Showing papers on "Detector published in 1978"

Detection of Optical and Infrared Radiation

Abstract: 1. Thermal Radiation and Electromagnetic Modes.- 2. The Ideal Photon Detector.- 3. Coherent or Heterodyne Detection.- 4. Amplifier Noise and Its Effect on Detector Performance.- 5. Vacuum Photodetectors.- 6. Noise and Efficiency of Semiconductor Devices.- 7. Thermal Detection.- 8. Laser Preamplification.- 9. The Effects of Atmospheric Turbulence.- 10. Detection Statistics.- 11. Selected Applications.- References.

On perceptual analyzers underlying visual texture discrimination: Part II

Abstract: In Part I Caelli and Julesz generated texture pairs of 4-disk micropatterns with identical dipole statistics. They found that this iso-dipole constraint could not prevent the quasi-collinearity of certain disk elements which, in turn, yielded effortless discrimination. They proposed two classes of perceptual analyzers to explain discrimination with these micropatern textures: Class A, corresponding to those which detect dipole differences; while Class B detectors, such as the quasi-collinear detector (QCD), acted when isodipole textures were presented. In this paper we show several new methods for generating iso-dipole textures with micropatterns consisting of 5 or more disks or non-disk shaped elements, and we report the discovery of two other Class B detectors, a corner detector (using a 6-disk method), and a closure detector (with 8---11 disk micropatterns). These QCD, corner, and closure detectors were verified by examining several hundred iso-dipole texture pairs. It appears that iso-dipole constraints make ineffective all other feature analyzers involved in effortless texture discrimination than the Class B types. These figural properties of collinearity, corners, and closure can be perceived without scrutiny and are precursors of form perception.

Application of the doppler ultrasound bloodflow detector in supraclavicular brachial plexus block

Abstract: A Doppler ultrasound bloodflow detector was used to localize the third division of the subclavian artery, rendering the supraclavicular approach to the brachial plexus safer and highly successful.

Pyroelectric detectors and materials

Abstract: A survey on point pyroelectric detectors and materials is given. The performance of a practical detector is characterized by the ratio of a response function and a noise function. Material parameters relevant to detector applications are identified and the crystal properties of these parameters are then discussed by the use of equations of state. The noise function is so defined that the performance of the practical pyroelectric detector as a circuit element can be directly examined and assessed with respect to the ideal thermal detector. Under special conditions, this noise function gives rise to four separate figures of merit of pyroelectric detectors. Finally the temperature dependence and the performance limitations of pyroelectric detectors are discussed.

Characteristics of integrated MOM junctions at DC and at optical frequencies

Abstract: We present a new metal-oxide-metal device (Ni-NiO-Ni, "Edge MOM") which is stable, reproducibly fabricated, and with a 10-10-cm2tunneling area. Performing detection experiments, the device's nonlinear I-V characteristic is shown to be invariant at audio frequencies, 10.6, 3.39, and 0.6328 μm. Similar devices with 10-8-cm2tunneling areas perform as well as the Edge MOM's in the visible and the near-infrared range, but deteriorate in performance at the 10-μm range. A dominant competing effect is a thermal-induced signal, which increases with frequency and temperature. Coupling mechanisms at the various regimes are investigated. The device can serve as a broad-band detector and mixer, and might in the future be a basic element of broad-band amplifiers and oscillators.

Multiple-phase flowmeter and materials analysis apparatus and method

Abstract: An apparatus and method for elemental analysis and non-invasive measurement of the mass flow rate and/or density distribution of a multiple-phase system The apparatus includes at least two X-ray sources, transmission detectors for the X-ray sources, fluorescence detectors, and collimators all of which are suitably indexed and multiplexed to provide information corresponding to the density distribution, elemental composition, phase composition, and/or flow rate of the system Energy selective detectors are included in the apparatus to provide selective fluorescent radiation detection for fluorescence emitted by elements excited by the X-rays as a technique for obtaining an indication of the elemental composition of the system X-ray sources and transmitted X-ray detectors are used to detect the density of the multiple-phase system at each point in a cross-section of the system Corresponding second X-ray sources and detectors are mounted a moderately short distance from the first X-ray source and detector combination The total mass flow rate and density distribution of the system is the integral over the area of the conduit for a plurality of point mass transfer rates and densities A conventional computer system is included as part of the flowmeter and materials analysis apparatus to correlate and process the readings obtained by the various detectors and obtain thereby the mass flow rate, density and elemental composition of the multiple-phase system

