L'effet MagnétoElectrique (ME) traduit la polarisation d'un élément diélectrique et l'aimantation d'un diélectrique lorsqu’il est soumis, respectivement, à un champ magnétique et à un champ électrique. Cette propriété a permis de mettre en œuvre des capteurs Magnéto(Elasto)Electrique pour la mesure du champ magnétique ou électrique. De nombreuses études sur les couplages de matériaux (forme, taille, dimension…) ont été effectuées afin d’améliorer les performances en terme de sensibilité et de bruit de ces capteurs. Les meilleurs niveaux de bruit (en termes de densité spectrale) mesurés pour ce type de dispositif en mode passif sont, respectivement, de 5 pT/sqrt(Hz), 0,2 pT/sqrt(Hz) et environ une cinquantaine de 50 fT/sqrt(Hz), respectivement à 1 Hz, en zone de bruit blanc et à la résonance.Certains laboratoires, dont le GREYC, s’intéressent plus particulièrement à l’étude des performances ultimes de capteurs magnétiques en optimisant, notamment, l’électronique de conditionnements et en utilisant leurs propriétés non linéaires. Cette thèse s’inscrit dans ce cadre. Elle avait pour objectif l’étude des performances de capteur Magnéto(Elasto)Electrique en mode non linéaire et aux basses fréquences. Pour cela, des structures originales de conditionnent ont été développées en termes de polarisation, d’excitation et d’asservissement. L’étude théorique des performances montre que le bruit du capteur peut atteindre des niveaux bien inférieurs au pT/sqrt(Hz) à 1 Hz pour les capteurs étudiés, si les performances obtenues ne sont pas limitées par le bruit de l’électronique de conditionnement et leur sensibilité. Cette étude a été l’objet de ce travail de thèse. / The MagnetoElectric effect traduces the polarization of a dielectric element and the magnetization of a dielectric under respectively a magnetic field and an electric field. This property allows the development of Magneto(Elasto)Electric sensors for measuring a magnetic or an electric field. Several analyses regarding the material coupling (shape, size, dimensions…) have been made in order to increase the performances in terms of sensibility and in terms of noise of these sensors. The best noise levels (in term of spectral density) measured for these types of sensors are respectively 5 pT/sqrt(Hz), 0.2 pT/sqrt(Hz) and around 50 fT/sqrt(Hz) at 1 Hz, at white noise zone and at resonant frequency.Some laboratories, including the GREYC, are interested more specifically on the studies of the ultimate performances of magnetic sensor by optimizing the conditioning electronics and by using their nonlinear properties. This thesis lies in this framework. It had for objective, to study the performances of the Magneto(Elasto)Electric sensor in nonlinear mode and at low frequencies. For these, some original conditioning structures have been developed in terms of polarization, excitation and servo system. The theoretical study of these performances show the sensor intrinsic noise can reach lower than pT/sqrt(Hz) at 1 Hz for the studied sensor if the obtained performances are not limited by the conditioning electronics and their sensitivity. This study has been the object of this thesis work.

