Showing papers on "Pulse duration published in 1968"

Determination of Threshold Failure Levels of Semiconductor Diodes and Transistors Due to Pulse Voltages

Abstract: Theoretical predictions of circuit failure in an Electromagnetic Pulse (EMP) environment require a knowledge of failure levels for each component of the circuit due to surge voltages or currents. For most circuits, the semiconductor devices are the weakest elements with respect to such failure. This paper presents the results of an extensive experimental program to determine pulse power failure levels of semiconductor junctions. Approximately 80 different types of silicon diodes and transistors were studied with variations in junction areas from 10-4to 10-1 cm2 and with widely varying junction geometries. Power levels of up to two kilowatts, with time durations of 0.1 to 20 microseconds, were applied to semiconductor junctions in both forward and reverse polarity modes. A semi-empirical formula, based on experimental data and on a simple thermal failure model is given. From the formula one can make order-of-magnitude estimates of the failure level as a function of pulse length for many silicon diodes or transistors whose junction area is known.

Nonstationary nonlinear optical effects and ultra-short light pulse formation

Abstract: A theory of nonstationary nonlinear wave phenomena occurring in the field of ultrashort high-intensity light pulses is developed (harmonic generation and parametric amplification stimulated Raman scattering). The main equations are given, the group velocity mismatch effects are studied, and special attention is paid to the high-conversion conditions. The possibilities of picosecond pulse narrowing on account of linear and nonlinear nonresonance parametric amplification and harmonic generation are studied in detail. The factors that determine the minimum light-pulse duration (dispersion broadening) are examined. A nonstationary theory of stimulated Raman scattering (SRS) is developed. Expressions for minimum pulse duration in forward and backward SRS are given. Reduction of Raman amplification with a picosecond pump is discussed.

Thermoelastic Stress Production in Solids

Abstract: Theoretical calculations of the consequences of the thermoelastic mechanism for production of stress in solids by pulsed energy input have been performed, and the effect of variations in the acoustic impedance of a transparent backup material and variations in the pulse duration as compared to the acoustic transit time across the penetration depth of the incident energy have been investigated. Experimental verification of the theoretical calculations has been done using a Q‐switched ruby laser as an energy source with samples of absorbing glass as targets. It is found that the experimental results give good agreement in the shapes of the stress pulses produced, and fair agreement in the absolute amplitude of the stress, with no adjustable parameters being required. The calculations and experiments demonstrate the validity of the thermoelastic stress‐production mechanism in solids when no phase transformation occurs.

Experiments on the observation of neutron emission at a focus of high-power laser radiation on a lithium deuteride surface

Abstract: Theoretical calculations indicate that laser radiation may be used to heat a deuterium plasma to temperatures at which thermonuclear neutron emission may be observed. Using a neodymium glass laser, producing a 20-joule pulse of approximately 10-11-second pulse length, preliminary evidence of neutron emission has been obtained.

Exact solution of a π-pulse problem

Abstract: The exact solution describing steady-state resonant pulse propagation in a two-level inverted medium is given. This steady-state pulse is often referred to as a 180° or π-pulse. No approximation of a slowly varying envelope is made, and hence the solution satisfies the second-order wave equation as well as the equations of motion of the density matrix of the system. As a result the theory is able to describe very short pulses, whose width can be of the order of the period of the optical carrier. The model for the system includes a nonresonant loss and a finite value of the transverse relaxation time T 2 , but neglects dispersion in the host medium. The steady-state pulse is found to be frequency modulated and asymmetric in shape.

Generation of thermoelastic stress waves by impulsive electromagnetic radiation.