The ORNL 10-meter small angle X-ray scattering camera

Abstract: A new small-angle X-ray scattering camera which utilizes a rotating-anode X-ray source, crystal monochromatization of the incident beam, pinhole collimation, and a two-dimensional position-sensitive proportional counter has been developed. Because the sizes of the X-ray focal spot, the sample and the resolution element of the detector are each approximately 1 × 1 mm, the camera was designed so that the focal spot-to-sample and sample-to-detector distances may each be varied in 0.5 m increments up to 5 m to provide a system resolution in the range 0.5 to 4.0 mrad. A large, general-purpose specimen chamber has been provided into which a wide variety of special-purpose specimen holders can be mounted. The detector has an active area of 200 × 200 mm and has up to 200 × 200 resolution elements. The data are recorded in the memory of a minicomputer by a high-speed interface which uses a microprocessor to map the position of an incident photon into an absolute minicomputer memory address. With this interface, over 105 events s−1 can be recorded. The data recorded in the computer memory can be processed on-line by a variety of programs designed to enhance the user's interaction with the experiment. Among these are routines for background and detector-sensitivity correction, contour and perspective plotting of the two-dimensional data, a variety of averaging schemes for determining circular averages and/or one-dimensional slices of the data, file-management programs to handle the large quantity of data produced by a two-dimensional detector, and an interactive package for communications with a central computing facility via a dedicated hardwired link. At the highest angular resolution (0.4 mrad) the flux incident on the specimen is 1.0 × 106 photons s−1 with the X-ray source operating at 45 kV and 100 mA. The performance of the instrument is demonstrated with several examples, among which are scattering patterns from voids in neutron-irradiated nickel, plastically deformed polyethylene and collagen fibrils. Results from a kinetic study of the crystallization of polyethylene are also reported.

Simultaneous dual-energy computer assisted tomography

Abstract: A dual-energy detector system for use in computer assisted tomography. This system produces two independent sets of information from one scan, namely, high-energy and low-energy data. The system employs two cooperating detectors. The first one responds primarily to low-energy photons, allowing most high-energy photons to pass through. The second detector lies behind the first and detects the remaining photons. Thus, two electrical signals are generated which contain information in two different energy ranges, which signals can be computer-processed. The attenuation coefficients at these two energies are sufficiently different so that differential diagnosis and chemical identification may be aided. The computer-processed signals may be employed to provide any of (a) beam-hardening correction, (b) chemical identification and composition of tissues, such as lesions, bone, etc., (c) localization of injected contrast material, or (d) attenuation coefficients for radiation therapy planning.

Detection in Laplace Noise

Abstract: The discrete time detection of a known constant signal in white stationary Laplace noise is considered. Exact expressions describing the performance of both the Neyman-Pearson optimal detector and the suboptimal linear detector are presented. Also, graphs of the receiver operating characteristics are given. The actual performance of the Neyman-Pearson optimal detector is compared to that predicted by a Gaussian approximation to the distribution of the test statistic.

