Current Pulses Research Articles

Energy-efficient picosecond spin-orbit torque magnetization switching in ferro- and ferrimagnetic films.

Electrical current pulses can be used to manipulate magnetization efficiently via spin-orbit torques. Pulse durations as short as a few picoseconds have been used to switch the magnetization of ferromagnetic films, reaching the terahertz regime. However, little is known about the reversal mechanisms and energy requirements in the ultrafast switching regime. In this work we quantify the energy cost for magnetization reversal over seven orders of magnitude in pulse duration, in both ferromagnetic and ferrimagnetic samples, bridging quasi-static spintronics and femtomagnetism. To this end, we develop a method to stretch picosecond pulses generated by a photoconductive switch by an order of magnitude. Thereby we can create current pulses from picoseconds to durations approaching the pulse width available with commercial instruments. We show that the energy cost for spin-orbit torque switching decreases by more than an order of magnitude in all samples when the pulse duration enters the picosecond range. We project an energy cost of 9 fJ for a 100 × 100 nm2 ferrimagnetic device. Micromagnetic and macrospin simulations unveil a transition from a non-coherent to a coherent magnetization reversal with a strong modification of the magnetization dynamical trajectories as pulse duration is reduced. Our results show the potential for high-speed magnetic spin-orbit torque memories and highlight alternative magnetization reversal pathways at fast timescales.

Fretting Wear of Titanium Alloys during the Passage of Current Pulses

Fretting Wear of Titanium Alloys during the Passage of Current Pulses

Optical diagnostics of vacuum arcs in the process of DC interruption

Abstract Vacuum circuit-breakers (VCBs) are commonly used in emerging mechanical DC circuit-breakers. The electrical performance of VCBs in DC interruption duties has been extensively investigated, but basic physics such as the excitation temperature of plasma species, electron/vapor densities and emission of droplets in such applications were rarely reported. In this paper, we focus on how the short high frequency (HF) current pulse affects erosion of electrodes as well as generation of flying droplets by using laser shadow photography. Spectroscopy was adopted to obtain spectra and calculate the excitation temperature of CuI. Shack–Hartmann wavefront sensors were applied to measure neutral and electron density, in tests where di/dt, breaking current and the direction of the injected HF current varied. Indeed, the in-phase injection of the HF current caused an intense arc, but the pulse was too short to make either the cathode or anode melt. Since the plasma is in a nonequilibrium state, the excitation temperature of CuI is relatively low. Electron densities in different tests all approach similar values right before current zero. Neutral densities show strong fluctuation and independence on instantaneous current.

Microscopic characteristics and properties of co-based coating by pulse current-assisted laser cladding on high carbon steel

Laser cladding has the advantages of a short processing cycle and good processing quality, and has been extensively researched in the field of rail property enhancement. The current study focuses mostly on enhancing the mechanical properties of rails by altering the laser process parameters and using complicated materials. However, the enhancement of mechanical properties such as corrosion and friction resistance by laser cladding is limited. As an effective metallurgical processing method, pulse current can be used to control the microstructure and improve the mechanical properties by altering the solidification process of the metal. In this paper, the effects of pulse current parameters (pulse current frequency, current peak, and duty cycle) on microscopic characteristics, such as microstructure number of pores, and microhardness, as well as mechanical properties, such as wear and corrosion resistance, of stellite-6 coatings created by pulse current-assisted laser cladding (PC-ALC), on the U71Mn substrate were investigated. The results showed that the electromagnetic action of the current refined the grains and reduced the number of pores in the PC-ALC coating. The degree of grain fineness increased, then decreased, as the current intensity increased. When compared with the microhardness without pulse current, the average hardness of the HAZ and coating rose by 49.7 % and 167 %, respectively. The results showed a positive link between corrosion resistance and current frequency, but a negative correlation between corrosion resistance and current peak. The corrosion resistance was improved by increasing the current duty cycle from 25 % to 50 %. The wear resistance of coatings was positively related to microhardness, and the coating reached the wear stabilization stage with a friction loss of about 0.5 %. The tests indicated that PC-ALC coatings had good corrosion and friction resistance for rail repair, extending their service life.

Research on Process Characteristics and Properties in Deep-Penetration Variable-Polarity Tungsten Inert Gas Welding of AA7075 Aluminum Alloy

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove.

