Injection Of Current Pulses Research Articles

All-solid-state pulsed current injection source based on the light initiated multi-gate semiconductor switches.

To study the damage and protection mechanism of the transient electromagnetic pulse to the cables of the electronic equipment under test, an all-solid-state pulsed current injection source with light initiated multi-gate semiconductor switches is developed. The output peak current range of the prepared all-solid-state pulsed current injection source was 0.1-1kA, the risetime was 18ns, and the pulse width was 520ns. In addition, the waveforms of the output peak current were consistent.

Carbon Nanofiber/PEDOT Based Macro-Porous Composite for High Performance Multifunctional Neural Microelectrode

Brain study methods mainly rely on neurochemical detection and electrophysiology, respectively to study the molecular dynamics [1] and electrical activity [2] in the brain cellular environment. Since the brain functioning relies on careful orchestration of both neurotransmitter and neuroelectric activities, coupled monitoring of them holds great promise in elucidating the brain functioning mechanisms and its related diseases e.g. Parkinson’s, epilepsy, etc [3]. Most of the conventional implantable neural interfacing technologies are comprised of noble metals on silicon/ polymer substrates. They suffer from inferior electrical properties, mechanical tissue-electrode mismatch, incompatible surface area, and low signal-to-noise ratio [4]. To address the need, researchers around the world are developing innovative soft materials with multimodal functionalities, especially the organic flexible materials such as conductive polymers and carbon allotropes, to fuel the next-generation multimodal neural electrode devices [5].Here in this work, we present a new macro-porous, conductive, and stable nanocomposite, made up of carbon nanofibers (CNFs) and PEDOT polymer, coated on a flexible neural microelectrode array (Fig. 1A-B). A fully controlled one-shot electrodeposition strategy was developed using chronopotentiometry technique, to coat flexible Au-microelectrode surfaces with macro-porous CNF/PEDOT nanocomposite. The oxidized CNFs were used as a dopant and infused within the conductive PEDOT, electrochemically, in such a way that their excellent electronic, mechanical, chemical properties, and resulting combined performances can be exploited to yield better quality neural recordings, electrical stimulation and neurotransmitter detection. At first, CNFs were oxidized to be dispersible in water (unlike raw CNFs) by vortex and sonication. Later, CNF/PEDOT composite was deposited on Au-electrodes galvanostatically, resulted in a 3D porous and fibrous network (Fig. 1B-D). Then, CNF/PEDOT deposits were characterized through electrochemical impedance spectroscopy (EIS) and pulse current injection. The composite microelectrodes showed low impedance, 16 ± 2 kΩ for a typical electrode area of 1250 µm2, at 1kHz (value corresponding to the neuron firing frequency) (Fig. 1E). Voltage transient responses were measured, at continuous 1ms-biphasic current pulses (cathodic first) in biologically relevant aCSF media, resulted in a charge-injection limit value of 7.6 ± 1.3 mC/cm² (Fig. F). Among all reported organic nanostructured composite materials that were deposited on flexible metallic substrates, CNF/PEDOT displayed superior electrical properties and charge injection capabilities [5]. Next, the capability of CNF/PEDOT composite electrode for in-vitro Dopamine (DA) sensing was evaluated by chronoamperometry, at 130mV vs SCE (oxidation potential of DA). The current responses submitted to DA injections resulted in linear regression (Fig. 1G, R²>0.99), with a high sensitivity of 13.4pA/nM.µm², compared to similar electrochemical sensors [6]. Overall, these electrodes displayed excellent electrical properties: low impedance (16 ± 2 MΩ.µm2 at 1 kHz) and high charge injection capabilities (7.5 ± 1.3 mC/cm²) making them promising candidates for bidirectional electrophysiology, while being capable to detect neurotransmitters like dopamine. Finally, integrated upon flexible neural probes, these composite microelectrodes were tested in-vivo on mouse brain slices as recording and stimulating electrodes (Fig. 1H). They displayed excellent performances, being capable to record spontaneous activities of neurons (sharp wave-ripples and single unit action potentials) and allowed to stimulate electrically the brain slice tissues, to obtain safe and stable evoked potentials. The obtained results show a great prospect for CNF/PEDOT composites for developing next-generation microelectrodes for applications in neural therapies.Figure 1. (A) Optical micrograph of flexible neural probe. (B) CNF/PEDOT deposition on 4 Au-microelectrodes of the implant. SEM images, (C) top view and (D) cross-sectional view of the composite electrode. (E) EIS measurement on modified microelectrodes from 10 Hz to 7 MHz in aCSF at 0V Vs Ag/AgCl. (F) Voltage transient of a CNF/PEDOT microelectrode resulting from the injection of a biphasic current pulse (90 µA with 1 ms pulse width). (G) Linear regression curve of CNF/PEDOT electrode current response at 130mV vs SCE to dopamine injections. (H) Electrophysiological recordings in the hippocampal region (CA1 and CA3) of a mouse brain slice, using flexible microelectrode array modified with CNF/PEDOT composite.AcknowledgmentsAgence Nationale de la Recherche (ANR-15-CE19-0006 and ANR-19-CE19-0002-01) and French RENATECH network.References Lama R.D., Karl Charlson, Arun Anantharam, Parastoo Hashemi, Analytical Chemistry, 84(19): p 8096-101 (2012).Normann R.A. and E. Fernandez, Journal of Neural Engineering, 13(6): p 061003 (2016).Ledo A., Cátia F. Lourenço, João Laranjinha, Greg A. Gerhard, and Rui M. Barbosa, Analytical Chemistry, 89(22): p 12383-12390 (2017).Enming Song, Jinghua Li, Sang Min Won, Wubin Bai, and John A. Rogers, Nature Materials, 16, 590-603 (2020).Zaid Aqrawea, Johanna Montgomeryb, Jadranka Travas-Sejdicc,d, Darren Svirskis, Sensors and Actuators B, 257,753–765 (2018)Jong-Min Moon, Neeta Thapliyal, Khalil Khadim Hussain, Rajendra N.Goyal, Yoon-Bo Shim, Biosensors and Bioelectronics, 102 , 540-552 (2018). Figure 1

