Current Distribution Profile Research Articles

Multi-Step junction termination extension design and simulation study for 4H-SiC Schottky barrier diode

This paper presents a structure for designing Junction Termination Extension (JTE) in Silicon Carbide (SiC) power devices, particularly for Schottky Barrier Diodes (SBD). The P-type island composite multi-step JTE configuration has been developed by optimizing the number, length, and thickness of JTE steps. The JTE with step number of 4 and step length of 8 μm (SBD-n4L8) achieved a breakdown voltage of 1626 V at the same drift layer thickness of 10 μm, outperforming other step-based JTE structures. At reverse voltage of 1200 V, the SBD-n4L8 demonstrates a decrease in reverse leakage current with a uniform step-like current distribution profile. Subsequent analysis of the underlying mechanisms showed that, with step thickness of 2 μm, the SBD-n5L8 located at the corner and edge of the terminal region significantly reduced the peak electric field by more than 12.6 %.

EPOCHS IX. When cosmic dawn breaks: evidence for evolved stellar populations in 7 < z < 12 galaxies from PEARLS GTO and public NIRCam imaging

ABSTRACT The presence of evolved stars in high-redshift galaxies can place valuable indirect constraints on the onset of star formation in the Universe. Thus, we use PEARLS GTO (Prime Extragalactic Areas for Reionization and Lensing Science Guaranteed Time Observations) and public NIRCam (Near Infrared Camera) photometric data to search for Balmer-break candidate galaxies at 7 < z < 12. We find that our Balmer-break candidates at z ∼ 10.5 tend to be older (115 Myr), have lower inferred [O iii] + Hβ equivalent widths (120 Å), have lower specific star formation rates (6 Gyr−1) and redder UV slopes (β = −1.8) than our control sample of galaxies. However, these trends all become less strong at z ∼ 8, where the F444W filter now probes the strong rest-frame optical emission lines, thus providing additional constraints on the current star formation activity of these galaxies. Indeed, the bursty nature of epoch of reionization galaxies can lead to a disconnect between their current spectral energy distribution (SED) profiles and their more extended star formation histories. We discuss how strong emission lines, the cumulative effect of weak emission lines, dusty continua, and active galactic nuclei can all contribute to the photometric excess seen in the rest-frame optical, thus mimicking the signature of a Balmer break. Additional medium-band imaging will thus be essential to more robustly identify Balmer-break galaxies. However, the Balmer break alone cannot serve as a definitive proxy for the stellar age of galaxies, being complexly dependent on the star formation history. Ultimately, deep Near Infrared Spectrograph (NIRSpec) continuum spectroscopy and Mid-Infrared Instrument (MIRI) imaging will provide the strongest indirect constraints on the formation era of the first galaxies in the Universe, thereby revealing when cosmic dawn breaks.

Wideband dual-polarized linear-circular and linear-cross angular stable THz reflective polarizer based on a modified square loop FSS.

A simple wideband reflective type linear-cross and linear-circular polarization converter for terahertz (THz) applications is proposed in this paper. The top frequency selective surface (FSS) consists of a thin gold coated figure of eight square loop with the connected strip line corners on a thin grounded polyamide dielectric substrate. For the y/x-polarized incidence, the design exhibits linear-circular conversion with an axial ratio (≤3dB) from 0.49-0.50, 0.60-0.83, 1.16-1.62, and 1.81-1.85 THz with 2.02%, 32.17%, 33.09%, and 2.19% fractional bandwidth (FBW), respectively. In addition, it also performs the linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) from 0.53-0.56, 0.92-1.07, and 1.69-1.75 THz having 5.50%, 15.08%, and 3.49% FBW, respectively. Multiple plasmonic resonances are the reason behind different polarization conversions and are confirmed with surface current distribution profiles of the FSS and ground. The metasurface's performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) oblique incidences. The polarizer's unit cell architecture is compact with structural dimensions of 0.121×0.121×0.041λL3, where λL is the lowest operating frequency's free-space wavelength. The authors believe this design is compact, with angular stable multi-band multi-conversion ability that will significantly impact the THz applications in real time.

