Current Density Field Research Articles

Diffusion Limited Current Density: A Watershed in Electrodeposition of Lithium Metal Anode

AbstractLithium metal is considered to be a promising anode material for high‐energy‐density rechargeable batteries because of its high theoretical capacity and low reduction potential. Nevertheless, the practical application of Li anodes is challenged by poor cyclic performance and potential safety hazards, which are attributed to non‐uniform electrodeposition of Li metal during charging. Herein, diffusion limited current density (DLCD), one of the critical fundamental parameters that govern the electrochemical reaction process, is investigated as the threshold of current density for electrodeposition of Li. The visualization of the concentration field and distribution of Faradic current density reveal how uniform electrodeposition of Li metal anodes can be obtained when the applied current density is below the DLCD of the related electrochemical system. Moreover, the electrodeposition of Li metal within broken solid electrolyte interphases preferentially occurs at the crack spots that are caused by the non‐uniform electrodeposition of Li metal. This post‐electrodeposition leads to more consumption of active Li when the applied current density is greater than the DLCD. Therefore, lowering the applied current density or increasing the DLCD are proposed as directions for developing advanced strategies to realize uniform electrodeposition of Li metal and stable interfaces, aiming to accelerate the practical application of state‐of‐the‐art Li metal batteries.

Simulation of the electrical stimulation of the rat brain using sleep frequencies: A finite element modeling approach

A realistic rat brain model was used to simulate current density and electric field distributions under frequencies characteristic of sleeping states (0.8, 5, and 12 Hz). Two anode-electrode setups were simulated: plate vs. screws-anode, both with a cephalic cathode. Our simulations showed that these frequencies have limited impact on electric field and current density; however, the highest frequency evidenced higher values for both variables. The type of electrode setup had a greater effect on current distribution and induced fields. In that sense, the screws setup resulted in higher values of the modeled variables. The numeric results obtained are within the range of available data for rodent models using the finite elements method. These modeled effects should be analyzed regarding anatomical consequences (depth of penetration of the currents) and purpose of the experiment (i.e., entrainment of brain oscillations) in the context of sleep research.

Three-dimensional unsteady model of arc heater plasma flow

Arc jets are unique facilities used to evaluate the performance of Thermal Protection Systems (TPS) for hypersonic vehicles. They produce high pressure and high enthalpy plasma flow to simulate the extreme heat encountered during atmospheric entry. The constricted arc heater part of an arc jet increases the test gas temperature by Joule heating. This study details the development of the three-dimensional unsteady plasma flow analysis tool, ARCHeS (ARC Heater Simulator). Coupled Navier-Stokes, radiative transfer and Maxwell equations yield current density, magnetism, radiation, and flow field solutions. The present work constitutes the first demonstration of an unsteady three-dimensional plasma flow simulation of high pressure and high enthalpy arc heater that captures kink instabilities of the electric arc. It is found that the arc attachment is mainly driven by upstream arc instabilities.

Integral Modeling of AC Losses in HTS Tapes With Magnetic Substrates

This article presents an integral modeling approach for computing ac losses in high-temperature superconductors near magnetic materials. The current density and magnetic field distributions are calculated by solving Maxwell's equations in integral form in the active parts. Equivalent surface and interface current densities are considered in the magnetic material to take into account its magnetic field-dependent relative permeability. The proposed approach is applied to compute ac losses in a second-generation high-temperature superconducting tape with a magnetic substrate. The obtained results are compared with the finite element method using H formulation to check the validity and performances of the proposed integral approach.

Enhanced critical current density in K-doped Ba122 polycrystalline bulk superconductors via fast densification

SummaryIron-based superconductors are expected to be used in strong magnet applications owing to their excellent superconducting properties. The process of sintering a mechanically alloyed precursor powder is effective in achieving a high upper critical field and critical current density in BaFe2As2 (Ba122) polycrystalline bulk materials. However, when this process is applied to K-doped Ba122, which shows the highest critical temperature in the Ba122 family, suppressing the vaporization of potassium is challenging. In this study, spark plasma sintering (SPS) method was applied to K-doped Ba122 to achieve fast densification. In contrast to the conventional synthesis method, which requires several tens of hours, optimally K-doped bulks with near theoretical density were obtained after only 5 min of SPS, and the magnetic critical current density reached 105 A/cm2 at 5 K. The demonstrated superconducting properties suggest that this fast densification technique is a useful tool for applying K-doped Ba122 to bulk trapped field magnets.

