High Current Amplitude Research Articles

Electrooptic-sampling at variable multidecade repetition rates utilizing a directly modulated semiconductor laser

The generation of single optical pulses under simultaneous suppression of relaxation oscillations at variable multidecade repetition rates from 10 MHz to several GHz is demonstrated. For this purpose special variable pulse width Gaussian to squarewave-like electrical pulses with a FWHM as low as 60 ps are generated. Simultaneously, high current amplitudes of up to 300 mA at variable repetition rates from 10 MHz up to 8 GHz are realized. The described technique is applied in an electrooptic-sampling system for the measurement of high-frequency signals on planar hybrid-integrated circuits.

Spatial distribution of neural activity evoked by electrical stimulation of the cochlea

Activity in the central auditory system was mapped with 2-deoxyglucose (2-DG) autoradiography, using either pure tones or electrical stimulation of the normal cochlea. Electrical stimulation with both monopolar (distant reference electrode) and bipolar prostheses near threshold increased 2-DG uptake in auditory nuclei in a manner similar to that seen with a pure tone: increased 2-DG uptake was restricted to a small frequency region of brainstem and mid-brain auditory nuclei. The position of this area was related to the cochlear location of the prosthesis. At higher current amplitudes only the bipolar prosthesis retained spatial restriction of evoked neural activity, while stimulation through a monopolar prosthesis produced evoked activity in all frequency regions of auditory nuclei and in non-auditory nuclei. Activation of non-auditory structures was consistent with spread of current through the brainstem, rather than activation of peripheral nerves. At all current amplitudes, a monopolar prosthesis evoked higher levels of 2-DG uptake than a bipolar prosthesis. The results suggest that while a bipolar prosthesis provides greater spatial restriction of evoked neural activity and a greater dynamic range, a monopolar prosthesis produces higher levels of evoked activity.

Human skeletal muscle: Phasic type of electrical stimulation increases its contractile speed

Skeletal muscles, exposed to a prolonged period of specific functional demands, respond adaptively. Electrical stimulation, when employed as a technique for subjecting selected muscles to altered use, enables precise entrainment of the pattern of functional activity. In this investigation, the vastus lateralis muscle in a group of volunteers was stimulated. The stimulation program typical of a phasic type of activity (high frequency, high current amplitude, short pulse duration) intermittently subjected the stimulated muscles to brief periods of intense activity, followed by relatively long pauses. The activation-relaxation time ratio chosen was 1 to 13. It was determined to prevent the muscles from fatiguing. The effects of the chronic stimulation program were established by measurements of the time course of contraction and relaxation and fatigue of the vastus lateralis muscle. Chronic phasic electrical stimulation increased the speed of muscle contraction by 15% while the fatigue characteristics remained unchanged.

Fine structural changes in electrostimulated human skeletal muscle. Evidence for predominant effects on fast muscle fibres.

Physical education students were subjected to electrical stimulation of relatively high frequency and current amplitude for 19 days. A quantitative study of several morphological parameters was performed on biopsy samples from gastrocnemius, using stereological methods at both light and electron microscopic levels. The main results were: muscle fibre size was increased; nuclear volume was also increased, suggesting that a proliferation of nuclei had occurred; this was paralleled by an increased content of nuclear DNA. The size of single myonuclei was increased, and their heterochromatin fraction was decreased, these changes being most pronounced in type II fibres. The increase in the mitochondrial fraction was also greatest in type II fibres. It is concluded that this type of electrical stimulation has predominant effects on type II fibres.

Phase resetting in a model of cardiac Purkinje fiber

The phase-resetting response of a model of spontaneously active cardiac Purkinje fiber is investigated. The effect on the interbeat interval of injecting a 20-ms duration depolarizing current pulse is studied as a function of the phase in the cycle at which the pulse is delivered. At low current amplitudes, a triphasic response is recorded as the pulse is advanced through the cycle. At intermediate current amplitudes, the response becomes quinquephasic, due to the presence of supernormal excitability. At high current amplitudes, a triphasic response is seen once more. At low stimulus amplitudes, type 1 phase resetting occurs; at medium amplitudes, a type could not be ascribed to the phase resetting because of the presence of effectively all-or-none depolarization; at high amplitudes, type 0 phase resetting occurs. The modeling results closely correspond with published experimental data; in particular type 1 and type 0 phase resetting are seen. Implications for the induction of ventricular arrhythmias are considered.

How pulsed operation affects aluminium bond wires

AbstractAluminium bond wires are exposed to pulsed current with varying duty cycles, pulse widths and current amplitudes. How these parameters influence the temperature rise in the wire and what it takes to damage or break it are studied. There are two possible failure modes. One is burn‐out due to high current amplitude, the other is metallurgical flexure fatigue at the bond heel. Both failure modes are described. The thermal time constant of the wire is determined for different wire lengths. SEM studies of wires during pulsing are made to see structural changes in the wire when it heats. The bond wire may suffer from damage, which affects the reliability, but it may still function electrically.

Modifications of Commutation Circuits for a Three-Phase Inverter, Connected with the Neutral Conductor

The self-commutated three-phase bridge connection with a common turn-off device using the neutral conductor of the three-phase system is chosen as an example to illustrate modified commutation circuits. These can extend the possibilities of operation of the three-phase bridge. although they may have othersuitable applications too. A particular turn-off device is first described for the use of this bridge as inverter for three-phase drive systems, which enables this inverter to be used for multiple pulse current control. Subsequently various commutation circuits are described which are to avoid a forced charge reversal of a large highly energized commutation capacitor. Instead of the normally used resonant circuit by which the capacitor will be recharged with a high current amplitude and therefore with high losses. a small additional auxiliary capaCitor will be used in these new circuits to reverse the voltage in the commutation circuit with a lower current and with lower losses. Moreover these circuits will allow a replacement of the large expensive turn-off capacitor by a cheaper d.c. capacitor.

Device Degradation by High Amplitude Currents and Response Characteristics of Discrete Resistors

In designing or analyzing electronic circuits for nuclear radiation hardness it is important to know the response of components and their failure levels due to high level current pulses. Theoretical and experimental studies have been conducted on film, carbon composition and wirewound resistors to determine the power or voltage required to cause failure as a function of pulse width. Certain film resistors exhibit failure at the millijoule total energy level which is within the same energy range of concern for many semiconductor devices. Larger wattage carbon composition and wirewound resistors on the other hand were able to absorb tens of joules of energy without failure corresponding to tens of megawatts of power for 1 microsecond pulses. Simplified failure and response models are described.

Switching effect in liquid semiconductors

The paper gives the results of observation of switching in liquid Se and Sb 2 S 3 . The stable reversible switching of high-amplitude currents at high temperatures is shown. Considerable attention is paid to studying the nonlinearity of the volt-ampere characteristic in the region before switching in the fields exceeding (1–5) × 10 4 V/cm.