Les fluctuations du taux de dégagement de chaleur sont souvent responsables d’intensification des flux thermiques aux parois, de vibrations et d’émissions sonores qui peuvent éventuellement dégénérer en instabilités thermo-acoustiques auto-entretenues. Ces phénomènes instationnaires dégradent les performances des foyers, provoquent un vieillissement prématuré de certains éléments de la chambre de combustion, voire des dégâts plus importants sur l’installation. Ces perturbations sont cependant difficiles à mesurer dans les foyers car il n’existe pas de diagnostic qui permette d'accéder directement au taux de dégagement de chaleur. L’objectif de ce travail est d'explorer deux alternatives aux solutions existantes pour accéder aux fluctuations du taux de dégagement de chaleur avec une bonne résolution temporelle. Ces nouvelles méthodes sont testées dans des configurations génériques parfaitement prémélangées pour des écoulements laminaires. La première méthode est une technique acoustique, qui repose sur la détermination du temps de vol d’ondes ultrasonores qui traversent l’écoulement. Les fluctuations du temps de vol de ces ondes sont utilisées pour détecter des perturbations de la largeur des gaz brûlés le long du chemin acoustique. Cette information permet de reconstituer les fluctuations du taux de dégagement de chaleur dans des flammes prémélangées. Les premières validations de cette méthode sont présentées pour des flammes en l'absence de perturbation externe lorsqu'elles présentent une instabilité de type Kelvin-Helmholtz pilotée par les phénomènes de flottabilité du panache des gaz brûlés. Des mesures sont ensuite conduites pour des flammes soumises à des modulations harmoniques de l'écoulement. Les données obtenues dans ces configurations sont comparées à des mesures optiques ainsi qu'à des prévisions analytiques. La seconde méthode est une technique optique utilisant un système d’interférométrie laser Doppler permettant de déterminer les fluctuations de densité intégrées le long du chemin optique. On montre dans un premier temps que les perturbations de densité sont principalement causées par des fluctuations du taux de dégagement de chaleur lorsque les flammes sont confinées. Un lien est établi pour reconstituer les perturbations du taux de dégagement de chaleur exploitant le signal de l'interféromètre. La technique est validée pour des flammes pulsées pour différentes richesses et débits. Les données obtenues sont comparées à des mesures reposant sur la chimiluminescence de la flamme. Un bon accord est obtenu pour des modulations harmoniques de l'écoulement à différentes fréquences et niveaux de perturbation. Ce travail permet de valider le principe de ces deux techniques pour détecter les perturbations du taux de dégagement de chaleur lorsque l'accès optique à la zone de combustion est réduit et lorsque des informations quantitatives résolues temporellement sont nécessaires. / Heat release rate disturbances are the sources of additional thermal stresses, direct and indirect combustion noise and undesirable vibrations. In extreme cases, these perturbations may even cause destructive combustion instabilities. These quantities are difficult to measure in practical burners. The objective of this work is to develop two alternative diagnostics to measure heat release rate fluctuations in unsteady flames. These techniques are validated in generic configurations for perfectly premixed laminar flames. The first method is an acoustic technique, which is based on the measurement of the travel time of ultrasonic waves through the flames. Fluctuations of the sound propagation time transmission through unsteady flames are used to estimate perturbations in the burned gases width along the acoustic path. This information is then used to reconstruct heat release rate fluctuations. This technique is validated in the cases of unstable laminar premixed flames driven by buoyancy forces and for flames submitted to harmonic flow velocity modulations. Analytical expressions are derived linking fluctuations in heat release rate and disturbances of the sound travel time. Measurements made with this acoustic technique are compared with optical detections based on the flame chemiluminescence and with predictions from an analytical model. Good agreements are obtained between these different methods validating the proposed technique. The second method envisaged is an optical technique based on a Laser Interferometric Vibrometer used to measure integrated density perturbations along the optical path of a laser beam. It is shown that density disturbances along this path result mainly from heat release rate fluctuations when the flames are confined. A link is established to reconstruct heat release rate disturbances from the signal of the interferometer. The technique is validated in the case of pulsated laminar premixed flames. Measurements are compared to line-of-sight integrated chemiluminescence emission measurements. A good agreement is obtained for harmonic flow modulations at different forcing frequencies and perturbation levels for flames operating at different flow conditions. This work validates the principle of this alternative technique for detecting heat release rate perturbations.

