Showing papers by "Varian Associates published in 1977"

Gyromagnetic resonance fourier transform zeugmatography

Abstract: An improved technique is disclosed for forming two- or three-dimensional images of a macroscopic sample by means of gyromagnetic resonance. A train of free induction decay transient resonance signals are induced and detected from a sample in a region to be imaged. A sequence of pulsed magnetic field gradients are applied during the series of free induction decay signals to derive sets of gyromagnetic resonance data as a function of the changing magnetic field gradients. Two- or three-dimensional images are reconstructed from the sets of resonance data by two- or three-dimensional Fourier transformation.

Lens system for acoustical imaging

Abstract: An object surrounded by media of differing acoustical impedances (e.g., an anatomical organ surrounded by other kinds of tissue within the human body) is acoustically imaged by an array of ultrasonic transducers affixed to the outer surface of an ultrasonic lens. In a preferred embodiment, the lens is homocentric, with the common center of curvature of the inner and outer surfaces of the lens being located at a relatively small acoustic aperture in the body so that object points distributed over a relatively large solid angle from the aperture can be imaged with minimum lens aberations. Where the object to be imaged is a human heart, the acoustic aperture is most conveniently located at an intercostal space between adjacent ribs.

Method and system for cardiac computed tomography

Abstract: System and method are set forth enabling reconstruction of images of desired "frozen action" cross-sections of the heart or of other bodily organs or similar objects undergoing cyclic displacements. Utilizing a computed tomography scanning apparatus data is acquired during one or more full rotational cycles and suitably stored. The said data corresponding to various angular projections can then be correlated with the desired portion of the object's cyclical motion by means of a reference signal associated with the motion, such as that derived through an electrocardiogram--where a heart is the object of interest. Data taking can also be limited to only the times when the desired portion of the cyclical motion is occurring. A sequential presentation of a plurality of said frozen action cross-sections provides a motion picture of the moving object.

Thermostatable flow cell for fluorescence measurements

Abstract: This thermostatable flow cell for fluorescence measurements enables rapid thermal equilibration and precise temperature control. For a flow cell volume of less than 20 microliters, a selected temperature in the range up to 20° C. above ambient can be attained within five seconds, and this selected temperature can be maintained stable within 0.1° C. The cell comprises a cylindrical cavity whose walls include a metallic portion for heat conduction and a transparent window portion for light acceptance and fluorescence observation. The metallic portion of the cell is formed from a cell block to which a temperature sensing means is affixed. The window portion is affixed to the cell block by an inert bonding material. A thermoelectric device responsive to the temperature sensing means causing heating or cooling of the cell block as necessary to provide thermal equilibration at the selected temperature.

Silicon nitride film and method of deposition

Abstract: A dense film of silicon nitride is deposited by a plasma discharge in a vapor of azidotrimethylsilane (AZS) (CH 3 ) 3 SiN 3 . AZS is less reactive and easier to handle than the previously used silane SiH 4 . The resulting film is more stable chemically than the silicon nitride produced by other processes. It is useful for protective and anti-reflective coatings, for insulating, and for masking, particularly on semiconductive devices.

Target profile for sputtering apparatus

Abstract: A planar diode sputtering source employs an anode and a generally concave cathode. The interior surfaces of the cathode include an outer portion providing a lip for protecting a surrounding cooling jacket from sputtering, a middle portion configured to optimize the average match between the surface thereof with a surrounding magnetic field for long useful life, and an inner portion. The middle and outer portion are faired together to minimize localized target erosion leading to premature target depletion or failure. The inner portion joins the middle portion with surface tangents meeting at an angle which minimizes local erosion at this juncture.

Rf pick-up coil circuit for a wide tuning range nuclear magnetic resonance probe

Abstract: In a wide tuning range nuclear magnetic resonance spectrometer, the probe structure includes a series resonant pick-up coil circuit disposed in RF magnetic field exchanging relation with the sample under analysis for detecting nuclear magnetic resonance of the sample. A variable capacitor is series resonated with the inductance of the pick-up coil and the capacitor is arranged for tuning the series resonance of the pick-up coil over a wide tuning range, for example, from 6 to 32 megahertz. The low series resonant impedance of the pick-up coil, as of 1.5 to 5 Ω, is matched to the relatively high input impedance, as of 50 ohms, of a low noise RF amplifier by means of a pair of series connected transmission line transformers for transforming the 50 ohm input impedance of the amplifier to the low series resonance impedance of the pick-up coil. The transmission line transformers are formed of two wire lines, one wire being connected in series with the pick-up coil and the other wire being arranged so that a current is induced to flow therein due to the distributed inductance and capacitance of the two wire line. The induced current is added, at the low impedance end of the transformer, to the current flowing in the first wire, whereby a broadband impedance transformer is obtained. Two such transformers are employed in series with the pick-up coil for transforming the low impedance of the coil to the relatively high input impedance of the preamplifier. The transformers are broadband so that the impedance is well matched over the entire tuning range of 6 to 32 megahertz.