Microfabricated solid-state surfaces, also called atom chip', have become a well-established technique to trap and manipulate atoms. This has simplified applications in atom interferometry, quantum information processing, and studies of many-body systems. Magnetic trapping potentials with arbitrary geommetries are generated with atom chip by miniaturized current-carrying conductors integrated on a solid substrate. Atoms can be trapped and cooled to microKelvin and even nanoKelvin temperatures in such microchip trap. However, cold atoms can be significantly perturbed by the chip surface, typically held at room temperature. The magnetic field fluctuations generated by thermal currents in the chip elements may induce spin flips of atoms and result in loss, heating and decoherence. In this thesis, we extend previous work on spin flip rates induced by magnetic noise and consider the more complex geometries that are typically encountered in atom chips: layered structures and metallic wires of finite cross-section. We also discuss a few aspects of atom chips traps built with superconducting structures that have been suggested as a means to suppress magnetic field fluctuations. The thesis describes calculations of spin flip rates based on magnetic Green functions that are computed analytically and numerically. For a chip with a top metallic layer, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity. Based on this result, scaling laws for loss rates above a thin metallic layer are derived. A good agreement with experiments is obtained in the regime where the atom-surface distance is comparable to the skin depth of metal. Since in the experiments, metallic layers are always etched to separate wires carrying different currents, the impact of the finite lateral wire size on the magnetic noise has been taken into account. The local spectrum of the magnetic field near a metallic microstructure has been investigated numerically with the help of boundary integral equations. The magnetic noise significantly depends on polarizations above flat wires with finite lateral width, in stark contrast to an infinitely wide wire. Correlations between multiple wires are also taken into account. In the last part, superconducting atom chips are considered. Magnetic traps generated by superconducting wires in the Meissner state and the mixed state are studied analytically by a conformal mapping method and also numerically. The properties of the traps created by superconducting wires are investigated and compared to normal conducting wires: they behave qualitatively quite similar and open a route to further trap miniaturization, due to the advantage of low magnetic noise. We discuss critical currents and fields for several geometries. / Mikrotechnologische Oberflächen, sogenannte Atomchips, sind eine etablierte Methode zum Speichern und Manipulieren von Atomen geworden. Das hat Anwendungen in der Atom-Interferometrie, Quanteninformationsverarbeitung und Vielteilchensystemen vereinfacht. Magnetische Fallenpotentiale mit beliebigen Geometrien werden durch Atomchips mit miniaturisierten stromführenden Leiterbahnen auf einer Festkörperunterlage realisiert. Atome können bei Temperaturen im $mu$ K oder sogar nK-Bereich in einer solchen Falle gespeichert und gekühlt werden. Allerdings können kalte Atome signifikant durch die Chip-Oberfläche gestört werden, die sich typischerweise auf Raumtemperatur befindet. Die durch thermische Ströme im Chip erzeugten magnetischen Feldfluktuationen können Spin-Flips der Atome induzieren und Verlust, Erwärmung und Dekohärenz zur Folge haben. In dieser Dissertation erweitern wir frühere Arbeiten über durch magnetisches Rauschen induzierte Spin-Flip-Ratenund betrachten kompliziertere Geometrien, wie sie typischerweise auf einem Atom-Chip anzutreffen sind: Geschichtete Strukturen und metallische Leitungen mit endlichem Querschnitt. Wir diskutieren auch einige Aspekte von Aomchips aus Supraleitenden Strukturen die als Mittel zur Unterdrückung magnetischer Feldfluktuationen vorgeschlagen wurden. Die Arbeit beschreibt analytische und numerische Rechnungen von Spin-Flip Raten auf Grundlage magnetischer Greensfunktionen. Für einen Chip mit einem metallischen Top-Layer hängt das magnetische Rauschen hauptsächlich von der Dicke des Layers ab, solange die unteren Layer eine deutlich kleinere Leitfähigkeit haben. Auf Grundlage dieses Ergebnisses werden Skalengesetze für Verlustraten über einem dünnen metallischen Leiter hergeleitet. Eine gute Übereinstimmung mit Experimenten wird in dem Bereich erreicht, wo der Abstand zwischen Atom und Oberfläche in der Größenordnung der Eindringtiefe des Metalls ist. Da in Experimenten metallische Layer immer geätzt werden, um verschiedene stromleitende Bahnen vonenander zu trennen, wurde der Einfluß eines endlichen Querschnittsauf das magnetische Rauschen berücksichtigt. Das lokale Spektrum des magnetischen Feldes in der Nähe einer metallischen Mikrostruktur wurde mit Hilfe von Randintegralen numerisch untersucht. Das magnetische Rauschen hängt signifikant von der Polarisierung über flachen Leiterbahnen mit endlichem Querschnitt ab, im Unterschied zu einem unendlich breiten Leiter. Es wurden auch Korrelationen zwischen mehreren Leitern berücksichtigt. Im letzten Teil werden supraleitende Atomchips betrachtet. Magnetische Fallen, die von supraleitenden Bahnen im Meissner Zustand und im gemischten Zustand sind werden analytisch durch die Methode der konformen Abbildung und numerisch untersucht. Die Eigenschaften der durch supraleitende Bahnen erzeugten Fallen werden erforscht und mit normal leitenden verglichen: Sie verhalten sich qualitativ sehr ähnlich und öffnen einen Weg zur weiteren Miniaturisierung von Fallen, wegen dem Vorteil von geringem magnetischem Rauschen. Wir diskutieren kritische Ströme und Felder für einige Geometrien.