Femtosecond pulse amplification on a chip

Femtosecond laser pulses enable the synthesis of light across the electromagnetic spectrum and provide access to ultrafast phenomena in physics, biology, and chemistry. Chip-integration of femtosecond technology could revolutionize applications such as point-of-care diagnostics, bio-medical imaging, portable chemical sensing, or autonomous navigation. However, current chip-integrated pulse sources lack the required peak power, and on-chip amplification of femtosecond pulses has been an unresolved challenge. Here, addressing this challenge, we report >50-fold amplification of 1 GHz-repetition-rate chirped femtosecond pulses in a CMOS-compatible photonic chip to 800 W peak power with 116 fs pulse duration. This power level is 2–3 orders of magnitude higher compared to those in previously demonstrated on-chip pulse sources and can provide the power needed to address key applications. To achieve this, detrimental nonlinear effects are mitigated through all-normal dispersion, large mode-area and rare-earth-doped gain waveguides. These results offer a pathway to chip-integrated femtosecond technology with peak power levels characteristic of table-top sources.

Laying the foundations for selective-fish guidance using electricity: multi-species response to pulsed direct currents

To develop effective technology that employs electric fields to simultaneously guide valued freshwater fish whilst limiting the range expansion of undesirable invasive species, there is a need to quantify the electrosensitivity of multiple families. This experimental study quantified the electrosensitivity of two carp species that, in UK, are invasive (grass carp, Ctenopharyngodon idella, and common carp, Cyprinus carpio) and compared the values with those previously obtained for adult European eel (Anguilla anguilla), a species of conservation concern in Europe. Electric field strengths (V/cm) required to elicit physiological responses (twitch, loss of orientation and tetany) were identified across four pulsed direct current (PDC) electric waveforms (single pulse-2 Hz, double pulse-2 Hz, single pulse-3 Hz and double pulse-3 Hz). Grass carp were sensitive to differences in waveform with tetany exhibited at lower field strengths in the single pulse-2 Hz treatment. Both cyprinid species responded similarly and were less sensitive to PDC than adult European eel, although loss of orientation occurred at lower field strengths for grass than common carp in the single pulse-3 Hz waveform treatment. This variation in electrosensitivity, likely due to differences in body length, indicates potential for electric fields to selectively guide fish in areas where invasive and native species occur in sympatry.

Using pulse current to tailor hydride networks while improving the strength and plasticity of pure titanium

Interstitial hydrogen atoms in titanium usually deteriorate the mechanical properties of titanium by brittle hydride phase or hydrogen-enhanced localized plasticity. In this study, hydride was used as the second phase to improve the tensile strength and elongation of TA1 pure titanium. The continuous coarse hydride network is precipitated in TA1 pure titanium after the hydrogen-charged. Then pulse current treatment is used to decompose the original coarse hydride network and reduce the size and number of hydride strips. Finally, a small uniform hydride network is formed in TA1 pure titanium. The results of tensile experiments indicate that the tensile strength of hydrogen-charged TA1 pure titanium treated by pulse current increases from the 286.4 MPa to 316.1 MPa and the elongation increases from the 47.6 % to 56.8 %. The improvement of mechanical properties demonstrate that the small and uniform hydrides can significantly improve the mechanical properties of TA1 pure titanium. In hydrogen-charged TA1 pure titanium treated by pulse current, the increment of strength is mainly caused by hard phase hydrides, and the increase in plasticity is attributed to the role of twins in coordinating deformation during plastic deformation. This study manifests that in addition to being used as a temporary alloying element to optimize the microstructure of titanium, hydrogen can also be directly act as a second phase in titanium to improve the mechanical properties.

Distribution of relaxation times-based analysis of aging mechanisms and prediction of heating domain for alternating current pulse self-heating lithium-ion batteries

Lithium-ion batteries (LIBs)-based electric vehicles (EVs) often encounter challenges such as the reduction in endurance mileage and the increase in charging time at low temperatures. To address these issues, the alternating current (AC) pulse self-heating in LIBs emerges as a pivotal method to overcome performance limitations of EVs at low temperatures. However, employing AC pulsing with high amplitude and low frequency can potentially lead to battery degradation. In this study, the state transitions and aging causes of LIBs during the self-heating are meticulously examined using the distribution of relaxation times (DRT) method. The results reveal that at an AC frequency of 50 Hz or higher, even with amplitudes up to 12 C, there is no degradation for the battery used in this study. For aged LIBs, the significant rise in impedance of solid electrolyte interphase (SEI) due to lithium plating, is the main factor driving battery aging during AC self-heating. Subsequently, an electrochemical-thermal coupling (ETC) model grounded in the degradation mechanism has been developed and experimentally validated to accurately predict the optimal heating domain for self-heating. This approach holds significant implications for the rapid selection of self-heating parameters for facilitating efficient battery performance enhancement.