[pt] A maioria dos métodos de avaliação de ondas vibratórias é realizada através do contato entre o sensor e o objeto a ser analisado. Esse requisito de contato impõe algumas limitações de quais objetos podem ser avaliados, como por exemplo, o tamanho do mesmo. Uma técnica que expandiu a capacidade de medição se comparado aos sensores tradicionais de vibração é a vibrometria laser doppler. Ela possibilita medições não intrusivas com alta resolução espacial e tempo de teste reduzido. Dentre as várias aplicações que se beneficiam das aquisições com o vibrômetro laser doppler, o imageamento fotoacústico se encontra no centro do objetivo deste trabalho. O imageamento fotoacústico é uma tecnologia emergente que supera o alto espalhamento óptico em amostras biológicas utilizando o efeito fotoacústico. Ele combina aspectos de imageamento óptico e ultrassom e, consequentemente, algumas de suas vantagens: imagear certos componentes biológicos em profundidades de alguns centímetros e com alto contraste. A técnica mais direta de obter imagens em um sistema fotoacústico é a excitação pontual da amostra e a detecção por varredura. O foco deste trabalho é analisar e implementar uma técnica óptica para detecção das vibrações ultrassonoras em um sistema fotoacústico. Foram avaliados diferentes sistemas interferométricos experimentais, tanto por mapeamento pontual quanto por campo pleno. O princípio da interferometria e a teoria das medições quantitativas são apresentados para explicar as técnicas experimentais utilizadas para aquisição das ondas vibratórias. Igualmente, a técnica de processamento do sinal vibratório é discutida. Dentre as técnicas testadas experimentalmente, duas foram implementadas, analisadas e discutidas em detalhe e seus resultados foram apresentados e comparados entre si. A primeira técnica discutida é o Laser Optical Feedback Imaging (LOFI), um interferômetro heteródino que utiliza a dinâmica do laser e a sua grande sensibilidade ao fenômeno de reinjeção óptica para realizar medições de alta precisão do sinal retroespalhado da amostra. Essa técnica realiza suas aquisições ponto a ponto, através do do escaneamento do feixe do laser na superfície da amostra. Esse modo de aquisição possui um tempo de teste e processamento elevado, mas com alta resolução espacial e com a possibilidade de medir a região transitória. A segunda técnica utilizada para a aquisição de medidas de vibrações ultrassonoras é o estroboscópio Mach-Zehnder, um interferômetro de campo pleno que possibilita a aquisição do padrão de speckle de toda a região de interesse da amostra com baixo tempo de aquisição e processamento. Dessa forma, essa técnica tem um grande potencial para aplicações em tempo real. Os resultados experimentais de ambos os sistemas são apresentados e discutidos em detalhe. Um transdutor piezoelétrico é utilizado para as medições com os dois sistemas, com as mesmas características de teste. Adicionalmente, são apresentados os resultados com a técnica LOFI quando o ganho não-linear é compensado. Esse tipo de teste não é possível no sistema estroboscópico Mach-Zehnder campo pleno, considerando que apenas o LOFI é capaz de realizar medidas transitórias. Para concluir o trabalho, são discutidos e comparados os principais parâmetros para as técnicas testadas: ruído, potência do laser, resolução espacial, resolução temporal, e tempo de aquisição. / [en] Photoacoustic imaging combines aspects of optical and ultrasound imaging and, consequently, combines some of their particular advantages: imaging of specific tissue components in a depth up to several centimeters becomes possible with a high image contrast. The most straightforward strategy to produce photoacoustic images is point-wise excitation and detection in a scanning mode. The main focus of this work is to analyze and implement optical techniques to detect ultrasound vibrations in a photoacoustic system. We evaluate different interferometric systems, both point scanning and full field. Two techniques that were implemented and further discussed are the Laser Optical Feedback Imaging (LOFI), which is a sensitive, point scanning, heterodyne interferometer that uses the dynamics of the laser, and a full field, stroboscopic Mach-Zehnder to acquire ultrasound vibration measurements.We discuss the results from each system and its advantages with the intended application.