<p>Induction machines convert more than 55% of electrical energy into various other forms in industrial and domestic environments. Improved performance, especially by reduction of losses in induction machines hence can significantly reduce consumption of electricity. Many design and control methods are adopted to make induction machines work more efficiently, however certain design compromises are inevitable, such as skewing the rotor to improve the magnetic noise and torque characteristics increase the cross current losses considerably in a cage rotor, degrading the efficiency of the motor. Crosscurrent losses are the dominating stray losses which are dependent on several factors among them are percentage skew and the contact resistance between the rotor bars and laminations. It is shown in this thesis that implementing a design change which has non-skewed asymmetrical distribution of rotor slots can serve the same purpose as skewing i.e., reduction of the magnetic noise, thereby avoiding the negative effects of skewing the rotor slots especially by reducing the cross-current losses.</p><p>Two design ethodologies to introduce asymmetry in rotor slots are proposed and the key performance characteristics like torque ripple, radial air gap forces are computed both numerically and analytically. Radial forces obtained from the finite element method are coupled to the analytical tool forcalculating the magnetic noise. A spectral method to calculate and separate the radial forces into vibration modes and their respective frequencies is proposed and validated for a standard 4-pole induction motor. The influence of rotor slot number, eccentricity and skew on radial forces and magnetic noise are studied using finite element method in order to understand the vibrational and acoustic behavior of the machine, especially for identifying their sources. The validated methods on standard motors are applied for investigating the asymmetrical rotor slot machines.</p><p>Radial air gap forces and magnetic noise spectra are computed for the novel dual and sinusoidal symmetrical rotors and compared with the standard symmetrical rotor. The results obtained showed reduced radial forces and magnetic noise in asymmetrical rotors, both for the eccentric and noneccentric cases. Based on the results obtained some guide lines for designing  asymmetrical rotor slots are established. Magnitudes of the harmful modes of vibration observed in the eccentric rotors, which usually occur in reality, are considerably reduced in asymmetrical rotors showing lower sound intensity levels produced by asymmetrical rotors. The noise level from mode-2 vibration in a 4-pole standard 15 kW motor running with 25% static eccentricity is decreased by about 6 dB, compared to the standard rotors. Hence improved performance can be achieved by removing skew which reduces cross current losses and by employing asymmetrical rotor slots same noise level can be maintained or can be even lowered.</p><p> </p><p> </p>

Cette thèse de doctorat s'inscrit dans un projet pour le développement du transport ferroviaire piloté par la société ALSTOM Transport. Il répond aux prévisions de quadruplement des déplacements interurbains et régionaux en France à l'horizon 2020 en respectant les contraintes environnementales très sévères, dont les normes restrictives du niveau de bruit émis par les trains. Une réduction importante du bruit émis par le moteur est donc nécessaire. Notre mission dans ce projet a été de développer un outil capable de prédire le bruit d'origine électromagnétique produit par les moteurs synchrones à aimants permanents, équipés d'un bobinage distribué ou concentré, et alimentés par des tensions MLI. Pour cela, un modèle multi-physique a été développé.Un couplage numérique - analytique a été mis en place pour calculer les forces magnétiques dans l'entrefer. La perméance globale d'entrefer et les inductances synchrones sont ainsi calculées grâce à des simulations éléments finis en statique, et très rapides. Un niveau de précision et de rapidité de résolution inégalé est obtenu pour le calcul des forces magnétiques. L'alimentation MLI, la perméabilité des clavettes, la saillance du rotor et l'asymétrie des dents du stator sont pris en compte. La rapidité de l'outil permet un couplage avec un superviseur d'optimisation. Deux prototypes ont