High Peak Currents Research Articles

Electrogenerated chemiluminescence from R(bpy)3(2+) ion-exchanged in carbon nanotube/perfluorosulfonated ionomer composite films.

The electrochemistry and electrogenerated chemiluminescence (ECL) of ruthenium(II) tris(bipyridine) (Ru(bpy)(3)(2+)) ion-exchanged in carbon nanotube (CNT)/Nafion composite films were investigated with tripropylamine (TPA) as a coreactant at a glassy carbon (GC) electrode. The major goal of this work was to investigate and develop new materials and immobilization approaches for the fabrication of ECL-based sensors with improved sensitivity, reactivity, and long-term stability. Ru(bpy)(3)(2+) could be strongly incorporated into Nafion film, but the rate of charge transfer was relative slow and its stability was also problematic. The interfusion of CNT in Nafion resulted in a high peak current of Ru(bpy)(3)(2+) and high ECL intensity. The results indicated that the composite film had more open structures and a larger surface area allowing faster diffusion of Ru(bpy)(3)(2+) and that the CNT could adsorb Ru(bpy)(3)(2+) and also acted as conducting pathways to connect Ru(bpy)(3)(2+) sites to the electrode. In the present work, the sensitivity of the ECL system at the CNT/Nafion film-modified electrodes was more than 2 orders of magnitude higher than that observed at a silica/Nafion composite film-modified electrode and 3 orders of magnitude higher than that at pure Nafion films. The CNT/Nafion composite film-modified GC electrodes also exhibited long-term stability.

Current waveform parameters of CN tower lightning return strokes

Lightning strikes to the Toronto Canadian National (CN) Tower have been observed since 1978. In this paper, a brief description of the lightning measurement systems is provided, with emphasis on the current measurement system. Current and field measurement systems with broad bandwidths and high resolutions have been operational since 1991. Typical current derivative and current waveforms of a CN Tower lightning return stroke are also presented. Extensive cumulative statistics of waveform parameters (maximum steepness, risetime to maximum steepness, wavefront peak, risetime to wavefront peak, and absolute peak) of lightning return-stroke current signals measured at the CN Tower during a 10-year period have been derived. The statistical analysis shows that in 50% of the current records: the current wavefront maximum steepness exceeds 18.8 kA/μs, the risetime to maximum steepness exceeds 138 ns, the current wavefront peak exceeds 5 kA, the risetime to wavefront peak exceeds 636 ns and the current absolute peak exceeds 7.2 kA. The statistical analysis also shows that first return strokes feature lower current steepness and higher current peak when compared with subsequent return strokes. Recommendations concerning instrumentation and techniques for the proper measurement of lightning return-stroke currents are discussed. The presented statistical results will be of assistance in the establishment of more sophisticated protective measures against lightning hazards, especially at elevated objects.

Comparison of photometric measurements and charge moment estimations in two sprite‐producing storms

In one relatively small storm on July 2, 2000, 276 sprites were observed between 04:00–07:00 UT. These sprites were largely confined to 70–85 km altitude, were relatively faint and diffuse, and were typically associated with very high peak currents and short time duration. A second storm, on July 4, 2000, had a much larger spatial extent and 27 sprites were observed between 04:00–07:00 UT in a wide range of shapes and time scales spanning 40–90 km altitude. These sprites were produced by 20–120 kA CG's, had complex optical signatures, and were frequently associated with observed ELF radiation. We hypothesize that relatively small storms mainly produce sprites in the form of diffuse glow whereas larger storms with higher cloud tops can initiate streamer discharges leading to more spectacular sprites.