Abstract: The penetration and absorption of electromagnetic radiation through a thin layer adjacent to the surface of an elastic half-space provides a sudden heat source distribution through the layer, and, in consequence, stress waves are generated. A solution for uniaxial motion is given in the limit situation when the pulse duration approaches zero in comparison with the wave travel time over the absorption depth, together with the neglect of thermal diffusion on this time scale. The radiation absorption is assumed to decay exponentially with depth. These simplifying features lead to stress wave profiles which clearly illustrate the effective nature of the wave propagation, so that the present solution provides a useful complement to previously obtained solutions of a more general nature. In the case when the surface is stress-free, following initial build-up (here instantaneous) of compressive stress within the absorption layer, a tensile wave propagates outward from the layer. Numerical data are presented to show that the peak tensile stress can attain significant levels within distances of a few absorption depths.

Frequency dependent pulse widths for cp 1133.

Abstract: MEASUREMENTS of average pulse shape made at the Arecibo Ionospheric Observatory have shown that the duration of an average pulse from the pulsar CP 1133 increases progressively with decreasing radio frequency. The effect results in a pulse duration at 40 MHz roughly twice that at 430 MHz. We give here the observational results for CP 1133. Other Arecibo observations show that CP 0834 behaves in a similar way, and the effect may well be common to all pulsars.

Pulse broadening in a mhd copper vapor laser

Abstract: Stimulated emission has been observed from an electrically accelerated copper plasma at 5106 and 5782 A in a device employing a series of plasma guns which inject the vapor into the laser resonator. In addition to facilitating room temperature operation of a copper laser, this technique provides a flowing active medium which has extended the pulse duration by more than four‐fold over that originating from a stationary vapor.

Rapidly Pulsing Radio Sources

Abstract: Observations of a new type of rapidly varying radio source have recently been reported1. The principal characteristics of the four sources so far discovered may be summarized as follows—sharp pulses of radiation are received, separated by comparatively long intervals which themselves are remarkably constant (with variations of ≲ 1 part in 2 × 107 during the past 3 or 4 months). The pulse duration is no more than ~ 0·016 s, while the period is 1#x00B7;3372795 ±0#x00B7;0000020 s (ref. 1). We understand that the other objects show similar sharp pulses at intervals of the order of 1 s, which, although not identical, strongly suggest that a new type of physical system has been discovered. Hewish et al. propose that the objects may be pulsating white dwarfs or neutron stars. Although this may prove to be correct, there are certain difficulties associated with the constancy of the observed period. We suggest an alternative explanation for the observed phenomena.

Pulse discrimination circuitry

Abstract: An indication of a data pulse is produced each time a pulse signal being discriminated exceeds a threshold value in a bit cell, hereafter designated a threshold bit cell. Upon the detection of an amplitude peak in the first bit cell following a threshold bit cell, which may be substantially less than the threshold value, the pulse signal is examined during the second bit cell following the threshold bit cell. When the examination establishes that the peak amplitude of the pulse signal during the second bit cell exceeds the threshold value, an indication of a data pulse for the first bit cell is produced. When the examination establishes that the peak amplitude of the pulse signal during the second bit cell fails to exceed the threshold value, no indication of a data pulse for the first bit cell is produced.

Pulse rate to analog converter

Abstract: A system for providing an analog output signal whose average amplitude is proportional to the frequency of an input signal including a constant pulse width generator responsive to the input signal for providing a series of pulses each of which has a predetermined duration at the same frequency as the input signal and an averaging circuit responsive to the series of pulses for providing an analog signal whose average amplitude is a function of the duty cycle of the constant pulse width generator.

Apparatus for analyzing complex waveforms containing pitch synchronous information

Abstract: A complex waveform containing pitch synchronous information is applied in parallel to a peak detector and a zero crossing detector. A first monostable is activated by the output signal of the zero crossing detector to provide a first pulse of fixed duration. A sawtooth waveform is activated by the trailing edge of the first pulse. The sawtooth waveform will have an amplitude linearly proportional to time. The leading edge of the next sawtooth waveform will activate a sample and hold circuit to sample and store the sawtooth waveform. A second monostable is activated by the output signal of the peak detector to provide a second pulse of a duration less than the fixed duration. The second pulse switches on (gates) an averaging circuit which is coupled to average the output signal of the sample and hold circuit for the duration of the second pulse. This results in an output signal which is an average of the times between successive zero crossings of the complex waveform within the duration of the second pulse.