No description available.

A load-enhanced methodology has been proposed to enable the in situ detection, localization, and characterization of damage in metallic plate-like structures using Lamb waves. A baseline-free load-differential method using the delay-and-sum imaging algorithm is proposed for defect detection and localization. The term “load-differential” refers to the comparison of recorded ultrasonic signals at various levels of stress. Defect characterization is achieved by incorporating expected scattering information of guided waves interacting with defects into the minimum variance imaging algorithm, and a method for estimating such scattering patterns from the measurements of a sparse transducer array is developed. The estimation method includes signal preprocessing, extracting initial scattering values from baseline subtraction results, and obtaining the complete scattering matrix by applying radial basis function interpolation. The factors that cause estimation errors, such as the shape parameter used to form the basis function and the filling distance used in the interpolation, are discussed. The estimated scattering patterns from sparse array measurements agree reasonably well with laser wavefield data and are further used in the load-enhanced method. The results from fatigue tests show that the load-enhanced method is capable of detecting cracks, providing reasonable estimates of their localizations and orientations, and discriminating them from drilled holes, disbonds, and fastener tightness variations.

This thesis presents fundamental research in the field of laser vibrometry for the application to vibration measurements. A key concern for laser vibrometry is the effect of laser speckle which appears when a coherent laser beam scatters from an optically rough surface. The laser vibrometer is sensitive to changes in laser speckle which result from surface motions not in the direction of the incident beam. This adds speckle noise to the vibrometer output which can be indistinguishable from the genuine surface vibrations. This has been termed ‘pseudo-vibration' and requires careful data interpretation by the vibration engineer. This research has discovered that measurements from smooth surfaces, even when no identifiable speckle pattern is generated, can produce noise and therefore reference to speckle noise, in such circumstances, is inappropriate. This thesis has, therefore, adopted the more general term of pseudo-vibration to include noise generated from any surface roughness or treatment, i.e. including but not limited to speckle noise. This thesis develops and implements novel experimental methods to quantify pseudovibration sensitivities (transverse, tilt and rotation sensitivity) with attention focussed on commercially available laser vibrometers and consideration is given to a range of surface roughnesses and treatments. It investigates, experimentally, the fundamental behaviour of speckles and attempts to formulate, for the first time, a relationship between changes in intensity to pseudo-vibration sensitivity levels. The thesis also develops and implements models for computational simulation of pseudo-vibrations using the fundamental behaviour of speckles. The combination of experimentation and simulation improves current understanding of the pseudo-vibration mechanisms and provides the vibration engineer with a valuable resource to improve data interpretation. Two experimental methods of quantifying pseudo-vibration sensitivity are developed and successfully applied in the evaluation of transverse, tilt and rotation sensitivity for two models of commercial laser vibrometer. These evaluations cover both single beam (translational vibration measurement) and parallel beam (for angular vibration measurement) modes. The first method presented requires correction of the vibrometer measurement with an independent measurement of genuine velocity to produce an iii apparent velocity dominated by the required noise components. The second method requires a differential measurement using two vibrometers to cancel common components such as genuine velocity, leaving only uncorrelated noise from each measurement in the resulting apparent velocity. In each case, a third measurement is required of the surface motion component causing pseudo-vibration and this is used to normalise the apparent velocity. Pseudo-vibration sensitivity is then presented as a map showing the spectral shape of the noise, as a mean and standard deviation of harmonic peaks in the map and as a total rms level across a defined bandwidth. The simulations employ a novel and effective approach to modelling speckle evolution. Transverse and tilt sensitivity are predicted for the first time and are verified by the experimental study. They provide the vibration engineer with the potential to estimate pseudo-vibrations using a simple piece of software. The laser beam spot diameter has a large influence on the pseudo-vibration sensitivity. Transverse sensitivity has been quantified as around 0.03% and 0.01% (per order) of the transverse velocity of the surface for beam spot diameters of 100 μm and 600 μm respectively. Larger beam spots have been shown to significantly reduce transverse sensitivity and measurements from smoother surfaces have also shown a reduced level of transverse sensitivity. Tilt sensitivity has been quantified at about 0.1 μms-1/degs-1 and 0.3 μms-1/degs-1 (per order) of angular velocity of the surface for beam spot diameters of 100 μm and 600 μm respectively. Smaller beam spot diameters significantly reduce tilt sensitivity. The surface roughness or treatment has been shown to have little effect on the level of tilt sensitivity. Rotation sensitivity has been quantified at approximately 0.6 μms- 1/rads-1 and 1.9μms-1/rads-1 (per order) of rotation velocity of the rotor for 90 μm and 520 μm. Smaller beam spot diameters have shown a significant reduction in rotation sensitivity and measurements on smoother surfaces have shown a reduced rotation sensitivity. Focussing the laser beam approximately on the rotation axis has also shown a significant reduction in rotation sensitivity. Parallel beam rotation sensitivity has been quantified at 0.016 degs-1/rads-1 and it is demonstrated that this can adequately be estimated using the single beam rotation sensitivity.