Novel broadband angular stable linear‐circular and linear‐cross polarizer based on inductive grid loaded H‐dipole in both reflection and transmission modes

A novel broadband linear-circular and linear-cross polarization converter for K to Ka-band applications is demonstrated in this work. The proposed structure primarily consists of an inductive grid in orthogonal with an H-shaped dipole as top Frequency Selective Surface (FSS) and a modified horizontal dipole as bottom FSS; a 1 mm thin FR-4 substrate is separating both. During transmission, it can convert the linearly polarized EM wave to a circular one, with Axial Ratio (AR) ≤ 3 dB from 13.08 to 25.13 GHz with 63.07% Fractional Bandwidth (FBW). In addition, this polarizer can work in reflection mode also when the bottom FSS is replaced by a Perfect Electrical Conductor (PEC), demonstrating the linear-circular polarization with AR (≤3 dB) from 16.94 to 18.64 GHz (RHCP/LHCP) and 24.5–40.32 GHz (LHCP/RHCP) with FBW 9.56% (Ku-band), and 48.81% (K- and Ka-band), respectively. Besides, linear-circular conversion, it performs linear-cross conversion in reflection mode with polarization conversion ratio (PCR) above 90% from 19.71–22.22 GHz, 43.57–48.81 GHz, 53.50–55.32 GHz with 13.89%, 11.34%, 3.32%, FBW, respectively. The equivalent circuit model of the proposed converter is extracted. Surface current distribution profiles at multiple plasmonic resonances are investigated to understand the reason behind the multi-polarization conversion. The performance is angular stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) incidences for reflection as well as transmission modes. The unitcell is compact with periodicity 0.114λL × 0.114λL and a thickness of 0.044λL, where λL is the free-space wavelength of the lowest frequency. This design's novelty lies in dual-mode stable angular performance in both reflection and transmission cases. Also, highly miniaturized architecture and circular rotation switching in the consecutive bands make this design suitable for real-time scenarios.

Secondary Reduction of Refractory Metals near the Smooth Cathode during Molten Salt Electrolysis. 1. Derivation of Fundamental Equations for the Process Model

A model of the steady-state process of the refractory metal ion secondary reduction with an alkali or alkaline earth metal formed on a smooth cathode during the electrolysis of molten salt is presented. The secondary reduction is localized near the cathode. The model takes into account the molecular diffusion of the initial components and the thermodynamics of the secondary chemical reaction, the Fick’s first law, the Faraday law, and the Nernst equation. Expressions are obtained for the calculating of concentration profiles, the velocity profile of the secondary reduction reaction inside the diffusion layer, and the secondary reduction current distribution profile over the thickness of the diffusion layer.

Simulations of fluid flow, mass transport and current distribution in a parallel plate flow cell during nickel electrodeposition

Abstract A laboratory filter-press flow cell with parallel plate electrodes is designed for nickel electrodeposition on mild steel from a diluted solution. Design features, such as electrolyte manifolds and turbulence promoters, produced by 3D printing, following computational fluid dynamics (CFD) simulations, are used to minimize jet flow and edge effects on current density. A hydrodynamic analysis is performed by solving the Reynolds averaged Navier-Stokes (RANS) equations with the k − e turbulence model. The averaged convective-diffusion equation is solved for mass transport simulations, while wall functions are used to simulate tertiary current distribution considering the side reaction of hydrogen evolution (HER). The flow cell design minimizes electrolyte flow and current density edge effects at the entrance to the cell by using an electrolyte manifold followed by polymer mesh turbulence promoter and a flow calming zone before the reaction region of the flow channel. The experimental validation of nickel electrodeposition agrees with the predicted tertiary current distribution profiles.

