<p>A magnetostrictive material elongates when it is subjected to a magnetic field. This effect can then be used to design powerful actuators. The department of electromagnetic engineering has been working with magnetostricitve material and their applications since the 1980s and is presently engaged in a project focusing on magnetostrictive transducer utilisation for the aeronautic field.</p><p>The focus of the presented work has been to develop and improve methods and tools supporting the development of magnetostrictive actuators.</p><p>The axial-radial model was previously developed at the department and is well suited for circular cross sections of magnetostrictive rods. It is, however, common to laminate the magnetostrictive rods resulting in rectangular cross sections. The use of Cauer circuits allows modelling of the shielding effect. This shielding effect results in non-homogenous magnetisation and stress in both rectangular and circular cross sections of the rod. A model based on Cauer circuits, including a hysteresis model based on experimental data, was developed during the project. Furthermore, it is demonstrated how figures of merit and the use of finite element methods can be used to find optimised designs in a systematic and computational efficient way. The<i> modified generalised Fabry factor</i> <i>and the magnetisation inhomogeneity coefficient</i> are two proposed new figures of merit.</p><p>A Magnetostricitve material is characterised through an experimental procedure. Usually, magnetostrictive material exhibit large hysteresis. An important part of the material characterisation is the post-processing of the measurement data, including a de-hysterisation procedure. In the thesis, a de-hysterisation method which ensures energy consistent data is presented. Energy consistent material data is essential to achieve energy consistent simulations of magnetostrictive systems.</p><p>It is also demonstrated how the knowledge at the department can be utilised in international projects. In an ongoing project, the department is engaged in two sub tasks. In one of these sub tasks a high torque actuator is to be developed for the helicopter industry. The developed magnetostrictive models are used to perform system simulations of such actuator systems. In the other sub task a device for power harvesting from vibrations is analysed. It has now been shown how to adapt the load impedance in order to extract maximal electric power from the device.</p>

Multivalent interactions are common in nature, such as influenza virus infecting epithelial cells, clearance of pathogens by antibody-mediated attachment to macrophages, etc. To mimic nature, we utilized a bottom-up approach to develop various multivalent self-assembling systems based on leucine-zipper peptides. We tethered several pairs of leucine-zipper peptides to PAMAM dendrimers to form leucine-zipper dendrimers (LZDs). We conjugated Fos/Jun to the dendrimer to make D0Fos4 and D0Jun4, and studied the interactions between these LZDs and their cognate peptide target, either Jun or Fos. Our experiments showed that the D0Fos4 can non-covalently assemble four copies of Jun, and this approach can be further used for the rapid non-covalently assembling of multimeric ligands. We also pursued the multivalent target of GPCRs with a Fos/Jun assembly, and found the complex can potentially be used as a molecular switch to target GPCRs with controlled ligand activity. In a related project for bio-material design based on self-assembly of LZDs, we synthesized a different pair of LZDs, D-Ez4 and D-Kz4, and established that they can assemble at neutral pH to form helical fibrils which display higher order self-organized structures, providing a new methodology for bio-material design. In another effort for studying multivalent interactions, we conjugated three copies of the F23, mini-protein that binds the HIV-1 capsid protein, to a trimesic acid and obtained a trivalent inhibitor, Tri-F23. Tri-F23 showed enhanced binding in ELISA against gp120, but was not significantly more effective preventing HIV entry. This methodology provides a new strategy for developing multivalent inhibitors for preventing HIV-1 infection at the entry level. In a related area, we are developing imaging agents based on quantum dots that can detect GPCRs on whole cells and at the single molecule level. To this end, a new method was developed for biocompatible amphphilic polymers to coat quantum dots. This amphiphilic polymer facilitates rapid quantum dot conjugation to any ligand with a free thiol or engineered cysteine. Several GPCR targeted peptides have been utilized for imaging receptors on whole cells and as single molecules. These efforts will guide the rational design of multivalent ligands for targeting GPCRs and other cell surface proteins.

