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A photoacoustic spectrometer was developed and built for measuring absorption of light by collected particles. Major advantages of the photoacoustic method are that it measures absorption directly, it is insensitive to scattered light, and it is readily used at different wavelengths. To evaluate the performance of the spectrometer, comparisons were made between photoacoustic absorption spectra and spectra calculated with Mie thoery. Pure powders with varied optical properties were used in the comparison, including carbon, hematite, and others. Results were reasonable in both absolute magnitude and spectral shape. Aerosol particles were collected in different environments in southern Arizona under background conditions in the mid-troposphere, and in a moderately polluted city. Results for the two locations, and two size ranges, are compared and contrasted in this thesis. Absolute magnitudes of absorption coefficients, measured at green wavelengths, are used to summarize many important results. Absorption by fine urban aerosol was 6 ± 4 x 10⁻⁷ m⁻¹, and four times larger than absorption by coarse urban aerosol. Normalized photoacoustic absorption spectra for urban aerosol are uniform with wavelength; background aerosol spectra have a relative increase in absorption at near UV wavelengths compared to near IR wavelengths. Urban aerosol absorption can be attributed to carbon particles larger than approximately 0.1 micron. Absorption by hematite (alpha iron oxide) particles in more strongly wavelength dependent than absorption by carbon particles, of the same size. This wavelength dependence is still not great enough to be attributed to hematite alone--although submicron hematite particles may be the dominant absorber in coarse background aerosol. (Abstract shortened with permission of author.)

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published_or_final_version / Physics / Master / Master of Philosophy

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La détection et l’évaluation des défauts est un processus utilisé afin d’estimer la durée de vie restante d’une structure dont la performance doit persister au-delà du temps établi au début. Le concept de Surveillance de l’Intégrité des Structures (Structural Health Monitoring – SHM) concerne le diagnostic de l’état d’intégrité des matériaux constituantes d’une structure. Cet état peut être altéré en temps par des multiples facteurs comme : l’usure de la structure due à la fatigue des matériaux, l’action des paramètres de l’environnement, ainsi que l’apparition des évènements accidentelles. Partant de ces considérations, la thèse doctorale intitulée Caractérisation des processus d’endommagement des matériaux composites à base de fibres de carbone propose de développer une étude originelle, avec du potentiel dans la création d’un système optimale pour la détection des défauts des matériaux composites depuis la phase initiale. Le travail suit systématiquement un parcours de recherche théorique et expérimentale. Il débute de la générale – l’étude des méthodes de dépistage des défauts connues et utilisées en présent il continue par l’étude des senseurs et des systèmes de senseurs pouvant être intégrés dans les matériaux composites, principalement de ceux utilisés en industrie. Les expérimentations effectuées utilisent trois méthodes différentes de détection des défauts et, finalement, est élaborée une analyse multicritères pour identifier la méthode optimale de détection des défauts qui pourrait être utilisée pour le contrôle et, aussi, pour le suivi en temps réel. / The detection and the evaluation of defects is a process used to estimate the lifetime of the materials and structures. The concept of Structural Health Monitoring - SHM concerns the diagnosis of the health state of the constituent materials of a structure. This state can be altered in time by some factors such as: the wear of the structure due to material fatigue, the action of the environmental parameters or/and the occurrence of accidental events. Based on these considerations, the doctoral thesis entitled “STUDIES AND RESEARCHES REGARDING DAMAGE DETECTION IN STRUCTURES” proposes to develop an original study, with the potential in the creation of an optimum system for the detection of defects in composite materials since the initial phase. The work is based on a coupling between theoretical and experimental approaches. In order to develop a multi-criteria analysis to identify the optimal method of detecting defects the experiments analysis were carried out using three different methods.