<p>Laser vibration sensing can be used to classify military targets by its unique vibration signature. A coherent laser radar receives the target´s rapidly oscillating surface vibrations and by using proper demodulation and Doppler technique, stationary, radially moving and even accelerating targets can be taken care of. </p><p>A frequency demodulation method developed at the former FOA, is for the first time validated against real data with turbulence, scattering, rain etc. The issue is to find a robust and reliable system for target recognition and its performance is therefore compared with some frequency distribution methods. The time frequency distributions have got a crucial drawback, they are affected by interference between the frequency and amplitude modulated multicomponent signals. The system requirements are believed to be fulfilled by combining the FOA method with the new statistical method proposed here, the combination being suggested as aimpoint for future investigations.</p>

Laser vibration sensing can be used to classify military targets by its unique vibration signature. A coherent laser radar receives the target´s rapidly oscillating surface vibrations and by using proper demodulation and Doppler technique, stationary, radially moving and even accelerating targets can be taken care of. A frequency demodulation method developed at the former FOA, is for the first time validated against real data with turbulence, scattering, rain etc. The issue is to find a robust and reliable system for target recognition and its performance is therefore compared with some frequency distribution methods. The time frequency distributions have got a crucial drawback, they are affected by interference between the frequency and amplitude modulated multicomponent signals. The system requirements are believed to be fulfilled by combining the FOA method with the new statistical method proposed here, the combination being suggested as aimpoint for future investigations.

Disertační práce pojednává o polarizačních nedokonalostech optických komponentů, které jsou využívány ke kontrole a k transformaci polarizačního stavu světla. Získané teoretické výsledky jsou pak využity ve vybraných aplikacích, jež ke své činnosti využívají právě polarizace světla. Konkrétně se jedná o zařízení měřící vibrace oscilujících objektů, dále o interferenční měření dvojlomu v transparentních materiálech a konečně, o vybraná témata z optické kvantové komunikace.

This Thesis relates to the continually advancing field of microelectromechanical systems (MEMS). With MEMS technology, there are many different areas of concentration available for research. This Thesis addresses analysis and preliminary characterization of a cantilever-type MEMS chemical sensor for detection of chemicals and organic components operating at room temperature (20˚C and sea level pressure of 1 atm). Such sensors can be useful in a wide variety of applications. There currently exist several different types of MEMS chemical sensors. Each is based on a different detection method, e.g., capacitive, thermal, resistive, etc., and is used for specific tasks. Out of all currently available detection methods, the most common is the gravimetric method. The gravimetric sensor works by absorbing the chemical in a special material, usually a polymer, which alters the overall mass of the sensing element that can then be measured, or detected, to identify the chemical absorbed. One of the more exciting developments in the field of gravimetric chemical MEMS has been with the advancement of cantilever-type sensors. These cantilevers are small and usually on the order of only about 300 m in length. In order to utilize the gravimetric method, a cantilever is coated with a polymer that allows an analyte to bond to it and change its mass, which in turn changes the resonant frequency of the cantilever. The change in frequency can then be measured and analyzed and from it, the amount of absorbed mass can be calculated. Current research in the cantilever-type resonating sensors for the detection of hydrogen is developing measurement capabilities of 1 ppm (part-per-million). In this Thesis number of sample cantilevers were qualitatively assessed and their dimensional geometry measured. Based on these measurements, frequency data were obtained. In addition, the overall uncertainty in the resonant frequency results was calculated and the contributing factors to this uncertainty were investigated. Experimental methods that include laser vibrometry, optoelectronic laser interferometric microscopy (OELIM), and atomic force microscopy (AFM), were utilized to measure the frequency responses of the samples. The analytically predicted natural frequencies were compared to the experimental data to determine correlation subject to the uncertainty analysis. Parametric analyses involving chemical absorption processes were also conducted. Such analyses considered different parameters, e.g., damping and stiffness as well as changes in their values, to determine contributions they make to the quality of the frequency data and the effect they have on sensitivity of the MEMS cantilever-type chemical sensors. Once these parametric analyses were completed, it was possible to estimate the sensitivity of the cantilever, or the ability for the cantilever to detect frequency shifts due to absorption of the target chemical. Results of the parametric analyses of the fundamental resonant frequency were then correlated with the sensitivity results based on the chemical absorption. This Thesis correlates many results and ideas and probes problems revolving around the analysis and characterization of a MEMS cantilever-type chemical sensor.