La polykystose rénale autosomique dominante (PKRAD) est la maladie génétique rénale la plus commune touchant 1/500 personnes. Elle se caractérise principalement par la formation de kystes rénaux dans tous les segments du néphron, entraînant l’insuffisance rénale, et par des manifestations extrarénales kystiques (foie, pancréas, rate) et non-kystiques (anomalies cardiaques, vasculaires et cérébrales). Deux gènes, PKD1 et PKD2, sont responsables de 85 et 15% des cas respectivement. Ces gènes encodent les polycystine-1 (PC-1) et -2 (PC-2) qui forment un complexe à la membrane plasmique et ciliaire des cellules épithéliales rénales. PC-1 est une protéine transmembranaire de 4302 acides aminés possédant un court domaine intracellulaire incluant un motif coiled-coil impliqué dans l’interaction entre PC-1 et PC-2 in-vitro. L’importance du coiled-coil est démontrée par des mutations affectant spécifiquement ce motif chez des patients PKRAD. Le mécanisme pathogénétique responsable de la PKRAD est indéterminé. Chez la souris, la PKRAD se développe suite à l’ablation (Pkd1-/-) ou lors de la surexpression (SBPkd1TAG) de Pkd1, ce qui suggère un effet de dosage. Des anomalies ciliaires sont aussi souvent associées à PKRAD. Mon objectif était de déterminer in-vivo le mécanisme pathogénétique de la polycystine-1 dans le développement des symptômes PKRAD rénaux et extrarénaux et plus spécifiquement, le rôle du motif coiled-coil dans le mécanisme de kystogenèse. Pour ce faire, nous avons généré deux constructions, Pkd1 sauvage (Pkd1TAG) et Pkd1 tronquée de son motif coiled-coil (Pkd1ΔCoiled-coil), par recombinaison homologue à partir du BAC-Pkd1 sauvage comprenant la séquence murine entière de Pkd1. Trois lignées de souris Pkd1TAG générées par microinjection démontrent un niveau d’expression de Pkd1 qui corrèle avec le nombre de copie du transgène (2, 5 et 15 copies). Les souris Pkd1TAG reproduisent la PKRAD en développant des kystes rénaux dans toutes les parties du néphron et des cils primaires plus longs que les contrôles non transgéniques. Les analyses physiologiques supportent que les souris Pkd1TAG développent une insuffisance rénale et démontrent une augmentation du volume urinaire de même qu’une diminution de l’osmolalité, de la créatinine et des protéines urinaires. De plus, les souris Pkd1TAG développent des kystes hépatiques, des anomalies cardiaques associées à des dépôts de calcium et des anévrismes cérébraux. La sévérité du phénotype augmente avec l’expression de Pkd1 appuyant l’hypothèse d’un mécanisme de dosage. Nous avons aussi déterminé que l’expression du transgène Pkd1TAG complémente le phénotype létal-embryonnaire des souris Pkd1-/-. D’autre part, nous avons générés 4 lignées de souris Pkd1ΔCoiled-coil (2 et 15 copies du transgène) dont le nombre de copies corrèle avec le niveau d’expression du transgène. Ces souris Pkd1ΔCoiled-coil, contrairement aux Pkd1TAG de même âge, ne développent pas de kystes et possèdent des cils primaires de longueur normale. Afin d’évaluer le rôle du motif coiled-coil en absence de polycystine-1 endogène, nous avons croisé les souris Pkd1ΔCoiled-coil avec les souris Pkd1-/-. Contrairement aux souris Pkd1-/- qui meurent in-utéro, les souris Pkd1ΔCoiled-coil; Pkd1-/- survivent ~10 à 14 jours après la naissance. Elles démontrent des kystes rénaux et pancréatiques sévères, un retard de croissance et des anomalies pulmonaires. Tous les segments du néphron sont affectés. Mon projet démontre que la surexpression de Pkd1 est un mécanisme pathogénique de la PKRAD tant au niveau rénal qu’extrarénal. De plus, il démontre que le motif coiled-coil est un élément déterminant dans la kystogenèse/PKRAD in-vivo. / Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder affecting 1:500 people worldwide, independently from sex and origin. ADPKD is characterized by formation of large bilateral kidney cysts affecting all segments of the nephron and increasing progressively in size and number leading to end stage renal failure by mid-fifty. Moreover, this systemic disease includes several extrarenal symptoms such as intracranial aneurysms, valvular defects and cysts formation in the liver and the pancreas. PKD1 and PKD2 genes mutations are involved in 85 and 15 % of the clinical cases. PKD genes encode polycystin-1 (PC-1) and -2 (PC-2), which both form a complex at the cell and ciliary membrane of renal epithelial cells. PC-1 is a large transmembrane protein with a small intracellular tail including a coiled-coil motif implicated in PC-1/PC-2 interaction in-vitro. Interestingly, specific mutations affecting the coiled-coil motif cause ADPKD in humans. The pathogenetic mechanism of ADPKD is unknown. In mice, both ablation (Pkd1-/-) or overexpression (SBPkd1TAG) of Pkd1 cause ADPKD, suggesting a dosage model. Ciliary anomalies are also linked to polycystic kidney disease. Herein, we evaluated in-vivo the role of Pkd1 in the development of renal and extrarenal manifestations of ADPKD and more specifically, the role of the coiled-coil motif in cystogenesis. We generated two constructions, wildtype Pkd1 (Pkd1TAG) and coiled-coil deleted Pkd1 (Pkd1ΔCoiled-coil), by homologous recombination from the wildtype Pkd1-BAC comprising the whole Pkd1 murine sequence. Three Pkd1TAG mice lines have been generated by microinjection and show expression patterns correlating with the copy number of the transgene (2, 5 and 15 copy). All Pkd1TAG mice develop renal cysts affecting all nephron segments as in ADPKD and longer primary cilia compared to wildtype mice. Physiologic analysis supports renal failure by increased urinary output and decreased of urinary proteins, osmolality and creatinin levels. Pkd1TAG mice also show cysts in the liver, cardiac and valvular anomalies associated with calcium deposition and cerebral aneurysms. The severity of the phenotype increased with Pkd1 expression suggesting a dosage model. Importantly, the Pkd1TAG transgene rescue embryonic lethality of Pkd1-/- mice. Furthermore, we generated 4 lines of Pkd1ΔCoiled-coil mice of 2 and 15 copies of the transgene correlating also to the level of expression. Compared to age-matched Pkd1TAG, Pkd1ΔCoiled-coil mice develop no cysts and show normal cilia length. To gain more insights on the role of coiled-coil motif in absence of endogenous Pc-1, we mated Pkd1ΔCoiled-coil with Pkd1-/- mice. Compared to the lethal embryonic Pkd1-/- mice, Pkd1ΔCoiled-coil; Pkd1-/- live ~ 10 to 14 days. They show severe renal and pancreatic cysts as well as growth retardation and pulmonary defects. My study demonstrates that Pkd1 overexpression is a pathogenic mechanism to induce ADPKD renal and extrarenal phenotype. Moreover, this work shows that the coiled-coil motif of polycystin-1 is a critical determinant in ADPKD cystogenesis.

