Current Shunt Research Articles

Tunable magnetoelastic anisotropy in epitaxial (111) Tm3Fe5O12 thin films

Ferrimagnetic insulators with perpendicular magnetic anisotropy are of particular interest for spintronics due to their ability to mitigate current shunting in spin–orbit torque heterostructures and enable low switching energy, high-density storage magnetic devices. Rare earth iron garnet Tm3Fe5O12 (TmIG) is one such material where prior studies have shown that the negative magnetostriction coefficient and isotropic in-plane tensile strain enable the magnetoelastic anisotropy to overcome the demagnetization energy and stabilize perpendicular magnetic anisotropy. However, the investigation of the tunability of the magnetoelastic anisotropy between thin films that possess perpendicular magnetization and quantification of the magnetoelastic constants has not been reported. Here, we quantify the evolution of magnetic anisotropy in (111)-oriented, epitaxial, 17 nm thick thin films of TmIG using a systematic variation of in-plane epitaxial strain (ranging 0.49%–1.83%) imposed by a suite of commercially available garnet substrates. Within the confines of the imposed strain range and deposition condition, the distortion from cubic symmetry is found to be approximately linear within the in-plane strain. The magnetic anisotropy field can be tuned by a factor of 14 in this strain range. The magnetoelastic anisotropy constant, B2, is found to be approximately constant (∼2500 kJ m−3) and more than 2× larger than the reported bulk value (∼1200 kJ m−3) for a cubic distortion between 90.17° and 90.71°. B2 is found to decrease at cubic distortions of 90.74° and larger. Our results highlight strain engineering, and its limitations, for control of perpendicular magnetic anisotropy.

A −4–4 V Input Common-Mode Range Bidirectional Current Shunt Monitor

This study describes a novel bidirectional current shunt monitor (CSM) circuit operating at both positive and negative common-mode (CM) voltages. The proposed CSM circuit mainly consists of two comparators, three error amplifiers, several current-mirror transistors and a few resistors. One comparator is used to detect current flowing direction, and the other one is utilized to ensure good operation of CSM circuit with both positive and negative CM voltages. The proposed CSM circuit has been implemented in SMIC 0.18[Formula: see text][Formula: see text]m standard CMOS process and its performances have been verified by simulations. The simulated results show that the proposed CSM circuit, at a supply voltage of 5[Formula: see text]V and with an input CM voltage range from [Formula: see text] to 4[Formula: see text]V, can sense a voltage difference of 4–40[Formula: see text]mV and keep a constant scaled gain of 100[Formula: see text]V/V. The gain error is less than 0.65% and the common-mode rejection ratio (CMRR) is higher than 130[Formula: see text]dB at 1[Formula: see text]kHz. Simulation results show that the output voltage of CSM circuit varies linearly with the CSM input sense voltage.

Electrical characterization of CIGS thin-film solar cells by two- and four-wire probe technique

A precise characterization of thin-film solar cells is of huge importance for obtaining high open-circuit voltage and low recombination rates from the interfaces or within the bulk of the main materials. Among many electrical characterization techniques, the two- and four-wire probe using the Cascade instrument is of interest since the resistance of the wires and the electrical contacts can be excluded by the additional two wires in four-wire probe configuration. In this paper, both two- and four-point probes configuration are employed to characterize the CIGS chalcogenide thin-film solar cells. The two-wire probe has been used to measure the current–voltage characteristics of the cell which results in a huge internal resistance. Therefore, the four-wire connection is also used to eliminate the load resistance to enhance the characterization’s accuracy. The load resistance in the two-wire probe diminishes the photogenerated current density at smaller voltage ranges. In contrast, the proposed four-wire probe collects more current at higher voltages due to enhanced carrier collection efficiency from contact electrodes. The current conduction mechanism is also identified at every voltage region represented by the value of the ideality factor of that voltage region. It is observed that a longer time given to the charge collection results in increased current density at a higher voltage. According to the results and device characteristics, a novel double-diode model is suggested to extract the saturation current density, shunt and series resistances and ideality factor of the cells. These cells are shown to be efficient in terms of low recombination at the interfaces and with lower series resistance as the quality of the materials is in its most possible conductive form. The measured internal resistance and saturation current density and ideality factor of the two measurement configurations are measured and compared.

