Unipolar Current Pulses Research Articles

High-power source of 200–350 nm spontaneous emission excited by unipolar current pulses

Spectral, energy, and temporal characteristics of pulse discharge in xenon have been experimentally studied. Upon passing from an oscillatory regime to unipolar pulses of discharge current, the power of emission in the wavelength interval 200–350 nm increases, while the emission pulse full width at half maximum (FWHM) decreases. A quartz pulsed discharge lamp excited by a generator based on high-current high-voltage diodes radiates in the 200–350 nm interval at a peak radiant intensity above 65 kW/sr and at a pulse FWHM ∼ 2 μs.

CdSe Thin Film Preparation by Unipolar Current Pulse Electrodeposition Technique

AbstractCdSe thin films were prepared using unipolar current pulse electrodeposition technique on fluorine doped SnO2 coated glass plates. The electrodeposition bath consisted of aqueous solution including CdSO4, SeO2 and pH was adjusted using H2SO4. Growth of CdSe was accomplished under wide range of variables like current density, pulse on and off time in order to elucidate the effect on crystalline structure, grain size and optical properties. A low current density and increased off time favored grain orientation and crystallinity. Increased current density and on time favored grain size reduction.

Pulsed electrodeposition of CdTe thin films: effect of pulse parameters over structure, stoichiometry and optical absorption

Abstract CdTe thin films were electrochemically deposited using unipolar current pulses of high magnitude between 2.5 and 30 mA/cm 2 in an aqueous solution. Parametric study of the effect of periodic current pulse magnitude, average current and ON and OFF duration was undertaken to understand the effect of pulse variables on CdTe film properties. Increasing pulse deposition current modifies crystalline growth phase from single cubic to mixed cubic and hexagonal growth phases. In addition to the modification in CdTe growth phases, there is an increasing tendency of the oxide formation particularly CdTeO 3 . Increase in pulse current density or average current yields Cd rich CdTe films. The optical absorption coefficient decreases with the decrease in pulse current density, whereas an increase is observed as the OFF time decreases. The optical energy gap is found to increase with OFF time. A systematic study on the effect of pulse variables over the structure, compositional and optical properties of CdTe film is described.

High-Voltage RSD Switches of Submegaampere Current Pulses of Microsecond Duration

Two versions of a switch circuit based on an assembly of reverse switch-on dynistors (RSDs) with a 25-kV operating voltage connected in series are described. Their main feature is a decrease in the device dimensions as a result of introducing two successively triggered low-power dynistor units into the control circuit and assembling several RSD structures in a common ceramic housing. The first circuit version is used in the discharge circuit of the capacitive energy storage in the operation into a mismatched load and can switch alternating pulses with a 750-μs duration with amplitudes of the first pulses of the forward and reverse currents of 130 and 15 kA, respectively. The second version employs the crowbar regime and makes it possible to form unipolar current pulses with a 190-kA amplitude and a 500-μs duration in the load circuit.

Depinning of the charge density wave under inhomogeneous conditions in the blue bronze K0.30MoO3

In order to explore non-local effects in the CDW depinning in the blue bronze K 0.30 MoO 3 , we have studied the influence of longitudinal dc current I dc flowing in the vicinity of the bottom surface of the sample on the threshold field E t.p measured on the top surface with unipolar rectangular current pulses I p flowing through the bulk of the sample. When I dc and I p have the same (resp. opposite) sense. E t.p decreases (resp. increases) with I dc . In both cases. the excess CDW current I CDW depends on I dc and obeys a power law: I CDW α [V p -V t,,p (I dc )] β with an exponent β -1.3 which does not change with I dc. .

CDW dynamics in the quasi-one-dimensional molecular conductors (Per) 2M(mnt) 2, (M=Au and Pt)

A comparative study by pulsed current techniques of the Charge Density Wave (CDW) dynamics and the temperature dependence of the non-linear electrical transport threshold field, E t, for the quasi-one-dimensional molecular conductors (Per) 2M(mnt) 2, with M=Au and Pt, is presented. The voltage response to unipolar current pulse shows a similar regime in the two compounds with a quite rigid CDW. E t has a fast increase upon cooling in both compounds but has much larger values for M=Pt and presents a non universal temperature dependence.

The effects of conducting breaks on electrostatic discharges (ESDs) on optical solar reflector (OSR) panels

Charging tests were performed on a 21-cm*21-cm panel covered with a square of 25 fused-silica OSRs. In subsequent tests the middle rows and for columns were replaced with ITO (indium tin oxide)-coated OSRs. This did not stop the propagation of discharges, which apparently jumped across the conducting gaps generating multiple unipolar current pulses. A propagation model can be used to predict transient amplitude and propagation delay across conducting gaps (separation between the current pulses). >

Cardiac stimulator for the study of refractory period control using current pulses of programmable duration and shape.

A programmable current stimulator has been developed that allows unipolar current pulses of complex shape, long duration and high current to be generated. The stimulator conforms to the safety requirements for devices connected directly to the heart. It incorporates additional safety features to prevent unintended current being delivered, even under fault conditions. The stimulator has been used to investigate the effects of long duration current pulses on the refractory period of cardiac tissue. The flexibility of the device suggests that it may well have uses in other fields of electrophysiology.

