Current Pulse Amplitude Research Articles

Inferences on upward leader characteristics from measured currents

We analyzed in detail currents associated with upward unconnected leaders (UULs) initiated from the Kennedy Space Center (KSC) Industrial Area Tower (IAT). Current measurements of UULs in natural lightning are relatively rare and provide important insights into the development and propagation of upward leaders. Eight UULs were initiated from the KSC-IAT between August 1, 2018 and November 15, 2019. All UULs were positive as they occurred in response to downward negative leaders that attached to ground near the tower. The KSC Mesoscale Eastern Range Lightning Information System (MERLIN) located these nearby strokes at distances ranging from 185 to 783 m from the tower, with the median being 538 m. The peak current for these strokes ranged from 13 to 69.3 kA, with the median being 26.7 kA. From the perspective of charge transferred, these UULs can be considered to be a bipolar lightning phenomenon; they transferred negative charge to ground between the inception of their current and the current-polarity reversal, following which, they effectively transferred positive charge to ground. We labeled the former time-period as the UUL development phase and the latter as the collapse phase. The median duration and charge transferred for the development phase were 789 μs and − 6.4 mC, respectively, and for the collapse phase were 388 μs and 4.7 mC, respectively. Overall, the net charge transferred to ground by UULs was negative. During the development phase, UUL-currents consisted of faster (total durations of the order of 10 μs) impulses overlaid on slower (millisecond-scale) “background” current. The background-to-peak UUL current-pulse amplitudes ranged from 3.4–289.2 A with the median being 30.1 A. The median pulse total duration and full-width at half-maximum (FWHM) were 14.1 μs and 4.9 μs, respectively. The median background-to-peak and 10-to-90% risetimes were 3.2 and 2.0 μs, respectively. Interpulse intervals ranged from 4.2–132.8 μs, with the median being 20 μs. Generally speaking, pulse amplitudes were larger, background currents were higher, and interpulse intervals were shorter at later times during UULs. It is likely that the UULs with higher background currents at later times were more closely approached by a downward leader branch versus the lower-current UULs.

Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage

In this study, the surface discharge current pulses of polyetheretherketone (PEEK) material under positive repetitive square voltage in a nitrogen atmosphere are measured. The influences of different voltage amplitudes and frequencies on the detail parameters of forward discharge and backward discharge current pulses are statistically analysed. The results show that as the square voltage amplitude increases, the current pulse amplitude, fall time and pulse width of both forward and backward discharge current increase, and the rise time does not change significantly. As the voltage frequency increases, current pulse amplitude, fall time and pulse width of both forward and backward discharge current decrease, and the rise time does not change significantly. Due to the independence of the discharge at different repetitive cycles, the specific discharge process in one cycle is analysed in detail to explain the influence mechanism of the voltage amplitude and frequency on the discharge current. By mean of the Richardson–Schottky and the Cavallini relaxation model, the relationship between discharge voltage ratio and surface charge, and the decay process of surface discharge are analysed. Furthermore, the influences of amplitude and frequency of the positive repetitive square voltage on the PEEK surface current pulses are explained qualitatively.

Numerical modeling of the switching processes in the second generation HTS tapes under the electric pulses impact

This paper presents the results of complex multiphysical modeling of nonequilibrium states arising in high-temperature superconducting composites under the pulsed current impact. The time dependences of the voltage on the superconducting tape under the influence of current pulses for the pulse amplitudes from 0.6 to 2 values of the critical current of the tape are obtained. Two linear modes of the sample voltage behavior during the electric current load are distinguished. A stable HTS sample switching at the current pulse amplitudes less than 1.7 Jc and the development of irreversible dynamic thermal instability for the higher currents are shown. The simulation was performed by the finite element method in the Comsol Multiphysics software package.

Prediction of radio interference from HVDC transmission lines based on corona discharge characteristics

Many research works have proved that it is viable to predict the radio interference (RI) of high-voltage alternating current transmission lines by corona cage test. However, it is uncertain whether the same method can be adopted for RI prediction of high-voltage direct current (HVDC) transmission lines, since the corona performance of HVDC lines is obviously affected by the widely distributed space charge. In this study, the detailed corona current characteristics, such as the current pulse amplitude, rise time, half-wave time, and repetition frequency are systematically studied by the reduced-scale experiment and the relationship between the average corona current and the RI excitation current is confirmed. Furthermore, based on the experimental study, a method for predicting the RI level of HVDC transmission lines by the corona cage test is proposed. The RI level of a ±800 kV bipolar HVDC transmission line is predicted and compared with the measured result, which verifies the validity of the proposed method.

