Short Current Pulses Research Articles

Development of the specialized integrated circuit for signal readout from micro-strip structures of a coordinate detectors

The paper presents current status of development of a specialized 64-channel integrated circuit (IC, ASIC) for front-end electronics of coordinate detectors in the Budker INP. The ASIC is produced using 180 nm process. During the recording phase the IC allows integration of short current pulses from strips of a coordinate sensor, and storing of up to 100 corresponding charge values in the analogue memory with minimum time interval of 100 ns. Maximum input charge is equal to 2×106 electrons, equivalent noise charge is ∼2.7×103 electrons.Conversion of the data, stored in the analogue memory, to digital form is performed by an external ADC during the readout through an analogue multiplexer.

Effects of Localized Heating at Heterointerfaces on the Reliability of Organic Light-Emitting Diodes

Continuous-wave and pulsed-current stressing was conducted to evaluate the reliability of green phosphorescent organic light-emitting diodes (OLEDs). Through modifications of the ITO anode by different pretreatments and the hole transport layer (HTL) by incorporating inorganic component or dopants, we proved that the energy level misalignment at the ITO/HTL interface leads to localized Joule heating, accelerating material deterioration, and luminescence decay. Stressing with short current pulses was employed to suppress the heating effect. For OLEDs with a large interfacial barrier of 1.2 eV, the effective half life was increased by 70% under pulsed operation, whereas in OLEDs with an interfacial barrier of 0.5 eV, only 14% improvement was obtained, indicating a minor heating role.

Plasma of Vacuum Discharges: The Pursuit of Elevating Metal Ion Charge States, Including a Recent Record of Producing Bi13+

Metal ions in the plasma of vacuum discharges are commonly multiply charged with ion charge states from 1+ to 3+, reaching 4+ and 5+ for some metals. The elevation of metal ion charge states in vacuum discharge plasma is an interesting challenge for plasma physics because it requires a deeper understanding of the processes leading to a more intense ionization of the electrode material. It also has practical implications, for example, for metal ion sources: elevation of ion charge state leads to a proportional increase in ion beam energy for a given accelerating voltage. During the last two decades, various techniques have been used to increase the ion charge states, including: 1) application of a strong magnetic field to the cathode region of the vacuum arc; 2) application of supplemental microwave power to the discharge plasma; 3) injection of an electron beam into the discharge area; and 4) application of a short current pulse to the discharge as to transiently increase the discharge voltage and power, emulating the conditions of a high-current vacuum spark. In this paper, we briefly survey the different techniques of metal ion charge state elevation and then present new experimental results by utilizing the spark regime and combining it with a strong pulsed magnetic field applied to the cathode region. Beams of ions with high charge state, up to a record Bi13+, were extracted from vacuum spark plasma. It is argued that the addition of a magnetic field to the spark plasma magnetizes the electrons and limits plasma expansion, which leads to an increase in the electron temperature relative to the free expansion case and to an increase in the likelihood of electrons to cause ionizing collisions.

Real Time Monitoring of Electrostatic Potentials in the Vicinity of Electrodes Delivering Current Pulses Used in Neural Stimulation

