Purpose: Previous clinical studies have suggested a positive effect of low-frequency pulsed electromagnetic fields (PEMF) on wound healing and inflammation in the eye. We tried to test the value of PEMF treatment in a hyphema animal model with well-defined conditions. Methods: After injection of citrated autologous blood for the production of hyphema, 16 rabbit eyes were treated with 10 or 20 mT for 60 min on 4 days within the postoperative week. Two control groups with hyphema alone (n = 8) and PEMF irradiation without hyphema (n = 4) were also included. The rate of resorption was recorded daily. Histopathologic evaluation was performed. Results: The incidence of endothelial cell damage and fibrotic clots was markedly reduced in the 10-mT group while the resorption time of 8 days was identical with the control group. In the 20-mT group, the complication rate and the resorption time was increased versus the control group. Conclusions: The use of PEMF treatment is of some, however, limited value as it did not reduce the resorption time of hyphema but displayed a dose-dependent, beneficial influence on some serious side effects. Future clinical studies with low-dose PEMF irradiation are justified and should determine the optimal dosage and suitable indications of PEMFs as an adjunctive treatment in ocular inflammation or trauma. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

yes / There is an increasing need for accurate models describing the electrical behaviour of individual biological cells exposed to electromagnetic fields. In this area of solving linear problem, the most frequently used technique for computing the EM field is the Finite-Difference Time-Domain (FDTD) method. When modelling objects that are small compared with the wavelength, for example biological cells at radio frequencies, the standard Finite-Difference Time-Domain (FDTD) method requires extremely small time-step sizes, which may lead to excessive computation times. The problem can be overcome by implementing a quasi-static approximate version of FDTD, based on transferring the working frequency to a higher frequency and scaling back to the frequency of interest after the field has been computed. An approach to modeling and analysis of biological cells, incorporating the Hodgkin and Huxley membrane model, is presented here. Since the external medium of the biological cell is lossy material, a modified Berenger absorbing boundary condition is used to truncate the computation grid. Linear assemblages of cells are investigated and then Floquet periodic boundary conditions are imposed to imitate the effect of periodic replication of the assemblages. Thus, the analysis of a large structure of cells is made more computationally efficient than the modeling of the entire structure. The total fields of the simulated structures are shown to give reasonable and stable results at 900MHz, 1800MHz and 2450MHz. This method will facilitate deeper investigation of the phenomena in the interaction between EM fields and biological systems. Moreover, the nonlinear response of biological cell exposed to a 0.9GHz signal was discussed on observing the second harmonic at 1.8GHz. In this, an electrical circuit model has been proposed to calibrate the performance of nonlinear RF energy conversion inside a high quality factor resonant cavity with known nonlinear device. Meanwhile, the first and second harmonic responses of the cavity due to the loading of the cavity with the lossy material will also be demonstrated. The results from proposed mathematical model, give good indication of the input power required to detect the weakly effects of the second harmonic signal prior to perform the measurement. Hence, this proposed mathematical model will assist to determine how sensitivity of the second harmonic signal can be detected by placing the required specific input power.

A doubly resonant cavity was used to search for nonlinear radiofrequency (RF) energy conversion in a range of biological preparations, thereby testing the hypothesis that living tissue can demodulate RF carriers and generate baseband signals. The samples comprised high-density cell suspensions (human lymphocytes and mouse bone marrow cells); adherent cells (IMR-32 human neuroblastoma, G361 human melanoma, HF-19 human fibroblasts, N2a murine neuroblastoma (differentiated and non-differentiated) and Chinese hamster ovary (CHO) cells) and thin sections or slices of mouse tissues (brain, kidney, muscle, liver, spleen, testis, heart and diaphragm). Viable and non-viable (heat killed or metabolically impaired) samples were tested. Over 500 cell and tissue samples were placed within the cavity, exposed to continuous wave (CW) fields at the resonant frequency (f) of the loaded cavity (near 883 MHz) using input powers of 0.1 or 1 mW, and monitored for second harmonic generation by inspection of the output at 2f. Unwanted signals were minimised using low pass filters (</= 1 GHz) at the input to, and high pass filters (>/= 1 GHz) at the output from, the cavity. A tuned low noise amplifier allowed detection of second harmonic signals above a noise floor as low as -169 dBm. No consistent second harmonic of the incident CW signals was detected. Therefore, these results do not support the hypothesis that living cells can demodulate RF energy, since second harmonic generation is the necessary and sufficient condition for demodulation.