Ideal Ni-Based 4H–SiC Schottky barrier diodes with Si intercalation

The Ni-based 4H–SiC Schottky barrier diodes (SBDs) with Si intercalation have been investigated. The electrical properties of SBDs are characterized by temperature-dependent current-voltage (I–V) and capacitance-voltage (C–V) measurement. The morphologies of the metal-semiconductor interface are observed by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively, and the elemental compositions are determined by energy dispersive spectrometer (EDS). The current distribution profile and local I–V curves at the interface are measured by conductive AFM. The electric field distribution is simulated by Technology Computer Aided Design (TCAD). The results show that the 500°C-annealed SBDs, with nearly perfect interface morphology, display an ideal Schottky characteristic with the ideality factor (n) of 1.014. In spite of the appearance of a rough interface of the 600°C-annealed SBDs, they still exhibit an ideal characteristic due to maintaining the component uniformity at the interface. The intercalation method can be applied to fabricate the ideal 4H–SiC Schottky diodes.

Investigation on electrolyte jet machining of three-dimensional freeform surfaces

The increasing demand for optimized component surfaces with enhanced tribological, optical, chemical, biomedical, and geometric complexity is a key driver in the development of electrolyte jet machining (EJM) technology. To date the applications of EJM method have been limited to planar surface processing. Realization of three-dimensional freeform surfaces with high precision by EJM is of significant importance to advance the process. In this study, the characteristics and principle of multi-axis EJM of arbitrary-shaped workpieces were investigated for the first time. The resultant machined features were experimentally demonstrated under principal factors of inter-electrode gap distance, jet orientation relative to workpiece surface, jet orientation relative to gravity, and workpiece configuration. Furthermore, a simulation model of EJM considering jet orientation and workpiece curvature was built to analyze the electrolyte jet flow and clarify the principle of the current density distribution in the non-symmetric electrolyte flow. It is demonstrated that jet orientations directly affect the profiles of current density distribution and consequently result in varied machining results. In EJM of freeform surfaces, a smaller radius of curvature brings about more intensive concentration of current density distribution and consequently a larger machining depth. The same principles are confirmed in EJM of corner shapes with different angles.

Small-Signal Analysis of High-Performance VCSELs

In this paper, a comprehensive model to describe the small-signal modulation response of ultra-high performance single- and multi-mode vertical-cavity surface-emitting lasers (VCSELs), with modulation bandwidths exceeding 30 GHz, is presented. Traditionally, utmost simplified dynamic models are used to extract dynamic figures of merit from single-mode edge-emitting lasers. These methods are later on also applied to evaluate the dynamic performance of VCSELs, even though these devices have a very different geometrical layout and modal confinement. However, to understand the dynamic performance of high-speed VCSELs, a model supporting the transverse and longitudinal mode profile, and the driving current inhomogeneity in the active region, is needed. Therefore, multi-mode VCSEL rate equations are established here. Moreover, to access the dynamic figures of merit of these devices, a comprehensive analytical fitting function based on our carrier reservoir splitting approach is derived. Thus, because of the high carrier and photon densities inside these optimized VCSELs, the common carrier reservoir splits up as a result of numerous effects such as mode competition, carrier diffusion and spatial hole burning. These and other effects have a tremendous impact on the small signal modulation response shape and bandwidth, and also on the current distribution profile in the carrier reservoirs. Compared with our recently reported work, this novel model presented includes the effects of gain compression and inhomogeneous current injection between the different lasing modes. Consequently, it is found that the further tuning of our multi-mode VCSEL dynamic model, to include these effects, yields a more physical and consistent figures of merit of high-performance VCSELs.

Numerical Analysis of Hydrodynamics, Potential and Current Distribution, and Mass Transfer of Aluminum Ions in an Electrocoagulation Reactor Using CFD By Euler-Lagrange Approach

The reactor design for tannery wastewater treatment using computational fluid dynamics (CFD) techniques was carried out. The effluent contains different types of pollutants such as organic matter, salts, heavy metals, and dyes difficult to degrade. Due to the complexity of the effluent, a treatment based on an electrocoagulation process is proposed. In most of the references is mentioned that the characterization and design of this type of process is carried out empirically or semi-empirically, so in this work the influence of hydrodynamics, mass transfer of aluminum ions and secondary current distribution was studied. An electrochemical rotating cylinder electrode (RCE) reactor was used, with 6 working electrodes and an aluminum RCE as counter electrode. Besides, a decanter was incorporated in the reactor design. Current distribution and fluid velocity profiles as well as particle tracking animations were obtained. The most suitable geometry was designed from the theoretical results of the sedimentation process and aluminum ions generation. Finally, some operating parameters such as velocity inflow and velocity of the RCE were evaluated.