Neural stimulation by metal electrodes such as Pt and its alloys and W has been used previously to evoke electrical activity in neurons1. This process involves passing short extracellular current pulses (ca. 100 µs) aimed at modifying the extracellular potential (Vext) and thereby altering the cell membrane potential. However, direct experimental measurements of Vext during such stimuli have been lacking. Theory suggests that Vext depends on both space and time. We have developed a method (ohmic microscopy) to measure Vext quantitatively with both spatial and temporal resolution, while passing current across noble metal electrodes during voltammetric scans.2-4 The present work extends application of this technique to current stimulus protocols commonly used in neural stimulation, including functional neural stimulation in clinical settings. EXPERIMENTAL Thin wall glass capillaries were pulled to a diameter of ca. 10 µm for each barrel, and filled with an aqueous 0.1 M H2SO4 solution. Microreference (μ-ref) Ag/AgCl electrodes were made by inserting Ag wires coated with a layer of AgCl (0.125 mm in diameter) formed by dipping the wire in a saturated KCl aqueous solution for at least 12 h. The μ-ref Ag/AgCl electrodes were mounted on individual holders connected in turn to individual micromanipulators. Pt disk (diameter 1.6mm) as working electrode, Pt wire as counter electrode, and Ag/AgCl(saturated) as reference electrode, 0.1M H2SO4 with their tips aligned along the normal to the center of the Pt disk (see Fig 1) at prescribed heights. A current pulse of a few mA was then applied to the Pt disk using a function generator (Agilent 33220A) coupled to a potentiostat (Autolab, PGSTAT302N, Nova 1.10, Metrohm). The time response of the potential difference between the two μ-ref electrodes, denoted as, Δφsol, amplified 10 times (Ina141, Texas instrument), was recorded on an oscilloscope (Agilent DSO-X 2014A). A schematic diagram of the instrument setup is shown is Fig. 1. RESULTS AND DISCUSSION For these experiments a current pulse of 5 mA, 100 μs in duration was applied across the Pt disk electrode (see red curve in Fig. 2), while recording the potential difference, Dϕ, across the two μ-ref Ag/AgCl electrodes placed at 1 mm, and 2mm normal to the disk along its center line (see blue curve, Fig. 2). As indicate therein, during the passage of current Dϕ was found to be ca. 62.5 mV. This value compares very well, i.e. slightly over 2%, with that predicted by Newman5, i.e. 61.2 mV. Excellent agreement was also found for other current values, duty cycles, and placement of the μ-ref Ag/AgCl electrodes. Efforts are underway to measure the response of dissociated neurons as a function of the placement of the electrodes and the stimulation parameters. ACKNOWLEDGEMENTS This work was supported by a Grant from NSF. REFERENCE D. R. Merrill, M. Bikson, J. G. R. Jefferys, J . Neurosci. Methods, 141 (2005), 171C. A. Cartier, D. Kumsa, Z. Feng, H. Zhu, D. A. Scherson, Anal. Chem. 84 (2012), 7080Y. Chen , A. Belianinov, D. A. Scherson, J. phy. Chem. C, 112 (2008), 8754M. Ignatowitz, E. Oesterschulze, App. Phy. Lett., 101 (2012), 251601J. Newman, J. Electrochem. Soc., 113 (1966), 501. Figure 1

Automatic Meter Reading using Power Line Signaling and Voltage Zero-crossing Detection

In India, the electric power transmission and distribution loss is very high, about 7% in transmission and 26% in distribution. Though deployment of automated meter reading system will reduce losses, particularly in distribution, penetration of automated meter reading is low due to high costs involved. World over, the Two-Way Automatic Communications System (TWACS) is the most widely used power line communications technology offering two-way communication between substation and end users. The TWACS introduces disturbance on the power system voltage for short durations near zero-crossing to generate the outbound (from substation to end user) signal. To generate the inbound (from end user to substation) signal, short duration current pulses are introduced, near voltage zero-crossings. Information is generated as a sequential combination of voltage disturbances for the outbound signal and current pulses for the inbound signal. The current study proposes a low-cost modification of the TWACS to reduce voltage and current harmonics. The proposed system has been modelled and simulated using SIMULINK/SIMPOWER Systems. The simulation results show that there is a reduction in voltage harmonics from 0.84 to 0.17% and in current harmonics from 2.07 to 1.10%.

Evaluating Material Performance Between High-Current Contacts

A high-current test fixture (HiCTF) was developed to examine material response to repulsive forces generated between electrically conducting material pairs during short pulses of high current, similar to conditions experienced in Electromagnetic Launch applications. Based upon Holm's contact theory with additional preload and pressure distribution parameters, this test fixture was designed to use a loading press to apply preload to the test specimens while conducting current through the specimen contact interface. The fixture uses an aligned mechanical loading device to provide a preload across the contact interface of the specimen. The HiCTF will allow for investigation of contact response sensitivity as a function of its degradation, impact of geometry variation, surface conditions, material pairing, preload, and contact integrity. Statistically based experimental designs have been constructed and analysis methodologies developed that incorporate likelihood ratio analysis and the Neyer method. The Neyer D-optimal design method, used in sensitivity testing of explosives, shows promise as an appropriate test method for HiCTF results and will be used to provide sufficient information for comparisons and developmental thresholds. Results from HiCTF testing provide insight into the electrical contact phenomenon and high-current material response. This paper provides an overview of the HiCTF, its motivation, analysis methodology, results, observations, and lessons learned.