Fiber-pigtailing quantum-dot cavity-enhanced light emitting diodes

We report on a process for the fiber-coupling of electrically driven cavity-enhanced quantum dot light emitting devices. The developed technique allows for the direct and permanent coupling of p-i-n-doped quantum dot micropillar cavities to single-mode optical fibers. The coupling process, fully carried out at room temperature, involves a spatial scanning technique, where the fiber facet is positioned relative to a device with a diameter of 2 μm using the fiber-coupled electroluminescence of the cavity emission as a feedback parameter. Subsequent gluing and UV curing enable a rigid and permanent coupling between micropillar and fiber core. Comparing our experimental results with finite element method simulations indicates a cavity-to-fiber mode-coupling efficiency of ∼46%. Furthermore, we demonstrate pulsed current injection at a repetition rate exceeding 200 MHz as well as low-temperature operation down to 77 K of the fiber-coupled micropillar device. The technique presented in this work is an important step in the quest for efficient and practical quantum light sources for applications in quantum information.

PEMFC water diagnosis using PWM functionality signal and fractional order model

This study aimed to develop a new diagnostic technique to determine the hydration status of the proton-exchange membrane fuel cell (PEMFC). The Fouquet impedance model was used to represent the PEMFC impedance, while Laplace’s method transformed the complex model to a real model of explicit fractional order. The outcome of both models in different operating cases (normal, dry and flooded) were compared and yielded good precision. In addition, the explicit fractional order model was used to represent the impedance of the PEMFC, while the current pulse injection (CPI) method with pulse width modulation (PWM) was used to monitor the hydration status of the PEMFC. The PEMFC hydration state was diagnosed using the frequency analysis of the current signals to observe the frequency spectrum amplitude variation at 50 Hz and 1000 Hz in different cases of operation.