Design and experiments of double-switch electromagnetic pulse welding system

Limited by the current capacity of the discharge switch, the amplitude of the circuit discharge pulse current of electromagnetic pulse welding (EMPW) system is at a relatively low level, which greatly limits the application range of the EMPW technology. In this paper, the trigger vacuum switch (TVS) was selected as the discharge switch, and the double-switch synchronous conduction scheme was proposed. Based on two 20 kV/28 kJ single-switch electromagnetic pulse generation modular, a 20 kV/56 kJ double-switch electromagnetic pulse system was designed, which could generate a pulse current with the amplitude peak value of 360 kA when the charging voltage was 16 kV. Finally, the effective welding of 1 mm Mg/Al alloy plates was realized.

Experimental studies of the electrical and radiative characteristics of a channel surface discharge

Channel surface discharge (CSD) is a type of surface (sliding) discharges or dielectric barrier discharges in the incomplete stage. Experimental results of both incomplete (low-current) and high-current complete stages of the CSD are presented. The waveform of current pulse in the discharge incomplete stage as well as the influence of the voltage growth rate dU/dt on the discharge electrodes on waveform are studied. Experimental dependence of the CSD current pulse amplitude on the dU/dt rate is obtained in the incomplete stage over a wide range of variation of the dU/dt. For the CSD complete stage, the relation between the intensity of the discharge radiation in the UV region and the amplitude of the current pulse has been received. The dependence of the maximum electron concentration on the UV radiation intensity of the high-current stage CSD was obtained for the case when UV radiation from the CSD was used for ionization of atmospheric pressure nitrogen.

Pressure-dependent propagation of streamers under step voltage in a long point-plane gap in transformer oil

The effect of pressure on positive and negative streamer propagation in a mineral transformer oil is studied in an 80 mm point-plane gap under step voltage. Increased pressure causes reduced stopping length for non-breakdown streamers, higher breakdown voltage, reduced background current, reduced branching in positive streamers and virtually no change in negative streamer shape. The velocities and acceleration voltages are close to being independent of pressure, indicating that the velocity controlling mechanisms take place in the liquid phase. Amplitude and frequency of small current pulses (probably small reilluminations) during negative 1st mode is reduced with increasing pressure, but the effect on reilluminations during 2nd and 3rd mode is small in both polarities.

Numerical study on transient supercooling performance of annular thermoelectric cooler

Transient supercooling can effectively improve the performance of thermoelectric coolers (TECs), especially seen from the studies on flat-plate TECs. But for an annular facility, annular thermoelectric coolers (ATECs) are a better choice because their annular structures increase contact areas. For further studying it, a 3D transient model coupling temperature field and electric potential field is established to study the effects of pulse current amplitude (P), pulse width (τ), annular thermoelectric angle (θ), leg length (r) of thermoelectric element, convective heat transfer coefficient (h) and pulse current shape on the transient performance of ATEC made of variable properties materials. The results show that P and τ are still key factors for the said ATEC, let the P is constant, there is an optimal pulse width minimizing the cold end temperature. If the annular thermoelectric angle θ increases, ATEC with a cold end cross-sectional area larger than that of the hot end makes the supercooling poorer. Let the leg lengths r of the ATEC are 0.8 mm and 0.7 mm respectively, the minimum cold end temperatures (Tc,min) are 236.41 K and 246.18 K as the cross-sectional area of the cold end gets smaller but larger than that of the hot end. The larger of the h is, the better the heat will be dissipated from the hot end of the ATEC, till a certain value of h, the transient performance no longer changes significantly for no much more heat could be dissipated. As the study shown, applying different pulse current shapes leads to the acquisition of different supercooling indicators.

Level coding by phase duration and asymmetric pulse shape reduce channel interactions in cochlear implants

Conventional loudness coding with CIs by pulse current amplitude has a disadvantage: Increasing the stimulation current increases the spread of excitation in the auditory nerve, resulting in stronger channel interactions at high stimulation levels. These limit the number of effective information channels that a CI user can perceive. Stimulus intensity information (loudness) can alternatively be transmitted via pulse phase duration. We hypothesized that loudness coding by phase duration avoids the increase in the spread of the electric field and thus leads to less channel interactions at high stimulation levels. To avoid polarity effects, we combined this coding with pseudomonophasic stimuli. To test whether this affects the spread of excitation, 16 acutely deafened guinea pigs were implanted with CIs and neural activity from the inferior colliculus was recorded while stimulating with either biphasic, amplitude-coded pulses, or pseudomonophasic, duration- or amplitude-coded pulses. Pseudomonophasic stimuli combined with phase duration loudness coding reduced the lowest response thresholds and the spread of excitation. We investigated the channel interactions at suprathreshold levels by computing the phase-locking to a pulse train in the presence of an interacting pulse train on a different electrode on the CI. Pseudomonophasic pulses coupled with phase duration loudness coding reduced the interference by 4-5% compared to biphasic pulses, depending on the place of stimulation. This effect of pseudomonophasic stimuli was achieved with amplitude coding only in the basal cochlea, indicating a distance- or volume dependent effect. Our results show that pseudomonophasic, phase-duration-coded stimuli slightly reduce channel interactions, suggesting a potential benefit for speech understanding in humans.