Влияние параметров барьера и приложенного напряжения на характеристики импульсного поверхностного разряда

The results from an experimental study of impulse surface discharge occurring in an electrode system containing a dielectric plate are presented. On one of its sides, the plate had a corona-producing electrode made of 50 mm thick copper foil grounded through a current shunt for measuring the discharge current. On its other side, the plate had a high-voltage electrode, to which the voltage from a pulse generator was applied. The article presents the results from measurements of the initial voltage and the sizes of the surface discharge area in air when applying single voltage pulses with different pulse front steepness in the range 0,1–3,4 kV/ms and amplitude in the range 7–15 kV. The measurements were carried out for different dielectric barrier materials with the e values from 2 to 35. The dielectric barrier thickness was 0,9–1,8 mm. The study results have shown that the initial surface discharge ignition voltage depends essentially on the voltage pulse parameters, whereas the barrier characteristics have a weaker effect on this voltage. It has been determined that the discharge has different discharge zone length and different structure depending on the dielectric barrier properties and applied voltage parameters. The streamer zone sizes decrease with increasing the barrier material e value at the same voltage pulse steepness and increase with increasing the steepness for each barrier material. The data obtained for a wide range of external conditions can be used in numerical modeling of discharge.

Hydrocephalus shunt therapy: current titanium shunt valve implants obstructed by internal tissue proliferations identified as extracellular matrix membranes.

Shunt valves, required for treatment of hydrocephalus, demand for high performance rates and lifelong excellent function. To overcome problems with traditional silicone materials, adjustable and gravity-adapted titanium valves were developed. Even modern shunt valve systems are still subject to occlusion. The aim of the present study was to investigate dysfunctional silicone and titanium valves for presence of cellular and proteinous materials inside the housings by means of histopathology. A total of 19 explanted shunt valves from children between 2 and 182 months of age were investigated following dysfunction. After fixation in formalin and embedding in hard resin, slices were ground to a thickness of 5-30 μ. Besides standard histology, immunohistochemistry was performed using antibodies with markers for microglia, astrocytes, platelets, monocytes, and the proteins laminin, fibronectin, and collagen IV. Traces, layers, and plaques could be demonstrated in every investigated silicone or titanium valve with an implantation time of more than 6 days. Most of the tissue was found adjacent to silicone and titanium surfaces of the inner housing, the adjustment rotor, and ball-in-cone core. Markers for micro and astroglia stained positive in 40-60% of the specimen, mostly demonstrating a proteinous layer positive for laminin (80%), fibronectin (30%), and collagen IV (30%). Tissue reactions with formation of cellular and proteinous matrix components are common in obstructed silicone and titanium shunt valves. The tissue mimics astrocytic repair mechanisms genuine for basilar membrane matrix. The knowledge of these typical arachnoid patterns of colonization is a prerequisite for developing future shunt devices.

Mechanism of Current Shunting in Flexible Cu2Zn1−xCdxSn(S,Se)4 Solar Cells

Partial cation substitution is an effective way to inhibit defects and carrier recombination, which can improve the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. Herein, flexible Cu2Zn1−xCdxSn(S,Se)4 (x = 0–15%) solar cells are fabricated on Mo foils with partial Cd substitution for Zn via a green solution‐process. The best device performance can be achieved when Cd/(Zn + Cd) = 8%, with an efficiency up to 6.49% and a significantly improved device repeatability. The EU decreases from 24 to 15 meV, indicating that antisite defects and band tailings are effectively suppressed. C–V data reveal that Wd and Vbi are enhanced after doping Cd, resulting in a stronger built‐in electric field which facilitates Fermi‐level splitting and hence increases band bending of the absorber toward the junction interface. Furthermore, the mechanism of current shunting is studied using an equivalent circuit model with three parallel current pathways to fit J–V curves. The key parameters for the solar cell diode such as A, J0, and Rsh are significantly improved by partially substituting Zn with Cd, demonstrating that current shunting loss is suppressed and the junction quality is improved, resulting in a significant improvement in device repeatability.

