Showing papers on "Rise time published in 1969"

Magnetic field of lightning return stroke

Abstract: The magnetic flux density due to first and to subsequent lightning return strokes is calculated for distances from the strokes of 0.5 to 200 km. The basis of the calculations is various assumed forms for the channel current as a function of time and of channel height. Two new channel-current models are introduced for first strokes and one new model for subsequent strokes, in addition to the use of the models of Bruce and Golde and of Dennis and Pierce. The new models provide a better approximation to the real lightning channel current than do the previous models, but all models considered yield radiation fields far from the channel that are consistent with experiment. It is shown that, contrary to the claims of Norinder and co-workers, the magnetic-field rise time for a stroke within a distance of about 20 km is essentially unrelated to the current rise time in the stroke channel base. For subsequent strokes, field rise times of many tens of microseconds can be due to current rise times shorter than a microsecond. On the other hand, field rise times for subsequent strokes may be strongly influenced by current fall times. The analysis of Norinder and co-workers which relates peak channelbase current to peak magnetic field yields values of current that can be considered accurate to about a factor of 2.

Acoustooptical pulse modulators

Abstract: A theoretical analysis of acoustooptical pulse modulators is given Calculations are carried out that yield the intensity and rise time of the scattered light The optimum relationship between the dimensions of the optical and acoustic beam is given A fast high-efficiency modulator has been built based on the theoretical results The modulator is composed of a 350-MHz ZnO transducer sputtered on a quartz acoustic lens and an As 2 S 3 glass serving as the modulating material With 06 watt of electrical RF peak power driving the modulator, 70 percent of the light intensity (at 063μ) is deflected The rise time of the scattered light pulse is of the order of 6 ns

Design and performance of photo-cell systems for pulsed laser power and energy measurements

Abstract: The optical and electrical problems in the design of a beam-sampling detector for laser power, energy and pulse duration measurements are discussed with a view to achieving an accuracy of 2% relative to a fundamental detector for pulses down to 3 nsec duration. Experiments show that a beam sampler using an ITT F4000 biplanar vacuum cell mounted in a coaxial taper is capable of this accuracy, but that the silicon diodes (EG + G SD100, Mullard BPY13A) trap some of the photoelectric charge and then release it with a time constant of up to a few microseconds giving a pulse length-dependent sensitivity: they can be used for energy measurements, however. The Mullard 90CV vacuum photo-cell holds back about 6% of the photo-electric charge for about 1μsec and can also give erratic currents up to ten times the computed saturation current: effects probably due to residual gas in the cell. The limits set on performance by the rise time and maximum linear current of the various detectors are discussed. The design of a holder for the ITT F4000 photo-cell giving a rise time constant of 0.25 nsec is given.

The effect of finite flux rise time on recording performance

Abstract: An experimental and theoretical investigation has been made of the effect of finite flux rise time on transition length and delay time for thin recording media. This was done by tracing the field history of particles as they pass the write head and by assuming that the remanent magnetization of each particle depends on the maximum field it experienced. For linear rise times and for separation greater than half a gap width, analytic expressions have been derived showing the dependence of transition length and delay time on rise time and the other recording parameters. Numerical solutions valid for separations down to one quarter of a gap width and including exponential rise times are also shown.

Response time of F 4000 biplanar photocell in various holders

Abstract: The problem of designing a holder for use with the ITT F4000 (or FW114) biplanar photocell is discussed together with the intrinsic properties of the photocell The intrinsic photocell rise time combined with that of the simple holder described gives a 10-90% rise time of 280 ps This is virtually as fast as previously published designs for this photocell but also gives over twice the current (up to 4 A into 125 Ω) for the same cathode current, thus increasing the useful dynamic range The response of the photocell in its holder is combined with the response of a Tektronix type 519 cathode-ray oscilloscope to give an overall response and curves of true and observed pulse lengths which can be used to measure pulse lengths and peak powers for pulses down to 300 ps half-width

Holiday detector utilizing staggered capacitor discharges for producing a fast rise time high-voltage pulse

Abstract: An electrical detector operable to detect holidays or defects in insulating coatings or mastic coatings generally applied to pipelines has a portable DC power supply, a DC to DC converter, an energy storing means operable to store energy from the DC converter, and SCR interconnected with the energy storing means, an oscillator means for gating the SCR on to discharge the energy storing means through a double primary pulse transformer to produce a high voltage, fast time pulse on an exploring electrode, and an alarm circuit capable of audibly and/or visually indicating that a high voltage has arced through the pipeline coating at a holiday point.

Accurately switching bistable circuit

Abstract: A bistable circuit including an input steering gate having first and second branches for alternately applying input signals to respective sides of the bistable circuit, and an RC delayed transistor operative to disable one branch of the steering gate for a preselected time interval sufficient to permit complete switching of the circuit in response to slow rise time input pulses.

A complementary driver with a subnanosecond rise time

Abstract: A circuit specifically designed as a complementary driver for a high- speed scaling circuit is described. This circuit incorporates the principle of time-delayed negative feedback by using a passive delay line in the feedback path. The delay line provides optimum positioning of the bias voltage at the base of the nondriven transistor in a current-mode pair.

