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Conventional Extrinsic Fabry-Perot Interferometric (EFPI) sensors have been used to measure a variety of physical parameters like temperature, pressure and strain. A modified version of this geometry is successfully implemented to measure low-level magnetic field densities. A complete optical fiber based magnetometer system consisting of sensor head, laser source, opto-electronics, signal demodulation circuitry and display is designed, fabricated and tested. Various electronic signal demodulation schemes are discussed. The Quadrature Phase Shifted EFPI signal demodulation scheme, used in the system, is studied in detail. The scheme is designed and implemented in both analog and digital domain and the advantages and drawbacks of each type are presented. Primary limitations in the measurement of extremely low-level magnetic field densities are discussed and methods to overcome them using electronic signal processing schemes are suggested for future consideration. / Master of Science

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Hydropower has been around for more than a century and is considered a mature technology, but with recent advancements in power electronics and simulation capability new exciting ways to increase efficiency and reliability is possible. At Uppsala University a brushless exciter has been constructed for the experimental test rig, SVANTE. Power electronics are mounted on the shaft for control of the generator's excitation current. In addition a wireless control and measurement system is needed to provide the desired switching patterns to the power electronics and to evaluate performance of the system. In this thesis a shaft mounted embedded system for control and measurement is constructed as well as magnetic field sensors with measurement range up to 700mT. The computational power comes from a National Instruments sbRIO-9606. The system has 14 individual totem pole power electronics driving channels, 48 analog input channels for current signals and it communicates wirelessly through a bluetooth connection. The system is tested and works satisfactory but has not been mounted on the rotating side of the generator due to delays in the manufacturing.

This thesis deals with the subject of fibre optic magnetic field sensors utilizing iron garnet materials. Such materials exhibit a large Faraday rotation which make them advantageous for application in compact mag­netic field sensors. After an introduction, in which fibre optic sensors and optical methods to measure electric current are reviewed, the original research work is summarized. A system for the measurement of the magneto-optic properties of trans­parent materials is described. Measurement results, showing the influence of temperature, magnetic field direction and sample treatment on the magneto-optical proper­ties of YIG-crystals, are presented. The proper­ties of thin magneto-optical waveguiding films have also been studied using different light coupling methods. Measurement results obtained for holo­graphic grating, prism and edge (end-fire) light coupling to different substituted YIG films are presented. It is shown that the launching method may affect the properties to be measured. The design and performance of several versions of extrinsic guided wave fibre optic magnetic field sensors are then reported. The sensors employ substi­tuted YIG (Yttrium Iron Garnet, Y3Fe5O12) thin film waveguides as sensing elements. Polari­zation maintaining fibres were used as feed and return to provide two signal channels. The signals were combined in a balanced measure­ment system, providing insensitivity to both fluctuations in optical power and loss. Sensors have been made both with separate fibres to guide the light to and from the sensing element and with a single fibre for both functions. The two fibre version, although less ”elegant”, is found to have a better performance. This version also makes it possible to determine both the magnitude and sign of the magnetic field. Measurement results indicate a usable measurement range of at least several mT with a noise equivalent magnetic field level of less than 8 nT/root(Hz). The design and performance of multimode fibre optic magnetic field sensors utilizing the Faraday effect in an epitaxially grown thick (YbTbBi)IG film is also described. This type of sensor is found to be linear over a range from 27 mT to less than 270 nT. Sensor prototypes suitable for current monitoring in high voltage transmission lines have also been developed. / QC 20111209 / YIG