été dimensionnés et fabriqués dans le but de valider le modèle multi-physique / This thesis is part of a project for the development of rail transportation piloted by ALSTOM TRANSPORT. It meets the forecasts of fourfold increase of the interurban and regional travels in France before 2020, by respecting very severe environmental requirements, among which the restrictive standards of noise level emitted by trains. An important reduction of the noise radiated by motors is required. Our mission in this project was to develop a tool capable of predicting the electromagnetic noise produced by permanent magnet synchronous motors equipped with distributed or concentrated windings, and fed by a PWM converter. For that purpose, a multi-physics model was developed.A numerical - analytical coupling was set up to calculate the airgap magnetic pressures. Global airgap permeance and synchronous inductances are thus calculated thanks to statics finite element simulations. An unequalled level of precision and speed of resolution is obtained for the computation of airgap magnetic pressures. The PWM supply, the wedge permeability, the rotor shape and the asymmetry of stator teeth are taken into account. The quickness of the resolution allows coupling our tool with an optimization supervisor. Two prototypes were designed and built in order to validate the multi-physics model

Induction machines convert more than 55% of electrical energy into various other forms in industrial and domestic environments. Improved performance, especially by reduction of losses in induction machines hence can significantly reduce consumption of electricity. Many design and control methods are adopted to make induction machines work more efficiently, however certain design compromises are inevitable, such as skewing the rotor to improve the magnetic noise and torque characteristics increase the cross current losses considerably in a cage rotor, degrading the efficiency of the motor. Crosscurrent losses are the dominating stray losses which are dependent on several factors among them are percentage skew and the contact resistance between the rotor bars and laminations. It is shown in this thesis that implementing a design change which has non-skewed asymmetrical distribution of rotor slots can serve the same purpose as skewing i.e., reduction of the magnetic noise, thereby avoiding the negative effects of skewing the rotor slots especially by reducing the cross-current losses. Two design ethodologies to introduce asymmetry in rotor slots are proposed and the key performance characteristics like torque ripple, radial air gap forces are computed both numerically and analytically. Radial forces obtained from the finite element method are coupled to the analytical tool forcalculating the magnetic noise. A spectral method to calculate and separate the radial forces into vibration modes and their respective frequencies is proposed and validated for a standard 4-pole induction motor. The influence of rotor slot number, eccentricity and skew on radial forces and magnetic noise are studied using finite element method in order to understand the vibrational and acoustic behavior of the machine, especially for identifying their sources. The validated methods on standard motors are applied for investigating the asymmetrical rotor slot machines. Radial air gap forces and magnetic noise spectra are computed for the novel dual and sinusoidal symmetrical rotors and compared with the standard symmetrical rotor. The results obtained showed reduced radial forces and magnetic noise in asymmetrical rotors, both for the eccentric and noneccentric cases. Based on the results obtained some guide lines for designing  asymmetrical rotor slots are established. Magnitudes of the harmful modes of vibration observed in the eccentric rotors, which usually occur in reality, are considerably reduced in asymmetrical rotors showing lower sound intensity levels produced by asymmetrical rotors. The noise level from mode-2 vibration in a 4-pole standard 15 kW motor running with 25% static eccentricity is decreased by about 6 dB, compared to the standard rotors. Hence improved performance can be achieved by removing skew which reduces cross current losses and by employing asymmetrical rotor slots same noise level can be maintained or can be even lowered. / QC 20110221