A Study on the Effect of Porosity and Particles Size Distribution on Li-Ion Battery Performance

A pseudo two-dimensional model (P2D) is presented that describes the effect of the structural properties of the positive electrode on Li-ion cell performance during discharge. The validation of the mono-modal model was done by using Doyle's experiment and results [C.M. Doyle, University of California, Berkeley (1995)]. A large increase or decrease in the porosity beyond a specific value led to a sharp change in the cell voltage curve and lower cell capacities. The maximum specific energy was obtained in the porosity range of 0.55, while the specific power still had a high value. Furthermore, different particle size distribution models, including mono-modal, bi-modal and 3-particle models, were compared to each other. The mono-modal model was the ideal state with the lowest total polarization. The bi-modal and 3-particle models approached this ideal state when the volume fraction of the smallest particles in their structures increased. This structural arrangement in these models led to more uniform local current density distribution profiles resulting in a greater decrease in cell polarization. Different discharge current densities were applied to different particle size distribution models, and the results showed that the particle size distribution has a greater effect at higher discharge current densities.

Guiding Center Orbit Calculation for Evaluating the Current Density Distributions of the Electrons in Electron Cyclotron Heating on QUEST

In order to evaluate the magnetic surface current density distributions, the electron guiding center orbits were calculated with the equilibrium fitting plasma equilibrium analysis. The current density distributions in electron cyclotron-heated plasma were estimated from the orbit analyses in the equilibrium plasma shaping for the fundamental and the second-harmonic resonant electrons separately. The current density distribution profiles on the equatorial plane were obtained for the electrons with initially positive and negative velocities parallel to the magnetic field direction as well as the trapped electrons. The surface averaged current density profiles of the closed flux surfaces were also evaluated. A significant amount of the positive current density distributions appeared outside the last closed flux surface (LCFS), while all the negative current density distributions were evaluated inside the LCFS. The trapped electrons being the second-harmonic electron cyclotron resonant contributed the negative current inside the LCFS. The positive current density distributions outside the LCFS were significant for the driven current density for both the fundamental and second-harmonic resonances.

Temperature and current density distributions at spark plasma sintering of inhomogeneous samples

We analyze the effect of inhomogeneity in the properties of a material on the conditions of obtaining thermoelectrics by spark plasma sintering. Inclusions localized and distributed over the volume of materials with different values of electric and thermal conductivities are considered. It is found that the presence of macroscopic inhomogeneities changes the current density distribution in the cross section of the sample being sintered. It is shown that inhomogeneity in the properties of materials during sintering do not substantially affect the temperature field in the sample at the macroscopic level, but change the current density distribution profile. The ranges of variation of the current density in the regions with inhomogeneous electric and thermal conductivities are determined for various types of macroscopically inhomogeneous inclusions and their distribution. The applicability of various models for describing spark plasma sintering is considered.

Understanding the effectiveness of cathodic protection under disbonded coatings

Factors affecting the effectiveness of cathodic protection under disbonded coatings were studied using a partially covered two dimensional electrode array that simulates a crevice under a disbonded coating and allows for the mapping of electrochemical currents under the influence of cathodic protection (CP). This technique enabled the study of the effects of major factors, including crevice gap size, solution conductivity and applied CP potential on the distribution and evolution of CP currents over the electrode array surface. The effect of each of these factors on the overall current distribution profile has been explained using a new electrochemical model. This model suggests that, despite the detrimental effect of cathodic shielding, the steel under disbonded areas could still be protected, independent of the crevice geometry and solution resistivity, by means of concentration polarization instead of direct electrochemical polarization. A set of conditions for maintaining CP potentials more negative than −850mVCSE along disbonded coating areas was deduced from the proposed model and validated against potential profiles available in the literature. The possible practical implications of the current mapping technique used in this study for developing in-situ CP monitoring sensors has also been discussed.

