Showing papers on "Detector published in 1991"

Near-optimum detection in synchronous code-division multiple-access systems

Abstract: Communication networks using code division multiple access (CDMA) include applications where several packets of information are transmitted synchronously and simultaneously over a common channel. Consideration is given to the problem of simultaneously demodulating every packet from such a transmission. A nonlinear detection scheme based on a linear complexity multistage multiple-access interference rejection algorithm is studied. A class of linear detectors is considered as constituting the first stage for the multistage detector. A bit-error probability comparison of the linear and multistage detectors is undertaken. It is shown that the multistage detectors are capable of achieving considerable improvements over the linear detectors, particularly in near-far situations, i.e., in the demodulation of weak signals in the presence of strong interfering signals. This problem has been of primary concern for currently operational CDMA systems. >

The DELPHI detector at LEP.

Abstract: DELPHI is a 4π detector with emphasis on particle identification, three-dimensional information, high granularity and precise vertex determination. The design criteria, the construction of the detector and the performance during the first year of operation at the large electron positron collider (LEP) at CERN are described.

Choice of filters for the detection of gravitational waves from coalescing binaries.

Abstract: Coalescing binaries are one of the most promising candidates for the detection of gravitational waves with the advent of the new generation of laser interferometric gravitational-wave detectors. Signals from coalescing binaries will most probably not stand above the broadband noise of the detector. Their detection is possible by the use of special data analysis techniques such as matched filtering which takes advantage of the fact that the wave form can be fairly well predicted. The wave form of the coalescing binary signal is known very accurately. However, the parameters of the signal are not known priori and the signal needs to be correlated with several filters which are copies of the coalescing binary wave form for different values of the parameters. In this paper we present an algorithm to choose a lattice set of filters by a criterion that every signal of a certain minimal strength is picked up by at least one filter of the set. The wave form is characterized by three parameters: the time of arrival, the mass parameter, and the phase of the signal. We show that it is enough to have just two filters corresponding to the phase of the signal. Determination of the lattice for various values of the mass parameter involves a knowledge of the cross correlation function of two chirp wave forms with different values of the parameters. It is shown that for a considerable range of the mass parameter, the peak value of the correlation function, in a certain approximation, does not depend on the absolute values of the parameters but only on their difference. This leads to a very convenient way of constructing most of the lattice. The maximum possible distance up to which we can see is restricted by the threshold of the detector. There is a further limitation on this distance brought about by the fact that we can use only a finite number of filters. The number of filters which one can use depends on the available computing power. Hence, there is an empirical relation between computing power and the distance up to which we can see. In a restricted sense, the computing power decides the number of detectable events. Numerical experiments indicate that parallel processing is a promising new approach to on-line data analysis.

The SRI IDES statistical anomaly detector

Abstract: SRI International's real-time intrusion-detection expert system (IDES) contains a statistical subsystem that observes behavior on a monitored computer system and adaptively learns what is normal for individual users and groups of users. The statistical subsystem also monitors observed behavior and identifies behavior as a potential intrusion (or misuse by authorized users) if it deviates significantly from expected behavior. The multivariate methods used to profile normal behavior and identify deviations from expected behavior are explained in detail. The statistical test for abnormality contains a number of parameters that must be initialized and the substantive issues relating to setting those parameter values are discussed. >

Method and device for measuring concentration levels of blood constituents non-invasively

Abstract: A non-invasive device and method for monitoring concentration levels of blood and tissue constituents within a living subject such as a human or animal utilizes a polychromatic light source that emits light over a broad spectrum of wavelengths in the near infrared range. The light is passed through, or reflected from, a part of the subject such as a finger, ear lobe or other part of the body. That light is then separated into its various components by means of a grating or prism, and the near infrared band is focussed onto a linear array detector. A microprocessor uses the output of the array detector to measure the light transmitted (T), calculate the absorbance (log 1/T) and calculate the second derivative of the absorbance. A calibration equation is used for each constituent to be monitored to convert the second derivative measurements to a concentration level for that constituent. The device is programmed to take measurements between heart beats and to adjust for the temperature of the sample being taken. The device can be used to determine levels of various blood and tissue constituents, including glucose, cholesterol, alcohol, blood gases and various ions. The device is simple to use, painless and does not cause any physical discomfort, skin irritation or present any risk of infection to the user. The device can be used for clinical use or for home use and the memory of the microprocessor can be used to assist with record keeping and with dosage calculations. Previous non-invasive devices are not sufficiently accurate or convenient to use to replace the invasive testing systems presently used.