A Nanosecond level current pulse capture taper optical fiber probe based on micron level NV color center diamond

Abstract This work demonstrates a micron-sized nanosecond current pulse probe using a quantum diamond magnetometer. A micron-sized diamond crystal affixed to a fiber tip is integrated on the end of a conical waveguide. We demonstrate real-time visualization of a single 100 nanosecond pulse and discrimination of two pulse trains of different frequencies with a coplanar waveguide and a home-made PCB circuits. This technique finds promising applications in the display of electronic stream and to be used as a pulse discriminator to Simultaneously receive and demodulate multiple pulse frequencies. This method of detecting pulse current is expected to provide further detailed analysis of the internal working state of the chip.

Optimal extraction, phytochemical and electrochemical potential assessment of pigments from Persicaria Lapathifolia for dye-sensitized solar cell application

In this study, we concentrated on optimal extraction, phytochemical, and electrochemical assessment of natural pigments from the roots and flowers of Persicaria lapathifolia as new sensitizers in dye-sensitized solar cells. The extraction technique required optimizing the use of acidified ethanol with acetic acid and hydrochloric acid as flower and root extractants, respectively. Photo-electrochemical tests revealed that these pigments could improve the efficiency of DSSCS. The optical characterization revealed maximal absorbance peaks at 462 and 654 nm for root dye and 535, 606 and 666 nm for blossom dye. Phytochemical examination revealed the presence of anthocyanins flavonoids glycoside linkage and betacyanin in both extracts. The Cyclic voltammetry tests revealed oxidation potential peaks in root and floral dyes the HOMO and LUMO potentials were calculated for both dyes, revealing values that could help improve DSSC performance. The DSSCS sensitized with flower extract had an open circuit voltage of 0.649 V a brief current pulse of 3.8 mA and an efficiency of 1.6335%. On the other hand root, pigment-based DSSCS performed slightly inferior with a Voc of 0.55 V an Isc of 3.7 mA, and an efficiency of 1.33%. These findings point to the potential of Persicaria lapathifolia pigments to boost DSSC efficiency emphasizing the relevance of sustainable energy sources. More research and optimization are required to realize the potential of these natural pigments for DSSC applications. This study adds to the investigation of green energy options, notably rooftop photovoltaic systems, in response to an increasing desire for ecologically sound energy solutions.

Platinum nanoparticles-based electrochemical H2O2 sensor for rapid antibiotic susceptibility testing

With the increase of antimicrobial resistance, rapid antibiotic susceptibility testing (AST) to guide precise antibiotic administration has become increasingly important. However, current gold standard AST approaches tend to take up to 24–48 h. In this work, based on the nature of catalase-positive bacteria decomposing H2O2, we developed a rapid, portable, straightforward, and cost-effective phenotypic AST approach by detecting residual H2O2 using a Pt nanoparticles-based electrochemical sensor. The pulse current of the sensor exhibited a linear increase with rising H2O2 concentration, demonstrating a high sensitivity of ∼382.2 μA cm−2 mM−1. This approach showed superb diagnostic performance, with an area under the curve of 1 for 24 clinical samples of Escherichia coli and Staphylococcus aureus, with a total detection time of 60 and 45 min, respectively. Furthermore, the performance of the sensor showed no degradation even after 100 detections, promising a substantial reduction in AST costs. Overall, the proposed approach exhibited immense potential for diagnosing bacterial antibiotic resistance.

Fatigue performance of a fastener hole treated by a novel electromagnetic strengthening process

In this study, a novel non-contacting electromagnetic cold expansion process was proposed to improve the fatigue performance of hole component using a single power supply and a single coil. The stress state and deformation of the 6063-T6 aluminum alloy hole component during the electromagnetic strengthening process were investigated through numerical simulation. The residual stress around the hole edge was measured using XRD. Fatigue testing was performed to verify the effectiveness of the process on improving the fatigue life of the hole component. Results showed that the proposed electromagnetic strengthening process could effectively improve the fatigue life of the hole component. Fatigue life of the specimen via electromagnetic treatment is 3.42 times of that of the original specimen at a maximum stress of 120 MPa. Simulation results indicated that the generation of compressive residual stress was attributed to the falling stage of the pulse current, and the maximum compressive residual stress was −102 MPa.