Modeling the AC–DC Transfer Difference of Wideband Cage-Type Current Shunts

A cage-type, current-shunt construction design was adopted in this article as prospectively having a wide bandwidth. A lumped equivalent circuit model for current shunts assembled according to this design is described here. The ac–dc transfer differences of shunts with the nominal currents from 0.5 to 20 A are computed using standard two-port network theory. Cage-type current shunts were constructed and tested to validate the model. The measured ac–dc current transfer differences agree with the predicted values within the standard uncertainties in the whole frequency range of interest (10 Hz–100 kHz).

Advanced poly(vinyl alcohol) porous separator with overcharge protection function for lithium-ion batteries

The separator plays a key role in improving the safety and charge-discharge property of lithium-ion batteries. Herein, a home-made polyvinyl alcohol porous separator with three-dimensional porous structure is used as the substrate to allow a perfect distribution of the inexpensive electroactive polymer polytriphenylamine. The electroactive polymer exhibits a reversible electrochemical reaction belonging to doping and dedoping process between 3.0 and 4.5 V, which provides potential overcharge protection function for the functionalized composite separator. Due to maximum preservation of the original porous structure of the polyvinyl alcohol separator, the composite separator likewise possesses excellent electrolyte affinity and ionic conductivity. A blocking cell assembled with the composite separator still has a certain voltage clamp function even if the current density increases to 5.0 mA cm−2. Moreover, a half-cell (LiFePO4-Li) assembled with the composite separator exhibits a reversible voltage-regulated current shunt even after 50 overcharge cycles. At a high current density rate of 4.0 C, the half-cell can still provide a discharge capacity of 94 mAh g−1 and an effective overcharging shunting at 4.0 V.

Impact of Post-Deposition Recrystallization by Alkali Fluorides on Cu(In,Ga)Se2Thin-Film Materials and Solar Cells

Using thermal evaporation, Cu(In,Ga)Se2 (CIGS) layers were deposited at low temperature (350 °C) and high rate (10 μm/h) using a single stage process. They were then recrystallized using a variety of alkali fluorides: NaF, KF, RbF and CsF. To ensure that the substrate would not influence the study (via alkali diffusion), the samples were deposited on silicon wafers. The chemical, physical and electrical properties of the films were then characterized, demonstrating that all alkali fluorides behave as fluxing agents to enhance recrystallization and conductivity, and induce a (112) preferential orientation. Secondary ion mass spectrometry analysis showed that no modification of the elements' distribution occurs because of recrystallization. Solar cells were also fabricated and characterized, indicating that NaF can double the efficiency of solar cells compared to the as-deposited layers. This enhancement is accompanied by the disappearance of a rollover, voltage dependent current collection and shunt from the current density-voltage curves. However, even for the best recrystallization, the current is still limited to 28 mA/cm2, indicating that only a portion (0.75 μm) of the full device (2 μm) is activated.

Optimization of the Process Parameters of Resistance Spot Welding of AISI 316l Sheets Using Taguchi Method

Abstract Resistance spot welding (RSW) is a fabrication process that is being used in the automobile and aerospace industry since many years for joining low carbon or “mild” steel. Quality and strength of the welds depend upon the process parameters of RSW. The most effective parameters in this process are: current intensity, welding time, sheet thickness and material, geometry of electrodes, electrode force, and current shunting. This paper presents the experimental investigations for the optimization of tensile shear stress of RSW for stainless steel grade 316L sheets by using Taguchi method. The experiments were conducted using Taguchi’s L27 orthogonal array under varying process parameters, namely electrode diameter, welding current, and heating time. The experimental data were analyzed using signal-to-noise ratio (S/N ratio) to find the optimal process parameters. Analysis of variance (ANOVA) and F test were used to find the most significant parameters affecting the spot weld quality characteristics. Confirmation tests with optimal process parameters were conducted to validate the test results. From the results, it was found that it is possible to increase tensile shear stress significantly.