A Remote Control Brain Telestimulator with Solar Cell Power Supply

Abstract: A brain telestimulator system is described which can be used with primates weighing 3.0 kg or more. The 3×6×7 cm, 200 gm head-mounted receiver employs solar cells to maintain the charge on its battery, thereby permitting experiments to continue undisturbed for many months. The head unit develops across its output a cathodal, monophasic pulse whose duration, rate, and constant current are remotely controlled from the transmitter. Subject to a duty cycle of 0.1, these parameters are continuously and remotely variable: pulse repetition rate, 0-200 pulses per second; pulse duration, 0.1-3.0 ms; pulse current intensity, 0-1.0 mA with less than ± 3 percent variance for loads between 2500-10 000 ohms. Output pulse rise time is 30 , ?s. Any one of 12 electrode channels can be selected for stimulation by remote control activation of an electro-mechanical stepping switch in the head unit. Utilization of crystal control in the frequency modulated transmitter and head units permits multi-animal operation by providing separate bands in the 138 MHz region for independent stimulation of up to four animals. The sensitivity of the receiver has purposely been designed low (-35 dBm). Thus, with the present transmitter the system has a range of about 0.2 mile, which extends beyond the normal visual limits of observation of primate groups.

Zum Entladungsaufbau der Spuren in Funkenkammern

Abstract: The operation of streamer chamber has been studied by application of image converter and image intensifier. The high voltage pulse was produced by a Marx generator (pulse duration about 15 ns), the primary ionisation was generated by gasionizing radiation emitted by a spark lamp.

Pulse train extractor system

Abstract: This system consists of a clock generator which controls the rate at which pulses of an incident pulse train are advanced through a shift register. The input to and the output of the shift register are logically combined in an AND gate. When the clock frequency is adjusted to be related to the pulse repetition frequency (PRF) of the pulses so that a pulse is in the last stage of the shift register at the same time that a succeeding pulse is received at the input thereof, the AND gate produces an output pulse. This operation is repetitive resulting in extraction of the pulse train.

Method of regulation of the duration of repeated rectangular electric signal and devices for the practical application of the same method

Abstract: Method and apparatus are disclosed for varying the width of a rectangular pulse which controls the opening of an electromagnetic fuel injector, in accordance with engine speed. Reference pulses of short duration are generated in synchronism with engine rotation and these pulses are utilized to generate injection pulses, and control pulses. The termination of the control pulse, which is of predetermined width, is utilized to generate a linearly increasing reference voltage which reaches a predetermined voltage level, depending on the spacing between the preceding reference pulse and the following reference pulse. The voltage level reached by the reference voltage is utilized to cut off the injection pulse. The width of the injection pulse, and in consequence the quantity of fuel injected, is thus directly controlled by engine speed, i.e., by the spacing of the reference pulses.

Impulse Duration and Temporary Threshold Shift

Abstract: Subjects were exposed, on different test days, to 166‐dB (peak normal‐incidence) impulses 34, 58, 72, or 96 μsec in duration spaced 1 sec apart. For each pulse duration, the subjects were first exposed to one pulse, then the number of pulses was doubled on successive days until the temporary threshold shift (TTS) following exposure exceeded 30 dB. Intercorrelations of numbers of impulses required to reach criterion TTS at each duration were obtained; they were highest when durations were similar. At the largest pulse duration, a median of only four impulses was required to achieve criterion, some individuals exceeded criterion at one impulse, while others required hundreds. No evidence was seen of a 4‐kHz notch; maximum shift was at high frequencies (10–15 kHz) and relatively independent of impulse duration. There is reason to believe that if one exceeds allowable TTS in the speech‐range frequencies with this kind of impulse noise, there is a chance of producing permanent high‐frequency loss.