Current Density Distribution in the Lateral Direction of Conventional and Interdigitated Flow Field

In proton exchange membrane fuel cells, diffusion is a primary mechanism to transport gaseous species (oxygen and water vapor) between the flow channel and the catalyst layer in conventional flow field, whereas in an interdigitated flow field convection and diffusion both play vital role. Similarly, in a conventional flow field capillary effect is dominant in removal of liquid water, while in an interdigitated flow field both capillarity and the pressure difference between inlet and outlet channels contribute to the liquid water removal. Many computational studies available in literature have proven that this fundamental difference in transport mechanisms results in the differences in the overall cell performance and in the current density distribution in the land-channel direction between PEMFCs with interdigitated flow field and conventional flow field such as [1-2]. However, to best of our knowledge there is no study present in literature to experimentally show the current distribution in land-channel direction. Our objective is to measure current density distribution in the land-channel direction and compare current density distribution profile for interdigitated and conventional flow field. A segmented cell is developed to measure current density distribution in the land-channel direction at sub-millimeter resolution of 350 μm. This technique is then applied to study current density distribution in land-channel direction of PEM fuel cell with interdigitated flow field and conventional flow field (see Figure 1a and b). Figure 1. Current density distribution in the land-channel direction at 0.2 V, 60 oC and 90% RH a) conventional b) interdigitated flow field A. Kazim, H.T. Liu, P. Forges. Journal of Applied Electrochemistry, 29, 1409 (1999). L. Chen, H. B. Luan, Y.L. He, W. Q. Tao. International Journal of Thermal Sciences, 51 132 (2012). Figure 1

Influence of Convective Heat Transfer by Air Flow on Local Current/Temperatures along Microtubular Solid Oxide Fuel Cells In-situ Identified by Electrodesegmentation Method for Co- and Counter-flow Configurations

Contribution of spatial temperature variations to thermo-mechanical stresses along microtubular solid oxide fuel cells is often numerically estimated with local temperatures calculated by thermo-electrochemical models. This method is preferred due to the lack of experimental data. Not only to provide experimental data but also to reduce the temperature variations, in this paper we are analyzing the in-situ measured local temperatures and currents along a cell. We have measured the local properties by electrode-segmentation method for co- and counter-flow configurations at various air flow velocities. Gas flow configuration shows a substantial impact on both longitudinal temperature and current variations. Under the identical conditions, the counter-flow exhibits larger variations in both temperatures and currents. We conclude that air flow velocity determines the longitudinal temperature distributions, whereas its effect on the current distribution profile is negligible. With these findings, we anticipate larger thermo-mechanical stresses in the counter-flow configuration at high air flow velocities.

Study on Variability of Residual Current and Salinity Structure According to River Discharge at the Yeoungsan River Estuary, South Korea

The Yeoungsan River Estuary (YRE) made change of estuarine circulation environment at not only control of inflow of freshwater but also decreasing tide speed under construction of estuary bank. The estuarine circulation in the estuary made change rapidly at discharge of the estuary bank. We investigated variation of salinity and residual current in study area during freshwater discharge and non-discharge period. To determine effect of artificial freshwater discharge on the spatial and temporal variability of the residual current and salinity distribution, current and density profile data were analyzed in partially stratified YRE. The current and density data, obtained from two cross-sectional transects, was conducted during freshwater discharge and non-freshwater discharge. We observed flow rate and salt during 13h with 1h interval to investigate changes of marine environment. The residual current structure is complex, such as multi-layer, during non-freshwater discharge because tides and wind effects combined with topography influences. Strong freshwater discharge is influences to vertical mixing at the surface layer,however freshwater is not effected at the bottom layer. These distinction of freshwater effect causes the salinity gradient and strongly stratification. Freshwateris toward to open-sea through surface layer during freshwater discharge period. In other words, the distinction of residual current and the stratification are controlled according to whether artificial freshwater discharge or not.