Modeling of Field Emission from Laser Etched Porous Silicon

In many modern sciences, electron transfer is required, such as electron microscopes, microwaves, and screens. There have been numerous reports of the formation of microstructures on silicon surfaces using lasers in halogen-containing media and their optical, electrical and other physical properties. A silicon microstructured field emitter is modeled with Fowler-Nortium field diffusion theory, and the breakdown currents are consistent. Breakdown voltage, field gain coefficient, current and current density, and emitter region (in case of breakdown) are considered in the simulation. Comparison between simulation and experimental results shows that the microstructure has field emitter properties and can be used as a new field emitter.

The effect of sintering conditions on the superconducting properties of melanin doped MgB2

In this work, the melanin-doped MgB2 samples were prepared under the same condition at different sintering temperatures. The XRD quantitative analysis indicates an increase in crystallite size with increasing sintering temperature. The pinning mechanism tends to be a collective of surface and point pinning in an indication of the role of the impurities and secondary phases in the forming of flux pinning centers. The electrical and magnetic measurements show significant enhancement on critical current density obtained from the doped samples compared to the pure ones. Enhancing critical current density and critical fields depend on the sintering conditions. Sintering at low-temperature results in a high critical current density and critical field values. The resistivity and the related superconducting parameters measurements were also completed.

Enhanced flux pinning by magnetic CrB2 nanoparticle in MgB2 superconductor

Different from the non-magnetic pinning centers, the magnetic pinning centers have stronger flux pinning force due to the direct magnetic interaction between the magnetic pinning centers and the magnetic vortices, thus have been widely used to enhance the critical current density of various superconductors. In this article, nanoparticles of antiferromagnet CrB2 were introduced as magnetic pinning center to improve the flux pinning force density (Fp), irreversible field (Hirr), and critical current density (Jc) of MgB2. Compared to the pristine sample, the CrB2 doped MgB2 with low doping levels shows a significantly improved Jc and Fp, especially in the high field region. Hirr is also substantially enhanced. It is revealed that the magnetic flux pinning behavior of CrB2 doped samples obviously deviates from the surface pinning law followed by most pure MgB2. Through theoretical analysis and curve fitting, an extra pinning force superimposed on the surface pinning background is separated and identified, which follows the rule of point pinning. Such a pinning scenario is supported by the microstructure analyses which demonstrate that CrB2 nanoparticles are highly dispersed and embedded in MgB2 matrix, acting as effective pinning centers.

Study of anisotropy in the superconducting properties of FeTe0.55Se0.45 single crystal grown by the self-flux method

We report anisotropy in the superconducting properties of FeTe0.55Se0.45 bulk single crystal synthesized via the self-flux method. We have performed magnetotransport, magnetic and heat capacity measurements on single crystals of same batch. The grown crystals have also been characterized by XRD, XPS and Raman measurements. The superconductivity at T C ∼ 14 K has been affirmed by the temperature-dependent resistivity, magnetic, and specific heat measurements. The anisotropy in the upper critical field (H C2), coherence length (ξ), and critical current density (J C) have been studied from the magnetotransport and magnetic measurements, respectively, under applied magnetic fields of 0–12 T along the ab-plane and c-axis. The critical current density has been estimated by Bean’s critical state model at different magnetic fields (J C(H)) and temperatures (J C(T)) measured for H‖ab-plane and H‖c axis. The anisotropic behaviour has also been observed for J C(H). The presence of ‘peak effect’ or fishtail characteristic has been noticed in M–H loops for H‖c only, which shows a shift towards the lower fields with increasing temperature. The nature of the pinning mechanisms in the sample has been determined by the normalized pinning force density using the Dew Hughes scaling rule, and the analysis of experimental data indicates the presence of δl-pinning in the sample. The temperature-dependent electronic specific heat has been fitted with the exponential law and the evaluated coupling constant 2Δ0/kBTc is ∼3.42 which is close to the universal BCS value of 3.53. The observed low value of residual Sommerfeld coefficient ≈ 4.59 mJ mol−1 K2 indicates good quality of the grown single crystal.