Die dreidimensionale Positionsbestimmung unter Tage ist eine in der bergbautechnischen Praxis häufig gestellte Aufgabe. Die derzeit gebräuchlichen Verfahren basieren überwiegend auf zahlreichen relativen Messungen zwischen Festpunkten an der Erdoberfläche und dem zu bestimmenden Punkt unter Tage. Das hier vorgestellte Verfahren ist ein im geodätischen Sinn absolutes Verfahren. Die Punktbestimmung erfolgt direkt mit Hilfe der Festpunkte über Tage und dem unbekannten Punkt unter Tage. Relative Messungen zu benachbarten Punkten sind nicht notwendig. Die Grundlage des Verfahrens bildet die zeitliche Erfassung transienter elektromagnetischer Felder an einem zu bestimmenden Punkt unter Tage. Die Quellen dieser Felder sind gleichstromdurchflossene Drahtschleifen an der Erdoberfläche, die näherungsweise magnetische Dipole darstellen. Nach Abschalten des Stromes zerfällt das statische Magnetfeld und induziert elektrische Ströme in der leitfähigen Erde. Das transiente Magnetfeld wird unter Tage an einem Punkt für verschiedene Senderpositionen aufgezeichnet. Mit Hilfe eines Inversionsalgorithmus werden letztlich die dreidimensionalen Koordinaten des Messpunktes bestimmt. / Three-dimensional positioning in mines and caves is a common challenge. The methods currently used are based on numerous relative measurements. The method presented here is an absolute procedure in a geodesic sense. The coordinates of the unknown point are directly calculated using the surface points and the point underground. Relative measurements to neighboring points are not necessary. The localization procedure is based on recording transient electromagnetic fields under-ground. They are generated at the surface using direct-current carrying wire loops, which approximately represent magnetic dipoles. After shutoff the static magnetic field decays and induces electric currents in the conductive Earth. The transient electromagnetic field is recorded at an unknown point in the subsurface for different source positions. Finally, the three-dimensional coordinates of this point are reconstructed using an inversion algorithm.

Thesis (M. Tech.) -- Central University of Technology, Free State, 2008

Στην παρούσα διπλωματική εργασία μελετήθηκε και προσομοιώθηκε η επίδραση των μεταβατικών φαινομένων σε μεταλλικές κατασκευές. Συγκεκριμένα μελετήθηκαν οι επιπτώσεις της πτώσης ενός κεραυνού σε ένα πλοίο. Για την πραγματοποίηση αυτής της μελέτης χρησιμοποιήθηκε το πρόγραμμα προσομοίωσης emp3 , το οποίο έχει κατασκευασθεί από την εταιρία field precision και είναι κατάλληλο για τη μελέτη τέτοιων φαινομένων. Το emp3 στηρίζεται στη μέθοδο των πεπερασμένων στοιχείων στο πεδίο του χρόνου (FETD-FINITE-ELEMENT-TIME-DOMAIN) και καταλήγει σε συμπεράσματα με πλήρη επίλυση των εξισώσεων του Maxwell χρησιμοποιώντας μια ψευδογλώσσα επιπέδου assembly .Στο υποπρόγραμμα mesh.exe σχεδιάστηκε ένα πλοίο και το περιβάλλον του και στη συνέχεια δημιουργήθηκε το αρχείο .ein στο οποίο χωρίστηκε η διάταξη σε διάφορες περιοχές ανάλογα με τις ηλεκτρομαγνητικές ιδιότητες της καθεμίας, με σκοπό να παρατηρήσουμε τα ηλεκτρομαγνητικά πεδία που δημιουργεί το μεταβατικό φαινόμενο (κεραυνικό πλήγμα) στις τρείς διαστάσεις. Τέλος, τρέξαμε το αρχείο .ein στο emp3.exe και παραθέσαμε τα αποτελέσματα της προσομοίωσης που προέκυψαν τόσο από το υποπρόγραμμα vemp3.exe όσο από το υποπρόγραμμα