Infrared focal plane array technology

Abstract: Requirements for infrared focal plane arrays (IRFPAs) for advanced infrared imaging systems are discussed, and an overview is given of different IRFPA architectures. Important IR detector structures, including photoconductive, photovoltaic, metal-insulator-semiconductor (MIS), and Schottky barrier, are reviewed. Infrared detector materials and related crystal-growth techniques are discussed, emphasizing applicability to IRFPA designs and performance. Three types of input circuit used to couple the detector to the readout circuitry are discussed, namely, direct injection, buffered direct injection, and gate modulation. An overview is given of several readout techniques, including the CCD, MOSFET switch, CID, and CIM. Also discussed are related onchip signal processing topics as well as questions regarding producibility and array implementation. >

Surgical implement detector utilizing a resonant marker

Abstract: Apparatus for detecting a surgical implement (20) in human or animal tissue comprises a detector (8) responsive to the presence, within an interrogation zone (10), of a surgical implement (20) to which a marker (18) is secured. The marker (18) is adapted to produce identifying signal characteristics within a frequency band generated in the interrogation zone (10). Variations in the phase and/or direction of the interrogating field and changes in the electromagnetic coupling between markers (18) and receiver (25) optimize coupling therebetween.

Stereoscopic X-ray fluoroscopy system using radiofrequency fields

Abstract: During an X-ray procedure, the position and orientation of an invasive device, such as a catheter are measured with radio frequency fields and displayed stereoscopically. Instantaneous three-dimensional positions of the invasive device are displayed by superposition of a graphic symbol on static X-ray images obtained at two different view angles. The X-ray images are obtained only when deemed necessary by the operator to minimize X-ray dose. A single X-ray source and detector may be implemented since it is not necessary to obtain the X-ray images simultaneously.

Trap Detectors and their Properties

Abstract: The paper describes a new solid state detector which fulfils all the requirements of the ideal detector for optical radiation measurements. This trap detector is shown to be spatially uniform, linear, stable and to have a predictable relative spectral response so that it can be used to realize a relative spectral response scale with an uncertainty of less than 0,05%. The detector is also shown to be capable of disseminating an absolute spectral responsivity scale with an uncertainty of less than 0,02% at specific laser wavelengths and, independently, of realizing such a scale with an uncertainty of better than 0,05%.

Least sum of squared errors (LSSE) channel estimation

Abstract: A least sum of squared errors (LSSE) channel estimation algorithm is presented for estimating a channel impulse response from a known training sequence. Optimum training sequences are found and tabulated for different channel responses and training sequence lengths. The effect of channel estimation errors on the performance of some data detectors is also investigated. A simple approximation for the expected degradation in performance with channel estimation errors is derived.

Experimental study of migration depth for the photons measured at sample surface

Abstract: Optical imaging of in vivo tissue and noninvasive optical assessment of deep tissue requires knowledge concerning photon migration paths in the medium. We used intralipid emulsion as a phantom medium to study the distribution of the migration paths. An incident and receiving optical fibers were placed on the medium surface. Light at 760 nm was used. An absorber was placed in the medium at different locations to intersect different photon paths. The study shows that the incident photons migrate to the detector through the paths distributed in a region shaped a 'banana', with its two end connecting the source and detector and it mid portion reaching deepest. This region has a core connecting the source and detector through which the photons have maximum probability to take. The path distribution in depth across the mid portion of the 'banana' and through the core can be described by a random walk model, with its maximum probability at a certain depth below the surface. In this study, this maximum probability depth ranged from 3 millimeters to about 7 or 8 millimeters. The path distribution across the mid portion of the 'banana' horizontally and through the core can be described by a normal probability function. These distributions are affected by the optical properties of the medium and the source-detector separation. This study indicated the capability of using surface optical measurement to image the optical property distribution of in vivo tissue and to assess deep tissue optical properties.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Surgical implement detector utilizing a powered marker

Abstract: An apparatus for detecting a surgical implement (16) in human or animal tissue has means for defining a transmitting zone (14) encompassing a surgical wound (12) in the tissue. A battery powered marker (20) is secured to a surgical implement (16) positioned within the wound (12). Field generating means (27) are provided for generating within the transmitting zone (14) an electromagnetic field having a predetermined frequency band. A signal generating (22) means generates a signal having a predetermined frequency band. The signal generating (22) means is operative to cause the field generating (27) means to generate the electromagnetic field, providing the marker (20) with signal identity. A detecting means (30) having an antenna (32) located within the transmitting zone (14) of the marker (20) detects the marker (20) signal irrespective of the marker's orientation therewithin.