Simulation of Magnetic Electron Cut-off in a Vacuum Switch with an Anode in the Form of an Inductor

The simulation of the process of magnetic cut-off of electrons in a vacuum switch (VC) with an anode in the form of an inductor was performed. Calculations were performed according to the physico-topological model of physical processes in the vacuum switch, which took into account current distribution along electrodes, the trajectory of electrons emitted by the cathode and the conditions of current interruption in VC. Determination of current distribution along the anode, as well as configurations of electric and magnetic fields were performed according to a mathematical model based on Maxwell's equations for vacuum and conductive medium of the anode and boundary conditions adapted to the shape of the elements of the VC. Material equations were also used for certainty. The initial kinetic energy of electrons emitted from the cathode was set equal to zero. Their direction of departure from the cathode surface was determined by the direction of the lines of force of the electric field near the surface. Electron emission was given by the uniform distribution of emission points on the surface of the cathode tip. The calculation of the structure of the magnetic field was performed taking into account the secondary magnetic fields and the current distribution over the cross section of the anode inductor, which is caused by the skin effect.It is established that a decrease in the step of the inductor turns and an increase in the amplitude of the current pulse in it lead to an increase in the magnetic field strength in the cathode region, which improves the focusing of electrons. At anode-cathode voltage of 10 kV, the step of the inductor of 6 mm and the amplitude of the anode inductor current pulse of 900 A, all the electrons emitted from the cathode are focused outside the anode.The influence of design parameters on the electron cut-off efficiency is determined. For the investigated design, the optimal cathode-anode distance was 12 mm with a step between the turns of the inductor of 6 mm. The results of calculations showed that reducing the distance between the turns of the inductor increases the efficiency of electron cut-off, which confirms the physical adequacy of the mathematical model and the correctness of the calculations. Calculations also showed that at a cathode-anode distance below 12 mm, the focusing of electrons deteriorates.In the proposed design of the VC with the anode inductor in the form of three turns, the complete cut-off of electrons, i.e. the time of flight of electrons through the electrode system, at anode-cathode voltage of 10 kV, occurred by less than 1 ns at an inductor current pulse of 900 A. The inductor current pulse duration was 5 μs had the form of the half-sinusoid arc. The used method of modeling allows to establish in what part of the inductor pulse the full cut-off of electrons is provided.The obtained results can be used in the development of the VC with interruption of the current of vacuum-arc discharge.

The effect of the current pulse amplitude on the nanopore structures of 3D-AAO films

The microstructure of porous anodic aluminum oxide (AAO) has a crucial influence on its properties. In this paper, three-dimensional AAO (3D-AAO) film with mallet-shaped nanopores structure and 185–187 nm pore diameters was prepared by periodic pulse anodizing of high-purity aluminum foil in phosphoric acid using asymmetric sawtooth current waves. Highly ordered 3D-AAO membranes with periodically modulated nanostructure were achieved, and the nanopores were changed from mallet shape to Y-branched channels with a length of 249–742 nm by adjusting the amplitude of the asymmetric sawtooth current wave. The effect of current amplitude on the nanostructure of 3D-AAOs was analyzed by combining the scanning electron micrograph (SEM) of the samples and the V-T images during the anodization process. The results show that the anodization time of the high-potential anodization stage and the low-potential anodization stage in each cycle can be adjusted by changing the amplitude of the asymmetric sawtooth current wave, to realize the regulation of the 3D-AAO nanostructure. These 3D-AAO film with structural modulation may be used as templates for the fabrication of novel nanowires or nanotubes with excellent electromagnetic properties.