probe.exe και εξαγάγαμε κάποια συνολικά συμπεράσματα. Στο πρώτο Κεφάλαιο θα γίνει αναφορά στο φυσικό φαινόμενο του κεραυνού και συγκεκριμένα στους τρόπους δημιουργίας του,στις παραμέτρους του καθώς και στους παράγοντες που τον επηρεάζουν. Στο δεύτερο Κεφάλαιο θα γίνει ανάλυση των διεργασιών που ακολουθούν την πτώση ενός κεραυνού σε ένα πλοίο και συγκεκριμένα στις επαγόμενες τάσεις και στα παραγόμενα ηλεκτρομαγνητικά πεδία καθώς και στις βλάβες που προκαλούνται τόσο στο πλοίο όσο και στα εξαρτήματα του. Στο τρίτο Κεφάλαιο θα γίνει ανάλυση του προγράμματος προσομοίωσης emp3 ,της μεθόδου στην οποία στηρίζεται ,της ψευδογλώσσας που χρησιμοποιεί και του έτοιμου παραδείγματος bdeflect με σκοπό την κατανόηση της διαδικασίας προσομοίωσης και των αποτελεσμάτων. Στο τέταρτο Κεφάλαιο θα γίνει η παρουσίαση της διαδικασίας προσομοίωσης και των αποτελεσμάτων. Συγκεκριμένα παρατείθεται η κατασκευή της γεωμετρίας του πλοίου και του περιβάλλοντος του,ο χωρισμός της συνολικής διάταξης σε περιοχές με διαφορετικά ηλεκτρομαγνητικά χαρακτηριστικά, η εισαγωγή του κώδικα στο emp3.exe τα αποτελέσματα που εξήχθησαν στα vemp3.exe και probe.exe καθώς και ορισμένα συμπεράσματα που προέκυψαν από τη διεξαγωγή της παρούσας διπλωματικής εργασίας. / In this dissertation the effect of the transient phenomena in metallic structures was studied and simulated.Specifically. were studied the effects of a lighting stroke on a ship. In order to carry out this study,was used the simulation program emp3, which is manufactured by the company field precision and is suitable for the study of such phenomena. The emp3 program is based on the method FETD-FINITE-ELEMENT-TIME-DOMAIN and concludes with complete resolution of Maxwell's equations using a pseudocode level assembly.In the subprogram mesh.exe was designed the ship and its environment and then was created the .ein file, in which the construction was divided in different regions depending on the electromagnetic characteristics of each area, in order to observe the fields that were created by the transient phenomenon (lighting stroke), in three dimensions. Finally, we ran the file .ein in emp3.exe and presented the simulation results, which were obtained from both the subprogram vemp3.exe and the subprogram probe.exe and drew some overall conclusions. In the first chapter there will be a reference to the natural phenomenon of lightning strike and specifically to the ways of it's creation, its parameters and the factors that influence it.Ιn the second chapter there is the analysis of the processes, which follow the fall of a lightning stroke on a ship and specifically the induced voltages generated electromagnetic fields and also the harms caused both to the ship and it's components. In the third chapter there is the analysis of the simulation program emp3, the method which it is based on, the pseudocode which is used and the already existed example bdeflect in order to understande the process simulation and results.In the fourth chapter the simulation process and the results are given. Specifically, the construction of the geometry of the ship and its environment, the separation of the total provision in areas with different magnetic characteristics, the insertion of the code in emp3.exe,the results exported to vemp3.exe and probe.exe and some conclusions drawn during this thesis are presented.