In order for an industrial inspection system to be of utility in manufacturing it must be fast, accurate, and flexible [Chin 1986]. Current machine vision systems are very specialized and inflexible in nature. A reason for the inflexibility of current machine vision systems is the need for real-time processing of image data. Such a need has forced both the use of very specialized image processing hardware as well as the use of rather simple, very specialized computer vision algorithms to do the analysis. On the other hand, most, if not all, of today’s computer vision methods are not general purpose in nature. In the absence of truly robust general purpose methods, developing satisfactory machine vision solutions will continue to involve experimenting with machine vision hardware and software components. Given the current state of machine vision technology, it would seem that the best method for creating flexible machine vision systems is, perhaps, to define a subclass of inspection problems where all the problems within the subclass have a number of common features about them. Such a subclass must be of interest to a number of manufacturers. It must also be “reasonable” to solve, given the current state of the art. Once the subclass has been selected, the next logical step would seem to be to create a device that makes performing all the needed experiments on the various problems within the class easy to perform. Based on the above line of reasoning, this work has four major objectives. The first objective is to define a meaningful subclass of inspection problems that are a) of interest to a number of manufacturers, and b) represent inspection tasks that seem “reasonable” within the current state-of-the-art of computer vision. The subclass of inspection problems selected for this work is the longitudinal planar web inspection problem under the two-dimensional imaging restriction. The second objective of this work is to create a vehicle that will allow the types of experimentation usually associated with the development of machine vision systems to be facilitated. This vehicle created is called a “machine vision prototyper.” The third objective of this work is to use the machine vision prototyper system to attack a particular planar web applications problem. The application considered is the problem of locating and identifying surface defects in surfaced hardwood lumber in a species independent manner. The fourth objective of this research is to indicate how the prototyper system can be used to attack a second planar web application problem. This application problem is the inspection of hardwood parts coming out of a molder. The utility of the machine vision prototyper system as an experimental tool is demonstrated on two of the three possible types of longitudinal planar web inspection problems. The results include the development of a machine vision system for a hardwood surfaced lumber surface feature detection problem, and a discussion of how the prototyper can be used to attack the problem of inspecting hardwood parts coming out of a molder. / Ph. D.

A primarily software based Fourier Deep Level Transient Spectroscope (FDLTS) is built. The raw capacitance transient is acquired and digitized using capacitance meter HP4280A whereas the signal analysis is done using a customized software module. The software module calculates both the conventional DLTS spectrum and the Fourier DLTS spectrum. This home-made FDLTS set up was compared to a commercial conventional box-car DLTS system (Sula Technology's DLTS) as well as to a commercial Fourier DLTS system (Bio-rad) and it was found to be either equivalent to the commercial systems or even better in some respects. In one case, Fourier analysis using the home-made setup, led to the detection of a trap completely undetected by the commercial conventional DLTS. The FDLTS system together with the commercial conventional DLTS were used to study possible gold contamination in an industrial process. The study was accomplished by comparing conventional and Fourier DLTS spectra and corresponding calculated trap properties using Schottky barrier diodes fabricated on the suspect wafers and an intentionally gold diffused reference sample wafer. During the investigation minority carrier emission in DLTS using Schottky barrier diodes was observed. The study revealed the presence of some possible gold-like contamination which trapped minority carriers (i.e. electrons) in p type silicon. / Graduation date: 2003

Otitis media, which is an upper respiratory tract infection that affect the middle ear, is the second most common disease in childhood, outnumbered in prevalence only by the common cold. Diagnosis of middle ear inflammation is often performed in the primary healthcare where the normal procedure involves anamnesis and physical examination of the tympanic membranes (TM) of the patient, usually be means of otoscopy. The general aim of this thesis was to develop optical methods that enable quantification of TM characteristics associated with otitis media. Diffuse reflectance spectroscopy was applied to quantify TM erythema using previously suggested erythema detection algorithms. Healthy TM:s were significantly distinguished from TM:s with induced erythema (p < 0.01) and from TM:s in ears with mucous middle ear effusion (p < 0.05). A new technique for surface shape assessment based on an on-axis dual fibre array incorporated in an otoscope was developed and evaluated in ear models and on tympanic membranes from harvested temporal bones. The technique utilises the combined effects of source-detector fibre separation and fibre-to-sample distance on the detected light intensity. Optical phantoms, both polyacetal plastic solids and latex membranes, were utilised to demonstrate the ability of the surface shape assessment technique to differentiate between convex and concave surfaces – as a bulging tympanic membrane is typically associated with acute otitis media whereas a retracted eardrum is associated with otitis media with effusion. Monte Carlo simulations of the surface shape data were performed in order to validate the experimental results with a theoretical model that are consistent with light transport theory. Retracted and bulging tympanic membranes from harvested temporal bones could be separated with a single measurement, given that variations in measurement distance were accounted for and that measurement from normally positioned tympanic membranes were used for signal normalization. In conclusion, the studies implicate that for individual otitis diagnosis, the hyperaemic tympanic membrane was separated from the healthy by application of erythema indices using diffuse reflectance spectroscopy. Moreover, bulging and retracted positions of the tympanic membrane were separable by means of the source-detector intensity matrix. For further clinical studies it is reasonable to assume that data from both methods are needed for diagnosis.