Electrode contaminant plasma effects in 107 -A Z pinch accelerators

The dynamics of electrode heating, sheath flow, and contaminant plasma evolution in Sandia National Laboratories' high-power $Z$ accelerator is studied in a series of 2D relativistic particle-in-cell simulations. These dynamics can lead to the shunting of current before reaching the $Z$ pinch load, thus degrading load performance. Previous work has focused on current diverted in the upstream magnetically insulated transmission lines (MITLs) and post-hole convolute regions of $Z$. In these regions, losses were found to scale strongly with load impedance as well as the system vacuum and were calculated to be as high as 1--2 MA. Downstream from the convolute region in $Z$, current measurement is problematic, leading to a lack of understanding of the loss mechanisms in the small radius ($l3\text{ }\text{ }\mathrm{cm}$) MITL feeding the load. In this paper, we present the first ever 2D fully electromagnetic, fully kinetic simulations of plasma evolution and current shunting in the inner MITL region of $Z$. This region is defined by a radially converging MITL, which is a feature common to MA-scale $Z$ pinch accelerators. The electrodes in this region are rapidly heated via mainly Ohmic or skin depth heating. Plasmas quickly form, and surface contaminants are liberated as the temperatures exceed 700 K. Instabilities lead to a rapid plasma density fill of the inner MITL and subsequent current loss. The instability growth is likely due to the resistivity of the magnetized electrode plasma. The plasma, after exceeding ${10}^{15}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ density, leads to an additional 1--2 MA current loss in the inner MITL region.

Toward a Calculable Standard Shunt for Current Measurements at 10 A and Up To 1 MHz

Electrical current shunts are widely used as a resistance standard in metrology laboratories and precision instruments with the aim of measuring a high level of alternative and direct currents (ac and dc) with high accuracy. These ac current sensors are characterized by a broadband operating frequency bandwidth and are commonly calibrated up to 100 kHz. The use of a current shunt requires the preliminary knowledge of its magnitude deviation from dc and phase angle according to the frequency. The determination of these parameters is challenging at high frequencies and for high levels of current: typically beyond 100 kHz and 1 zA. For a current level of 10 A, existing current shunts exhibit a strong variation in magnitude and phase. The best magnitude performances of 10-A current shunt standards published so far are limited to $2~\mu \Omega /\Omega $ at 100 kHz. In this paper, we detail the theoretical basis of innovate shunts for current measurements from 50 mA to 10 A up to 1 MHz. The electrical modeling is valid from 50 mA to 10 A: only the $R_{\mathrm {dc}}$ value must be changed to get the electromagnetic response of any shunt standards designed for this range of current levels. For a 10-A shunt standard, the relative deviation from dc obtained by calculation is less than 0.2 and $20~\mu \Omega /\Omega $ in magnitude at 100 kHz and 1 MHz, respectively. The design as well as the electromagnetic modeling of the shunt is profoundly described in this paper.