La mousse métallique a des propriétés mécaniques et thermodynamiques uniques qui pourraient s'avérer utiles dans de nombreux domaines, tels que la construction légère et ingénierie automobile. Cependant, la mousse métallique n'est pas encore établie en génie.Une des raisons sont les difficultés et les prix élevés dans le processus de fabrication. Causée par drainage gravitaire en état liquide, peuvent se produire des distributions de matériel non homogènes. En outre, dépassant le drainage peut provoquer rupture de bulle et la génération de soufflures. Ces effets négatifs potentiellement peuvent être évités en ajoutant magnétique ou champs électromagnétiques au cours du processus de génération.Dans cette thèse, l'influence de ces champs est donc étudié en réalisant la phase de résolution des simulations. Ces simulations sont effectuées avec le code interne premier. Une modification de la modélisation de la collision était nécessaire pour enquêter sur l'agglomération de bulles dans le métal liquide.Calcul d'une configuration statique-drainage, les mécanismes de l'agglomération sont étudiés sans la présence de champs électriques ou magnétiques. Aux vitesses élevées de drainage, les bulles flottent. À des vitesses inférieures de drainage, les bulles s'agglomèrent dans la partie supérieure du domaine, formant des structures cristallines compacte.La préférence expérimentalement bien connue de commande cubes axés sur le visage, plus hexagonale compacte vous passez votre commande de volume égal bulles est reproduit numériquement. Appliquant davantage des simulations et expériences, un mécanisme de l'instabilité de la commande de façon hexagonale compacte est identifié, ayant pour résultat la préférence de commande de cubes axés sur le visage.Afin de déterminer les propriétés mécaniques de la mousse métallique solide avec la fraction de gaz faibles et aux fonctionnalités avantageuses et désavantageuses d'état d'arrangements de bulle, simulations par éléments finis de la mousse métallique solide avec cavités sphériques sont réalisées et comparées. Une influence significative de la quantité de cristaux de bulle sur la mécanique de la mousse se trouve. Le type de l'ordre cristallin est moins important.On étudie l'influence d'un champ magnétique horizontal sur l'agglomération de bulle. La résistance de drainage peut être augmentée sensiblement en ajoutant un champ magnétique. La structure résultante des bulles est moins sensible à un champ magnétique.Combinant un courant électrique horizontal et une perpendiculaire, champ magnétique horizontal se traduit par une force verticale de Lorentz. Cette force peut équilibrer la gravitation et donc, provoquer la rotation des bulles. Simuler cet État révèle une distribution homogène de bulle. Dans le même temps, friser les champs de force dans le voisinage de chaque bulle induire un mouvement continu en remuant. Petit champ électromagnétique forces n'empêchent pas les bulles d'agglomération, mais peuvent varier le montant de la commande cristallisé et par conséquent, les propriétés mécaniques de la mousse solide qui en résulte.En conclusion, un champ magnétique horizontal augmente la résistance de drainage, tandis que sa combinaison avec un courant électrique provoque des distributions de bulle homogène et peut modifier la structure de la mousse et la fraction de gaz. Les résultats de cette thèse pourraient aider à améliorer le processus de fabrication industrielle de mousse métallique ou même permettre la production de métal poreux avec la fraction de gaz définie par l'utilisateur. / Metal foam has unique mechanical and thermodynamic properties which could prove useful in many fields, such as light-weight construction and automotive engineering. However, metal foam is not yet established in engineering. One reason are the difficulties and high prices in the fabrication process. Caused by gravity-driven drainage in liquid state, inhomogeneous material distributions can occur. Also, exceeding drainage might cause bubble rupture and the generation of blow-holes. These negative effects potentially can be avoided by adding magnetic or electromagnetic fields during the generation process. In this thesis, the influence of these fields is therefore investigated by conducting phase resolving simulations. These simulations are carried out with the in-house code PRIME. A modification of the collision modelling was necessary in order to investigate the agglomeration of