Gyrotrons for high power millimeter wave generation

Abstract: The gyrotron is a new type of micrwave tube capable of producing high power output at millimeter wavelengths. Oscillator results have been described in recent Soviet publications This paper describes work in progress at Varian Associates, Inc. to develop an amplifier of the gyroklystron type to deliver 200 kW cw at 28 GHz. Considerable progress has been made with amplifier stability to the point that amplifier gains of up to 40 dB have been measured in a pulsed experimental amplifier. Current effort is concerned with improving efficiency. A pulsed oscillator is also described which produced 248 kW peak power at 28 GHz with 34% efficiency. A cw oscillator is under construction. Areas for future R and D are discussed. These include gyro-TWT amplifiers with increased instantaneous bandwidth (5 to 10%) and operation at harmonics of the cyclotron frequency to reduce the magnetic field requirements.

Analytical13C NMR: Detection, quantitation, and positional analysis of butyrate in butter oil

Abstract: The amount of butyrate contained in a complex mixture of butter oil triglycerides was 10.3 mole % as determined by natural abundance13C Fourier transform pulse nuclear magnetic resonance (NMR) spectroscopy. This NMR technique also demonstrated the primary isomeric positioning (>97%) of the butyrl group without the need for altering or fractionating the fat mixture.

Electron tube with dispenser cathode

Abstract: The performance of microwave tubes at very high frequencies is limited by the ability of their thermionic cathodes to provide high emission current density in combination with long life and low evaporation of active material. An improved tube uses a cathode comprising a porous metal matrix consisting of a compacted mixture of tungsten and iridium particles, impregnated with a molten barium aluminate. Other alkaline earth oxides may be used as additives. The impregnated cathode outgasses easily and has a long life because it is not dependent on thin surface films. Thermionic emission is improved compared to a tungsten matrix, and barium evporation is reduced. The combination of power and frequency obtainable from the microwave tube is thereby significantly increased.

Package for push-pull semiconductor devices

Abstract: A semiconductor package for containing two individual devices such that they may be externally connected in a push-pull relationship. Two transistors, each having an input and output pad are formed on the same dielectric wafer, in a spaced relationship with each other and a ground plane so as to form two separate transmission line paths. The transistors are wired either in a grounded emitter or grounded base configuration. A shunt inductor is formed by a metallized strip or lead bond from the collector of one transistor to the collector of the other transistor. This inductor reduces the influence of the parasitic capacitance in the equivalent output circuit of the transistors. Since the collectors of both transistors are at the same DC level it is not necessary to include a DC blocking capacitor in series with the inductor. This increases the reliability and the reproducibility of the circuit because bonding wires necessary in prior devices to connect the blocking capacitor in series with the output inductance is not necessary. This packaging technique increases the output impedance, decreases the internal losses, and increases the bandwidth when wired as a push-pull circuit.

Compression seal for elastomeric septum

Abstract: A sealing fixture in combination with a cap member provides a fluid-tight compression seal between an elastomeric septum and a tubular body. The septum is disposed transversely on a first end of the sealing fixture, which is of cylindrical configuration with an axial bore. A second end of the sealing fixture fits over the tubular body. The cap member covers the septum by being screwed down over a threaded portion of the outer wall of the sealing fixture. An aperture is provided in the cap member through which an injection device can be inserted to puncture the septum so as to deliver a quantity of fluid to, or to remove a quantity of fluid from, the tubular body via the bore in the sealing fixture. An outer wall portion of the sealing fixture adjacent the first end thereof is tapered inwardly to form a sharp junction with an inner wall portion of the sealing fixture. This inner wall portion adjacent the first end of the sealing fixture is parallel to the axis of the bore. As the cap member is screwed down over the first end of the sealing fixture, the sharp junction cuts into the septum. An edge portion of the septum overhanging the junction is compressed between the cap member and the tapered outer wall portion of the sealing structure, thereby providing a compression seal while leaving the central portion of the septum relatively stress free.

Heterojunction confinement field effect transistor

Abstract: An improved field-effect transistor is provided by forming the conducting channel boundary opposite the gate electrode as a heterojunction. For example a GaAs conducting channel may be bounded by an AlGaAs layer. The conduction electrons can penetrate the boundary very little and are constrained to the channel layer having good transport properties. The output conductance is reduced and the transconductance increased.