Characterization of DC Current Sensors With AC Distortion for Railway Applications

To assess the reliability of dc energy measurement equipment on-board trains, a setup was developed to characterize current transducers under realistic operating conditions. The operating principle is based on a current ratio measurement technique. The reference sensor is a high-precision zero-flux current transducer in combination with a broadband high-precision current shunt. The influence of ac distortion on this reference sensor was found to be within a few parts in 106 using an initial version of the setup, in which ac distortion was applied through a separate winding. A revised version of the setup employs a programmable electronic load to apply dynamic currents up to 600 A. The setup was used to characterize a 100 $\mu \Omega $ high-current shunt resistor. The effect of dissipative heating on the dc transresistance error was around 0.03 %, with a settling time of about half an hour. The short-term intrinsic current dependence was also around 0.03 %. The effect of ac distortion was within a few parts in 106. The intrinsic current dependence and the onset of the heating effect were also observed when exposing the sensor to a dynamic current profile that was recorded during a trip between two successive underground train stations on Metro de Madrid. These results demonstrate that the setup described in this paper is very effective for characterizing dc current sensors for practical railway applications. Future work will concentrate on even more demanding current signals, such as chopped signals, and on other types of sensors and measurement systems.

InGaN/GaN tandem solar cell parameter estimation: a comparative study

In this paper, two hybrid estimation approaches, hybrid genetic algorithm (TR-GA) and hybrid particle swarm optimization (TR-PSO), are used to estimate single-diode model InGaN/GaN solar cell parameters from J?V experimental data under AM0 illumination. These parameters are photocurrent density ($J_{ph}$), reverse saturation current density ($J_{s}$), ideality factor ($A$), series resistance ($R_{s}$), and shunt resistance ($R_{sh}$). The trust region (TR) method used in both approaches provides the initial conditions and helps to avoid the problem of premature convergence (due to local minimum). Simulation results based on the minimization of the mean square error between experimental and theoretical J-V characteristics show that both applied methods have a similar degree of efficiency in terms of precision, whereas the TR-PSO method is more efficient in terms of convergence speed. The effect of different extracted parameters on the characteristics J-V and P-V is evaluated in a simulation study of an identified model.

Electric field induced second harmonic (E-FISH) generation for characterization of fast ionization wave discharges at moderate and low pressures

The electric field in an ionization wave discharge in nitrogen at 20–100 mbar, initiated by positive polarity, high-voltage, ns duration pulses, is measured by ps second harmonic generation. The axial electric field component is determined both during the propagation of the ionization wave along the discharge tube, and after the wave reaches the grounded electrode, spanning the entire discharge gap. The temporal resolution of the present measurements is 200 ps, with the spatial resolution in the axial direction of approximately 0.5 mm. The second harmonic signal exhibits a quadratic dependence on the Laplacian electric field but indicates that in this pressure range most of the signal is generated within the wall of the tube. Absolute calibration of the signal is obtained from the current shunt data, after the ionization wave has reached the grounded electrode. Comparison of the data taken at different pressures shows that the peak value of the axial electric field in the wave front, 8–11 kV cm−1, has a fairly weak dependence on pressure, with the peak reduced electric field reaching ≈2000 Td at 20 mbar. Reducing the pressure from 100 to 20 mbar, while keeping the discharge pulse voltage waveform the same, steepens the ionization wave front considerably, from 3.0 to 1.0 ns full width at half maximum. The results demonstrate that ps second harmonic generation may be employed for electric field measurements in low-pressure discharges, discharges sustained in small diameter capillary tubes, and discharges sustained in gas mixtures with low nonlinear susceptibility, at the conditions when the detection of the signal generated directly in the plasma is challenging. High temporal resolution of the present measurements indicates a possibility of detection of non-local electron kinetics effects induced by a rapidly varying, high peak value electric field in low and moderate pressure ionization wave discharges.

Design and control of variable field permanent magnet motors

This is a survey paper focusing on permanent magnet motors with variable field capability. The synchronous motors, which have been applied to somewhat limited fields, have garnered attention as attractive electric drives. Due to a connection with rare‐earth magnet and power electronics‐based flexible control, current permanent magnet synchronous motors have achieved the best position in terms of high power and torque densities, high efficiency and flexible control capability. In order to satisfy the diverse demands of users, a motor is requested to ensure high‐efficiency operation at multiple operating points on the speed–torque plane. It is well recognized that maximum efficiency is attained under the condition that the copper loss is equal to the fixed loss, mainly composed of iron loss, at a given operating point. This is why permanent magnet synchronous motors should have the capability of adjusting the field excitation, similar to the direct current shunt motors. In this paper, recent trends of research and development of variable field permanent magnet motors are overviewed from the standpoint of design and control. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

UV LEDs based on p–i–n core–shell AlGaN/GaN nanowire heterostructures grown by N-polar selective area epitaxy**Contribution of an agency of the US government; not subject to copyright.