Rise time optimization of high-speed digital fanout circuits

Abstract: Rise times of digital fanout circuits consisting of current-switched transistor pairs are analyzed. It is shown that minimum rise time can be obtained by a finite number of stages having approximately identical current gains. In the limiting case when the rise time originates solely from the gain-bandwidth product of the transistors, the optimum current gain per stage is e/SUP 1/2/=1.65.

Preliminary Results of the Transient Response of Broadband Antennas.

Abstract: : The transient response of several wideband antennas are presented when excited with a 0.2 volt step having a rise time of approximately 100 picoseconds. In general severe time dispersion is seen and time dispersion ratios of 100 are noted. Antennas considered to be 'frequency independent' suffer severe phase versus frequency distortion. A ground plane antenna test range constructed to investigate wideband antennas is described. This range implies a short pulse generator and is useful in understanding the performance of antennas to extremely wide instantaneous bandwidth signals. (Author)

A quenching circuit of very short rise time for Geiger-M$uuml$ller counters

Abstract: A simple quenching circuit is described which reduces the dead time of Geiger-Muller counters by lowering the anode voltage immediately after the beginning of the discharge. The circuit delivers negative pulses with 300 V amplitude and 28 ns rise time. This extremely short rise time has not so far been achieved with similar circuits.

A direct-coupled hybrid IC amplifier with 1-ns rise time

Abstract: This paper describes the design and operation of a wide-band direct-coupled pulse amplifier, with a voltage gain of 10 and a rise time of 1 ns. Computer-aided analysis and simulation are used to optimize the design and to predict the performance of the amplifier. Good agreement is obtained between the predicted and experimental results. In an attempt to improve the frequency response through the reduction of parasitic capacitive and inductive effects, the amplifier has been fabricated as a hybrid IC by use of thin-film resistors and silicon chip transistors mounted on a ceramic substrate.

Subnanosecond pulse coupling of an He-Ne laser

Abstract: A 0.5ns rise time 2.5kV coaxial krytron pulse generator is described, which, together with an electro-optic modulator, comprises a laser intracavity coupler an order of magnitude faster than any yet reported. Iterative round-trip energy coupling has been demonstrated in accordance with theoretical predictions.

Thermal hysteresis in ferrite memory cores

Abstract: The effects of different writing and reading temperatures on the switching voltage waveform, permeability, and flux state of standard nickel-copper-manganese and copper-manganese ferrite memory cores have been investigated over a temperature range of 0 to 70°C. These temperatures are well below the Curie temperatures of the materials being tested. It has been found that writing at a higher temperature than the read temperature leads to increased low temperature voltage switching thresholds, higher low frequency ( 40 MHz) permeabilities, and flux states almost equal to the equilibrium value for the lower temperature. Read current pulse rise time and duration have been found to have no effect on the increase in threshold with temperature. Externally produced stresses have been used to simulate the effects of temperature changes on the core.

On Stored Energy and Bandwidth in TEM-Mode Microwave Networks

Abstract: From time domain considerations, a method is presented to calculate the energy stored in certain resonant TEM-mode microwave networks. The time average of the stored energy is then used to define an instantaneous signal bandwidth parameter through the definition of a Q or quality factor. It is demonstrated by experiment that the Q factor is inversely proportional to the rise time of the envelope of the step-modulated response of the network at resonance.

Large signal turn-on response of the junction transistors including nonlinear effects

Abstract: The large-signal transient behavior of transistors must be considered as nonlinear phenomena. In this paper, the nonlinearity of the transient behavior of transistors in the active region are considered, and the charge control method is extended to include this nonlinearity. Using a one-dimensional homogeneous-base transistor model, the current variation of small-signal time constants in the charge control concept are analyzed in terms of emitter efficiency, surface recombination, and generated field in the base region. From the results of the small signal analysis, the large-signal time constants have been defined as a function of injection ratio. From the charge control equation founded on the large-signal time constants, the rise time is calculated including the current variations of time constants and voltage variation of junction capacitance. The results of the analysis are also verified by experimental measurements.

Investigations of the transient responses of several semiconductor photocells employed in clinical dosimetry

Abstract: 1. It has been shown that the rise time for both kinds of phototransducers is approximately the same when the signal across the load resistance is equal. Consequently, the choice as a component in a detector for ionizing radiation of a silicon or gallium arsenide transducer is dictated by other factors (temperature stability, sensitivity, etc.). 2. When the light excitation levels are low (for instance, when a combination detector is employed in clinical dosimetry) and the load resistances are in the order of several kilohms, the time constants of the Si and GaAs transducers investigated amounted to between 0.2 and 0.6 µsec. Such a short rise time was entirely satisfactory for making the majority of dosimetry measurements and made it possible (in a number of cases) to simplify the amplifier portion of the dosimetry apparatus. 3. In those cases where higher requirements are imposed on the response speed of detectors (for the adjustment of x-ray apparatus, etc.), a series connection of several semiconductor components of the type mentioned must be employed. 4. In order to reduce errors during the measurement of the average current value for a pulse or for pulsed radiation, it is advisable to include additional capacity in the measuring circuit.