Current Pulse Generator Research Articles

Generation of femtosecond spin-polarized current pulses at Fe/MgO interface by quasi-static voltage

The generation of short spin-current pulses is essential for fast spintronic devices. So far, spin current pulses are generated by femtosecond laser pulses which drive spins from a ferromagnetic metal layer. However, the need for miniaturization, simplicity and energy efficiency favour electric-field control of spintronic devices over optic or thermal control. Here, we combine ab initio calculations of electronic density of states at MgO/Fe interface with continuous model for charge transport to investigate the dynamics of the spin-dependent potential. We demonstrate that the voltage-driven instability of the electronic band structure due to the electronic resonant states at the Fe/MgO interface results in the generation of the femtosecond spin-polarized current pulse with the spin polarization up to P=7 00 % that propagates from the interface to the bulk. The dynamics of the current pulses driven by the Stoner instability depends neither on the dielectric relaxation time nor on the details of how the instability is achieved by changing the voltage, i.e. as long as the voltage changes are slow (quasi-static) with respect to the time determined by the spin diffusion constant, being of the order of fs. The presence of the instability can be detected by THz time-domain spectroscopy or pump-probe techniques.

Structure of Self-Powered Modular High-Voltage and High-Current Pulse Generator for Magnetron

Structure of Self-Powered Modular High-Voltage and High-Current Pulse Generator for Magnetron

Braiding Operations for a Topological Josephson Junction Array Using a Bipolar Current Pulse Generator Controlled by SFQ Logic Circuits

Braiding Operations for a Topological Josephson Junction Array Using a Bipolar Current Pulse Generator Controlled by SFQ Logic Circuits

Experimental and Simulation Study of Pulse Current Generator

8/20 µs lightning pulse current generators (LPCG) used in testing surge arresters require a laborious production process that needs a high budget. An easily repairable, portable, and affordable test system with a maximum energy of 2.9 kJ and a voltage level of 24 kV that can alter its parameter values was described in this work. Simulation and experimental studies were carried out to investigate the effects of the resistor and coil elements in the Pulse Current Generator (PCG) circuit on the amplitude, front, and tail time of the pulse current. Most components of the experimental system were created using 3D printing technology with polylactic acid (PLA) material. The production costs were significantly reduced, according to equivalent pulse generators. Tests at different pulse currents and voltage levels were performed with the experimental system. Power capacitors may often fail due to overvoltage, switching, and partial discharge reasons. The high voltage (HV) power capacitors used in the pulse generator introduced in the study were obtained with the help of low voltage capacitor stacks. As a result, a less expensive, high-capacity capacitor system that is easily and quickly repairable in case of failure was achieved.

An All-Solid-State Rectangular Current Pulse Generator Based on Coupling Inductor

To explore the application of pulsed current in biomedicine, an all-solid-state rectangular pulse current generator (RCPG) is proposed. The RCPG uses a field programmable gate array (FPGA) as the control system and a solid-state semiconductor switching metal–oxide–semiconductor field-effect transistor (MOSFET) as the control switch. The RCPG is modular in design, with each module consisting of a diode, a switch, and a coupled inductor. Each inductor of the RCPG is coupled to each other, increasing the energy storage density of the system. When the switch is on, the inductors are charged in series. And when the switch is off, the inductors are discharged in parallel to the load. The energy on the inductor can be superimposed on the load in the form of a current. Through simulation, the principle of RCPG topology and its feasibility is verified. Finally, a five-stage RCPG miniaturized prototype was developed. The experiments show that the RCPG can be adjusted by adjusting the inductor parameters to meet different load requirements, such as biomedical. In addition, the number of modules can be increased to achieve higher current output.

INFLUENCE OF THE ENERGY PARAMETERS OF THE PRIMARY CIRCUIT ON THE CURRENT CHARACTERISTICS OF THE DIN-2K ACCELERATOR

Optimal voltage values were established for plasma guns and the pulsed current generator providing maximum break current values. The current values were determined for the plasma jumper formation region. The optimal time delay between the triggering of the plasma guns and the pulsed current generator has been established. The beam current was measured in the region behind the vacuum diode and in the plasma jumper region. The ultimate current was determined for the available plant geometry.