Two-flame burner for flame photometric detection

Abstract: A two-flame burner is used in a flame photometric detector for analyzing a sample material. The sample material is introduced via a first conduit structure into a hydrogen-rich first flame, and the combustion products and excess hydrogen from the first flame are passed via a second conduit structure into an oxygen-containing environment. A second flame is maintained at the exit end of the second conduit structure. The first and second conduit structures are composed of material that does not contribute to the coloration of the second flame during operation of the detector. Particular constituents of the sample material are detected by observing the presence of colors in the second flame indicative of the constituents. For example, the presence of sulfur is indicated by a blue coloration, and the presence of phosphorus is indicated by a green coloration. The presence of nitrogen is indicated by a coloration of the second flame resulting from a chemiluminescent molecular recombination of nitric oxide and oxygen atoms to form nitrogen dioxide molecules. The presence of any hydrocarbon can be indicated by a flame coloration resulting from a chemical reaction indicative of elemental carbon.

Field effect transistor having source and gate electrodes on opposite faces of active layer

Abstract: By positioning the source and gate electrodes on the opposite faces of the active layer, these electrodes can be brought closer together and may have their adjacent edges mutually aligned or even overlapping. The series source resistance and channel resistance can be greatly reduced, because of this closer spacing, which can not be attained when the electrodes are coplanar. By also locating the drain electrode on the same side of the active layer as the source, the source-to-drain spacing can be significantly reduced, reducing channel length and improving the high frequency performance of the transistor. Further, because the electrodes are located on both sides of the active layer, it is possible to provide a large area contact on the bottom, or substrate, side of the epitaxial wafer structure which can advantageously be used to provide a low thermal and electrical resistance connection for the source contact, for example. Finally, the fact that one or more of the electrodes can be contacted from the bottom of the wafer makes possible the simple parallel interconnection of electrodes to easily form multiple element power transistors.

Flame ionization detector

Abstract: Dimensionally optimized flame ionization detector for use in chromatography in which positive ions are caused to be collected by applying positive potential to flame tip. It has been discovered that there exists optimum dimensions of the collector electrode and the spacing between collector electrode and flame tip to resist glassing and corrosion without diminishing other operating parameters. The collector electrode inside diameter is in the range of 0.114 inch to 0.3 inch and the flame tip to collector electrode is in range from 1 mm to 3 mm.

Circumferential error signal apparatus for crystal rod pulling

Abstract: The circumference of a crystal rod is monitored and controlled during the rod growing process by providing relative rotation between the growing crystal rod and a melt of the crystal material as the rod is being pulled from the melt according to the Czochralski method, and by using a radiation-sensitive control system for adjusting growth conditions of the rod in response to variations in a radiation signal which is indicative of the circumferential dimension of the rod. An electronic circuit integrates the radiation signal over each complete rotation of the rod, thereby eliminating unnecessary adjustment of the growth conditions in response to diametric variations of the rod which recur regularly in each rotation.

Atomic absorption spectroscopy

Abstract: A method and apparatus for carrying out atomic spectroscopy, and particularly atomic absorption and atomic fluorescence spectroscopy. The method involves passing the emission spectrum of a light source through an atomized sample, changing the relationship between a selected emission line of the emission spectrum and a corresponding absorption line of the atoms of interest and measuring the absorption of that emission line by the sample before and after the aforementioned change in relationship. The change in emission and absorption line relationship can be effected by application of the Zeeman Effect, Stark Effect, or Doppler Effect. The apparatus, in one form, includes an electro-magnet operative to apply a magnetic field to the atomized sample and thereby cause splitting and shifting of the aforementioned absorption line, and the magnet is modulated to effect periodic variation of the spectral line relationship.

Concentrator arrangement for photovoltaic cell

Abstract: A lens or mirror is employed to concentrate sunlight onto a photovoltaic cell. The cell employs a broad conductor around the periphery of its active surface, and narrow higher resistance conductor strips over the inner part of the surface. The cell and mirror are sized, positioned and shaped such that the image of the sun on the cell's surface is non-uniform, with a proportionately higher concentration of light falling near the periphery of the cell adjacent the peripheral conductors. Thus, the generated current is greater at the periphery, so that less energy is lost due to series resistance of the surface conductors, for more efficiency compared to a uniformly illuminated cell. The non-uniformity can conveniently be obtained by utilizing the natural spherical aberrations of a simple spherical mirror or lens. Also the cell can be positioned relatively close to the mirror outside the focal plane, so that the illuminated area on the cell is larger than the focused image of the sun in the focal plane. Thus, for given diameters of cell and mirror, the arrangement is more compact, and much less sensitive to inaccuracies in mirror curvature.