In der vorliegenden Arbeit wird eine Methode zur Charakterisierung von Mikrosystemen mit beweglichen Komponenten dargestellt. Sie erlaubt, funktionsrelevante Parameter und deren Schwankungen produktionsbegleitend auf Waferlevel zu ermitteln. Dabei wird vorausgesetzt, dass die Sollform der Struktur und die Abweichungsarten bekannt sind. Die Methode beruht auf dem Vergleich von numerisch berechneten mit experimentell ermittelten Eigenfrequenzen der untersuchten Mikrosysteme. Dazu wird die Abhängigkeit verschiedener Eigenfrequenzen von den gesuchten Parametern mittels einer Parametervariationsanalyse berechnet und durch eine geeignete Funktion angenähert. Die Messung der dynamischen Eigenschaften erfolgt mit Hilfe eines Bewegungsanalysators, der auf einem Laser-Doppler-Vibrometer basiert. Im letzen Schritt werden die gesuchten Parameter berechnet. Kernpunkt der entwickelten Methode sind Messungen auf der Basis von speziellen Teststrukturen, die im Waferlayout neben den eigentlichen Nutzstrukturen platziert sind und parallel mit den Nutzstrukturen prozessiert werden. Es werden Algorithmen zur Generierung des Designs der Teststrukturen und ihrer Platzierung im Waferlayout entwickelt. Dabei werden das Design der Nutzstruktur und deren funktionsrelevante Parameter, der technologische Ablauf und materialspezifische Kennwerte berücksichtigt. Im Ergebnis liegt eine Bibliothek von Standard-Teststrukturen vor, die für produktionsbegleitende Messungen sowie für die Übertragbarkeit der Ergebnisse geeignet sind. Außerdem werden allgemeingültige Richtlinien zur Durchführung der Messungen an den Standard-Teststrukturen abgeleitet. Das Messverfahren wurde an unterschiedlichen Mikrosystemen mit beweglichen Komponenten überprüft und zu einer allgemeinen Messmethode für diese Klasse von Mikrosystemen erweitert. / In this work a method for the characterization of microsystems with movable components is presented. The method allows to determine the relevant parameters and their variations on wafer level if the nominal shape of the structure and the type of deviations are known. The method is based on a comparison of the numerically calculated and experimentally measured Eigenfrequencies of the microsystems. For that purpose, the relationships between various Eigenfrequencies and the searched parameters are calculated by parameter variation analysis and the results of this analysis are approximated with appropriate functions. A Laser Doppler vibrometer based motion analyzer is used to determine the frequency response function of the micromechanical structure and extract Eigenfrequencies. The comparison of the measured and the calculated frequencies provides values for the searched parameters. The key element of the developed method is the measurement on special test structures that are placed in the wafer layout next to the actual microsystems and processed in the same technological process parallel to the actual microsystems. Algorithms for designing the test structures and their placement in the wafer layout are shown, taking into account the design of the actual microsystems and the function parameters of the technological process as well as material characteristics. As a result, a library of standard test structures for function relevant parameters is available. A general guideline for the measurement on the test structures is presented. The presented method is verified on various microsystems and extended to a whole class of microsystems with movable components.