Charge-order dynamics in underdoped La1.6−xNd0.4SrxCuO4 revealed by electric pulses

The dynamics of the charge-order domains has been investigated in La1.48Nd0.4Sr0.12CuO4, a prototypical stripe-ordered cuprate, using pulsed current injection. We first identify the regime in which nonthermal effects dominate over simple Joule heating and then demonstrate that, for small enough perturbation, pulsed current injection allows access to nonthermally induced resistive metastable states. The results are consistent with the pinning of the fluctuating charge order, with fluctuations being most pronounced at the charge-order onset temperature. The nonequilibrium effects are revealed only when the transition is approached from the charge-ordered phase. Our experiment establishes pulsed current injection as a viable and effective method for probing the charge-order dynamics in various other materials.

Design of optoelectronic computing circuits with VCSEL-SA based neuromorphic photonic spiking

A detailed theoretical analysis of spiking dynamics of VCSEL-SA based Photonic Laser Neuron (PLN) has been presented, under continuous and pulsed current injection. The maximum output spiking frequency of laser neuron is 9 GHz on continuous input current injection. Optimization of the amplitude and width tuned with threshold has been carried out that are crucial input parameters to control the behavior of PLN. Based on the results, neuromorphic photonic OR, AND, NOT, XOR and the universal NAND, NOR logic gates have been designed using a single PLN. Higher computing circuits such as half-adder, half-subtractor, full-adder and full-subtractor have also been designed that highlight the potential of brain-inspired scalable ultrafast neuromorphic photonic computing circuits for a wide range of applications.

Quantum Spin Torque Driven Transmutation of an Antiferromagnetic Mott Insulator.

The standard model of spin-transfer torque (STT) in antiferromagnetic spintronics considers the exchange of angular momentum between quantum spins of flowing electrons and noncollinear-to-them localized spins treated as classical vectors. These vectors are assumed to realize Néel order in equilibrium, ↑↓⋯↑↓, and their STT-driven dynamics is described by the Landau-Lifshitz-Gilbert (LLG) equation. However, many experimentally employed materials (such as archetypal NiO) are strongly electron-correlated antiferromagnetic Mott insulators (AFMIs) whose localized spins form a ground state quite different from the unentangled Néel state |↑↓⋯↑↓⟩. The true ground state is entangled by quantum spin fluctuations, leading to the expectation value of all localized spins being zero, so that LLG dynamics of classical vectors of fixed length rotating due to STT cannot even be initiated. Instead, a fully quantum treatment of both conduction electrons and localized spins is necessary to capture the exchange of spin angular momentum between them, denoted as quantum STT. We use a recently developed time-dependent density matrix renormalization group approach to quantum STT to predict how injection of a spin-polarized current pulse into a normal metal layer coupled to an AFMI overlayer via exchange interaction and possibly small interlayer hopping-mimicking, e.g., topological-insulator/NiO bilayer employed experimentally-will induce a nonzero expectation value of AFMI localized spins. This new nonequilibrium phase is a spatially inhomogeneous ferromagnet with a zigzag profile of localized spins. The total spin absorbed by AFMI increases with electron-electron repulsion in AFMIs, as well as when the two layers do not exchange any charge.

A high-efficiency wideband coupler for nanosecond-level pulsed current injection.

Pulsed current injection (PCI), as a conducted vulnerability testing technique under nanosecond-level transient electromagnetic disturbance (TED), has gained great attention recently. Many kinds of TEDs, e.g., high-altitude electromagnetic pulse, very fast transient overvoltage, and electrical fast transients, have very fast rise time as well as pretty slow decay, whose frequency spectrum may cover a very wideband. Therefore, one of the challenges is that the existing inductive couplers cannot interact with the equipment under test (EUT) over the wideband efficiently, and consequently, they are inadequate to inject the proper disturbance at ports of EUT in PCI tests. To address this problem, a high-efficiency wideband PCI coupler is proposed in this paper. The coupling performance is analyzed theoretically based on the distributed-parameter model of an inductive coupler. By using the composited ferrites instead of the simplex Ni-Zn ferrites, the inductive coupling is enhanced. The capacitive coupling is also enhanced to improve the high-frequency performance by exploiting the distributed tubular winding. A PCI coupler with the dimension of 30 × 10 × 10cm3 is built to be validated experimentally. The 3 dB bandwidth has been improved from 421 kHz-14MHz to 77 kHz-39MHz, which indicates that the coupler can be applied efficiently over the frequency range of interest for PCI tests.