Thermionic electron source with bonded control grid

Abstract: For a grid-controlled electron source to operate at extremely high frequencies, as in planar triodes, the control grid must be situated very close to the emissive cathode. Mechanical and thermal distortions have put minimum limits on grid spacings and hence on the maximum operating frequency of grid-controlled tubes. To overcome these limits the grid structure is formed as a network of web members which are part of a laminated sheet having metal layers bonded to opposite surfaces of an insulating layer. One metal layer is affixed to the emissive surface of a metallic matrix cathode and the other metal layer forms the control grid.

Selective detection of multiple quantum transitions in nuclear magnetic resonance

Abstract: Selected orders of multiple quantum transitions may be detected by preparing a statistical non-equilibrium state of an assembly of gyromagnetic resonators of selected phase with respect to a subsequent mixing pulse. After an evolution period, t 1 , a 90° mixing pulse is applied and the free induction decay is sampled as a function of time, t 2 . The signal functions S i (t 1 , t 2 , φ i ) is developed for systematically varied values of t 1 and specially selected values of φ i . Linear combinations of the signal functions S i yield, after Fourier transformation a two dimensional spectrum of multiple quantum transitions limited by the choice of phase and linear combination. In another embodiment, a magnetic gradient pulse is applied during the evolution period and resulting multiple quantum transitions yield spectral peaks of width dependent upon the order of such transitions. In particular, all spectral peaks may be removed from resulting spectra save only zero order transitions.

Periodic permanent magnet focused TWT

Abstract: A traveling wave tube adapted for periodic magnetic focusing of the electron beam has a thin-walled, non-magnetic cylinder around the slow-wave circuit portion, forming part of the vacuum envelope. A stack of metal rings surrounding the cylinder has alternating non-magnetic rings and magnetic rings, the latter forming the periodic magnet pole pieces. The rings and the thin cylinder are all brazed together to provide a strong structure. Since the cylinder does not have to be self-supporting, it is made thin enough to allow close spacing between the pole pieces and beam, providing strong magnetic field and good focusing. The brazed joints between rings are not vacuum joints, so the probability of leaks is greatly reduced.

Resonant loss for helix traveling wave tubes

Abstract: This paper describes a scheme for suppressing backward wave oscillations (BWO) in high-power, PPM focused helix traveling wave tubes. The scheme consists of lossy, resonant meander lines deposited on each of the helix support rods and located between each helix turn By varying the length of the line, it can be made to resonate at the helix circuit's π-mode frequency. In this way the "resonator" provides loss in the vicinity of the π-mode, thereby inhibiting backward wave interaction. Test results have shown at least a four-fold increase in the BWO start current for a tube employing this resonant loss scheme.

Magnesium doping of AlGaAs

Abstract: Aluminum gallium arsenide is used as a transparent, conducting contact layer on the exposed surface of a gallium arsenide photovoltaic cell Increased conductivity for the high current generated when concentrated solar radiation strikes the cell, is provided by doping the AlGaAs layer with magnesium During the formation of the layer, Mg diffuses into the gallium arsenide to form a p-type layer and a p-n junction

Aspherical solar cell concentrator

Abstract: A light concentrator for use with photovoltaic cells has a novel aspherical shape to provide the desired distribution of energy over the surface of the cell. The cell is usually circular with a current-collecting bus electrode around the circumference of the active surface. To provide for minimum resistive losses due to the current generated in the cell and flowing to the bus, the light may be concentrated in a band just inside the bus with reduced or even zero energy density inside the band. This distribution is obtained by making the ray-deflecting surface of the concentrator as a figure of revolution whose generating line focuses incident rays arriving parallel to the axis of revolution onto a point removed from the axis. Thus, a point source at infinity is "focused" into a circle around the axis instead of the point focus of conventional optics. Solar light is "focused" into an annular ring. Since the concentrated light pattern is larger than the true image formed by conventional optics with the same focal length, for a given size of cell the focal length can be made shorter and hence the accuracy tolerance of the concentrator surface is greatly relaxed, providing a reduction of cost.

Reproducible mounting of prealigned optical assemblies

Abstract: A reproducible mounting for use in conjunction with prealigned optional assemblies. The mounting comprises a base member and a mating member attached thereto by fastening means cooperating with first, second and third noncollinerly disposed mounting holes whereby all six degrees of freedom between the base and the mating member are eliminating.

Helix traveling wave tubes with resonant loss

Abstract: To suppress spurious oscillations in a helix-type traveling wave tube (TWT), frequency-sensitive loading is produced by a lossy resonant circuit attached to a dielectric support and coupled to the fields of the interaction circuit. The lossy circuit is resonant near the band-edge frequency. It may be a section of delay line with reflective terminations. In one embodiment, it is a metallized pattern on a dielectric rod used to support the helix.