Time response of 50 μm thickness single crystal diamond detectors

Short current pulses of width around 1ns are generated by 50μm thickness single crystal diamond detectors, which makes them very attractive for fast timing nuclear experiments. The shape of the pulse is greatly affected by the applied electric field that influences both the pulse rise time and its width. An exponential behaviour is found for the rise time and pulse width vs electric field. Measurements performed with high bandwidth electronics yield rise time down to 300ps. It is also shown that for pulse duration in the nanosecond range, alternative electronic systems to the bulky and costly digital oscilloscopes, are commercially available.

Analysis of reliable sub-ns spin-torque switching under transverse bias magnetic fields

The switching process of a magnetic spin-valve nanosystem subject to spin-polarized current pulses is considered. The dependence of the switching probability on the current pulse duration is investigated. The further application of a transverse field along the intermediate anisotropy axis of the particle is used to control the quasi-random relaxation of magnetization to the reversed magnetization state. The critical current amplitudes to realize the switching are determined by studying the phase portrait of the Landau-Lifshtz-Slonczewski dynamics. Macrospin numerical simulations are in good agreement with the theoretical prediction and demonstrate reliable switching even for very short (below 100 ps) current pulses.

Ultrafast switching of antiferromagnets via spin-transfer torque

Picosecond switching of the staggered antiferromagnetic order is shown to be realizable through spin-transfer torques from a short current pulse. The coupled dynamics of sublattice magnetization is mapped onto a classical pendulum subject to gravity and a driving pulse, where switching occurs if the pendulum acquires sufficient kinetic energy during the pulse to overcome the maximum of the effective gravity potential. The optimal switching scheme is explored through the dependence of switch angle and magnetic loss on the duration and strength of the current pulse. The physics discussed here provides a general route towards multi-functional THz applications via the spin-transfer torque in antiferromagnetic materials.

Comparative Study of Pulsed Dielectric Barrier Discharges in Argon and Nitrogen at Atmospheric Pressure

In this paper, the mechanisms and characteristics of the pulsed dielectric barrier discharges in Ar and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> at atmospheric pressure are analyzed and compared by means of numerical simulation based on the 1-D fluid model. Under different operating conditions, including gap width d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , dielectric thickness d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , and relative dielectric constant ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , the important characteristic quantities of describing the discharge, i.e., maximum discharge current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , averaged electron density N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> -ave, and averaged dissipated power density Pave, are observed and studied in detail. This paper gives the following significant results. In Ar, the discharge occurs after the gap voltage has reached its maximum and is in the form of two short discharge current density pulses. In N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , the discharge starts from the increase of the gap voltage and presents the smooth development in a longer time being nearly equal to the pulsewidth. For the two gases, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , Ne-ave, and Pave decrease with the increase of d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , and these characteristic quantities decrease with the increase of d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , or with the decrease of ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> . In addition, the discharges in Ar maintain in the atmospheric pressure glow discharge (APGD), but the discharges in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> operate in the varying discharge modes, including the APGD, the weak APGD, and the atmospheric pressure Town send discharge. The development of the APGD in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> requires the smaller gap width, the thinner dielectric thickness, and the larger relative dielectric constant.

Turning Process Assisted in situ by Short Time Current Pulses

This article reports on a novel machining process technique: in situ electrically assisted turning process based on the influence of electropulsing. An in house generator was used to induce a current intensity of 90 A, a pulse duration between 50 and 200μs and frequencies between 100 and 300Hz. The influence of different electropulsing configurations assisting the machining process was studied, specifically on the surface properties and the power consumption in 1045 steel. The results show that the electrically-assisted turning process improves material machinability, decreasing the power consumption up to 104W and the specific cutting energy up to 22%. The assisted process also modifies the surface properties, the average surface roughness decreases within the range of 7 to 22% when compared to the conventional turning process.