Neural activity of functionally different retinal ganglion cells can be robustly modulated by high-rate electrical pulse trains

Objective. This study focused on characterising the response of four major functionally-different retinal ganglion cells (RGCs) to a high frequency stimulus (HFS) paradigm. Approach. We used in vitro patch clamp experiments to assess the viability of evoking a differential response between different RGC types—OFF-Sustained, OFF-Transient, ON-Sustained and ON-Transient—under a wide range of HFS and stimulation amplitude combinations. Main results. Of the four types, we found that the OFF-Sustained, OFF-Transient and ON-Transient RGCs could be differentially activated at various frequency and amplitude combinations, in particular, OFF-Sustained cells can be differentially targeted between 20–100 µA at all frequencies, OFF-Transient cells between 150–240 µA at 1 kHz and ON-Transient between 180–240 µA and 4–6 kHz. We further found that this differential activation held true when the stimulus duration was reduced from 300 ms to 50 ms. Finally, we found that the cell spiking response was not primarily dependent on total charge contained in the pulse train or current amplitude alone, but a combination of amplitude and frequency. Significance. These results indicate that HFS may be a promising method to target functionally-distinct neural pathways in the retina in an effort to improve the vision quality with retinal prostheses.

Pulse power supply of diode-pumped solid-state lasers

Recently, solid-state pumped semiconductor lasers have become increasingly widespread. Lasers of this type have several advantages over solid-state lasers with lamp pumping. First of all, this is high efficiency, long service life, small dimensions and weight. The use of semiconductor laser diodes for pumping solid-state active media imposes a number of rather stringent requirements on the power sources of laser diodes. The power source should provide rectangular current pulses with a flat top, a steep leading edge of the pulses and the absence of reverse current surges at the trailing edge.A pulsed power source for a diode pump system of a ytterbium-erbium laser was developed, manufactured and studied. In this source, the control unit provides functions for protecting the load in emergency conditions, controlling the charge of the storage capacitors to the required voltage and generating current pulses to power the laser diode line. The current is regulated by a field effect transistor operating in a linear mode. The load is included in the source circuit of the field-effect transistor, and the reference signal is generated by the DAC of the microcontroller. Such an approach made it possible to create a relatively simple, reliable and small-sized laser power source with a wide range of adjustment of the duration and amplitude of current pulses. This makes it possible to select the optimal operating mode depending on the characteristics of the active medium of the laser. Particular attention is paid to solving the problems of protecting expensive rulers of laser diodes from failure. The developed source can be used to pump other solid-state lasers with shorter lifetimes of the upper laser level than erbium.

Electromechanical installation based on a powerful current pulse generator for materials treatment

The electromechanical device containing an electromagnetic solenoid with a piston operating in the reciprocating motion mode was developed. Technologies with similar operating modes are widely used in various industries. Economical generator of powerful unipolar current pulses with unique systems is used in the electromechanical device. It allows its main parameters to be regulated in a wide range and with high speed: pulse reproduction frequency and amplitude. The principle of generator operation is based on the periodic discharge of pre-charged capacitors to a low-resistance active-inductive load. The parameters of the mechanical and electrical parts of the electromechanical device are calculated: the initial coordinate of the piston, the magnetomotive force resulting from a change in the inductance L(x), the spring elasticity, the resistance force of the piston proportional to its speed, amplitude, duration and frequency of current pulses. A simulation model of the device in the environment of Matlab-Simulink was developed. Plots of transients during the device idling and under load were constructed. The analysis of the device operating modes was performed. The developed electromechanical installation allows the process parameters to be adjusted.

(Invited) Current and Voltage Control of Intermediate States in Bipolar Rram Devices for Neuristor Applications

The control of the intermediate conductance levels in HfO2-based MIM capacitors for neuromorphic applications is presented in this work. Using voltage or current control signals shows significant differences. The potentiation levels can be controlled in a linear way using current as control signal. These levels are achieved in very short times and only depends on the current pulse amplitude magnitude. On the contrary, depression levels cannot be controlled by current but with voltage pulses. A proper control of synaptic behavior requires the combination of both types of signals.

Multistate Magnetization Switching Driven by Spin Current From a Ferromagnetic Layer

Spin-charge interconversion in ferromagnets has recently drawn great attention due to its ability to generate spin current via the anomalous Hall, planar Hall, or intrinsic spin Hall effect. In this work, we demonstrate the magnetization switching of perpendicular anisotropy ferromagnets by the transversely polarized spin current generated from an easy-plane ferromagnet such as (Fe, Mn)Pt and (Co, Fe)B. The spin-torque efficiency is characterized to be about 21% of that of the same structure with the easy-plane ferromagnet replaced by Ta. In addition, we find that the magnetization switching consists of multiple intermediate states, which can be robustly set by the applied current pulse amplitude and repetition number. This behavior can be used to mimic synaptic devices that is potentially useful for neuromorphic computing.