DC Characteristics of AlGaN/GaN HFETs Using the Modeling of Piezoelectric and Thermal Effects

In this paper, we report on the DC characteristics of the AlGaN/GaN HFETs using physical models on piezoelectric and thermal effects. Employing the models was found to be essential for a realistic prediction of the DC current-voltage characteristics of the AlGaN/GaN HFETs. Though use of the implementation of the physical models, peak drain current, transconductance, pinch-off voltage, and most importantly, the negative slope in the current were accurately predicted. The importance of the heat sink effect was demonstrated by the comparison of the DC characteristics of AlGaN/GaN HFETs fabricated from different substrates including sapphire, Si and SiC. Highest peak current was achieved from the device with SiC by an effective suppression of heat sink effect.

Electrochemical Behavior and Enhanced Stability of a Thin Film of Prussian Blue Deposited under Magnetic Field

Abstract Magnetic field was employed as a useful tool to improve stability of electroactive films deposited on substrate surfaces. To this aim, electrochemical preparation/deposition of Prussian blue (PB) was carried out in the presence of an external magnetic field to form a thin film onto a Pt substrate electrode. The results were compared with a conventional PB modified electrode throughout the research. For the electrode prepared in the presence of the magnetic field, a stronger voltammetric behavior with higher peak current was observed. It was accompanied by higher chemical and electrochemical stabilities of the deposited electroactive film. Spectroscopic measurements were also performed to investigate the influence of the applied magnetic film on the properties of the electroactive film deposited. The results were indicative of the fact that deposition under magnetic filed is accompanied by stronger chemical bonds and different elemental composition of the electroactive material formed on the electrode surface. Based on the experimental results, it was concluded that both Lorentz and magnetic forces are responsible for the behavior observed.

Effect of surface resistance of metal evaporated tape on discharge current

In the helical-scan tape system, the magnetoresistive (MR) head is used in the MICROMV consumer VCR format. A giant magnetoresistive head for high-recording density is more sensitive to electrostatic discharge (ESD) than an MR head. In order to evaluate the damage caused by ESD, a new charged tape model (CTM) was devised and it was compared with a model using an ESD gun. The surface resistance of metal evaporated tape was investigated with a view to minimizing discharge current through the MR head. As the surface resistance increased from 1.1e+3 to 1.8e+8 /spl Omega//sq, the peak discharge current decreased inversely proportional to the surface resistance and proportional to the applied voltage. The CTM supplied a short pulse (200 ns) but a high peak current. The ESD gun supplied a long pulse (more than 1 /spl mu/s) and its peak current decreased with the distance from the head. The authors conclude that the discharge current from the tape surface can be controlled by the surface resistance.

High Voltage Stimulation (HVS) for Enhanced Healing of Wounds

High voltage stimulation (HVS) influences tissue repair at the level of the wound environment. This article discusses research findings and clinical use of HVS for enhancement of wound healing. A brief review of theories and current scientific rationale for use of HVS is provided. Included is a brief examination of research dealing with high voltage peak current, and wound healing processes. This article summarises recent developments and trends in the use of HVS for healing in order to facilitate clinicians' decision-making capabilities, and their understanding of treatment options.

Statistical analysis of space–time relationships between sprites and lightning

We present a detailed statistical analysis of the association of 40 sprite events with lightning from the parent thunderstorm. Both temporal and spatial criteria were used to identify the parent cloud-to-ground (CG) lightning. Sprite images were GPS time stamped and their locations triangulated. In contrast to previous reports of nearly one-to-one association of sprites with positive cloud-to-ground (+CG) lightning, 11 events (27%) did not have a +CG recorded by the National Lightning Detection Network (NLDN), and 7 events (17%) had neither NLDN nor very low frequency (VLF) signatures associated with them. A negative cloud-to-ground (−CG) preceded one of these events by 9 ms . As expected for ∼16.7 ms integrated images, none of the sprites without a +CG had any discernible visual characteristic that would distinguish them from “regular positive sprites”. We have calculated the distribution of time intervals (Δ t= t sprite− t lightning) for the sprites that had a parent +CG flash registered by the NLDN or VLF systems, and the distribution of distances between the sprite nadir positions and the flash locations registered by the NLDN. The time interval (Δ t) distribution had a peak around 10– 20 ms and a mean of 30 ms (total). This distribution is broadly consistent with the characteristic single electron avalanche time scale associated with streamer growth between ∼70 and 85 km . The distribution of the distances (Δ s) between the nadir point of sprites and the parent +CGs showed that approximately two-thirds of the sprites occurred within 50 km lateral displacement from the parent +CG. The parent +CG peak current distribution had a maximum at 40– 50 kA and mean of 60 kA , suggesting that high peak currents (I⩾75 kA) are not a necessary prerequisite for sprites. The peak current distribution for all +CGs of the storm, with a maximum around 10– 20 kA and mean of 27 kA , exhibits a qualitatively different form from the peak current distribution of the parent +CGs producing sprites.