Pulse resolution system

Abstract: Apparatus in an earth bore logging system for restoring two or more closely occuring pulses which have become distorted through transmission from subsurface equipment to the surface to the extent that such pulses tend to merge into a single pulse of longer duration. Each pulse from the subsurface signal source is extended in duration to a predetermined pulse width when widely separated from adjacent pulses, and is extended to a greater extent when a successive pulse occurs during the predetermined pulse width period. The pulses are then transmitted to the surface where such extended pulses are amplitude normalized. Each normalized received pulse at the surface is used to generate a pulse having a duration proportional to the duration at which the amplitude of the normalized pulse exceeds a given level. Each of the trigger pulses in turn results in the production of a reference pulse terminating after termination of a trigger pulse of normal duration, representative of a single pulse before transmission. A first output pulse is generated in response to one of the trigger and reference pulses and a second output pulse is generated only upon time coincidence of the trigger pulse and termination of the reference pulse. The widths of the reference pulses may be automatically adjusted according to variations in the average widths of the trigger pulses.

Square and Sine Wave Modulation of the Beam from a 3 MV Van de Graaff Accelerator

Abstract: Methods of producing square and sine wave beam modulation of a 3 MV Van de Graaff accelerator are described. Square pulses are produced at frequencies from 100 kc to zero with up to a 100% duty cycle and a minimum pulse length of 8 μsec. The ratio of the off‐current level to the on‐current level is less than 5×10−4 and can be further reduced by a post‐acceleration deflection system to less than 10−5. The unit, which is triggered from a command pulse external to the machine, is in the top terminal of the Van de Graaff and has shown itself to be highly reliable over some 1000 h of machine operation. The sine wave modulation unit described here operates in the range 80–1000 cps with a modulation depth of up to 90% and higher harmonic contamination of less than 1%.

A versatile high-voltage pulse generator

Abstract: Generators of high-voltage pulses of sub-microsecond duration are most conveniently based upon the discharge of a coaxial cable through a spark-in-air switch. Several advantages result from the decision to charge up the outer, rather than the inner, conductor. Insulation problems are reduced as are also constructional and operational details. The most important advantage, however, lies in the ability to vary the pulse length. Rise-times of a few nanoseconds are easily obtained with the proposed generator.

Electronic protection apparatus

Abstract: 1,106,805. Protective arrangements. STARKSTROM-ANLAGENBAU ERFURT. 10 Sept., 1965, No. 38716/65. Heading H2K. An overcurrent protective arrangement for an A.C. circuit has a Schmitt trigger 8 which shapes the input current into pulses each having a duration dependent on the magnitude of the input current. These pulses are applied to a monostable circuit 12 and a negator 9, both connected to an OR element 15. When the pulse duration is sufficiently long, the monostable circuit 12 changes to its unstable stable and this circuit 12 and the negator 9 both apply an O signal to the element 15, so that a further negator 16 connected to the OR element 15 provides a 1 signal on each pulse. The frequency of these pulses is reduced by a frequency divider and the resulting pulses are applied to counting stages so that after a predetermined number of pulses a tripping circuit is energized, Fig. 2 (not shown). The negator 16 may also control an indicator 19 through a bi-stable circuit 17 and amplifier 18. A further monostable circuit (as 12) and a further OR element (as 15) may be associated with the negator 9 for response to a longer pulse duration and to control the tripping circuit without the delay of the counting stages.

Volume Reverberation as a Function of Single Frequency Pulse Lengths and FM Sweep Rates

Abstract: Volume‐reverberation tests were conducted with a vertically directional transducer at a frequency of 15.4 kHz. For each of two source levels, the system was capable of transmitting single frequency (SF) pulses of 10‐, 50‐, 100‐, 300‐, and 1000‐msec duration and 1000‐msec frequency‐modulated (FM) pulses swept 100, 200, and 400 cycles. The relationship between volume reverberation level and pulse length is investigated. The data show a less than linear dependence of volume reverberation on pulse length and a linear dependence on source level. Reverberation levels for FM and SF pulses of 1000‐msec duration are discussed. Although the amplitudes of the deviations from the mean reverberation are lower in the FM mode than the SF mode, no significant difference in mean levels is observed.