Spread spectrum receiver

Abstract: A spread spectrum receiver has first and second correlators which each compare a received signal with a respective reference signal. The output of each correlator is routed through a respective band pass filter and a respective AGC amplifier to a respective detector circuit which converts the output of the amplifier into a respective base band signal. The ouput of each detector circuit is supplied to a respective peak value detecting and holding section, which detects and holds for a predetermined time period peak values from the associated detector circuit. Each peak value detecting and holding circuit supplies the peak value currently held therein through a respective low pass filter which serves as an integrator to a data comparing section and to an adding section. The adding section adds the two peak values, and supplies the sum to control inputs of each of the AGC amplifiers for purposes of gain control. The data comparing circuit compares the peak values and produces an output which is demodulated data from the received signal.

The point‐spread function of a confocal microscope: its measurement and use in deconvolution of 3‐D data

Abstract: SUMMARY We have measured the point-spread function (PSF) for an MRC-500 confocal scanning laser microscope using subresolution fluorescent beads. PSFs were measured for two lenses of high numerical aperture—the Zeiss plan-neofluar 63 × water immersion and Leitz plan-apo 63 × oil immersion—at three different sizes of the confocal detector aperture. The measured PSFs are fairly symmetrical, both radially and axially. In particular there is considerably less axial asymmetry than has been demonstrated in measurements of conventional (non-confocal) PSFs. Measurements of the peak width at half-maximum peak height for the minimum detector aperture gave approximately 0·23 and 0·8 μm for the radial and axial resolution respectively (4·6 and 15·9 in dimensionless optical units). This increased to 0·38 and 1·5 μm (7·5 and 29·8 in dimensionless units) for the largest detector aperture examined. The resulting optical transfer functions (OTFs) were used in an iterative, constrained deconvolution procedure to process three-dimensional confocal data sets from a biological specimen—pea root cells labelled in situ with a fluorescent probe to ribosomal genes. The deconvolution significantly improved the clarity and contrast of the data. Furthermore, the loss in resolution produced by increasing the size of the detector aperture could be restored by the deconvolution procedure. Therefore for many biological specimens which are only weakly fluorescent it may be preferable to open the detector aperture to increase the strength of the detected signal, and thus the signal-to-noise ratio, and then to restore the resolution by deconvolution.

X-ray backscatter detection system

Abstract: A pencil beam of X-rays (11) is scanned over the surface of the body (12) of a person being examined. X-rays (16) that are scattered or reflected from the subject's body (12) are detected by a detector. The signal produced by this scattered X-ray detector (17) is then used to modulate an image display device (36) to produce an image (25) of the subject and any concealed objects carried by the subject. The detector assembly (17) is constructed in a configuration to automatically and uniformly enhance the image edges of low atomic number (low Z) concealed objects to facilitate their detection. A storage means is provided by which previously acqired images can be compared with the present image for analyzing variances in and similarities with the present image, and provides means for creating a generic representation of the body being examined while suppressing anatomical features of the subject to minimize invasion of the subject's privacy.

Television viewer monitoring system including portable data meter for each viewer

Abstract: In a system for monitoring and collecting data on the viewing habits of television viewers or radio listeners, to enable operators of networks or television stations, programmers and advertisers to determine the numbers of viewers watching particular programs, a portable personal data collection device comprises a detector for providing a station identifier identifying the particular broadcast signal being received by the receiver, a clock for providing a signal representing time, a memory for storing data, a cellular telephone module for communicating with a central location, a control for the cellular telephone module, and a microprocessor. The microprocessor stores in the memory data comprising the station identification, and the time at the beginning and end of receiving signals from that station. The control is arranged to control operation of the cellular telephone module to transmit the stored data to the central location. The control may respond firstly to a time signal representing a preselected time for operating the cellular telephone module to call the central location and secondly to communication being established with the central location before transmitting the data. Additionally, or alternatively, the control may respond to a call initiated from the central location to transmit the data. The data collection device may include a detector for detecting a channel selection signal from a television remote control to change the station identifier stored in memory. Manual inputs, for example pushbuttons, may be provided for confirming that the user is actually in attendance.

