Maximum Pulse Width Research Articles

A programmable, multichannel electronic system generating delayed pulses

Electronic emulating events in real-time are needed to test the validity of the simulation and theoretical work in many fields of modern science. The design of a 4-channel, stand alone electronic system generating pulses with programmable amplitude, width, and delay from a common trigger signal is described. The amplitude may be deterministic or random. It is selected with 16-bit resolution. The maximum pulse width is 32 μs. The maximum delay range may be changed from 200 ns (fine delay) to more than 14 m (coarse delay), delay resolution being always equal to 3 ps. Pulses burst with equal selected parameters may be repeated, the maximum repetitions value being equal to 2 14. The system output,which also includes pile-up shapes, can be used in different ways. For example, it can be used in nuclear spectroscopy as an input to a single charge sensitive preamplifier, or to more refined analog shapers. Moreover, it can be used in time spectroscopy as an input to both Common-Start, Multi-Stop and Mono-channel, Multi-Hit time-to-amplitude converters. The system is implemented around the Analog Devices ADSP-21060 Signal Processing Microcomputer. The system is autonomous in the pulse generation phase, while it is under computer control in the phase of system working protocol transfer from the computer to the ADSP-21060. Both PCI and VME transfer protocols are foreseen.

A compact rotating-mirror autocorrelator design for femtosecond and picosecond laser pulses

An interferometric rapid-scanning autocorrelator employing two antiparallel rotating mirrors in a variable arm is optimized for maximum optical path difference as a function of the separation of the two rotating mirrors. A very compact design (mirror separation≈mirror diameter) is possible without a reduction in the maximum pulse width that can be measured.

Improvement of surface properties by modification and alloying with high-power ion beams

Surface treatment and alloying experiments with Al, Fe, and Ti-based metals as well as Si wafers were conducted on the Repetitive High Energy Pulsed Power-I (RHEPP-I) accelerator [0.8 MV, 20 Ω, 80 ns full width at half maximum (FWHM) pulse width, up to 1 Hz repetition rate] at Sandia National Laboratories. Ions are generated by the magnetically confined anode plasma (MAP) gas-breakdown active anode, which can yield a number of different beam species including H, C, N, O, Kr, and Xe, depending upon the injected gas. Enhanced hardness and wear resistance have been produced by treatment of 440C stainless steel, by the mixing of a thin-film Pt coating into Ti-6Al-4V alloy, and of a Si coating into Al 6061-T6 alloy (Al-1.0Mg-0.6Si). Mixing of a thin-film Hf layer into Al 6061-T6 has improved its corrosion resistance by as much as four orders of magnitude in electrochemical testing, compared with untreated and uncoated Al6061. Processing of Si was used to validate simulation codes. When treated with nitrogen ions, melt and full epitaxial growth was observed to depths of 4–6 μm. Experiments are ongoing to further understand the microstructural basis for these surface improvements.

Thermal simulation of energetic transients inmultilevel metallisation systems

Thermal simulation of transients due to high current pulses in multilevel metailisation systems has been performed. Such transients can cause metallisation failure and are of particular concern for field-programmable gate array (FPGA) devices with voltage programmable links (VPLs). To prevent this failure, the maximum pulse width against current density has been determined for a three-level metal system. Comparison with a single-level system is also illustrated.

Theory of Chemical ProcessingUsing Pulsed Precipitators

A theoretical analysis is given, using methods of gaseous electronics and plasma chemistry, of the removal of S02 and nitrogen oxides from flue gases by use of pulsed electrical corona. Calculations indicate that the rate coefficients in a typical flue gas for the electron dissociation of nitrogen, oxygen and water vapour only become appreciable for values of E/N greater than about 80 Td; E is electric field strength and N the gas number density. Chemical calculations using these data indicate that 802 is removed by conversion to sulphuric acid by reactions with OH radicals, and that oxides of nitrogen are removed largely by reduction from N atoms. To attain these high values of E / N, it is necessary to use pulsed voltages of pulse width r-v1 us in order to avoid electrical breakdown. The maximum pulse widths allowable to avoid breakdown is estimated by requiring the total energy input to be less than that which heatsthe gas by 104 K.