Infrared focal planes in intrinsic semiconductors

Abstract: In this paper, we review the state-of-the-art of intrinsic semiconductor detector arrays and project future areas of development. Infrared focal planes in intrinsic semiconductors offer advantages over extrinsic semiconductor structures in both operating temperature and quantum efficiency. Although the device function of spectral filtering and detection of the incident photon flux is now well understood in intrinsic semiconductors, the function of signal processing has only recently been investigated. As a result, research is directed toward implementation of both hybrid devices, in which the signal processing is accomplished in a silicon multiplexer which is physically and electrically interfaced with an intrinsic semiconductor detector array, and monolithic charge transfer devices in which detection and signal processing are accomplished in the same semiconductor. In the monolithic approach, charge transfer devices have been demonstrated in InSb, and it is likely that similar devices will be realized in InSb related alloys and HgCdTe in the near future. Demonstration of a non-MIS charge transfer design would open up the monolithic approach to the IV-VI alloys. Hybrid focal planes incorporating ≳ 1000 element photodiode arrays have been realized in the III-V and the IV-VI alloys; the detector-multiplexer interface circuit will remain one of the key technical issues in the achievement of a high-performance hybrid focal plane.

Acoustic microscope and method

Abstract: An acoustic apparatus and method for microscopic imaging and spectroscopy. The apparatus includes a plurality of devices for exciting an object of interest so that acoustic waves are propagated from the object. These devices include lasers, x-ray sources, microwave generators, ultraviolet sources, and electric current generators. The acoustic waves propagated from the object of interest are detected and the object of interest and the acoustic wave detector are moved with respect to each other in a raster scanning pattern. The magnitude of the detected acoustic waves and the corresponding raster pattern of the object are recorded so that a visual image of the object can be obtained. In addition, the frequency of the exciting electromagnetic radiation that excites the object can be varied so that both the absorption spectra and the Raman frequency mode of the object can be determined.

Baseband differentially phase encoded radio signal detector

Abstract: A radio signal is applied to an in phase detector channel and a quadrature phase detector channel. Each detector channel includes, in cascade arrangement; an in phase downconverter means for downconverting the received radio signal to a baseband signal; a sampling means for sampling the baseband signal at a predetermined rate; and a matched filter means matched to the symbol waveform and wherein the sample pulses are stored over a predetermined period of time that corresponds to two data symbols. The sum of the pulses for the first data symbol and the sum of the pulses for the second data symbol are compared to determine if there has been a phase reversal between the two data symbols. The outputs of the in phase and quadrature phase channels are summed, which results in demodulation of the encoded data.

A Computer Assisted Ringdector Positron Camera System for Reconstruction Tomography of the Brain

Abstract: A ring detector positron camera system for brain metabolism studies is being constructed at the Institute of Physics, University of Stockholm, in collaboration with the Departments of Neuroradiology and clinical Neurophysiology, Karolinska Sjukhuset, Stockholm, Sweden. The instrument utilizes 95 NaI(Tl) detectors and will simultaneously record coincidences from 1900 detector combinations. Each detector is coupled in coincidence with forty detectors on the opposite side of the ring. In the conventional stationary mode of operation the experimental system resolution is 10.5 mm. A new sampling technique has been developed to reduce the system resolution. Based on this technique, an experimental system resolution of 7 mm has been obtained.

Pseudo-random-number-code-detection and tracking system

Abstract: A pseudo-random-number code detection and tracking system using a closed loop system wherein a detector having a non-linear response characteristic is responsive to a coded received signal and to a locally generated coded signal to produce an error signal. The error is used to control the characteristics of the local signal so as to cause the signals to become aligned. Means are further provided to dynamically control the non-linear response characteristics of the detector so that the coded received signal and coded local signal remain aligned over a controllable range of error signal levels. Thus, a relatively large range can be used during an acquisition operation and a relatively narrower range during the tracking operation.