Ultraviolet light-emitting diodes fabricated from N-polar AlGaN/GaN core–shell nanowires (NWs) with p–i–n structure produced electroluminescence at 365 nm with ∼5× higher intensities than similar GaN homojunction LEDs. The improved characteristics were attributed to localization of spontaneous recombination to the NW core, reduction of carrier overflow losses through the NW shell, and elimination of current shunting. Poisson-drift-diffusion modeling indicated that a shell Al mole fraction of x = 0.1 in AlxGa1−xN effectively confines electrons and injected holes to the GaN core region. AlGaN overcoat layers targeting this approximate Al mole fraction were found to possess a low-Al-content tip and high-Al-content shell, as determined by scanning transmission electron microscopy. Photoluminescence spectroscopy further revealed the actual Al mole fraction to be NW diameter-dependent, where the tip and shell compositions converged towards the nominal flux ratio for large diameter NWs.

Spin Hall magnetoresistance in Co2MnSn/IrMn/Pt heterostructures

Abstract Magnetic transport properties in Co2MnSn/IrMn/Pt trilayer structures have been investigated. Spin Hall magnetoresistance (SMR) enhancement in the trilayer structures has been observed, under the premise of exclusion current shunting effect. The experimental analysis indicates that the SMR enhancement may be closely related to the spin current enhancement reflected from the Co2MnSn/IrMn interface. Anomalous Hall resistance (AHR) study shows that its variation is quite similar to the SMR, suggesting that the SMR enhancement may also be closely related to spin-orbit coupled (SOC) scattering at the interface due to the coupling between IrMn and Co2MnSn layer. Temperature influences the SMR significantly in the trilayer structures at low IrMn thicknesses, which the IrMn has more ferromagnetic or ferrimagnetic orders than antiferromagnetic order. It indicates that the physical mechanism of the influencing of temperature on SMR of FM/AFI(AFM)/Pt trilayer structures need to be further investigated. The SMR changes its sign from positive to negative at temperatures lower than 50 K, revealing that spin-flop coupling between IrMn and Co2MnSn could happen at the interface.

Realization of Absolute Phase and AC Resistance of Current Shunts by Ratio Measurements

This paper presents a simplified method for realizing absolute phase and ac resistance for current shunts using only impedance ratio measurements. The method is based on three geometrically identical current shunts with different resistances, but with the same inductance, capacitance, and ac–dc resistance change. We demonstrate how the inductance, capacitance, and ac resistance can be calculated from the complex impedance ratio measurements, therefore realizing absolute current shunt impedance. The method gives competitive uncertainties of around $200~ \mu \Omega / \Omega $ for amplitude and $400~ \mu $ rad for phase at 1 MHz in the 1- $\Omega $ range.

Composite milliohm-meter for resistance measurement of precision current shunts in industrial environment

A composite milliohm-meter (Com-mOhm), based on standard four-wire Kelvin resistance measurement method, was developed for measurements of precision current shunts used in an industrial environment. The system is comprised of a precision, temperature compensated, low drift, high stability 100 mA current source and a 4 ? digit commercial multimeter. Due to the set of specific demands and conditions concerning the industrial applications of precision current shunts, standard measurement equipment and methods could not be implemented. The composite resistor standard was used for temperature stabilization of the precision current source based on precision voltage reference REF102. The measurement precision of ?0.1 milliohms is observed during measurement of 20 milliohm current shunts.