High-resolution encoding process for an integrated optical analog-to-digital converter

A technique is described for extending the resolution of an integrated optical multi-interferometer guided-wave analog-to-digital converter. The optical output waveform for each interferometer is symmetrically folded at twice a proper modulus. A small comparator ladder mid-level quantizes each interferometer's detected output to encode the analog signal in a symmetrical number system (SNS) format. By incorporating the SNS encoding, resolution greater than 1 bit per interferometer can be provided. Analog signal levels that can cause possible encoding errors are examined and their impact on the overall amplitude analyzing function is discussed. The maximum laser pulse width and maximum fluctuation in the sampling interval that can be tolerated is also discussed. Results indicate that 11-bit resolution can be provided with three interferometers and 39 comparators.

Limitations on peak pulse power, pulse width, and coding mask misalignment in a fiber-optic code-division multiple-access system

The authors analyze the effects of fiber dispersion and optical nonlinearity on a code-division multiple-access (CDMA) communications system. They assume that each transmitter has a unique phase-encoding mask to scramble the pulses, and that the intended receiver has the complementary phase-decoding mask to unscramble the pulses. The necessary nonlinear pulse propagation equation is derived using a new and systematic approach. The authors then determine the minimum allowable pulse width and the maximum pulse width for the system. They next calculate the maximum optical power, which is limited by the fiber's self-phase modulation. This power is significantly larger than the minimum detectable optical power determined by the noise in the electrical receiver, so that in practice any distortion caused by the fiber's optical nonlinearity can be avoided. From their calculations estimates for all important optical parameters are provided. The deleterious effect of a slight relative misalignment between the encoding and decoding masks is also investigated. >

Lasing of ArF with a microsecond electron beam

ArF(B-X) laser emission has been observed under long pulse electron-beam excitation at relatively low pump rate. ArF lasing only occurred with Ne buffered gas mixtures. Optimum performance of 1.93 J/ℓ at an intrinsic efficiency of 1.35% occurred with an Ar/F2 mixture of 1/0.075% using a Ne buffer to 4.0 amagats. Total energy of 290 mJ in a 2-cm2 beam with a 1.0-μs full width at half maximum pulse width was recorded.

The dependence of direct overwrite characteristics on the magnetization of dc-magnetron-sputtered films (abstract)

The magnetization of rare-earth transition-metal (RE-TM) films has been found to play an important role in single-layer film direct overwrite characteristics. In this study, the magnetization of films was varied by changing the compensation temperature and the Curie temperature, independently. Direct overwrite characteristics which were investigated included the minimum and maximum pulse width to erase and to write a certain size domain, the pulse-width margins for erase, and the erasable size of domain. A decrease in the compensation temperature, which leads to an increase in the magnetization at high temperatures, causes the minimum erasure pulse width to increase and the largest erasable domain size to decrease. However, a decrease in the compensation temperature causes the writing pulse width to decrease. The effects of magnetization on the direct overwrite characteristics were further investigated by applying external magnetic fields up to 580 Oe. The minimum pulse width to erase domains was found to increase with an increase of the applied field, which was in the direction to assist domain nucleation. The maximum erasure pulse width decreases rapidly with an increase of the magnetic field. The disappearance of the erasure margin when the gap between the compensation temperature and the Curie temperature increases results from the fact that the minimum erasure pulse width becomes equal to the minimum writing pulse width. In order to have a wide range of erasable domain sizes, while still maintaining a short writing pulse width, it is shown that film compositions must be adjusted to have both a low compensation temperature and a low Curie temperature.

Limitations of the lead oxide vidicon for dual-energy digital subtraction angiography

Dual-energy digital subtraction angiography (DSA) can be performed, with some modifications, using existing systems designed for conventional DSA work. However, the video camera generally found in such installations, the lead oxide vidicon, places significant limitations on the image quality of dual-energy DSA. If the video camera is operated in a 60 Hz, 266 line progressive scanning mode to maintain a nominal 30 subtraction images/s frame rate, the maximum available X-ray pulse width is limited to 5 ms. The resulting required increase in low-energy kVp reduces the dual-energy signal-to-noise ratio by approximately 40% for cardiac dual-energy DSA imaging. In addition, the performance of the video camera with respect to read-out lag is much more important for dual-energy DSA than conventional single-energy imaging. Measurements show that lag reduces the iodine contrast in dual-energy DSA by up to 20% when a 30 Hz vertical scan mode is used, and by up to 27% when a 60 Hz vertical scan mode is employed. Replacement of the lead oxide vidicon with a CCD camera removes these limitations.