Magnon- versus Electron-Mediated Spin-Transfer Torque Exerted by Spin Current across an Antiferromagnetic Insulator to Switch the Magnetization of an Adjacent Ferromagnetic Metal

The recent experiment [Y. Wang et al., Science 366, 1125 (2019)] on magnon-mediated spin-transfer torque (MSTT) was interpreted in terms of a picture where magnons are excited within an antiferromagnetic insulator (AFI), by applying nonequilibrium electronic spin density at one of its surfaces, so that their propagation across AFI deprived of conduction electrons eventually leads to reversal of magnetization of a ferromagnetic metal (FM) attached to the opposite surface of AFI. We employ a recently developed time-dependent nonequilibrium Green functions combined with the Landau-Lifshitz-Gilbert equation (TDNEGF+LLG) formalism to evolve conduction electrons quantum-mechanically while they interact via self-consistent back-action with localized magnetic moments described classically by atomistic spin dynamics solving a system of LLG equations. Upon injection of square current pulse as the initial condition, TDNEGF+LLG simulations of FM-polarizer/AFI/FM-analyzer junctions show that reversal of localized magnetic moments within FM-analyzer is less efficient, in the sense of requiring larger pulse height and its longer duration, than conventional electron-mediated STT (ESTT) driving magnetization switching in standard FM-polarizer/normal-metal/FM-analyzer spin valve. Since both electronic, generated by spin pumping from AFI, and magnonic, generated by direct transmission from AFI, spin currents are injected into the FM-analyzer, its localized magnetic moments will experience combined MSTT and ESTT. Nevertheless, by artificially turning off ESTT we demonstrate that MSTT plays a dominant role whose understanding, therefore, paves the way for all-magnon-driven magnetization switching devices with no electronic parts.

Real-time Hall-effect detection of current-induced magnetization dynamics in ferrimagnets

Measurements of the transverse Hall resistance are widely used to investigate electron transport, magnetization phenomena, and topological quantum states. Owing to the difficulty of probing transient changes of the transverse resistance, the vast majority of Hall effect experiments are carried out in stationary conditions using either dc or ac. Here we present an approach to perform time-resolved measurements of the transient Hall resistance during current-pulse injection with sub-nanosecond temporal resolution. We apply this technique to investigate in real-time the magnetization reversal caused by spin-orbit torques in ferrimagnetic GdFeCo dots. Single-shot Hall effect measurements show that the current-induced switching of GdFeCo is widely distributed in time and characterized by significant activation delays, which limit the total switching speed despite the high domain-wall velocity typical of ferrimagnets. Our method applies to a broad range of current-induced phenomena and can be combined with non-electrical excitations to perform pump-probe Hall effect measurements.

A Rotor Initial Position Estimation Method for Surface-Mounted Permanent Magnet Synchronous Machine

A new rotor initial position estimation method for surface-mounted permanent magnet synchronous machines (SPMSM) is presented in this paper. The proposed method is based on the magnetic saturation effect and is suitable to prevent starting failure and reverse rotation. Compared with conventional methods, the proposed method shows better effective estimation performance. New strategies for utilizing current responses and voltage pulse injection process are developed. As a result, only three pulses are needed in total at no cost of extra sensors, while maintaining at least 30-degree estimation resolution at the same time. Moreover, a boundary detection strategy (BDS) is proposed to enhance the estimation performance regarding the impact of current measurement noises. Further, based on the BDS, a concept of `boundary width' is proposed. By properly selecting the boundary width, the estimation resolution can be improved from 30 degrees to 15 degrees. Experimental results are given to verify the effectiveness of the proposed method.