Influence of convective air-cooling on hydrostatic stress induced atomic migration characteristics of a thin Cu-line with Cu-Sn IMC under a DC field

The present paper addresses the influential effect of convective air cooling on the stress-migration induced atomic flux divergence in a copper interconnect/line with copper-tin intermetallic compound under a DC field of high current density. Three identical thin copper lines, namely, a pure Cu line, a copper line with Cu-Sn intermetallic and a line with lead-free solder-joint are considered as the basis for conducting the present investigation of current-induced atomic migration. The associated two-dimensional fields of electric potential, temperature, thermal stress as well as atomic distributions are obtained by solving the relevant coupled multi-physics problems using computer-based numerical schemes. Finally, the stressmigration induced atomic-flux divergence characteristics of three Cu lines are compared with those of electromigration as a function of cooling air velocity under natural and forced convection to quantify the relative contribution of stress migration in the perspective of overall atomic diffusion.

On the compact modelling of Si nanowire and Si nanosheet MOSFETs

In this paper, three-dimensional technology computer aided design simulations are used to show that the electron concentration, current density, and electric field distribution from the interface at the lateral channels and from the top channel to the centre of the silicon wire, in nanowire and nanosheet structures, are practically same. This characteristic makes it possible to consider that the total channel width for these structures is equal to the perimeter of the transistor sheet, allowing to extend of the application of the symmetric doped double-gate model (SDDGM) model to nanowires and nanosheets metal-oxide-semiconductor field effect transistors, with no need to include new parameters. The model SDDGM is validated for this application using several measured and simulated structures of nanowires and nanosheets transistors, with different aspect ratios of fin width and fin height, showing very good agreement between measured or simulated characteristics and modelled. SDDGM is encoded in Verilog-A language and implemented in the SmartSPICE circuit simulator.

Numerical study of discharge characteristics of atmospheric dielectric barrier discharges by integrating machine learning

In recent years, with the development of gas discharge technology at atmospheric pressure, the application of low temperature plasma has received widespread attention in pollution prevention, disinfection, sterilization, energy conversion and other fields. Atmospheric dielectric barrier discharge is widely used to produce low temperature plasma in various applications, which is usually numerically investigated by using fluid models. The unique advantages of machine learning in various branches of physics have been discovered with the advancement of big data processing technology. Recent studies have shown that artificial neural networks with multiple hidden layers have a pivotal role in the simulation of complex datasets. In this work, a fully connected multilayer BP (back propagation) network together with a universal hidden layer structure is developed to explore the characteristics of one or more current pulses per half voltage cycle of atmospheric dielectric barrier discharge. The calculated data are used as training sets, and the discharge characteristics such as current density, electron density, ion density, and electric field of atmospheric dielectric barrier discharge can be quickly predicted by using artificial neural network program. The computational results show that for a given training set, the constructed machine learning program can describe the properties of atmospheric dielectric barrier discharge with almost the same accuracy as the fluid model. Also, the computational efficiency of the machine learning is much higher than that of the fluid model. In addition, the use of machine learning programs can also greatly extend the calculation range of parameters. Limiting discharge parameter range is considered as a major challenge for numerical calculation. By substituting a relatively limited set of training data obtained from the fluid model into the machine learning, the discharge characteristics can be accurately predicted within a given range of discharge parameters, leading an almost infinite set of data to be generated, which is of great significance for studying the influence of discharge parameters on discharge evolution. The examples in this paper show that the combination of machine learning and fluid models can greatly improve the computational efficiency, which can enhance the understanding of discharge plasmas.

Numerical study on discharge characteristics of atmospheric dielectric barrier discharges by integrating machine learning

