Browsing by Subject "Infrared detectors"

Now showing 1 - 3 of 3
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    Infrared detection in Melanophila acuminata
    (2001-05) Hammer, Daniel Xavier; Welch, Ashley J., 1933-
    The progression of science has often included mimicry of nature, inherent in which lies the solution of many seemingly insurmountable technical obstacles. One limitation humans have sought to overcome through arti cial means is their range of visual sensitivity, which is con ned to a small band of the electromagnetic radiation spectrum. Nature has given us two biological models for detection of infrared wavelengths: snakes and insects. The insects include Buprestid beetles of the species Melanophila acuminata (Coleoptera: Buprestidae), that can detect infrared radiation emitted from forest res with bilateral thoracic pit organs. Investigation of the pit organ of Melanophila beetles may lead to the development of a new class of highly-sensitive detectors that operate at ambient temperatures. The sensitivity threshold of infrared detection in Melanophila beetles was established using standard electrophysiological techniques and precise control of radiant ux dosimetry. These experiments determined the distance from which the beetles detect forest res and pointed to olfaction as the sense responsible for long-range orientation. Moreover, the response characteristics of action and generator potentials recorded from the infrared pit organ were measured. A tunable infrared ultrafast laser was used to measure the spectral sensitivity of the pit organ. The bulk optical and thermal properties of the organ tissue were examined with integrating sphere measurements and scanning probe microscopy, respectively. The material properties together with the action spectrum indicate that the pit vii organ may utilize its tissue properties speci cally to sense wavelengths in the mid-infrared atmospheric window (2{5 m). Two experiments were designed to provide physical evidence that the beetle infrared pit organ functions via a photo-thermal-mechanical transduction mechanism. In the rst mechanism experiment, a ber-based di erential-phase optical low coherence re ectometer was used to measure sub-wavelength displacement of the organ. Although the displacement upon absorption of infrared light is not unique to the organ tissue, the complex morphology of the displacement waveform supports the photo-thermalmechanical hypothesis. In the second mechanism experiment, the sensitivity as a function of pit organ temperature was measured with electrophysiological techniques. No dependence upon static temperature was found, which indicates that the beetle responds only to rapid temperature changes brought about, for example, by absorption of infrared light by the pit organ. Novel electrode assemblies were designed and built to record an infrared response from the interganglionic connectives in the thorax of the beetle. These electrophysiological experiments veri ed the conveyance of infrared information through speci c pathways to rostrally-situated sites in the nervous system of the beetle. These experiments were designed to determine the manner in which Melanophila beetles sense infrared light. Although many questions remain, the information gained may provide suggestions to aid in the development of new solid-state infrared detectors.
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    Solder joint inspection using thermal transient characteristics
    (1987) Schellhase, John Charles, 1962-; Not available
    Every year millions of dollars are spent by the electronics industry to identify and correct problems with defective solder joints. This preliminary study uses the thermal cooling transient characteristics of solder joints that have been warmed by short laser pulses to evaluate the quality of solder joints. Thermal radiation time constants are used to classify lap type solder joints since time constants are less susceptible to variations in the surface conditions on the solder joints which can cause large variations in the amount of thermal radiation being emitted by a warmed solder joint. The proposed algorithm uses four sequential thermal radiation data points gathered by an infrared detector after the short laser pulse in a laser inspection system. The thermal radiation time constant estimates for the solder joints are computed from the thermal radiation data and then employed to develop a preliminary process control chart of the form that could be used to monitor the reliability of the soldering process and signal when problems cause this process to deviate from normal production. The thermal time constants and the associated theoretical thermal radiation time constants that would be obtained using other infrared detectors can be estimated by using a temperature vs. emissive power relationship for the infrared detector in the inspection system of interest. Process control charts for other infrared detector systems can also be approximated by using the theoretical thermal radiation time constants obtained for other infrared detector systems. The results from the process control charts using thermal radiation time constant estimates are encouraging and show great promise of identifying when the soldering process begins to degrade and producing solder joints with poor quality. Also, the preliminary data involving solder joint cross sectional area for the lap joints show that the use of time constants to determine the quality of solder joints is supported by a linear correlation between a solder joint's cross sectional area and its thermal radiation time constant