The electron stationary picture method for high-speed measurement of reflection intensities from crystals with large unit cells

Abstract: A method for measuring X-ray intensity data from crystals with large unit ceils is presented. The method takes full advantage of the capabilities of the multiwire area detector diffractometer. This diffractometer is a high-speed data collection system utilizing a multiwire proportional chamber that can detect photons from all simultaneously occurring reflections and record the diffraction pattern as a two-dimensional histogram in a computer mass core memory. In the electronic stationary picture method of data collection, reflection intensities are extracted from a sequence of electronic pictures each of which is exposed while the crystal is stationary. Between successive pictures the crystal is rotated about a fixed axis by a small constant angle of approximately 0.05°. Because the integrated intensity of each reflection is extracted from several consecutive pictures, advance prediction of detector coordinates and picture number is required for all reflections and the data-extraction computer program is necessarily complex. Expressions are derived for reflection detector coordinates and setting angles, the system hardware and software are described, the data collection procedure is outlined, and the quality of 7 × 105 reflection intensities measured during six months of operation is analyzed.

Self-scanned photodiode array: high performance operation in high dispersion astronomical spectrophotometry

Abstract: We have developed a multichannel spectrophotometric detector system using a 1024 element self-scanned silicon photodiode array, which is now in routine operation with the high-dispersion coude spectrograph of the University of Texas McDonald Observatory 2.7-m telescope. We discuss operational considerations in the use of such arrays for high precision and low light level spectrophotometry. A detailed description of the system is presented. Performance of the detector as measured in the laboratory and on astronomical program objects is described, and it is shown that these arrays are highly effective detectors for high dispersion astronomical spectroscopy.

Record playback apparatus for optical data records

Abstract: Multi-layered optical data records and playback apparatus are described in which a plurality of optical data layers are provided on at least one side of a record substrate and the playback apparatus scans data tracks on such layers with a light beam to produce an electrical readout signal corresponding to the data in the scanned tracks. The playback apparatus includes selection means for selectively playing back data tracks on different ones of the data layers. The data track may be formed by lines of data spots of binary coded digital information or such spots may be frequency modulated or pulse length modulated analog information which are photographically recorded at extremely high data density so that they may be used to record audio or video signals including television signals. While the optical data records may be light transparent, they are preferably light reflective so that the playback light source and associated focusing and scanning means may be supported on the same side of the record as the light detector to provide a more compact playback apparatus. This also enables at least some of the same optical elements to be used for transmitting the reflected light beam to the detector that are used for transmitting the playback light beam from the light source to the record. Selection of one data track for playback may be accomplished by changing the focus of the light beam from one data layer to another, or by making the data tracks of optically different materials, such as using different color dyes or different photoluminescent materials, and selectively positioning corresponding color filters in front of the light detectors.

Position sensitive light detectors with high linearity

Abstract: The position linearity of position sensitive light detectors (PSD) of various designs was investigated. It was shown that existing detectors suffered from inherent nonlinearities. The maximum distortion was in the range of 35-40 percent within the center 64 percent of the active area. Design and fabrication of a detector with extremely high position linearity was described. By using a double-sided construction and by careful matching of the process parameters a maximum distortion of /spl sime/0.2 percent was attained within 100 percent of the active area. Finally, factors influencing the practically attainable linearity were analyzed.

Expanding the Bandwidth of TEM Cells for EMC Measurements

Abstract: This paper discusses the development of a modified (absorber-loaded) transverse electromagnetic TEM cell with expanded bandwidth for use in accurately characterizing electromagnetic interference (EMI) fields within a shielded environment. The cell is analyzed experimentally, both before and after the modification, to determine its radio-frequency (RF) characteristics, both as an RF transmission line and as an electromagnetic (EM) field simulator or detector. Comparative measurements are given to show the performance of the modified versus the unmodified cell in parameters such as voltage standing-wave ratio (VSWR), insertion loss, test-field uniformity, and reverse-coupling characteristics. The results of these measurements indicate an approximate two-fold increase in the upper useful frequency of the modified cell. An example of using the cell to evaluate the radiated emissions from a common electronic module (microprocessor timing circuit) is given. Finally, the technique of absorber loading is extended to larger cells, specifically a 3- × 3- × 6-m cell.