Quasi-active power factor correction with a variable inductive filter: theory, design and practice

The mains current in an AC/DC converter contains periodic current pulses, due to the action of the rectifier and the output buffer capacitor. The high current peaks cause harmonic distortion of the supply current and low power factor. Introducing active power factor correction in the form of a boost pre-regulator can reduce the level of harmonics. Passive power factor correction in the form of an input filter inductor is less expensive but the component is bulky because it must be sized to handle the full power range of the supply. This paper investigates the use of variable inductance (the inductance varies with current), which provides adequate harmonic reduction. Three types of inductors are investigated: an inductor with a fixed air-gap operating with a saturated core, a swinging inductor which has a stepped gap and a novel inductor construction with a sloped air-gap (SAG). Results are presented for a 200 W power supply and it is shown that the SAG inductor has the best performance in terms of harmonic response and size.

High-Efficient High Frequency Linked Zero Voltage Soft Switching PWM DC/DC Power Converter with ON/OFF-Assisted Synchronous Rectifier Scheme

Advanced development of the high frequency pulse modulated DC/DC power converters are indispensable in order to achieve smaller size, higher performances of the power supplies. In resent years the problems of the electromagnetic noise generation caused by the hard-switching pulse width modulation (PWM)—based high frequency operation of the switching power devices have been significant, including switching losses and switching surges. As result a variety of soft-switching power conversion circuit technologies have been attracted special interests for reducing switching power losses and minimizing electromagnetic interference. The soft-switching pulse modulation of DC/DC power circuit topologies can be divided into continuous current mode resonant type and quasi-resonant voltage mode type. The soft-switching DC/DC converters, a continuous current mode zero current soft-switching (ZCS) DC/DC converter with pulse frequency modulation (PFM) has been already put into a practical use. In this sort of power converters soft-switching commutation can be achieved over wide load variation ranges and high stability can be also performed, but high current peak stress through power semiconductor devices arises, however, and it causes relatively large increase of conduction power losses in the power semiconductor devices, high frequency transformers as well as rectifier diodes. As a result, the problem of a high efficiency for DC/DC power converter could not still unsolved.Thereupon, in this paper, quasi-resonant voltage mode based soft-switching PWM DC/DC power converter with a high frequency transformer link is presented, which has on/off assisted synchronous rectifier in its secondary side. The PWM operation of this converter is described in comparison with conventional one. Due to using power MOSFET as on/off assisted synchronous rectifier in the secondary side of the high frequency isolated transformer, it is possible to achieve stable zero voltage soft-switching (ZVS) conditions from no load to the rated load for minimum requirement of a magnetizing current. As result of a high value of the magnetizing inductance design, the power converter actual efficiency of this converter can be designed so as to above 97% in experiment. Moreover, results of a switching losses analysis are discussed from an experimental point of views in this paper. The effectiveness of the power converter treated hare is proved from a practical point of view by using 32kHz-2.5kW breadboard setup.

Magnetic loss measurement and calculation of a DC/DC converter

The use of a tapped inductor in the classical sepic converter leads to a high step-down ratio thus avoiding the extreme duty cycles of the active switch and the high peak currents in the active and passive switches. The function and some stress data of such a converter are summarized and the flux density and the current through the inductor during start-up are measured and simulated by the energetic model of ferromagnetic hysteresis and the magnetic losses of the inductors are calculated.

