current density, fill factor, and conversion efficiency. Comparisons are made between the images created with a global JSC and with the spatially-resolved JSC. Negligible variation is observed in the series resistance and dark saturation current density images, but a drastic change is observed in the efficiency images between these two methods.

Multiscale Model for Simulation of Large-Scale YBCO Solenoid Coils With <italic>J</italic> Infinite-Turn

Obtaining distributions of current density, magnetic field, and ac loss in coils is essential for practical applications. However, simulating large-scale 2-generation high-temperature-superconducting, YBCO coils is a challenging task. In this paper, we employ a multiscale model to successfully implement electromagnetic modeling of large-scale YBCO solenoid coils in two-dimensional axisymmetric geometry with the approximation of infinite turns (J infinite-turn). Based on the approximation, current penetration, magnetic field, and ac loss of coils can be obtained. The calculation results of multiscale models with J infinite-turn and uniform current density (J uniform) are compared with those from reference models which consider superconducting characteristics on each turn of coils with actual size based on H-formulation. Compared with J uniform, J infinite-turn improves the quality of current density and background magnetic field significantly and demonstrates good accuracy with errors less than 10% in terms of ac loss, whilst speeding up calculation by two orders of magnitudes than reference model. Also, the approximation shows more reliability if the coil is larger with more turns in pancakes.

Impact of Proximity Effects on Sheath Losses in Trefoil Cable Arrangements

Induced losses are a significant part of the total losses generated in HVAC cables. Presently, IEC 60287-1-1 is used to calculate the ratio of induced loss in a cable's metal sheath to its conductor loss ( λ 1), assuming uniform current density in both conductors and sheaths. Although this assumption is reasonable for smaller cables, it is questionable for larger cables in close proximity, such as three-core export cables in the Offshore Wind Farm projects. The effects of this non-uniform current density cannot be easily treated via a straightforward, purely analytical approach, since conductor currents are not effectively represented by linear ones in larger cables, while sheath currents are also unevenly distributed. The present study employs two-dimensional finite element models to evaluate how accurate the Standard method for calculating the λ 1 factor is in cables with a nonmagnetic armor. Their validity is further enhanced by means of filament method. The IEC 60287 appears to overestimate the temperature, particularly for larger conductor sizes, by up to 7 °C (8%). Finally, suitable reductive factors are suggested, which could improve the accuracy of the IEC method.

Abstract #34: Uniform Current Density Electrodes for a High-Resolution Deep-Brain-Stimulation Lead

Abstract #34: Uniform Current Density Electrodes for a High-Resolution Deep-Brain-Stimulation Lead

Preparation of dense Ta-LLZO/MgO composite Li-ion solid electrolyte: Sintering, microstructure, performance and the role of MgO

Cubic phase Li7La3Zr2O12 (LLZO), a member of the Li–Garnet family, is a promising solid electrolyte and has been widely studied in recent years. However, LLZO samples prepared via conventional ambient air sintering reported in the published literature often contain large grains with lower than desired (<94%) relative density. In this study, a non-contact method of co-firing with mother powder method is proposed to prepare high-quality Ta-doped LLZO–MgO composite ceramics. By sintering at 1150°C for 5 h, the ceramics can reach relative density of 98.2%, conductivity of 5.17 × 10−4 S cm−1 at 25 °C and fracture strength of ∼150 MPa. The sintered samples have uniform fine-grained microstructure and high critical current densities of 0.75–0.95 mA cm−2 at room temperature in Li–Li symmetry cell with Au modification. In addition, systematic sintering experiments and characterizations are conducted to explore the function of MgO in inhibiting the Ta-LLZO grain growth and its existing form inside the composite ceramics.

Numerical Simulation of a Two-Phase Flow for the Acrylonitrile Electrolytic Adiponitrile Process in a Vertical/Horizontal Electrolysis Cell

This paper investigated the effect of oxygen holdup on the current density distribution over the electrode of a vertical/horizontal electrolysis cell with a two-dimensional Eulerian–Eulerian two-phase flow model in the acrylonitrile (AN) electrolytic adiponitrile (ADN) process. The physical models consisted of a vertical/horizontal electrolysis cell 10 mm wide and 600 mm long. The electrical potential difference between the anode and cathode was fixed at 5 V, which corresponded to a uniform current density j = 0.4 A/cm2 without any bubbles released from the electrodes. The effects of different inlet electrolyte velocities (vin = 0.4, 0.6, 1.0 and 1.5 m/s) on the void fraction and the current density distributions were discussed in detail. It is shown that, for a given applied voltage, as the electrolyte velocity is increased, the gas diffusion layer thickness decreased and this resulted in the decrease of the gas void fraction and increase of the corresponding current density; for a given velocity, the current density for a vertical cell was higher than that for a horizontal cell. Furthermore, assuming the release of uniform mass flux for the oxygen results in overestimation of the total gas accumulation mass flow rate by 2.8% and 5.8% and it will also result in underestimation of the current density by 0.3% and 2.4% for a vertical cell and a horizontal cell, respectively. The results of this study can provide useful information for the design of an ADN electrolysis cell.