bubbles within liquid metal. Computing a static-drainage setup, the agglomeration mechanisms are investigated without the presence of electric or magnetic fields. At high drainage velocities the bubbles float. At lower drainage velocities the bubbles agglomerate in the upper part of the domain, forming close-packed crystalline structures. The experimentally well known preference of face-centred cubic ordering, over hexagonally close-packed ordering of equal-volume bubbles is reproduced numerically. Applying further simulations and experiments, an instability mechanism of hexagonally close-packed ordering is identified, resulting in the preference of face-centred cubic ordering. In order to determine the mechanical properties of solid metal foam with low gas fraction and to state advantageous and disadvantageous features of bubble arrangements, Finite-Element simulations of solid metal foam with spherical voids are carried out and compared. A significant influence of the amount of bubble crystals on the foam mechanics is found. The type of the crystalline ordering is less important. The influence of a horizontal magnetic field on the bubble agglomeration is investigated. The drainage resistance can be increased significantly by adding a magnetic field. The resulting structure of the bubbles is less sensitive to a magnetic field. Combining a horizontal electric current and a perpendicular, horizontal magnetic field results in a vertical Lorentz force. This force can balance gravitation and thus, cause rotation of the bubbles. Simulating this state reveals a homogeneous bubble distribution. At the same time, curling force fields in the vicinity of each bubble induce a continuous stirring motion. Small electromagnetic field strengths do not prevent the bubbles from agglomerating, but can vary the amount of crystallized ordering and therefore, the mechanical properties of the resulting solid foam. In conclusion, a horizontal magnetic field increases the drainage resistance, while its combination with an electric current causes homogeneous bubble distributions and can alter the foam structure and the gas fraction. The results of this thesis could help improve the industrial fabrication process of metal foam or even allow production of porous metal with user-defined gas fraction.

O presente trabalho teve como objetivo avaliar o risco de óbito por leucemia, neoplasias do sistema nervoso central e esclerose lateral amiotrófica em adultos em relação à exposição a CM, no Município de São Paulo. Foi realizado um estudo do tipo caso-controle populacional envolvendo 6224 sujeitos. Casos e controles foram extraídos da base de dados do PROAIM, e foram pareados por sexo, faixa etária e distrito administrativo de residência. Foram considerados casos todos os óbitos pelos desfechos específicos, em adultos com 40 anos ou mais, residentes no Município de São Paulo, ocorridos entre 2001 e 2005. Controles foram constituídos por óbitos por todas as outras causas ocorridos no mesmo período. A exposição foi avaliada de acordo com a distância das residências dos sujeitos para a linha de transmissão (LT) mais próxima. Foi encontrado um aumento do risco de óbito por leucemia entre os indivíduos que moravam mais próximo às LT, com OR ajustado de 1,8 (IC 95%: 0,8 - 4,3) e 2,5 (IC 95%: 1,0 - 7,2) entre os sujeitos que moravam a 50 m e entre 50 e 100 m das LT, respectivamente, em relação aos que moravam a mais de 400 m. / This work aimed at evaluating the risk of death by leukemia, brain tumor and amyotrophic lateral sclerosis in adults in relation to magnetic field exposure, in the city of São Paulo. A population-based case-control study was held, and 6224 subjects were enrolled. Cases and controls were selected from the PROAIM database, and were matched by sex, age and district of residence. Cases were all deaths ocurred between 2001 and 2005 by the specific causes, ocurring in adults 40 years and older, living in the city of São Paulo. Controls were selected from all other deaths ocurred at the same period. Exposure to magnetic fields was accessed according to the distance of the dwelling to the closest transmission line (TL). The risk of death by leukemia was elevated within the subjects living closest to the TL, with an adjusted OR of 1,8 (CI 95%: 0,8 - 4,3) and 2,5 (CI 95%: 1,0 - 7,2) for people living within 50 m and within 50 to 100 m away from the TL, respectively, in relation to people living at 400 m or further.