Microprocessing by intense pulsed electron beam

Generation of intense electron beams by superposing two discharges, namely, a low-pressure DC glow discharge and a high-current pulsed discharge at pressures and voltages very similar to that of the pseudospark gap devices, has been studied. The small beam diameter, high peak current, and short pulse length are the characteristics of the electron beam generated using this technique. This technique does not require high vacuum facilities, and applications such as microprocessing, X-ray generation, and preionization for high-power lasers are feasible. The electron beam current is in the range of 10-30 A. Microprocessing as drilling tenths of microns diameter holes in different materials such as copper, titanium, and tantalum has been performed. The microstructure of the irradiated materials has been investigated by means of scanning electron microscope (SEM) and atomic force microscope (AFM). Currently, the possibility of processing a matrix of holes is being considered. In this paper, preliminary study regarding the interaction of intense short electron beams with different metallic targets is presented. The electron generator consists of a fast filamentary discharge in low-pressure gases, and the filling gases such as helium, argon, or nitrogen at approximately 0.1 torr pressure are used. Some of the important characteristics of the device for drilling and micromachining are that the targets can be easily changed, and the beam can be deflected by means of a magnetic field. After the initial device characterization, several holes at different experimental conditions were drilled onto the target materials, and the interaction of the beam with these different targets was investigated by means of a scanning electron microscope.

Design considerations for a SASE X-ray FEL

The well developed theory of short wavelength SASE-FELs is now being used to design two X-ray lasers, LCLS and Tesla-FEL. However, the physics and technology of these projects present some unique challenges, related to the very high peak current of the electron beam, the very long undulator needed to reach saturation, and the importance of preserving the beam phase-space density even in the presence of large wake-field effects. In the first part of this paper, we review the basic elements of the theory, the scaling laws for an X-ray SASE-FEL, and the status of the experimental verification of the theory. We then discuss some of the most important issues for the design of these systems, including wake-field effects in the undulator, and the choice of undulator type and beam parameters.

Pulse excitation of micro-fluxgate sensors

Miniature fluxgate sensors with symmetrical closed core elements on both sides of the planar coils were manufactured using standard microtechnology. The new sensors have shown substantial improvement over the standard single-sided micro.-fluxgate sensors: for the same field range the sensor noise was reduced 10-times to 20 nT rms (20 mHz ... 10 Hz) and the perming suppressed below 5 /spl mu/T, for field shocks of 6 mT. The maximum sensitivity for sinewave excitation was 32 V//spl mu/T for 1 MHz frequency and 200 mA p-p excitation current amplitude. Pulse shape of the excitation current allows use of high current peaks to suppress perming, while the rms value is low. Using a 20% duty factor squarewave excitation with 180 mA p-p amplitude, the sensitivity was twice that of the sinewave excitation, while the chip temperature dropped from 80/spl deg/C to 40/spl deg/C.

Direct measurement of emission current distribution of Spindt-type field emitters

A specially designed Spindt-type emitter array is used to study field emission characteristics of the Spindt-type field emitter. Each pixel in the array contains only one tip, is independently addressable, and is spaced 110 μm from the adjacent pixels. The pixels are electrically and optically distinguishable from each other. The emission current distribution of 2560 field emitters in an array is directly measured as a function of gate voltage. The ratio of maximum current to minimum current is as high as 100:1. There are two peaks observed in the current distribution. The position of the high current peak is strongly dependent on the gate voltage, while the position of the low current peak is less sensitive to the gate voltage. The variations in beam size and beam position of individual field emitters are also measured. These variations within individual emitters are partly responsible for large beam size observed in field emission displays with pixels containing hundreds of emitters. Change in the current distribution of individual emitters was recorded as the emitters were aging. Statistically, the emitters operating at high current age faster than those at low current.