An experimental study on switching waveform design with gate charge control for power MOSFETs

Designing switching waveforms is a technique for mitigating a trade-off between loss and noise in switching power devices. A novel and simple method has been proposed to compute the gate waveform to realize a designed switching waveform. The gate current pulse is calculated to eliminate the deviation between the designed target waveform and the observed waveform at the moment using a linear combination of drain-source voltage or drain current responses to a small gate charge pulse train. In this paper, a verification system including a simple gate current pulse generator consisting of operational amplifiers and transistors was built together with a conventional voltage source gate driver, and validation of the proposed method was experimentally performed using the drain-source voltage waveform of a Si MOSFET during the turn-off phase. Applying the obtained drain-source voltage responses to the proposed method, the gate current pulse to be added to realize a given target waveform was calculated and superimposed on the output of the gate driver. The measured drain-source voltage waveform was well-matched to the target. In addition, the impact of the drain current values on the design of the drain-source waveform was verified.

Investigation of consolidation mechanisms induced by applied electric/electromagnetic fields during the early stages of spark plasma sintering

This work aims at investigating the role of the electric/electromagnetic fields generated by the pulsed current applied during Spark Plasma Sintering (SPS) process on the sintering mechanisms. The selected model material was a metallic granular medium composed of microsized particles of pre-oxidized copper. Its electrical behavior and correlated microstructural modifications were studied in two complementary enclosures. First, a demonstrator equipped with a modulable pulsed electric current generator has allowed analyzing, at low temperature and without mechanical loading, the effects related to the application of an electric wave, by controlling and modulating its characteristics (i.e. shape, frequency, amplitude). An abrupt electrical transition, named “Branly effect” from an insulating to a conductive state, is observed in the granular copper medium. The increase of pulses frequency is shown to strongly reduce the critical time to generate the electrical transition. Moreover, a commercial SPS device, with specific electrical and thermal instrumentation, was implemented by varying applied stress and using conductive and insulating dies. The analysis of the electrical behavior coupled with post-mortem microstructural observations allowed to highlight that the coupling between pulsed current and mechanical stress promotes specific mechanisms in SPS. Under high stress, interparticle contact area increase and the insulating oxide layer is damaged by microcracking. The coupling with the flow of the pulsed current involves local overheating and dielectric breakdown, favoring ignition of Branly effect. Micro-welds are formed between particles, creating privileged paths of the pulsed current and initiating densification at low temperature (250 °C).

Improvement of the measuring ultrasonic electromagnetic-acoustic transducer

Based on the analysis of previously published research and studies, it has been established that despite their significant advantages over traditional “contact” sensors in measurements, testing and diagnostics of thin dielectric coated (via paint, plastic, etc.) metal products, the available electromagnetic-acoustic transducers provide insufficient sensitivity and significant uncontrolled (“dead”) zone. This situation complicates testing of thin sheets, pipes, shells, tanks etc., and sometimes makes it impossible to measure the remaining thickness of the metal.
 The analysis of available research has shown that the possibility of transducers sensitivity increases via traditional increase in the magnetic induction value, and the high-frequency current value is practically exhausted. At the same time, the prospects for improving the design of electromagnetic-acoustic transducers were determined. The problems of traditional transducers were solved through development of a new electronic control circuit. For this, the control unit was designed to be distributed between ultrasonic shear pulse excitation devices, and as a result, for the device of ultrasonic signals reflected from the metalwork reception, the device sensitivity was increased. In addition, to provide the possibility to test and measure thin metal product thickness, the electronic circuit was supplemented with means of interference suppression after the powerful supply of the high-frequency current of the converter, which allowed significantly reducing the “dead” zone.
 A special stand was constructed to experimentally test the capabilities of the transducer developed, including a powerful high-frequency current pulse generator, an amplifier of received ultrasonic pulses and a digital oscilloscope. It has been experimentally demonstrated that the new electronic circuit of the non-contact sensor allows it to be qualitatively matched with the probing pulse generator and the amplifier of the received ultrasonic packet signals. As a result, the sensitivity of the transducer was increased by 2.5...3 times in relation to the amplitudes of bottom pulses and interference. At the same time, the diagnostics of metal products with thickness 30...50% less than the traditional sensitivity threshold of non-contact device is ensured.

Terahertz Spin Current Pulses in Antiferromagnetic Oxide: The Role of Vacancy‐Induced Ferromagnetism

Antiferromagnetic oxides have attracted increasing attention for their outstanding peculiarities in spintronics. Crystal lattice defects that are present in antiferromagnetic oxides can influence their physical properties, such as vacancy‐induced ferromagnetism. Meanwhile, the generation and manipulation of ultrafast spin currents of antiferromagnetic insulators are highly desired. Although the generation and detection of terahertz spin current pulses in antiferromagnetic oxides have been realized, the effect of vacancy‐induced ferromagnetism on spin current in antiferromagnetic oxides is not yet known. Herein, the role of vacancy‐induced ferromagnetism on the terahertz spin current in antiferromagnetic nickel oxide thin films is reported. Structural and magnetic characterizations reveal that nickel vacancies effectively break the strong antiferromagnetic exchange coupling, giving rise to the coexistence of antiferromagnetism and ferromagnetism in NiO thin films. Notably, the enhancement of terahertz radiation associated with the photo‐induced ultrafast spin current of NiO thin film with the strongest ferromagnetism is the most significant. Besides, the nonlinear susceptibility tensor parameters related to the antiferromagnetic property of NiO thin films also change distinctly. The findings indicate that the defects of antiferromagnetic materials play a decisive role in the application of antiferromagnetic spintronics in the terahertz field.