In recent years, with the development of gas discharge technology at atmospheric pressure, the application of low temperature plasma has drawn widespread concern in pollution prevention, disinfection, sterilization, energy conversion and other fields. Atmospheric dielectric barrier discharge is widely used to produce low-temperature plasmas in various applications, which is usually numerically investigated by fluid models. The unique advantages of machine learning in various branches of physics have been discovered with the advancement of big data processing technology. Recent studies have shown that artificial neural networks with multiple hidden layers have a pivotal role in the simulation of complex datasets. In this paper, a fully connected multilayer BP network together with a universal hidden layer structure is developed to explore the characteristics of one or more current pulses per half voltage cycle of atmospheric dielectric barrier discharge. The calculated data are used as training sets, and the discharge characteristics such as current density, electron density, ion density, and electric field of atmospheric dielectric barrier discharge can be quickly predicted by means of artificial neural network program. The computational results show that, for a given training set, the constructed machine learning program can describe the properties of atmospheric dielectric barrier discharge with almost the same accuracy as the fluid model. Also, the computational efficiency of the machine learning is much higher than that of the fluid model. In addition, the use of machine learning programs can also greatly extend the calculation range of parameters. Limited discharge parameter range is considered a major challenge for numerical calculation. By substituting a relatively limited set of training data obtained from the fluid model into the machine learning, the discharge characteristics can be accurately predicted within a given range of discharge parameters, leading to the generation of an almost infinite set of data, which is of great significance for studying the influence of discharge parameters on discharge evolution. The examples in this paper show that the combination of machine learning and fluid models can greatly improve the computational efficiency, which can enhance the understanding of discharge plasmas.

Morphology and Field Emission of ZnO Nanomaterials at Different Positions

By simply adjusting the temperature and the number of materials, rod-like ZnO with different morphology, such as ZnO nanoneedles, were synthesized by a flexible thermal evaporation method. The ZnO nanorod array has the lowest turn-on field, the highest current density, and the highest emission efficiency due to its good contact with the substrate and relatively weak field shielding effect. Experiments show that the morphology and orientation of one-dimensional ZnO nanomaterials have a great influence on its conduction field and emission current density, and the nanoarrays also contribute to electron emission. The research results have a certain reference value for the application of ZnO nanorod arrays as cathode materials for field emission devices.

CNT supported NiO hierarchal nanostructure on stainless steel substrate for efficient field emitters

The field emission application has recently focused on assembling nanoscale building blocks into three-dimensional (3D) hierarchical or hybrid nanostructure. The hierarchical nanostructure provides better field emission than a single nanostructure. In the present study, the chemical vapor deposition (CVD) method was used to synthesize 1D carbon nanotube (CNT) on stainless steel (SS) substrate. Nickel (Ni) was then sputtered on the synthesized CNT, and the sputtered substrate was treated hydrothermally in LiOH solution. The deposited Ni on CNT forms Ni(OH)2, and after oxidation, it was converted to NiO nanostructure. The structure, morphology, and chemical state of the samples were characterized by XRD, FESEM, Raman spectroscopy, and XPS. The SS-CNT exhibited a turn-on field and maximum emission current of 5.5 V/μm and 275 µA/cm2, respectively. However, SS-CNT-Ni demonstrated reduced field emission responses with turn-on field and maximum current 8.7 V/μm and 68 µA/cm2, respectively. The field emission response has been enhanced in the case of the SS-CNT-NiO sample as compared to the other structures. The turn-on field and maximum current densities were 5.1 V/µm and 719 µA/cm2 for the SS-CNT-NiO, respectively.

The Effect of Corona Wire Position and Radius in a Duct-Type ESP with Wavy Collecting Plates

Electrostatic precipitators (ESPs) have become one of the most effective methods for removing harmful particles from various industries. Many investigations in this subject are constantly developing due to the inherent benefits of using an ESP, and there are many robust initiatives taking place today all over the world. Different configurations of collection and discharging electrodes must be investigated to improve the ESP performance of ESPs. Many studies are working to enhance existing models in different ways. The geometry of the electrodes and the collecting plates is one area that could be improved. This paper investigates the wavy designs of collecting electrodes with varied corona electrode radius (range of variable corona radius (0.07-0.6 mm)) and position in a single-stage ESP. Wavy plates (WPs) and Inverted wavy plates (InvWPs) are compared to flat plates (FPs) using a numerical simulation tool. The results of this work show the impact of changing the corona radius when wavy and inverted wavy collecting electrodes are used on the electric potential, electric field strength, current density, and space charge density distribution, and particle collection efficiency. When compared to InvWPs and FPs, WPs show the highest performance in this range of particles. Although InvWPs can be utilized to reduce current density or space charge density, they do not increase particle collection efficiency.