Single shot and burst repetitive operation of thyristors for electric launch applications

Electric gun applications require switches with simultaneous high peak currents, di/dt, and action capability. The development by Silicon Power Corporation (SPCO) of a 125 mm diameter symmetric thyristor which utilizes a unique compact package with decreased thermal resistance from junction to sink has addressed the thermal resistance problem and conduction area limitations. The development of the reversely switched dynistor (RSD), an asymmetric thyristor, by the Ioffe Institute in Russia, has addressed the commutation power dissipation problem by using a unique and highly interdigitated gate structure in the anode and a high current driver. Tests were conducted on both types of devices by discharging a low impedance pulse forming network (21 mF or 17 mF total capacitance) via the device under test into either a matched load or a short. Test peak current varied from 151 kA to 221 kA. Testing was performed, in the same test circuit as the 125 mm thyristor, on an 80 mm diameter RSD. The paper places in perspective the overall performance of these devices and the implications for future designs and applications. The implication of this work is that combining the design principles of both types of devices to the solution of the thermal limitations of thyristors could increase the peak current capability of a 2.5 kV 125 mm symmetric thyristor by a factor greater than 2 and the di/dt by an order of magnitude. Specifically, the thyristor should reliably switch, into a shorted load under repetitive conditions, a 0.5 ms duration pulse with a peak current of 400 kA and a di/dt of 25 kA//spl mu/s.

A Family of Electroluminescent Silyl-Substituted Poly(p-phenylenevinylene)s: Synthesis, Characterization, and Structure−Property Relationships

A series of intense photoluminescent (PL) polymers containing silyl groups with chain length from C1 to C18 has been successfully synthesized through polycondensation reaction. Introducing silyl groups into a conjugated polymer affords the polymer good processability, amorphousness, good film-forming ability, and sharp emission. A systematic analysis of this series of polymers indicates that increasing the side chain length of the polymers will slightly lower the thermal stability while increasing the molecular weight. UV−vis absorption and PL emission spectra of the polymers are quite similar. Cyclic voltammetric (CV) investigation of the polymers reveals that the side chain length plays an important role in the redox behavior of the polymers. Shorter side chain polymers possess better reproducibility of CV scans and higher peak currents, which implies that the chemical/electrical stability and charge injection and/or transporting ability for shorter side chain polymers are better than those for longer ones. Devices fabricated from poly[2,5-bis(decyldimethylsilyl)-1,4-phenylenevinylene] (DS-PPV) with the configuration of ITO/DS-PPV/Mg:Ag and ITO/PEDOT:PSS/DS-PPV/Mg:Ag indicate that the hole injection is the determining factor for device performance. Addition of the hole injection layer can improve the current efficiency and power efficiency by about 7 times and lower the turn-on voltage from 7.5 to 4.0 V for the two types of devices.

Hot Spots Caused By Contact Inhomogeneities In 4H- And 6H-SJCSchottky Structures

By manufacturing of large area Schottky contacts to semiconductor surfaces, the interface area will have a number of inhomogeneities (e.g. grain size effects, diffusional creeps, other boundary effects, etc.). These inhomogeneities lead to the local characteristics at the interface. It means that the interaction of several metals or other materials at the semiconductor interface will lead to the formation of different local barriers at the different sub-regions. The electrical and thermal behavior of such effects is studied using SPICE simulation package SCHOTSIC, developed at the Department of Electronics, TTU. This package simulates both electrical and thermal processes in Schottky diode using standard SPICE environment. Iterative simulation process is used to coupe with self-heating effect. The Schottky contact of simulated model has two areas with different properties. It is simulated on different SiC polytypes, ambient temperatures, doping concentrations and different Schottky contact properties. The strong current crowding effect in the vicinity of boundary, where the transition from higher barrier height to lower barrier height takes place, could be observed on every set of model parameters. Taking into account the geometrical dimensions of the structure, the rapid changes in current behavior are taking place in a very small area of the contact. The current reaches its peak values (both maximum and minimum) only on some micrometers of lateral dimension. It means also that the heating effect in these particular points is higher as could be expected due to extra small area. The simulations have been shown so far that there is no risk of device burndown because of inhomogeneities in Schottky contact. Despite this, there are still doubts on it because of high current peaks in local areas with lower barrier heights. Advanced Computational Methods in Heat Transfer VI, C.A. Brebbia & B. Sunden (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-818-X