Development of contactless switching devices for asynchronous machines in order to save energy and resources

To limit the inrush currents in the stator windings, various schemes for starting an asynchronous electric motor are used. In addition, the existing devices have a complex control system, which creates certain difficulties in installation and operation. But the analysis of scientific literature and materials from certain sources testifies to the insufficient study of this problem. In scientific work, the advantages and disadvantages of a new type of contactless starter are compared with contact and non-contact starters of various types. An original circuit of a new type of thyristor starter with a simplified design has been developed and manufactured, which has the ability to smoothly start and control the power consumption of asynchronous machines. Computer simulation of a new type of contactless starter with pulse-width modulation control in the Matlab Simulink program has been carried out: a pulse current is supplied to the controlled thyristor electrode on the basis of the pulse-width modulation control and the thyristor opens and passes the current, the resistance is set to decrease the input signal level. The design of the proposed starter is based on the combination of a thyristor starter with logical control, which has the ability to smoothly start and remote control of the power consumption of asynchronous electric motors, which has the ability to save energy and resources. Modern methods of implementing a logical control system, a pulse current generator with RLC filters, are proposed, and the task of remote monitoring and control of power consumption of asynchronouselectricmotors is set.

Method and apparatus for dynamic testing of structural joints

The dynamic testing technique is used during the design phase of structures and series production. This test evaluates the structural capacity, especially of the assemblies, to withstand different forces and rates of impact encountered under realistic operational conditions. This study proposes a magnetic pulse exciter for high-speed impact loading in dynamic tests because of its capability to provide single and repeatable pulse loading over a wide range of force up to 20 kN and pulse durations from 10 up to 1000 ms. The method transforms accumulated electrical energy in a capacitor bank into mechanical energy. For experimental investigations, flat and cylindrical coil devices were used for a capacitor-type pulse current generator. The proposed method has been experimentally validated on timber beams in a specified volume of force loading. The technique demonstrated a potential for controlling force and energy parameters. The effects of operating voltage on coil and ‘metal plate - coil’ distance on the amplitude of dynamic loading have been investigated. Aluminium and steel plates fastened to the object at the point of impact were used to improve excitation efficiency. The developed technique can be used in experimental studies on model joints and real objects.

Stress-strain magnetoactive propulsion system

It is possible to create deformations in magnetically active polymeric materials by applying magnetic fields to them. This work develops a symmetrical design scheme of the device, in which the drive and control are carried out by two actuators located on opposite sides. The symmetric scheme with control from two sides allows transporting objects (cargo) in mutually opposite directions (forward and backward). It is proposed to use a magnetically active gel together with a magnetically active elastomer as magnetically active materials. The resulting force effect in the device actuator is produced by interaction of magnetic fields of electromagnets with magnetic fields of permanent magnets. Expressions for obtaining alternating magnetic fields which create conditions for generating alternating magnetic forces in the actuator of the device are given. A prototype design with a controller control device in which signals are generated for an optimum current pulse generator with adjustable duty cycle and duration is presented.

Низковольтные гетеротиристоры InP для генерации импульсов тока длительностью 50-150 ns

Current switches based on low-voltage InP heterothyristors with a maximum blocking voltage of 20V were developed and studied. In current pulse generation mode, the efficient operation of InP heterothyristors with a low-resistance load in the form of a capacitor was demonstrated. It has been shown that the minimum turn-on delay time is about 6 ns at a control current amplitude of 60 mA. The possibility of generating current pulses with a duration of 53–154 ns and amplitudes of 38–130 A was demonstrated when the capacitor values were changed in the range of 56–1000nF.

Upgraded Control of an On/Off Circuit in a Double-Circuit Pulse Current Generator

Upgraded Control of an On/Off Circuit in a Double-Circuit Pulse Current Generator

High-current space-charge-limited pulses using ultrashort laser pulses.