Impact of the Deionized Water on Making High Aspect Ratio Holes in the Inconel 718 Alloy with the Use of Electrical Discharge Drilling

Nickel-based superalloys are being increasingly applied to manufacture components in the aviation industry. The materials are classified as difficult-to-machine using conventional methods. Nowadays, manufacturing techniques are needed to drill high aspect ratio holes of above 20:1 (depth-to-diameter ratio) in these materials. One of the most effective methods of making high-aspect-ratio holes is electrical discharge drilling (EDD). While drilling high aspect ratio holes, a crucial issue is the flushing of the gap area and the evacuation of the erosion products. The use of deionized water as the dielectric fluid in the EDD offers a considerable potential. This paper includes an analysis of the influence of the machining parameters (pulse time, current amplitude and discharge voltage) on the process performance (drilling speed, linear tool wear, taper angle, hole’s aspect ratio, side gap thickness), during the EDD with the use of deionized water in the Inconel 718 alloy. The obtained through holes were subjected to the extended analysis. The impact of the initial working fluid temperature and pressure on the conditions of the flow through the electrode channel was also subjected to the analysis. The deionized water properties were changed by applying an initial temperature. Based on the results of an analysis of the previous research, the EDD of the through holes was performed for a pre-set initial temperature (~313.15 °K) and initial pressure of the working fluid (8 MPa) and selected process parameters. An analysis of the results indicates increasing of hole’s aspect ratio by about 15% (above 30), decreasing the side gap thickness by about 40% and enhanced surface integrity.

High-voltage and high-current crowbar system based on pseudospark switches: from system design to verification

This paper presents a high-voltage and high-current crowbar system using pseudospark switches to produce a fast front edge and prolonged pulse current with low ripple amplitude. The crowbar system mainly consists of a main switch, a crowbar switch, an energy storage capacitor, and an inductive load. The basic parameters of the pseudospark switch crowbar system: the storage capacitance is 5 μF, the typical operation voltage is 30 kV, the peak discharge current is about 46.2 kA, the rise time is 4.3 μs, and the pulse duration time is approximately 109 μs, which is nearly 25 times of the rise time. In this paper, we report the timing setting for crowbar system. Experimental results show that crowbar timing should be set slightly after first current maximum, which has a great advantage of increasing the time scale without any reduction in the loss-free peak current. In addition, the pulse current characteristics are also studied. In the research, crowbar inductance Lc and crowbar resistance Rc have significant effects on the ripple amplitude and load current amplitude of pulse current. The experimental results also show that the crowbar current Ic can reach nearly twice of the coil load current Iload with low crowbar inductance Lc. The over-current capacity of the crowbar switch needs to be greater than that of the main switch. The experimental results in this paper can be used to optimize the inductive load current in high-voltage and high-current crowbar system.

High-speed modulation of a terahertz quantum cascade laser by coherent acoustic phonon pulses

The fast modulation of lasers is a fundamental requirement for applications in optical communications, high-resolution spectroscopy and metrology. In the terahertz-frequency range, the quantum-cascade laser (QCL) is a high-power source with the potential for high-frequency modulation. However, conventional electronic modulation is limited fundamentally by parasitic device impedance, and so alternative physical processes must be exploited to modulate the QCL gain on ultrafast timescales. Here, we demonstrate an alternative mechanism to modulate the emission from a QCL device, whereby optically-generated acoustic phonon pulses are used to perturb the QCL bandstructure, enabling fast amplitude modulation that can be controlled using the QCL drive current or strain pulse amplitude, to a maximum modulation depth of 6% in our experiment. We show that this modulation can be explained using perturbation theory analysis. While the modulation rise-time was limited to ~800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible.

A multi-channel parameters adjustable magnetic field generator.

In order to increase the security and flexibility of the magnetic field generator, a multi-channel parameters adjustable (MCPA) magnetic field generator is designed and implemented in this paper. The circuit topology of the MCPA magnetic field generator is presented. The working principle of MCPA is analyzed. The pulse current is measured and verified by experiments. The results show that the pulsed current amplitude is adjustable under 1000 A, the adjustment range of the effective pulse width is 0-160 µs, and the adjustment range of the frequency is 1-10 Hz. The magnetic field intensity at 2.5 cm below the scalp of the brain was measured when the three channels were working at the same time. It can be seen that the intensity of the magnetic field in the central area is apparently higher than that in the surrounding. The channels of MCPA can also be chosen flexibly as needed. Therefore, it has a very high application and research value in the field of biological magnetism therapy.