Effect of fast frequency double pulse current on microstructural characteristics and mechanical properties of wire arc additively manufactured Ti-6Al-4V alloy

This study introduces an innovative technique known as fast-frequency double pulse wire arc metal additive manufacturing (FFDP-WAAM). This method employs periodic fluctuations in arc plasma and force to enhance the stirring effect within the molten pool, resulting in the fragmentation of β grains and the formation of finer prior-β grains. The microstructure primarily comprises α', attributed to the high cooling rates and minimal heat accumulation. Compared to the conventional gas tungsten arc welding-based WAAM (CGT-WAAM) process, FFDP-WAAM significantly reduces α-variant selection, thereby achieving a more uniform α phase orientation distribution. Additionally, ultrasonic vibration in the FFDP-WAAM process facilitates recrystallization and mitigates residual strain. The tensile strength and elongation of the FFDP-WAAM specimens reached 939.2 MPa and 9.0 %, respectively, whereas the CGT-WAAM specimens showed a lower tensile strength of 830 MPa and elongation of 9.2 %. The enhanced strength, fatigue life and microhardness of Ti-6Al-4V produced by FFDP-WAAM is ascribed to the refined grain-size distribution. Furthermore, the low Schmid factor (SF) distribution and the stable triangular structure of Category I α-clusters are anticipated to contribute to the increased strength of the FFDP-WAAM-fabricated wall.

Micromagnetic analysis of magnetic vortex dynamics for reservoir computing

Reservoir computing (RC) has generated significant interest for its ability to reduce computational costs compared to traditional neural networks. The performance of the RC element is quantified by its memory capacity (MC) and prediction capability. In this study, we utilize micromagnetic simulations to investigate a magnetic vortex based on a permalloy ferromagnetic layer and its dynamics in RC. The nonlinear dynamics of the vortex core (VC), driven by continuous oscillating magnetic fields and binary digit data as spin-polarized current pulses, are analyzed. The highest MC observed is 4.1, corresponding to the nonlinear VC dynamics. Additionally, the prediction capability is evaluated using the Nonlinear Auto-Regressive Moving Average 2 task, demonstrating a normalized mean squared error of 0.0241 highlighting the time-series data prediction performance of the vortex as a reservoir.

Confined antiskyrmion motion driven by electric current excitations

Current-driven dynamics of topological spin textures, such as skyrmions and antiskyrmions, have garnered considerable attention in condensed matter physics and spintronics. As compared with skyrmions, the current-driven dynamics of their antiparticles – antiskyrmions − remain less explored due to the increased complexity of antiskyrmions. Here, we design and employ fabricated microdevices of a prototypical antiskyrmion host, (Fe0.63Ni0.3Pd0.07)3P, to allow in situ current application with Lorentz transmission electron microscopy observations. The experimental results and related micromagnetic simulations demonstrate current-driven antiskyrmion dynamics confined within stripe domains. Under nanosecond-long current pulses, antiskyrmions exhibit directional motion along the stripe regardless of the current direction, while the antiskyrmion velocity is linearly proportional to the current density. Significantly, the antiskyrmion mobility could be enhanced when the current flow is perpendicular to the stripe direction. Our findings provide novel and reliable insights on dynamical antiskyrmions and their potential implications on spintronics.

Impact of CC and PCTIG Welding on SMO 254 Joints Using Alloy 625 Filler

Objectives: This investigation analyzes the microstructure, mechanical and corrosion characteristics of SMO 254 joints welded using constant current TIG (CCTIG) and pulse current TIG (PCTIG) with alloy 625 (ERNiCrMo-3) filler metal. Method: Optical microscopy and SEM with EDAX were employed for microstructural characterization and phase analysis. Mechanical properties were assessed through Vickers microhardness, tensile, and Charpy impact tests, followed by fracture analysis. Findings: EDAX point analysis indicates reduced Mo segregation and the absence of Nb segregation in PCTIG weldments. The overall corrosion resistance remains acceptable despite a slightly higher corrosion rate in PCTIG weldments. The study highlights the superior mechanical properties and microstructural control achieved with PCTIG welding, making it a preferable technique for SMO 254 joints. Novelty: Notably, the research establishes PCTIG as a superior method for welding SMO 254, demonstrating that it not only refines the grain structure but also significantly enhances mechanical properties, particularly toughness, by 50% compared to CCTIG. Keywords: SMO 254, SASS, Microstructural characterization, Mechanical properties, CCTIG, PCTIG