Protection Performance Test of Power Line Filter by Pulsed Current Injection Method

In order to test the protection performance of power line filter against conducted interference from high-altitude nuclear electromagnetic pulse (HEMP), this letter uses pulse current injection (PCI) method to test the power line filters. By calculating the residual current peak value, the conduction interference suppression of the filter is judged. The experimental results show that when the input current pulse peak is 1.0kA, 1.5kA, 2.0kA, 2.5kA, the traditional power line filters cannot meet the electromagnetic pulse conduction protection requirements of MIL-STD-188-125-1 and -2. With the increase of the input current peak, the residual current peak increases, or increases to a maximum value then decreases. Therefore, when testing the protection performance of the filters, it is necessary to perform pulse current test at different injection levels. Based on the test results, a method to improve the protection performance of the power line filters against HEMP was proposed. The experimental data showed that the peak values the residual current is greatly decreased. The test results laid the foundation for improving the power line filter against HEMP.

Modeling and Performance Evaluation of Inductive Couplers for Pulsed Current Injection

Pulsed current injection (PCI) is an important conducted susceptibility testing technique. In several related standards, the short-circuit current waveforms of the pulse generators are defined and the coupling methods are mentioned, whereas the performance of the couplers and the injected electrical quantities have not been clearly defined. Therefore, the couplers with different performance criteria would lead to various injected electrical quantities and consequently rather different experimental effects. This article focuses on modeling and quantitatively evaluating the performance of inductive couplers. The key issue in modeling is how to measure the frequency-dependent characteristics of ferrite cores under high-power operating conditions (up to several kA); therefore, an impulse injection method is proposed and validated by a 400-kV pulse generator with the rise time of 5 ns to measure the frequency-dependent characteristics of ferrite cores. The validation test confirms that the bandwidth of the modeling procedure can cover the bandwidth of interest for PCI tests. The criteria of performance evaluation for inductive couplers are proposed in frequency domain as well as in time domain. In addition, the criteria are compared for two inductive couplers with different ferrite materials, which shows that the criteria are not only significant in comparing and selecting couplers quantitatively, but also of critical importance in the design phase.

Thermal dynamic imaging of mid-infrared quantum cascade lasers with high temporal–spatial resolution

The time-resolved (TR) temperature profile of actively biased mid-infrared quantum cascade lasers (MIR QCLs) was measured by using charge-coupled-device (CCD)-based thermoreflectance microscopy (TRM) with an ultrafast temporal resolution of 50 ns and a high spatial resolution of 390 nm. Based on the measured TR two-dimensional (2D) temperature profiles, the heat generation and dissipation dynamics within the lasers have been investigated. It is found that the active-region temperature increases quickly to a peak value (up to ∼100 °C above ambient room temperature) within 500 ns upon pulsed current injection of 6 A. The heat dissipation to the top and bottom cladding layers of the device is initially comparable, yet it evolves differently with time. Within 1–2 μs, the heat dissipation to the top cladding is substantially reduced and most of the heat is drained to the substrate through the bottom cladding layer. This constrained heat dissipation results in the elevated temperature in the active region, leading to thermal quenching of lasing operation, which is confirmed by experimental light–current–voltage measurement and theoretical thermal modeling. The TRM is an enabling tool for probing internal thermal dynamics of many active electronic and photonic devices, particularly for those needing special heat and thermal arrangement.

A Magnetization State Initialization Control Scheme for Variable Flux Memory Machines Without Requiring Position Sensor Information

Variable flux memory machines (VFMMs) normally suffer from excessively low initial magnetization state (MS), which will cause a large starting current or even startup failure. This article proposes an MS initialization control scheme for VFMMs equipped with incremental encoders, in which the required rotor position is estimated by injecting high-frequency square-wave voltage. Based on the estimated initial rotor position, the MS initialization can be accurately and smoothly achieved by applying a ${d}$ -axis current pulse. The general framework of the proposed scheme is demonstrated first. The voltage pulse magnitude determination of the bipolar injection method is then particularly discussed to realize the polarity detection within a full flux regulation range. The implementation of the ${d}$ -axis current pulse injection method for the MS initialization based on the estimated rotor position is subsequently introduced. Finally, the feasibility and effectiveness of the proposed MS initialization control scheme are experimentally verified on a manufactured VFMM prototype.