A high-voltage pulse integrated thyristor

The results of investigations of a small-size integrated thyristor recently developed at the Ioffe Physical Technical Institute of the Russian Academy of Sciences are presented. The operating voltage of the thyristor is 3300 V. The thyristor shows high switching performance in the regime of commutation of short current pulses with a high rise rate. The amplitude of a current pulse with a duration of 600 ns reaches 3.3 kA, while the current density is ∼37 kA/cm2.

Applying Catalytic Sensor in Non-volatile Wireless Sensor Networks

Fundamental solutions were developed and energy-saving parameters of a catalytic sensor operation were chosen for using a catalytic sensor in non-volatile wireless sensor networks.Energy-saving mode is based on cyclic method, where every cycle includes short current pulse and the pause between pulses does not exceed regulated by normative documents “response time” for sensors working in continuous mode.To reduce current pulse duration, heating and measuring processes are combined. Two-staged pulse shape was chosen for this, the first stage accelerates heating, the second one is measuring, where we reduce sensor supply voltage and heating temperature, form transient cooling of the sensing element, then measure cooling rate, which is proportional to measured concentration of flammable gas in the air.

Suppression of thermoelectric Thomson effect in silicon microwires under large electrical bias and implications for phase-change memory devices

We have observed how thermoelectric effects that result in asymmetric melting of silicon wires are suppressed for increasing electric current density (J). The experimental results are investigated using numerical modeling of the self-heating process, which elucidates the relative contributions of the asymmetric thermoelectric Thomson heat (∼J) and symmetric Joule heating (∼J2) that lead to symmetric heating for higher current levels. These results are applied in modeling of the self-heating process in phase-change memory devices. While, phase-change memory devices show a clearly preferred operation polarity due to thermoelectric effects, nearly symmetric operation can be achieved with higher amplitude and shorter current pulses, which can lead to design of improved polarity-invariant memory circuitry.

Self-pulsing discharges in pre-heated air at atmospheric pressure

The paper presents investigations of self-pulsing discharges in atmospheric pressure air pre-heated to 300–1000 K. Despite using a direct-current power supply, two self-pulsing discharge regimes, a repetitive transient spark (TS) and a repetitive streamer (RS) were generated. The pulse repetition frequency, on the order of a few kHz, can be controlled by adjusting the generator voltage. The TS is a discharge initiated by a streamer, followed by a short (tens of ns) spark current pulse (∼ 1 A), associated with the total discharging of the internal capacity of the electric circuit. The TS is suitable for the study of ‘memory’ effects (pre-heating, pre-ionization) on the mechanisms of streamer-to-spark transition and electrical breakdown in atmospheric pressure air. The TS regime was stable below ∼600 K. Above ∼600 K, a stable repetitive streamer (RS) regime was observed. In this regime, the breakdown and spark did not occur. After the initial streamer, the internal capacity of the electrical circuit discharged partially. With further pre-heating of the gas, the stable TS appeared again at ∼1000 K.

Macrospin modeling of sub-ns pulse switching of perpendicularly magnetized free layer via spin-orbit torques for cryogenic memory applications

We model, using the macrospin approximation, the magnetic reversal of a perpendicularly magnetized nanostructured free layer formed on a normal, heavy-metal nanostrip, subjected to spin-orbit torques (SOTs) generated by short (≤0.5 ns) current pulses applied to the nanostrip, to examine the potential for SOT-based fast, efficient cryogenic memory. Due to thermal fluctuations, if solely an anti-damping torque is applied, then, for a device with sufficiently low anisotropy (Hanis0 ∼ 1 kOe) suitable for application in cryogenic memory, a high magnetic damping parameter (α∼0.1−0.2) is required for reliable switching over a significant variation of pulse current. The additional presence of a substantial field-like torque improves switching reliability even for low damping (α≤0.03).