La Magnéto-Impédance Géante (GMI pour Giant Magneto-Impedance) présente un certain nombre d’avantages, tels la haute sensibilité, la haute résolution de détection, la large bande passante et la flexibilité de l’élément sensible qui rendent cette technologie très prometteuse pour la réalisation de capteurs de courant flexibles, sans contact, capables de mesurer à la fois les courants continus (DC) et alternatifs (AC).Ce travail de thèse vise à explorer la faisabilité d’un capteur de courant flexible à base de GMI, en portant une attention particulière sur l’impact des paramètres d’influence qui conditionnent largement les solutions de mise en œuvre du capteur.Les effets de la température et des contraintes mécaniques de flexion et de torsion, qui s’appliquent dans un environnement de mesure réel, sont caractérisés en prenant en compte les grandeurs intrinsèques du fil nécessaires à la réalisation d’un capteur industriel. L’impact de la mise en œuvre et du conditionnement électronique vis-à-vis de ces grandeurs d’influence est aussi étudié. Les effets des perturbations magnétiques externes et de l’excentration du conducteur sous test dans la boucle de mesure sont quantifiés et une solution de blindage est proposée. Enfin, le prototype de capteur obtenu à l’issue de ces travaux est présenté, ainsi que ses performances, en dégageant les pistes d’optimisation et d’amélioration. / The GMI effect displays several advantages, such as high sensitivity, high detection resolution and bandwidth, and mechanical flexibility. These advantages predispose this technology to the implementation of flexible contactless current sensors measuring both DC and AC currents.This thesis work aims at exploring the feasibility of a flexible GMI current sensor. A particular attention to the impact of influence parameters which largely condition the design solutions of the sensor has been paid.The effects of temperature and mechanical constraints such as bending and torsion, which apply in a real measuring environment, are characterized by taking into account the intrinsic features which are necessary to the design of the sensor. The impact of the general measuring configuration and electronics are also studied. The effects of magnetic disturbances and of the position of the current-carrying conductor in the measuring loop are quantified and an adequate shielding method is proposed. Finally, the sensor prototype obtained at the end of this work is described with its performances and the possible optimization and enhancement ways.

Le véhicule électrique rassemble beaucoup d'équipements électrotechniques. Tous sont potentiellement source de champ magnétique dans l'habitacle : zone confinée où se trouvent les passagers. Il est illusoire de réaliser un modèle numérique complet tant le nombre de paramètres est important. Il est également impossible de placer des capteurs de champ partout à l'intérieur de l'habitacle. Après une étude approfondie des caractéristiques du champ magnétique mesuré dans l'habitacle, nous proposons d'allier modèle a priori et mesure de champ dans une approche Bayésienne du problème inverse. Basée sur le développement en harmonique sphérique du champ, l'apport d'information a priori oriente la solution et permet l'identification de nombreux paramètres avec très peu de mesure. / Electric vehicles have a lot of electrical devices onboard. All of them may generate electromagnetic field inside the car: a quite small space containing the passengers. A complete modeling of the vehicle can hardly be done because of the parameters number. The magnetic field measurement everywhere inside the car is also impossible. We first measure the magnetic field inside the car to study its characteristics. Then we propose to merge together a priori modeling with measurements into a Bayesian approach of the inverse problem. Based on spherical harmonic decomposition of the magnetic field, a priori information helps the resolution and gives the identified parameters with a very few measurements.

Lors de la réalimentation des auxiliaires d’une tranche nucléaire, l’étape la plus à risque est la remise sous tension brusque du transformateur à cause des surtensions. Dans un soucis perpétuel d’amélioration de la modélisation de ces transitoires, les modèles et techniques doivent évoluer. Le but de ces travaux de thèse est de proposer de nouvelles méthodologies permettant d’évaluer les paramètres mal connus de la modélisation. Lors des mises sous tension des lignes électriques, une méthodologie s’appuyant sur l’identification (optimisation ou techniques issues du traitement du signal) permet de déterminer les paramètres variables de la modélisation. Cependant, un des paramètres influents pour les surtensions est le flux rémanent. Face aux problèmes actuels rencontrés pour l’estimer (méthode non directe, dérive, …), une nouvelle méthode basée sur la mesure des flux de fuites du circuit magnétique est proposée. Des mesures réelles utilisant des capteurs de technologie « fluxgate » sont réalisées et permettent d’estimer le flux rémanent. / During the re-energization of the auxiliaries of a nuclear power plant, the more dangerous step is the re-energization of the power transformer, because of the temporary overvoltages. In order to improve the transient modeling, models and techniques may be improved. The purpose of this thesis is to suggest new methodologies to identify the uncertain parameters of the model. When the line re-energization occurs, an identification methodology (optimization or methods using signal processing) allows determining the model variable parameters. However, one of the most important parameters in the overvoltages is the residual flux. Given the actual problems found on estimation strategies (no direct method, derivation,…), a new method established for the leakage flux measurement of the magnetic circuit is proposed. Real measurements using « fluxgate » technology sensors were realized, permitting to estimate the residual flux.