Optical position and orientation sensor

Abstract: An optical position determination system is described which determines the six degrees of freedom (i.e. position of orientation) of an object with respect to a two-dimensional position sensing detector. The system comprises at least three energy beams physically connected to the object and directed to corresponding points of incidence on a surface of the position sensing detector. The energy beams are selectively energized to enable the position sensing detector to provide outputs indicative of the positions of the points of incidence. A microcomputer is responsive to those outputs to calculate the position of their common point of intersection. A single position sensing detector is thereby able to provide complete, three-dimensional information on the position of the object.

Near‐unity quantum efficiency of AlGaAs/GaAs quantum well infrared detectors using a waveguide with a doubly periodic grating coupler

Abstract: Quantum well infrared detectors based on a waveguide with a doubly periodic grating coupler are shown to provide quantum efficiencies of nearly unity with respect to unpolarized polarization. This is a factor of six larger than for a conventional 45° polished edge detector with the same quantum well characteristics. As a further advantage the detector response becomes nearly insensitive to the polarization direction of the incident radiation. Detectors have been fabricated and tested. Measurements lead to a maximum quantum efficiency of 92% with respect to unpolarized radiation, with a response linewidth =0.8 μm, thus confirming theory.

Optical glucose sensor apparatus and method

Abstract: An optically based apparatus for non-invasively determining the concentration of optically active substances in a specimen comprises, a source of a beam of spatially coherent light (10) which is acted upon to produce a rotating linear polarized vector therein. A beam splitter (24) splits the beam into a reference beam (26) and a detector beam (30) for passage through the specimen. The detector beam (30) is received upon exiting the specimen and compared with the reference beam (26) to determine the amount of phase shift produced by passage through the specimen. This amount of phase shift is converted into concentration of the optically active substance in the specimen.

Spatial light modulator scanning system

Abstract: A system for scanning objects is disclosed. The system consists of a light source, a spatial light modulator, and appropriate optics for directing the light from the source to the spatial light modulator and to the object to be scanned. Individual elements upon the modulator are activated to reflect those pixels' width of the light to the object. A detector is mounted such as to receive reflections from the object to be processed. The system can be hand-held, mounted into a counter, or used in other applications such as edge detector scanners.

Confocal scanning optical microscope using single-mode fiber for signal detection

Abstract: A single-mode fiber is employed as a detector in a confocal scanning optical microscope (CSOM) instead of a pinhole and its optical property is studied. The optical system is always coherent, which is fundamentally different from the CSOM with a finite-sized pinhole. The coherent transfer function and the axial response are calculated. Experimentally, the coherent image is taken and the axial response is also measured.

Linear approximation for measurement errors in phase shifting interferometry

Abstract: This paper shows how measurement errors in phase shifting interferometry (PSI) can be described to a high degree of accuracy in a linear approximation. System error sources considered here are light source instability, imperfect reference phase shifting, mechanical vibrations, nonlinearity of the detector, and quantization of the detector signal. The measurement inaccuracies resulting from these errors are calculated in linear approximation for several formulas commonly used for PSI. The results are presented in tables for easy calculation of the measurement error magnitudes for known system errors. In addition, this paper discusses the measurement error reduction which can be achieved by choosing an appropriate phase calculation formula.

X-ray imaging particularly adapted for low Z materials

Abstract: An imaging device for increasing the ability to recognize, in x-ray produced images, materials of low atomic number A flying spot scanner illuminates an object to be imaged in a raster pattern; the flying spot repeatedly sweeps a line in space, and the object to be imaged is moved so that the illuminating beam intersects the object At least a pair of x-ray detectors are employed, each pair associated with signal processing apparatus and a display The two detectors employed (and the associated electrons and display) are selected from a set of three which includes a transmitted detector located at the line in space which is repeatedly traversed by the pencil beam, a forward scatter detector which is located further from the x-ray beam than the object to respond to photons scattered by the object being illuminated out of the path of the beam, and a back scatter detector which is located closer to the x-ray source than the object being imaged and also arranged to detect photons scattered out of the beam path by the object In another embodiment of the invention all three detectors and their associated electronics/displays are employed