Measurement of the electron density in Transient Spark discharge

This paper presents our measurements of the electron density in a streamer-to-spark transition discharge, which is named transient spark (TS), in atmospheric pressure air. Despite the dc applied voltage, TS has a pulsed character with short (∼10–100 ns) high current (>1 A) pulses, with a repetition frequency on the order of kHz. The electron density ne ∼ 1017 cm−3 at maximum is reached in TS with repetition frequencies below ∼3 kHz, using relatively low power delivered to the plasma (0.2–3 W).The temporal evolution of ne was estimated from the resistance of the plasma discharge, which was obtained by a detailed analysis of the electric circuit representing the TS and the discharge diameter measurements using a fast intensified charge-coupled device (iCCD) camera. This estimate was compared with ne calculated from the measured Stark broadening of several atomic lines: Hα, N at 746 nm, and O triplet at 777 nm. Good agreement was obtained, although the method based on the plasma resistance is sensitive to an accurate determination of the discharge diameter. We have found that this method is also limited for strongly ionized plasmas. On the other hand, a lower ne detection limit can be obtained by this method than from the Stark broadening of atomic lines.

Synthesis of Carbon Nanotubes and Nano-onions Using Electric Field Induced Needle-Pulsed Arc Discharge Plasma

Carbon nano-onions and multi-walled carbon nanotubes (MWCNTs) are synthesized by needle-pulsed arc discharge plasma. In a simple production apparatus, a needle pulsed plasma is applied between two graphite electrodes in the presence of an electric field between anode and cathode. The possibility of carbon nanotube production by short pulsed arc discharge technique is investigated in this article. The pulse width is 0.3 μsec. Acetone vapor as carbon source is introduced to plasma. A magnetic field, perpendicular to the plasma path, is provided. The advantages of using short pulsed plasma are studied in this work. The results show that applying a DC electric field between electrodes, increases plasma tendency toward cathode, enhances the chance of plasma-hydrocarbon interaction, prevents carbon ions from dispersion and finally makes it possible to produce CNTs by low-power short pulses in an arc-discharge plasma reactor. The products are examined using SPM techniques. In this work, adding an electric field to the pulsed plasma techniques, suggests a new method to produce carbon nano particles (CNPs) by short current pulses with lifetime of below one microsecond.

Transformations in WC lattice and polytype formation in the process of sintering of W/C60 mixture

WC nanoparticles having size from nanometers to tens of nanometers surrounded by amorphous carbon and onion-like carbon structures were obtained by milling W/C60 mixture and subsequent sintering by short pulse of electric current. We performed transmission electron microscopy studies of the obtained sample. Almost all of the WC nanoparticles possessed stacking faults in {100} planes stacking. It is known from scientific literature, that such a stacking fault is equivalent to the rotation of the tungsten carbide cells at 90° in the plane of the defect, and it favors the formation of Σ=2 boundary between the grains of WC, rotated at 90° relatively to each other. In a big number of nanoparticles in our sample we observed such an orientation of the neighboring grains. Sometimes a single nanoparticle consists of several grains having Σ=2 and higher Σ boundaries. Also we observed polytype in WC not reported earlier, appearing due to the consequence of stacking faults in (100), and we propose the structure of this polytype. We believe, that the formation of polytypes and Σ=2 and higher Σ boundaries took place during the sintering of W/C60 mixture and happened due to the specific features of the tungsten carbide formation and carbon diffusion through the tungsten.

A High Voltage High Frequency Resonant Inverter for Supplying DBD Devices with Short Discharge Current Pulses

In this paper, the merits of a high-frequency resonant converter for supplying dielectric barrier discharges (DBD) devices are established. It is shown that, thanks to its high-frequency operating condition, such a converter allows to supply DBD devices with short discharge current pulses, a high repetition rate, and to control the injected power. In addition, such a topology eliminates the matter of connecting a high-voltage transformer directly across the DBD device and avoids the issues related to the parasitic capacitances of the latter which disturbs the control the power transfer to the plasma. The design issues of the converter, including the inverter and its switches, the resonant inductor, and the parameter drift compensation are studied. An experimental validation is performed: a mega Hertz resonant converter using GaN FET switches has been manufactured and tested with an excimer lamp.