Steroid‐Tipped Leads Versus Porous Platinum Permanent Pacemaker Leads: A Controlled Study

There is little data directly comparing steroid-tipped permanent pacemaker leads to otherwise state-of-the-art porous platinum leads. Eighteen patients receiving unipolar generators capable of low voltage outputs were randomized at the time of implant to receive either steroid-tipped leads or porous platinum leads. All leads were unipolar, tined, passive fixation, and placed in the right ventricular apex or atrial appendage. This study is single center. At implant, threshold pulse width was determined at 3 voltages (2.5, 1.5, and 0.8 V). Follow-up thresholds were determined at weeks 1, 2, 3, and 4, and at 3 and 6 months. There was no difference in implant thresholds or amplitudes for sensing. By 2 weeks postimplant, lower thresholds were noted for the steroid leads, and this discrepancy grew more significant with time. There was no significant postimplant rise in threshold for steroid-tipped leads. At 6 months, the average threshold pulse width for ventricular steroid leads at 0.8 V was 0.3 +/- 0.1 msec. In contrast, five patients with standard leads did not capture at maximum pulse width at 0.8 V (P less than 0.0001). There was no significant difference in the amplitude of the chronic atrial electrogram. This study shows steroid-tipped leads to offer a significant advantage in reducing thresholds early postimplant and chronically.

Formation of InxGa1−xAs/GaAs heteroepitaxial layers using a pulsed laser driven rapid melt-solidification process

Heteroepitaxial InxGa1−xAs/GaAs structures have been formed for the first time by pulsed laser induced mixing of molecular beam epitaxy deposited In films (∼200 Å) on GaAs (100) substrates. The process occurs by a melt-induced, rapid-mixing and solidification process driven by a XeCl pulsed excimer laser. The laser has a 27 ns full width at half maximum pulse width at 308 nm with its energy density of 0.28–0.61 J cm−2 homogenized into a 4×4 mm square area which is stepped across the wafer. InxGa1−xAs layers with x values, as determined by both x-ray diffraction and Rutherford backscattering spectrometry simulation ranging from x=0.21–0.26 and thicknesses of 77–94 nm, have been formed. The formation of single-crystal layers has been verified by 4He ion channeling and cross-section transmission electron microscopy.

Catheter‐Mediated Electrical Ablation: The Relation Between Current and Pulse Width on Voltage Breakdown and Shock‐wave Generation

Barotrauma from arc induced shock waves may result in dangerous sequelae during ablation of arrhythmogenic foci. In this report, maximum pulse amplitude and pulse width determinations were made to assess avoidance of shock-wave generation using rectangular constant current pulses. Energy delivery appears to be optimal between 80-100 microseconds. If higher energies are required, multiple pulses will be needed to avoid barotrauma.

Efficient flashlamp-pumped IBr laser

The operating characteristics and scaling parameters of a flashlamp-pumped, 4-m-long IBr laser were investigated to further evaluate its potential as a solar-pumped laser. A peak power of 3 kW/cm2 at 2.7 μm was achieved at 4-Torr IBr pressure. A gain of 0.07 m−1 was measured at a maximum capacitor discharge energy of 4 kJ. The threshold input power necessary for lasing was found to decrease by a factor of 4 and the laser pulse width increased fourfold as the active gain length was increased from 1 to 4 m. A maximum pulse width of 120 μs was achieved with 10-Torr argon diluent added to 4-Torr IBr. Quenching of the excited state by the parent molecule was shown to be unimportant for pressures less than 4-Torr IBr. An intrinsic efficiency in the range of 12% has been measured for flashlamp-pumped IBr.

Slip deformation and melt threshold in laser-pulse-irradiated Al

We have examined pulse laser-irradiated 〈110〉 Al single crystals near the threshold energy for melting by ion channeling and electron microscopy. We find that slip deformation occurs at incident energies <3.5 J/cm2, where melting does not occur for our 20 nsec (full width at half maximum) pulse width, as well as at energies ≳3.5J/cm2, where a near-surface layer is melted. This slip deformation results in an increase in the channeling minimum yield χmin, which is attributed to small-angle misalignments between slip planes across the surface. The abrupt increase in χmin with melting suggests that channeling can provide a sensitive monitor of the threshold for melting.