Effect of the Electromagnetic Susceptibility of Metal Interconnects: A Simulation Study

Large induced electromotive force will be generated on the metal interconnections under the action of strong electromagnetic pulse, thereby generating a large induced current. For copper metal interconnects commonly used in modern integrated circuits, large currents will cause electromigration, resulting in short or open in the circuit, causing damage to devices and circuits. In order to study the damage of metal interconnects under the action of electromagnetic pulse, in this paper, the induced electromotive force of metal interconnects under the action of HPM is derived through theoretical analysis, then analyzing the influence of different electromagnetic pulse parameters on the induced electromotive force of interconnects by the use of electromagnetic simulation software COMSOL. Using the established metal interconnect model, the electromagnetic sensitivity effect of metal interconnect is studied by analyzing the electric field distribution, current density and temperature distribution on the interconnect under electromagnetic pulse.

Observations of Pitch Angle Changes of Electrons and High‐Frequency Wave Activities in the Magnetotail Plasma Bubble

AbstractPlasma bubble, a low‐entropy flux tube, is usually regarded as the bearer of plasma flux transport in the magnetotail. In this study, we perform a complete analysis of electron dynamics in a plasma bubble in the Earth's magnetotail based on the high time‐resolution data from the Magnetospheric Multiscale (MMS) mission. An electron jet is observed at the center of this plasma bubble. Simultaneously, intense electric field and significant current density, as well as the strong energy dissipation are detected associated with this electron jet. The pitch angle distributions (PADs) of high‐energy electrons exhibit different features at different substructures in this plasma bubble. In Region‐1 and Region‐3, pancake‐type PAD is formed; the PAD becomes isotropic type in Region‐2. The electrons pitch angle changes to field‐aligned distribution in Region‐4. All these changes of electron PADs in substructures can be interpreted mainly by the capture of magnetic mirror and betatron cooling. High‐frequency waves, including whistler waves and electrostatic waves, are detected in several parts of the plasma bubble. The observations of abundant electron‐scale phenomena or processes reveal that the electrons are very dynamic in the large‐scale plasma bubble.

Investigation of transport properties, flux pinning mechanisms and fluctuations induced conductivity of SiO2 nanoparticles doped YBa2Cu3O7-d thick films on silver substrates

In this study, we examined the pinning mechanism and fluctuations induced conductivity, and we report the superconducting critical parameters variation of fine SiO2 nanoparticles added YBa2Cu3O7−d (Y123) composite thick films of ∼100 μm in thicknesses on Ag substrate. Composite films (Y123 + x SiO2)/Ag were produced by the solid-state reaction process. Here, x = 0.00 and 0.01 wt% content of SiO2 nanoparticles (12 nm in diameter) were considered. The X-ray powder diffraction (XRD) together with Rietveld refinement and the scanning electron microscopy (SEM) were used to survey the structure and the morphology of thick films. Both composite films reveal a dense granular structure and similar compositions in phases. A small quantity of fine SiO2 particles intensifies the critical current density versus magnetic field Jc(H) and gives more weight to the strong pinning component of the Jc. Some important critical physical parameters of the composite films were obtained from the fluctuations induced conductivity analyses. The electrical conductivity was deduced from the electrical resistivity measurements and explained through Aslamazov–Larkin model. A small quantity of fine SiO2 particles upgrade the superconducting features, particularly the lower and the upper critical magnetic field (Bc1 and Bc2) at temperature 0 K.

Formation of Super‐Assembled TiOx/Zn/N‐Doped Carbon Inverse Opal Towards Dendrite‐Free Zn Anodes

AbstractUncontrolled growth of Zn dendrites and side reactions are the major restrictions for the commercialization of Zn metal anodes. Herein, we develop a TiOx/Zn/N‐doped carbon inverse opal (denoted as TZNC IO) host to regulate the Zn deposition. Amorphous TiOx and Zn/N‐doped carbon can serve as the zincophilic nucleation sites to prevent the parasitic reactions. More importantly, the highly ordered IO host homogenizes the local current density and electric field to stabilize Zn deposition. Furthermore, the three‐dimensional open networks could regulate Zn ion flux to enable stable cycling performance at large current densities. Owing to the abundant zincophilic sites and the open structure, granular Zn deposits could be realized. As expected, the TZNC IO host guarantees the steady Zn plating/stripping with a long‐term stability over 450 h at the current density of 1 mA cm−2. As a proof‐of‐concept demonstration, a TZNC@Zn||V2O5 full cell shows long lifespan over 2000 cycles at 5.0 A g−1.