Depinning of the charge density wave in pure and non-stoichiometric blue bronzes A 0.30MoO 3 (A=K, Rb)

We report the observation of non-linear voltage response to unipolar current pulses in pure A 0.30MoO 3 (A=K, Rb) and non-stoichiometric Rb 0.28MoO 3 blue bronzes near threshold for depinning of the charge density wave. In both types of samples, the transient response waveforms involve overshoot at the leading edge and a tail at the trailing edge of the pulse whose time decays obey stretched exponential laws exp-(t/τ)β (O<β<1). The characteristic times are found to be approximately one order of magnitude larger in Rb 0.28MoO 3 than in pure samples. The results are discussed in terms of charge density wave phase dislocations coupled to point lattice defects.

An isolated current monitor for low-frequency asymmetrical current waveforms

An isolated current monitor circuit with a bandwidth of 30 mHz to 100 kHz and a peak current handling capacity of 50 A is described. The monitor, which was designed to enable 100 ms unipolar rectangular current pulses to be observed, is connected into the circuit as if it were a normal ammeter and its output is displayed by an oscilloscope.

High permeability and low remanence tape wound transformer cores

Single layer tape wound toroidal cores have a small effective air gap. By simultaneously winding several layers of tape, which are properly coated with an inert medium, the effective air gap of the cores can be increased. This winding method permits us to alter the shape of the hysteresis loop, to make it more round. Cores with a rounded hysteresis loop are required for differential transformers used in ground fault circuit interrupters which have to respond to AC and unipolar current pulses. We present here calculations and data for the effective air gap of multilayer wound cores so that the permeability and the remanence of such cores can be predicted, or the number of layers required to achieve a certain hysteresis loop can be calculated.

A simple computer method for predicting the transient response of ultrasonic NDT probes

This paper describes a computer method for predicting the transient response of compressional wave ultrasonic probes employing piezoelectric disc transducers. Simple programs provide detailed predictions for both the form of the ultrasonic pulse transmitted to a test material and also the voltage output corresponding to the reception of the said ultrasonic pulse. The effects of intermediate layers lying between transducers and backings and between transducers and test materials are included. The electrical input to a transmitting prode is assumed to be a single, unipolar current pulse, whilst a receiving probe is assumed to work into an electrical open circuit. Excellent agreement between theoretically predicted and experimentally observed waveforms has been obtained for specially constructed immersion probes.

Characterization of self-aligned transfer gates for 1µm bubble contiguous-disk devices

Self-aligned transfer gates for contiguous disk bubble devices have been characterized at 200kHz. These devices require a single masking level to define both the current control conductors and ion-implantation pattern. Switch operation relies on a unipolar current pulse in the major loop which stripes the bubble between major and minor loops along a bridging charged-wall; directionality is provided by the crystalline symmetry effects in the drive layer. Representative transfer pulse parameters for a 28 Oe (8%) overlapping bias field margin are: (i) transfer-in, amplitude 115 mA ±25%, width 0.1μs ±15% and phase margin \pm16\deg . (ii) transfer-out, amplitude 160 mA ±9%, width 0.88μs ±10% and phase margin \pm10\deg . The transfer pulse requirements are discussed in terms of the behaviour of the charged-walls in the garnet drive layer.

Dollar-sign transfer for magnetic bubbles

The evolution and characteristics of dollar-sign transfer gates for use in bubble mass memories are described. With this type of gate both directions of transfer require only a single conductor and unipolar current pulses. Directionality is achieved by the phase relationship between the transfer current pulse and the rotating field. It is shown that ordinarily the transfer function performs bidirectionally over the entire propagation range at current amplitudes of the order of 35 mA. Experiments on a 20 kbit chip indicate that over a range of rotating field between 25 and 35 Oe and a bias field range of 74 to 85.5 Oe, the worst-worst margins on the transfer current amplitude, phase and pulsewidth are ±14%, ±11° and ±23%, respectively.

Direct current make and break thresholds for pacemaker electrodes on the canine ventricle.

Thresholds to anodal make, anodal break, cathodal make and cathodal break have been studied throughout the cardiac cycle in 13 dogs under pentobarbital anesthesia. Unipolar direct current pulses were applied through epicardial pacemaker electrodes to the left ventricle. Make and break responses were separated by letting the break and make occur in the refractory periods of the following and preceding cycle, respectively. Four distinct threshold interval curves were obtained from each of 17 electrodes. The anodal break and cathodal break curves showed an early diastolic dip. Dips were deepest in the anodal break curves. These also had the shortest effective refractory period. Thresholds for cathodal make and anodal make first dipped steeply, then gradually sloped down towards end-diastolic levels. The magnitude of end-diastolic mean threshold values increased in the following order: cathodal make, anodal make, cathodal break, anodal break. Comparison of threshold interval curves for make and break responses with those for shorter rectangular anodal and cathodal curves throughout the cardiac cycle supports the hypothesis that the threshold behavior to a short rectangular pulse is determined by whichever of two thresholdsis lowest: make or break at that particular cycle interval.