Descargas atmosféricas representam uma das principais causas de interrupção no fornecimento de energia para os consumidores, e embora tenham efeitos mais intensos quando incidem diretamente nas redes elétricas, é o caso das descargas indiretas que chama mais atenção, já que elas ocorrem com maior frequência. Tanto as primeiras descargas que geralmente ocorrem com maior intensidade de corrente, quanto as descargas subsequentes que têm menor tempo de frente associado, irradiam campos eletromagnéticos que ao se acoplarem com as redes elétricas geram surtos que podem causar tanto a interrupção do fornecimento de energia quanto danos a equipamentos. A presença de edifícios na região de incidência da descarga atmosférica afeta a propagação das ondas irradiadas, criando diferentes padrões de campos resultantes, os quais são responsáveis por sobretensões induzidas. Embora tanto a descarga atmosférica em si quanto a caracterização do ambiente ao seu redor sejam de natureza complexa para sua representação, ferramentas computacionais bem estruturadas podem representar o fenômeno de forma satisfatória, como é o caso da ferramenta computacional desenvolvida neste trabalho utilizando o método das diferenças finitas no domínio do tempo. O presente trabalho apresenta dois estudos para verificação da influência de edificações na propagação de campo irradiado por descargas atmosféricas. O primeiro estudo avaliou o comportamento das componentes do campo elétrico e do campo magnético irradiados, comparando resultados obtidos com e sem a presença de edificações numa pequena região. Tanto os parâmetros geométricos dos três edifícios considerados neste estudo, como a permissividade e a condutividade elétrica do solo e dos edifícios, foram variados para identificar a sua influência nos campos irradiados. Os resultados mostraram diferentes comportamentos das componentes dos campos resultantes em função da variação desses parâmetros, observando-se inversão de polaridade, oscilações na forma de onda e tanto redução quanto aumento do valor de campo. O segundo estudo avaliou um caso mais geral em que a componente vertical de campo elétrico foi tomada em nove pontos diferentes de uma região tipicamente urbana, com a presença de 102 edifícios. Os valores de campo avaliados em cada ponto, dez metros acima do solo, consideraram a incidência aleatória de 28 descargas atmosféricas distintas, cada uma atingindo o topo de um dado edifício. Os resultados desse segundo estudo mostraram que exceto nos casos em que a descarga atmosférica ocorre próximo do ponto analisado, há reduções significativas do campo elétrico vertical. Desta forma é possível perceber que não apenas a existência de edifícios, mas a sua concentração com diferentes características elétricas e geométricas, podem influenciar significativamente a propagação de campo irradiado. Os valores calculados a partir da ferramenta desenvolvida podem ser usados em conjunto com modelos de acoplamento, para o cálculo de sobretensões induzidas em redes elétricas, em situações realistas com configurações mais complexas. / Atmospheric discharges represent one of the main causes of interruption in power supply to consumers, and although they have more intense effects when direct impact on energy lines, are the case of indirect discharges that draws more attention, since they occur more frequently. Both the first discharges, occurring generally with greater intensity of current, as subsequent discharges that have shorter front time associated, radiate electromagnetic fields which engage with the electrical networks generating surges that can cause so much disruption of power supply as damage to the equipment. The presence of buildings in the lightning incident area affects the propagation of the radiated waves, creating different patterns of resultant fields, which are responsible for induced overvoltages. Although both the lightning itself and characterization of the surrounding environment are of a complex nature for its representation, structured computational tools can represent satisfactorily the phenomenon, such as the software tool developed here using the finite difference time domain method. This work presents two studies to verify the influence of buildings in the propagation of lightning irradiated field. The first study assessed the behavior of the components of the electric field and magnetic field irradiated, by comparing results obtained with and without the presence of buildings in a small region. Both the geometric parameters of the three buildings considered in this study, as the permittivity and electrical conductivity of the soil and buildings, were changed to identify their influence on radiated fields. The results showed different behaviors of the components of the resulting field due to the variation of these parameters, observing polarity inversion, oscillations in the waveform and either a reduction or increase of the field value. The second study evaluated a more general case where the vertical component of the electric field was taken at nine different points of a typical urban area, in the presence of 102 buildings. The field values evaluated at each point, ten meters above the ground, considered the effect of 28 different random lightning, which hit the top of a given building. The results of this second study showed that except in cases where atmospheric discharge occurs near the analyzed point, there are significant reductions of the vertical electric field. Thus it can be seen that not only the existence of buildings, but its concentration with different electrical and geometrical characteristics, can significantly influence the propagation of irradiated field. The values calculated from the developed tool can be used in conjunction with coupling models for calculating induced overvoltages on power lines, in realistic situations with complex configurations.