10-kV Transmission Line Experimental Platform for HEMP Immunity Test of Electrical Equipment in Operation

To investigate the high-altitude electromagnetic pulse (HEMP) immunity of electrical equipment in operation, a 10-kV transmission line (TL) experimental platform is built in this paper. The conducted transient electromagnetic disturbance (TED) could be injected to the electrical equipment of 10-kV TL with power on or power off. The TED is produced by the pulsed current injection (PCI) generator, whose rise time is less than 20 ns and full width at half maximum is in the range of 500 ~ 550 ns on short-circuit state with 60 Ω resistor. On the other hand, the 10-kV TL is equivalently designed in cross section to make its characteristic impedance being 330 Ω to conform to the value of practical case. The voltages and currents applied on the tested equipment can be measured at nano-second level simultaneously, which are of great use to learn the effect mechanisms and compare the results under different working conditions. Some 10-kV pin-type porcelain insulators are tested under different conditions, which shows the capacity of the proposed platform to test immunity of 10-kV electrical equipment.

방호시설에 설치된 HEMP 필터의 전도성 PCI 검증시험을 위한 디커플러 설계 및 제작

When a high-altitude electromagnetic pulse(HEMP) power line filter is installed in a protection facility, the pulsed current injection (PCI) acceptance test is performed. A verification test is required even if the acceptance criteria are met. The injection current of the PCI generator may damage the external power source because a verification test is performed while the HEMP filter is connected to the power supply. Current decouplers have limited capacity and use; thus, they should be designed according to the actual environment. In this study, a decoupler is designed and fabricated for the PCI verification test. It is confirmed that the fabricated decoupler can be used as a protection circuit of the power supply by using a test-bed similar to that in the actual protection facility.

GaN 2DEG Varactor-Based Impulse Suppression Module for Protection Against Malicious Electromagnetic Interference

A GaN-based metal–semiconductor–metal varactor with a two-dimensional electron gas (2DEG) layer is proposed and fabricated. The capacitance variation of this fabricated varactor biased at different external voltages is studied and measured, and the frequency-dependent capacitance and resistance of the varactor are simulated by a corresponding empirical formula. A high-frequency protective filter is further constructed and placed under a large pulsed-current injection in a malicious electromagnetic interference immunity test. The results show that the proposed GaN-based module can reduce the large pulsed current to an acceptably small level. Thus, the GaN-based 2DEG varactor is an attractive candidate for applications designed to protect the upcoming 5G high-frequency system from risks such as electrostatic discharge, lightning, and electromagnetic pulses.

On-wafer fabrication of etched-mirror UV-C laser diodes with the ALD-deposited DBR

We have demonstrated an on-wafer fabrication process for AlGaN-based UV-C laser diodes (LDs) with etched mirrors and have achieved lasing for 100 ns pulsed current injection at room temperature. A combined process of dry and wet etching was employed to achieve smooth and vertical AlGaN (11¯00) facets. These etched facets were then uniformly coated with a distributed Bragg reflector by atomic layer deposition. A remarkable reduction of the lasing threshold current density to 19.6 kA/cm2 was obtained owing to the high reflectivity of the etched and coated mirror facets. The entire laser diode fabrication process was carried out on a whole 2-in. wafer. We propose this mirror fabrication process as a viable low-cost AlGaN-based UV-C LD production method that is also compatible with highly integrated optoelectronics based on AlN substrates.

Comprehensive Design Procedure and Control of a Hybrid Circuit Breaker with Adaptable Pulse Current Injection

Comprehensive Design Procedure and Control of a Hybrid Circuit Breaker with Adaptable Pulse Current Injection