The maximum current that can be delivered by a 1-D vacuum diode is limited due to the space-charge reduction of the accelerating field. For a steady-state operation, this is given by the Child-Langmuir space-charge limit. However, for pulsed diode sources, the instantaneous current can be much higher than this limit, as long as the pulse length is much less than the transit time across the diode gap. This enables the generation of high current pulses with pulse durations of the order of tens of picoseconds using photocathodes driven by ultrashort laser pulses. The generation of such short and powerful electromagnetic pulses is important for numerous applications such as ultrawideband radar or as photocathode sources for accelerators. In this work, the limiting current pulse is investigated in the case of a very short, square-top initial pulse and it is found that these pulses propagate in a self-similar manner, remaining as a square-top charge cloud in space throughout their acceleration and propagation. The resultant current and pulse duration turn out to be dependent on only three parameters, which are the applied voltage, the vacuum transit time, and the fraction of the saturation charge density in the initial charge cloud. The resultant scaling of the resultant peak current and pulse duration are calculated numerically as a function of starting sheet-charge density, allowing the calculation of the resultant pulses for any ultrashort, pulse-driven vacuum photodiode design.

Pulsed direct current magnetic energy harvesting by robotic spot-welding in smart automotive factory

A magneto-mechano-electric (MME) generator is considered as a promising candidate for power supplying to IoT sensors in a smart factory by harvesting noise magnetic field. However, most studies have carried out only with alternating current (AC) magnetic field from laboratory and home surroundings. Here, we demonstrate a pulsed direct current (DC) magnetic field-driven MME generator to harvest energy from spot-welding process in a manufacturing facility of Hyundai Motor Company. By one-spot-welding process, the MME generator generated a open-circuit peak voltage of 7.4 V as well as a peak power of 0.8 mW. The generated electricity was utilized to charge the 10 µF capacitor from 0 to 4.8 V with five times spot-welding, meaning a lot of electricity could be harvested by thousands of spot-welding during vehicle assembly process. Finally, we demonstrated self-powered IoT system by charging 3.3 mF capacitor using MME generator to power multifunctional IoT sensor.

SMALL SIZE “DI-2” ACCELERATOR WITH THE PLASMA CURRENT SWITCH AND INDUCTIVE ENERGY ACCUM ULATOR AS A MATERIAL IRRADIATION TEST RIG

This scientific paper delves into the basic characteristics of the updated “DI-2” accelerator, i.e., currents, voltages and pulse duration as a function of a delay time between the pulses generated by the major pulse current generator (PCG) and the PCG for plasma guns (PG). Consideration was given to the possibility of the use of heavy-current accelerators “VGIK-1” and “DI-2” as test rigs to study the effect of the heavy-current electron beam onto the surface of different materials to modify their physical and chemical properties.

Pulsed hydraulic-pressure-responsive self-cleaning membrane.

Pressure-driven membranes is a widely used separation technology in a range of industries, such as water purification, bioprocessing, food processing and chemical production1,2. Despite their numerous advantages, such as modular design and minimal footprint, inevitable membrane fouling is the key challenge in most practical applications3. Fouling limits membrane performance by reducing permeate flux or increasing pressure requirements, which results in higher energetic operation and maintenance costs4-7. Here we report a hydraulic-pressure-responsive membrane (PiezoMem) to transform pressure pulses into electroactive responses for in situ self-cleaning. A transient hydraulic pressure fluctuation across the membrane results in generation of current pulses and rapid voltage oscillations (peak, +5.0/-3.2 V) capable of foulant degradation and repulsion without the need for supplementary chemical cleaning agents, secondary waste disposal or further external stimuli3,8-13. PiezoMem showed broad-spectrum antifouling action towards a range of membrane foulants, including organic molecules, oil droplets, proteins, bacteria and inorganic colloids, through reactive oxygen species (ROS) production and dielectrophoretic repulsion.

Magnetic implosion of thin aluminum foil liners

Metal liner implosions driven by a pulsed current generator are used in research on inertial confinement fusion, generation of soft x-ray pulses and megagauss magnetic fields. The energy density in the plasma column formed during the liner stagnation is largely determined by the initial radius and the radial convergence of the liner. When the liner implosion time is close to the current rise time, the liner initial radius is proportional to the current rise time. The paper presents the results of experiments on the fast implosion of cylindrical liners on the MIG generator (2 MA, 80 ns) at the Institute of High Current Electronics, Tomsk, Russia. Liners 0.7–1.0 mm in diameter were made from a 1.8 to 2.5 μm thick aluminum foil. A low-density plasma was pre-injected into the liner area. As the Lorentz force sweeps away the pre-injected plasma, the current switches to the liner in 1–3 ns. Then the liner is imploded in 3–7 ns by a current close to the peak generator current. The stagnation radius measured via time-integrated pinhole camera images was found to be not more than 25 µm. Such a radius of the stagnated plasma assumes that the plasma mass density is several times higher than the solid aluminum density.