Distributed PEFC Performance during Cationic Contamination

In our previous studies (1-3), severe performance degradation of PEFCs was observed due to cationic impurities. In this study, we investigate how cations affect the spatial performance distribution in a PEFC using a segmented cell.The segmented cell hardware consists of an aluminum anode flow field, a segmented aluminum cathode flow field, two aluminum end plates and one cupper current collector. All the aluminum parts were gold plated. Cathode flow field was divided into eight segments. Eight pieces of equal size aluminum current collectors were placed inside a PTFE block and straight flow channels were machined through both the PTFE and the aluminum segments (Figure 1). Total active area of the cell was 5 cm2. 2.85 mM CaSO4solution was introduced in the air stream through a nebulizer (1-3) at a rate of 110 uL/min, corresponding to 21.2 ppm based on dry air flow rate.Figure 2 shows the voltage and current density distribution profile in each segment. The cell was operated at a constant total current of 1 A. During the baseline test of 24 hours, pure air was injected through cathode. The current in each segment remained constant through this period. Following the baseline test, the contaminant was injected in the air stream. The segments closest to the gas inlet were first affected by the contaminant. The current density in the segments closest to the gas inlet decreased while the segments closest to the outlet increased. Since it was a constant current test, when the current in the segments closest to the gas inlet decrease, other segments picked up that current to maintain total current constant.During the baseline test, voltage remained constant in all segments. After contaminant injection, the cell voltage started to decrease and after 50 hours, voltages in each segments fluctuated. The voltage fluctuation was found to be mainly due to mass transport loss. The contaminant solution evaporated and deposited on the flow field and the GDL surface (Figure 3), and entered into the GDL which caused the mass transport losses. Moreover, the aluminum flow fields corroded and corrosion byproducts also deposited on the flow field and GDL surface. Throughout the test, there was no significant variation in voltage between segments. Acknowledgements The authors gratefully acknowledge financial support from NSF (CBET-0748063), DOE-EERE through University of Hawaii-Hawaii Natural Energy Institute (DE-EE0000467).

Current and clamping pressure distribution studies on the scale up issues in direct methanol fuel cells

The focus of the present study is to obtain the performance on a larger area (45cm2) equivalent to that obtained on a smaller area (4cm2) single cell DMFC overcoming performance losses associated with scale-up of single cell DMFCs due to uneven clamping pressure distribution on MEA through the end-plates and non-uniform distribution of reactants to MEA. The current distribution profile along the cathode flow field channel is measured using a segmented current measurement plate to understand the influence of uneven clamping pressure distribution on the MEA. Uniform current distribution in a single cell DMFC with 45cm2 electrode area is achieved using angular ribbed end-plates. Also, in the present study performance of conventional DMFC is compared with that of mixed-reactant (MR), i.e. methanol and air. Performance of DMFC operating on mixed reactant (MeOH+air) at anode and air at cathode is superior compared with DMFC operating on aqueous methanol at anode and air at cathode. A power density of 55mWcm−2 at 0.3V is obtained for a DMFC single cell with an effective area of 45cm2 using angular ribbed end-plates and MR at anode and air at cathode under ambient conditions. Pressure film test is conducted to obtain the clamping pressure distribution and cyclic voltammetry is performed to obtain the electrochemical surface area of small and large area electrodes.

Analysis of the terminal effect on the resistance tape at its constant and variable local conductivity

The regularities of current distribution in a rectangular electrochemical cell with equipotential anode and resistance tape cathode were studied by means of mathematical and physical modeling. For the case of uniform resistance tape and linear cathode polarization, the criteria of electric field similarity on the tape were obtained and the effect of different parameters was studied. A good quantitative agreement between the calculated and experimental profiles of current distribution along the tape was obtained. It was shown that a decrease in ohmic loss and corresponding weakening of the terminal effect are promoted not only by an increase in average conductivity κt,av but also by the variable profile of the local tape conductivity κt(x) increasing to the current lead. Different shapes of increasing κt(x) profiles were considered. For the linear κt(x) profiles increasing and decreasing to the current lead, with the equal average tape conductivities, it was shown theoretically and confirmed experimentally that linear κt(x) profile increasing to the current lead noticeably improves the uniformity of current distribution over the tape in comparison with κt,av, while a similar but reverse (decreasing to the current lead) κt(x) profile sharply enhances the terminal effect.