L'Imagerie par Résonance Magnétique (IRM) est une modalité d'imagerie médicale reposant sur l'utilisation de champs électromagnétiques pour acquérir des images tomodensitométriques du corps humain. Bien qu'appartenant à la catégorie des rayonnements non-ionisants (RNI), des effets transitoires peuvent être ressentis par les personnels travaillant à proximité d'une IRM. Ces travailleurs sont dits exposés aux champs électromagnétiques, même si les différents comités d’experts s’accordent pour dire qu’aucun effet d’accumulation de dose ou d’effet à long terme n’a été trouvé. Ces effets à court terme, allant d’un goût métallique au niveau de la bouche à la stimulation nerveuse et à l'échauffement, sont connus et identifiés. Ils peuvent néanmoins provoquer une gêne, voire un danger, pour le travailleur. Ces préoccupations concernent spécifiquement le champ magnétique permanent (de 1,5 T à 7 T) utilisé par l'IRM. Un groupement d'experts mandatés par l'Organisation Mondiale de la Santé (OMS) a ainsi déterminé l'évaluation de l'exposition des travailleurs au champ magnétique statique comme une priorité importante. Les travaux de cette thèse ont permis de répondre à cette demande en définissant et en implémentant un dispositif de mesure autonome et léger permettant la mesure de cette exposition ainsi que la caractérisation des mouvements du travailleur. La justesse de la mesure d'induction magnétique réalisée par le dispositif est garantie par une méthode de correction numérique prenant en compte les défauts de linéarité et d'orthogonalité du capteur. Basée sur les données du capteur, une méthode d'ajustement de la mesure d'induction magnétique a ensuite été définie. Cette méthode permet, à partir d'une mesure réalisée au niveau du torse du travailleur, d'extrapoler la valeur d'induction magnétique au niveau de la tête de celui-ci. Enfin, une validation pratique du dispositif de mesure a été effectuée à travers un suivi de l'exposition des travailleurs IRM de trois centres d'imagerie médicale : imagerie clinique, imagerie interventionnelle et IRM ultra hauts champs (7~T). Des méthodes d'extraction de métriques permettant l'analyse précise et la comparaison de l'exposition des travailleurs au champ magnétique statique ont été proposées. Les travaux présentés dans cette thèse ont ouvert des perspectives intéressantes, permettant de réaliser le suivi à long terme de l'exposition des travailleurs au champ magnétique statique de façon quasi autonome. De plus, une industrialisation des outils et méthodes définis a pu être réalisée et est actuellement en cours de validation / The Magnetic Resonance Imaging (MRI) is a medical imaging modality using electromagnetic fields (EMF) in order to perform human body tomodensitometric images. Even if these fields are Non-Ionizing Radiations (NIR), some transitory effects can be felt by the staff working in the vicinity of the MRI. Such workers are qualified as “exposed” to EMF, even if all expert comities agree to say that no accumulative or long term effects have been identified yet. Short term effects are known and identified, from metallic taste in the mouth, nerve and muscle stimulation, to biologic tissue heating, which can be troublesome or dangerous. The main exposure concern comes from the MRI permanent static magnetic field (ranging from 1.5 T to 7 T). An expert comity, mandated by the World Health Organization (WHO), has therefore defined the evaluation of the exposure of the MRI workers to the static magnetic field as a priority. This was the focus of this PhD thesis. A light and autonomous static magnetic field monitor (called "exposimeter") has been developed. It allows the recording of the three-dimensional magnetic fields as well as workers’ movements. Its magnetic induction measurement accuracy has been ensured by a specific calibration, which takes into account non-linearity and non-orthogonality of the magnetic sensors. Based on exposimeter data, a magnetic induction extrapolation method has then been developed. This method allows the estimation of the EMF exposure at the head with sensors placed on the torso. Finally, a practical validation of the device has been performed in multiple MRI clinical and research centers, included clinical MRIs (1.5 T and 3 T), an interventional MRI (1.5 T) and an ultra-high field MRI (7 T). Metrics have been defined in order to precisely analyze and compare workers exposure. All the works presented in this PhD thesis open new perspectives such as long term static magnetic field exposure follow-up. Moreover, industrial transfer of the device has been performed and is currently being validated