Biophysical and pharmacological characterization of voltage-sensitive calcium currents in neonatal rat inferior colliculus neurons

Calcium conductances have been found in neonatal inferior colliculus neurons, however the biophysical and pharmacological profiles of the underlying calcium currents have not yet been characterized. In this study, we examined which types of voltage-activated calcium currents comprise the whole-cell inward current of neonatal inferior colliculus neurons (10–22 μm in diameter). On the basis of their voltage-dependence and pharmacological sensitivities, three major components of barium currents were identified. A low threshold voltage-activated current that activated around −70 mV, a mid threshold voltage-activated current that activated near −50 mV, and a high threshold voltage-activated current that activated around −40 mV. Low and mid threshold voltage-activated currents were present in 33% and 41% of the recordings, respectively, whereas high threshold voltage-activated currents were recorded in all inferior colliculus neurons tested. Nickel chloride (50 μM) and U-92032 (1 μM), which both block low threshold voltage-activated currents, reduced the amplitude of low threshold voltage-activated peak currents at a test potential of −60 mV by 72% and 10%, respectively. In addition, 50 μM nickel chloride and 1 μM U-92032 reduced the amplitude of mid threshold voltage-activated peak currents measured at −20 mV by 55% and 21%, respectively. Further pharmacological analysis indicated the presence of multiple types of high threshold voltage-activated currents in neonatal inferior colliculus neurons. The dihydropyridine nimodipine (1 μM), a selective L-type current antagonist, reduced the amplitude of high threshold voltage-activated peak currents by 25%. In addition, FPL 64176 (1 μM), a non-dihydropyridine L-type current agonist caused a dramatic 534% increase in the amplitude of the slow sustained component of the tail current measured at −40 mV. These data indicate that inferior colliculus neurons express L-type channels. ω-Conotoxin GVIA (1 μM), a selective blocker of N-type current, inhibited high threshold voltage-activated peak currents by 28% indicating the presence of N-type channels. ω-Agatoxin IVA (300 nM), a potent P/Q-type antagonist, reduced high threshold voltage-activated peak currents by 27%, suggesting that inferior colliculus neurons express P/Q-type channels. Concomitant application of nimodipine (1 μM), ω-conotoxin GVIA (1 μM) and ω-agatoxin IVA (300 nM) onto inferior colliculus neurons decreased the control high threshold voltage-activated peak currents only by 62%. Thus, inferior colliculus neurons may express at least one more type of calcium current in addition to low and mid threshold voltage-activated currents and L-type, N-type and P/Q-type high threshold currents.

Pulse handling capability of energy storage metallized film capacitors

The aim of this work was to point out the current performance of metallized polypropylene film capacitors. Many tests have demonstrated that the contact between the sprayed terminations and the metallized electrodes is one of the most critical points for capacitors manufactured with this technology, generally when the capacitors are used in impulsive conditions. This is the case of energy storage application. The effects of pulses having high peak current, but short duration (20-40 /spl mu/s), are compared to the effects of pulses having lower peak current, but higher duration (200-300 /spl mu/s). The comparison is made between pulses having the same I/sup 2//spl middot/t. The modalities of manufacture and the conditions during metallization, winding, and spraying processes are examined in the context of certain mechanical problems during the pulse transient, with particular attention to the connections on the sprayed terminations. The possibility to detect the beginning of detachment of sprayed ends by the use of photodiodes has been taken into consideration. The result of these studies has been an improvement in the performance of energy storage capacitors meeting the discharge and life requirements of the National Ignition Facility (NIF), Lawrence Livermore Laboratory, class capacitors.