Infrared image sensors

Abstract: Second-generation infrared image sensors are becoming available in a variety of infrared detector materials, including photovoltaic HgCdTe, PtSi, and lnSb and photoconductive extrinsic silicon, PbS, and PbSe We review the background of the evolution of infrared detector materials and summarize the formats and configurations available now in prototype production Capsule data summaries are provided to assist the reader in understanding the operating range of spectral response, temperature, and other performance parameters such as uniformity for each detector material type

A neural network approach to real-time condition monitoring of induction motors

Abstract: A neural network-based incipient fault detector for small and medium-size induction motors is developed. The detector avoids the problems associated with traditional incipient fault detection schemes by employing more readily available information such as rotor speed and stator current. The neural network design is evaluated in real time in the laboratory on a 3/4 hp permanent magnet induction motor. The results of this evaluation indicate that the neural-network-based incipient fault detector provides a satisfactory level of accuracy, greater than 95%, which is suitable for real-world applications. >

Coherent emission from two‐dimensional Josephson junction arrays

Abstract: Coherent emission has been generated by two‐dimensional arrays of SIS Josephson junctions and detected in a junction coupled to the array through a dc‐blocking capacitor. The detector junction exhibits Shapiro steps at frequencies corresponding to the voltage across single array junctions and ranging from 60 to 210 GHz. The maximum power coupled to the detector junction occurs at 150 GHz and is estimated to be 0.9 μW, based on simulations of the detector circuit. Possible mechanisms for coherent emission from two‐dimensional arrays are discussed.

Adaptive nonuniformity correction for IR focal-plane arrays using neural networks

Abstract: With rapid advancements in infrared focal plane array (IRFPA) technology, greater demands are being placed on nonuniformity correction (NUC) techniques to provide near-BLIP performance over a wide dynamic range. Standard NUC techniques involve calibrating each detector using reference temperature sources before imaging the IRFPA. Usually the correction needs to be re-calibrated after a short period of time due to IRFPA drift or to adjust for changes in the level of background flux. Adaptive NUC techniques eliminate the need for calibration by continuously updating the correction coefficients based on radiance levels of the scene being viewed. In this manner, continuous compensation can be applied adaptively for individual detector non-idealities and background changes. Two adaptive NUC techniques are discussed; one is a temporal highpass filter and the other involves a neural network with lateral interconnects to nearest neighbor pixels. Both have similarities to biological retinal processing. Questions of implementation and stability are discussed and performance results are given for several test image sequences which were obtained from an MWIR HgCdTe array and a HIDAD uncooled array. We conclude that adaptive techniques will be very useful in future IRFPA sensors, primarily because of their ability to adapt over a wide range of background flux without calibration sources, but also because they can offer improved sensitivity under most operating conditions.

Heat-treating apparatus with batch scheme having improved heat controlling capability

Abstract: A heat-treating apparatus which heat-treats a multiple of objects such as a plate or the like, with a batch scheme. A reaction chamber houses the multiple of the objects to be treated. An electrical heater is provided outside of the reaction chamber for heat-treating the multiple of objects to be treated at a predetermined temperature. A temperature detector detects a temperature within the reaction chamber and has main and reserve temperature detectors. A damage detector detects damage to the main and reserve temperature detectors. A controller controls the electrical heater normally in accordance with a detection output from the main temperature detector of the temperature detector. When the damage of the main temperature detector is detected by the damage detector, the controller controls the electrical heater in accordance with a detection output from the reserve temperature detector of the temperature detector.

Particle detector for rough surfaces

Abstract: A surface inspection apparatus having multiple inspection stations to inspect a wafer for a number of characteristics. The wafer is placed on a chuck connected to a rack-and-pinion or equivalent system so that the wafer simultaneously rotates and translates under the fixed position of the inspection stations. A single light source may be used by all stations in turn. One station may be a particle detector with collection optics receiving a small select portion of the light scattered from the wafer surface. A second station may be a roughness detector with a collection system to direct a large portion of scattered light to a detector. A position sensitive detector may be used to determine the slope of the wafer surface at an inspection point when the wafer is not clamped to the chuck, giving a measure of surface deformation. These or other stations are positioned about either of two inspection points at which the beam from the light source may be directed. The inspection points are spaced one wafer radius apart to minimize the required wafer motion for a complete surface scan.