Real-time harmonic pitch detector

Abstract: A real-time harmonic pitch detection algorithm has been developed on the Lincoln Digital Voice Terminal (LDVT). The algorithm was designed to be fast and to perform well when the input speech is degraded (i.e., telephone quality) or corrupted with acoustically coupled noise. The algorithm determines the fundamental frequency from the spacing between harmonics in a selected portion of the spectrum. The algorithm was incorporated into a real-time linear prediction vocoder and compared favorably in informal listening tests with the Gold-Rabiner time-domain detector under a variety of adverse conditions.

Split-detector computed tomography: a preliminary report.

Abstract: A split-detector system, consisting of a thin CaF2 scintillator followed by a thick Nal crystal, was installed in an EMI Mark I scanner. Energy discrimination is possible because the CaF2 crystal responds primarily to low-energy photons; dual-energy images can be obtained from only one scan. Calculations and preliminary experiments show that the split-detector separates energies better than the 100-140 kVp method. It was possible with the split detector to differentiate between two weak solutions of CaCI2 and KI which had the same computed tomography number (44 H), under normal scanning conditions.

Heart rate measurement system

Abstract: A pulsed IR reflectance plethysmograph for heart rate measurement and display in a digital watch or as a medical instrument using, for example, a pulsed LED light emitting diode for transmitting light pulses and a photodiode for receiving light pulses reflected from a finger. The LED and photodiode are mounted in a small sensor on the watch or medical instrument. The photodiode is connected directly to a signal conditioning circuit which rapidly removes unwanted asynchronous ambient background light signals such as from sunlight, by means of a switched ambient light subtractor circuit which performs the subtraction without requiring amplification or conversion of the detector signal photocurrent to another electrical parameter. The signal current after cancellation of the ambient background signal is sampled in an integrate and hold circuit to provide a heart systolic pressure wave. The synchronous steady state IR pulse carrier envelope signal is cancelled by a perfect second-order feedback loop via an integrating amplifier and a switched transconductance element that operates with fast response, even under conditions of large overloads that occur at the sensor. Pulses of the heart systolic pressure wave are then detected to determine the pulse rate which is displayed. When only the presence of an unmodulated IR light carrier is to be detected, as in an IR light beam detector, an ambient light subtractor in accordance with the invention is provided in an unswitched configuration that removes ambient light with a minimum number of components over an extremely wide dynamic range.

Capacitive intrusion detector circuitry utilizing reference oscillator drift

Abstract: Protected objects are connected together to form an antenna. Preferably, the cabinet for the detector circuitry is also included in the antenna. The antenna is excited by a voltage controlled oscillator (VCO). The capacitive reactance of the antenna changes when an intrusion occurs. This causes the frequency of the VCO signal to undergo an instantaneous change. A phase comparator compares the phase of the VCO signal with the phase of a reference oscillator signal. An instantaneous change in the frequency of the VCO signal due to a change in the capactive reactance of the antenna when an intrusion occurs is reflected by a shift in phase between the VCO signal and the reference oscillator signal. This causes the phase comparator signal to change. A deriving means, preferably including a dual differentiator circuit, which derives the rate of the rate of change of the phase comparator signal, and a differential comparator, which is triggered by the dual differentiator circuit in the event of an intrusion, activates a signaling circuit so as to produce an alarm when an intrusion occurs. Since the antenna is connected to the VCO and there is no bidirectional coupling between the VCO and the reference oscillator, the electronic security apparatus is incapable of defeat by connection of a frequency generator to the antenna, because inherent drift in the reference oscillator eventually produces an alarm. Additional features are also disclosed.

Automatic lighting control system

Abstract: This invention relates to an automatic lighting control system which employs a photosensitive detector in one leg of a bridge circuit for sensing the total effective level of both the natural and artificial illumination within an interior space. The unbalanced output of the bridge is fed into a pair of differential comparators for deriving a digital error signal representative of the level of illumination falling outside an acceptable range. A digital error signal is loaded into an intermediate shift register responsive to a clock signal. If an error signal of the type requiring a change in illumination is present, then a subsequent clock pulse will command a shift register to add or interrupt power to one or more lighting modules which supply artificial illumination to the interior space.