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Laser-based fibre-optic sensor for measurement of surface properties
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This project deals with the design and development of an optoelectronic sensor system and its possible use in online applications There are two different configurations of this sensor a sensor for surface roughness and another for defect detection. In each configuration the mechanical and optical design are almost identical-optical fibres convey light to and from a surface. Light source driving circuits and photodetection circuits were developed for each sensor. Data acquisition and analysis algorithms were developed for each sensor.
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In digital phosphor-based imaging modalities, one important intermediate stage is the optical coupling between the phosphor material and the optical sensor. The performance of the optical compatibility is affected by surface-roughness issues, for which further research should be paid. This paper investigates the surface-roughness influence between the CsI phosphor material and the optical sensing materials (i.e., the silicon dioxide-SiO2, the indium tin oxide-ITO, and the indium gallium arsenide-InGaAs) employed in several image devices. Results showed that for all sensing materials, the transmission factor t of the optical signal follows qualitatively the variation of their refractive indexes and quantitatively the variation of the surface roughness and the incident polar angle. Finally, with respect to light wavelength, the curve of variation was found to be continuous for ITO and SiO2 sensing materials; however, lower and sharper variations were observed in the first case.
The performance characteristics of a Tencor Surfscan 4000 wafer surface scanner have been evaluated using ideal polystyrene latex (PSL) spheres and irregularly shaped real-world particles of Si and SiO2. The particles were uniform in size and were deposited on bare silicon wafers and used as standard calibration wafers to study the scanner response. Particles in the 0.1 to 1.0 μm diam range were used. The sizing accuracy, counting efficiency, lower detection limit, and count repeatability of the scanner were studied systematically. The full Maxwell's electromagnetic equations also have been solved numerically on a supercomputer to obtain the light-scattering cross section of the particles on bare silicon wafers. The calculation compares favorably with the experimental results. Because of the high refractive index of silicon, the wafer surface scanner detects Si particles to a considerably smaller size than PSL. The data suggest that Si particles as small as 0.1 μm have been detected by the Surfscan 4000 with 90% counting efficiency even though the nominal lower limit of the instrument is 0.3 μm based on PSL calibration.
Until now, it has been difficult to detect subtle changes in luster on surfaces in commercial and industrial applications. Thanks to Omron Electronics' new E3X-NL photoelectric fiber-optic sensor, the necessary level of discrimination among surface backgrounds, can be achieved using the proprietary free-angle optics (FAO) technology. Omron's polarized light multilayer film technology, FAO, uses a polarized beam splitter made by layering different types of dielectric films on glass. The splitter divides the light that is reflected from the object and transmits only the required component of light to the appropriate receivers.
The principles of photoelectric sensing, with particular emphasis on excess gain measurement, are discussed. The relationship between excess gain and sensing distance is examined using an opposed mode sensor pair as an example. The retroreflective excess gain curves are plotted using a Model BRT-3 3-in. diameter retroreflector. Proximity mode sensing and its effect on excess gain is also examined.
A modulated photoelectric sensor operates on a principle very similar to that of a radio station and radio receiver in that is must be 'tuned' to respond to its own light source and to ignore extraeous light. The article describes the system components and reviews operating current modulation, modes of detection, excess gain, and contrast.
Values obtained for different types of granite using a portable Talysurf instrument and a gloss meter are compared. The effects of mineral grain size and 'pull-out' have to be taken into consideration when analyzing the results.
If the semiconductor industry is to achieve contamination-free manufacturing, analytical instrumentation must continue to evolve. The basic research reported in this article suggests that multiple scattered-light detectors should be included in the next generation of surface particle detection equipment. Wafer scanners using such angle-resolved detection methods could provide information about particle composition and morphology while eliminating the sizing ambiguity associated with integrating optics.
A photoelectric sensor is an electrical device that responds to a change in the intensity of the light falling on it. The development history of such a device is presented, starting from rugged incandescent forerunners up to current industrial photoelectric sensors. This tutorial on photoelectric sensing covers light sources and sensing modes.
Part 1 of this article covered the basic operation of photoelectric controls. In this second of two parts, photoelectric control logic is examined. Photoelectric control logic can be divided into two categories. The first consists of devices that 'condition' the signal between the detector and the output device. These are typically logic modules mounted inside the photoelectric control and include timing or counting functions. The second category is output switch control logic wired in series or parallel, providing an output to the load only when the correct combination of controls is energized.
Accurate measurement of small displacements is an important procedure in many areas of science and technology. A number of techniques are available, but for a non-contact approach optical schemes offer significant advantages over other methods. A development with great potential for optical interferometric sensors and measurement systems is the technique of white light interferometry. This approach utilizes a broadband light source and two interferometers coupled in series. One interferometer forms the measurement interferometer (the sensor) and the second reconstructs the interferometric fringe pattern. The resolution of the measurement is then dictated by the resolution attainable in this second 'recovery' interferometer. Various techniques allow for sub-micron resolution over a large dynamic range. The technique is readily applicable to the accurate measurement of displacements and vibration.