20 Seconds to fabricate high-performance NiFe-based anode for seawater electrolysis via bidirectional pulse current method

Direct electrolysis of seawater to produce green hydrogen has attracted great attention. While the development of efficient and rapid manufacturing processes for high-performance electrodes, particularly for the oxygen evolution reaction (OER), remains trail. Here, we introduce an innovative approach to fabricate high-performance NiFe-based OER electrodes using an ultrafast and eco-friendly bidirectional pulse current (BPC) method, which remarkably shortens the production time to only 20 s. Our BPC method alternates oxidation and reduction currents within a single period, promoting the in-situ formation of porous NiFe(oxy)hydroxide nanosheets through dissolution/deposition processes. Moreover, this methodology creatively utilizes the “Cl− induced effect”, typically a hindrance in other electrochemical systems involving seawater or brine, to enhance the synthesis of electrodes from NaCl-based electrolyte devoid of additional Ni/Fe cations. The prepared NiFe-based electrode (NFF O-R 20 s) demonstrates remarkable OER catalytic activity, with optimal overpotentials (ηj) of 272, 308 and 367 mV at current densities (j) of 10, 100 and 1000 mA cm−2, respectively. Impressively, it maintains a low cell voltage of 1.59 V after enduring 1000 h of operation under the industrially current density of 300 mA cm−2, with a direct current energy consumption of 3.8 kWh Nm−3 H2 for overall alkaline seawater electrolysis. Our BPC preparation approach provides a promising path to construction high-catalytic activity, good-stability electrode, and low-energy consumption direct seawater electrolyzer.

Atomic-scale understanding of microstructural evolution in electrochemical additive manufacturing of metallic nickel

Atomic-level manufacturing is fundamentally concerned with the precise removal, addition, and migration of material at the atomic and close-to-atomic scale (ACS). Tip-based electrochemical deposition, a quintessential ACS electrochemical additive manufacturing technique, offers promising prospects for achieving bottom-up fabrication of metallic micro/nano structures. However, the complex physicochemical reactions involved in electrodes lead to a limited understanding of the mechanisms underlying atomic electrodeposition and structural evolution. For the first time, this study proposes electric double-layer controlled electrochemical kinetics and investigates the effect of direct current (DC) and pulse current (PC) on nickel atomic electrodeposition using molecular dynamics (MD) simulations. The findings reveal that compared to DC electrodeposition, PC electrodeposition results in more orderly deposition morphology, improved surface smoothness, reduced dislocation density, and lower crystal distortion, with these effects being particularly pronounced under low pulse duty ratio conditions. In addition, the pulse frequency significantly influences the morphology and structure of the deposit. The high pulse frequency yields smoother surfaces with local protrusions, while the low frequency favors the formation of orderly and dense structures excepting slightly increased roughness. This study provides critical insights into understanding the microscopic mechanisms of atomic-scale electrodeposition processes and achieving atomically controlled tip-based electrochemical additive manufacturing of micro/nanodevices.

Formation of directed wide-aperture flows of runaway electrons in air-filled magnetized diodes.

This paper presents the results of research, development, and testing of magnetically insulated air diodes with replaceable graphite and stainless-steel tubular and coaxial cathodes of various configurations capable of generating directed bunches of runaway electrons. At the anode, the bunches have cross sections shaped as circles or rings with an outer diameter of 1-2cm. The durations of the bunches, which carry currents of a few to tens of amperes, range from tens of picoseconds to 100ps, and their charges range from tenths of a nanocoulomb to a few nanocoulombs. The kinetic energy of the bunch electrons at the peak of the current pulse is typically of the order of 150keV. The bunch parameters are set (and varied) by varying the amplitude and duration of the subnanosecond high-voltage pulse driving the diode; they depend on the cathode material and on the strength and profile of the applied external magnetic field. The bunches, retaining their cross-sectional structure, are brought out from the diode, along the field lines, through a thin foil or mesh anode into the open space with a quasi-uniform magnetic field between two Helmholtz coils. In this space, the samples to be irradiated with electrons, similarly to objects exposed to radiation in various experiments and technological applications, can be placed.