Kink and displacement instabilities in imploding wire arrays

Cylindrical arrays of parallel wires can be imploded by the magnetic forces generated by currents through the wires to form hot, dense Z-pinch plasmas. Analytic growth rates of displacements and deformations of wires in imploding wire arrays are calculated. Arrays of six or more wires are reasonably stable against asymmetric displacements. The growth rate of the kink instability on a single wire of linear mass density μ, radius a, and carrying current I peaks at λmax = 0.7I/μ1/2ca at a kink wavelength of about 4a. The most unstable kink modes of n-wire arrays are the symmetric (l = 0) radial modes and antisymmetric (l = n/2) tangential modes. The effect of a center wire is to tend to destabilize radial kink modes and stabilize tangential modes. In the experimental parameter range of the largest current generators, the number of kink growth times before collision is insensitive to values of maximum current and current pulse width. In general, the kink instability will grow nonlinearly if the initial array radius is more than a few plasma wire radii. In the limit of long wavelengths, the kink instability is shown to be equivalent to the displacement instability.

Measurement techniques for assessing the influence of electromagnetic fields on implanted pacemakers.

A method is described for assessing quantitatively the influence of electromagnetic fields on the function of implanted cardiac pacemakers. This influence may occur either indirectly by the action as an antenna of the catheter, or directly by induction into the pacemaker's electronic circuit. The technique comprises: measurement of the influence of electric voltages of various frequencies applied directly across the generator's output connections; determination of the aerial factor of the catheter configuration; combination of the data acquired to a diagram of overall sensitivity of the combination, in which a 10% variation of maximum output pulse amplitude, pulse width, or repetition rate of the pacemaker, whichever occurs first, has been chosen as a limit; comparison of this sensitivity/frequency curve with the electromagnetic field strength produced by several commonly used apparatus; and measurement of the direct influence of fields on the pacemaker itself. It is concluded, that disturbance of pacemaker action may occur in the vicinity of apparatus designed to produce electromagnetic fields, such as broadcast transmitters, diathermy applicators, and radar sets. Normal household appliances appear to be safe in the respect investigated.

Temperature-insensitive integrable multivibrator

A new technique for integrable multivibrators is presented. Sensitivities to supply voltages and temperature variations are very slight. Pulsewidths are primarily determined from passive components. This circuit has high speed and duty cycle very close to 100 percent. A minimum pulsewidth of 100 ns is possible at a power consumption of 4 mW. Rise and fall times are 35 ns independent of pulsewidth. The maximum pulsewidth is limited by the timing capacitors required. IN addition, the resulting circuits can be integrated in monolithic form.

Moderator Studies for a Repetitively Pulsed Test Facility (RPTF)

Pulsed reactors are being investigated for the purpose of producing high-intensity pulsed-neutron beams for research. Leakage-emission-time-distribution measurements as a function of neutron energy have been carried out using the Resselaer Polytechnic Institute (RPI) electron linear accelerator in conjunction with a disk chopper and neutron diffraction spectrometer. Data were obtained simultaneously with the chopper and crystal spectrometer by looking at opposite sides of the moderator. This experiment was designed to investigate the importance of different variables in determining the pulse characteristics of moderators. The eventual objective is to optimize the maximum thermal-neutron intensity and minimum pulse width from pulsed-fission-neutron sources. Neutron time and energy distributions were measured for light water, polyethylene, Lucite (a metacrylate plastic), powdered zirconium hydride, and ammonia. The water, polyethylene, and zirconium-hydride samples were measured at room temperature and all the materials except water were also measured at liquid-nitrogen temperature. The effects on pulse characteristics of homogeneously poisoning light water samples were studied, as well as the effects of heterogeneously poisoning polyethylene. The effect of varying the thickness of the moderator was also investigated. Pulse widths at half-maximum of 11 µ sec at 0.05096 eV and 24 µ sec at 0.01274 eV were observed for solid ammonia and heterogeneously poisoned polyethylene samples. For neutron energies between 0.08 and 0.01274 eV, solid ammonia gave the best observed figure of merit, peak intensity/(FWHM)2. The data show that neutron pulse characteristics from a moderator can be altered significantly by varying the material and its temperature, as well as by adding poison and optimizing the geometry. Time distributions were observed in the energy region of 0.012 to 0.63 eV. The time resolution, in this energy region, for the diffraction spectrometer ranged from 2.8 to 10.8 µ sec compared with 7.6 µ sec for the chopper.

Tunnel Diode-Transistor Binary Scaler

This paper describes a new type of tunnel diode-transistor binary scaler which is very simple in concept and in design. It is capable of operating reliably at input pulse repetition rates in excess of 200 MHz. A significant feature of the scaler is that there is no maximum input pulse width restriction. Input and output circuits which allow the scaler to operate over a wide range of input driving conditions and to be cascaded directly with similar scalers are also presented.