Alors que l’Imagerie par résonance magnétique (IRM) permet d’obtenir un large éventail de données anatomiques et fonctionnelles, les scanneurs cliniques sont généralement restreints à l’utilisation du proton pour leurs images et leurs applications spectroscopiques. Le phosphore jouant un rôle prépondérant dans le métabolisme énergétique, l’utilisation de cet atome en spectroscopie RM présente un énorme avantage dans l’observation du corps humain. Cela représente un certain nombre de déEis techniques à relever dus à la faible concentration de phosphore et sa fréquence de résonance différente. L’objectif de ce projet a été de développer la capacité à réaliser des expériences de spectroscopie phosphore sur un scanneur IRM clinique de 3 Tesla. Nous présentons ici les différentes étapes nécessaires à la conception et la validation d’une antenne IRM syntonisée à la fréquence du phosphore. Nous présentons aussi l’information relative à réalisation de fantômes utilisés dans les tests de validation et la calibration. Finalement, nous présentons les résultats préliminaires d’acquisitions spectroscopiques sur un muscle humain permettant d’identiEier les différents métabolites phosphorylés à haute énergie. Ces résultats s’inscrivent dans un projet de plus grande envergure où les impacts des changements du métabolisme énergétique sont étudiés en relation avec l’âge et les pathologies. / Although magnetic resonance imaging (MRI) provides a wide array of anatomical and functional contrasts, clinical MRI systems are typically limited to imaging of tissue water and spectroscopy based on hydrogen atoms in more complex molecules. Given the important role of phosphate metabolism in virtually all biological processes, there has been considerable interest in the development of technology allowing detection and spectroscopy of magnetic resonance signals associated with phosphorus in the human body. This poses a number of technical challenges, due to the lower natural abundance and resonant frequency of phosphorus. The objective of this project was to develop and implement a basic in vivo phosphorus capability on a clinical 3 Tesla MRI scanner. We present here the various steps toward building and testing a working prototype of MR coil tuned to phosphorus frequency. We also provide information on building a set of test phantoms required for this project that can be used for signal calibration. Finally we show preliminary phosphorus spectra from muscle, in human subjects, demonstrating the main constituents in high-energy phosphate metabolism. These results pave the way for future applications in which the metabolic physiology of the human brain will be studied during aging and in disease.

No description available.

Bacterial cytoskeleton is an exciting and relatively new field of research. Recent findings have proven that microbes are well-organized and neatly structured organisms. In this study we have shown that intermediate filament-like proteins with a characteristic rod domain architecture of coiled coil segments separated by non-coiled coil linkers, are widely spread among bacteria. We identified and characterized an intermediate filament-like protein (named FilP after filamentous protein) in Streptomyces coelicolor. It shares the characteristic biochemical property of eukaryotic intermediate filaments of formation of spontaneous filaments in vitro without requiring any energy or co-factor. We have provided here a preliminary model of its assembly in vitro. FilP also forms in vivo filaments in S. coelicolor hyphae, which are strongest at the sub-apical location of growing vegetative hyphae. We have proposed that FilP cytoskeletal network provides rigidity to the hyphae, especially at the growing tips, by interacting with an essential coiled coil protein DivIVA and possibly other partner elements, yet to be found. S. coelicolor is a well-studied model organism with a complicated life cycle. It germinates from a spore and spreads by forming branched vegetative hyphae. Lack of nutrients in the environment initiates formation of aerial hyphae in the air, perpendicular to the vegetative ones. The aerial hyphae differentiate into spore chains and eventually grey-pigmented dispersed individual spores are released. The signals involved in sporulation including cell division and chromosome segregation are not clear yet. We characterized here a novel locus consisting of two genes: a small putative membrane protein with no defined function, named SmeA and a member of the SpoIIIE/FtsK family, called SffA. The expression of this locus appears to be dependent on whiA and whiG-whiH-whiI pathways. This finding is intriguing as it can provide insight to the relationship between two apparently unrelated pathways, both leading to the same function of septation and maturation during sporulation.

No description available.

O presente trabalho trata de uma modelagem eletromagneticamente acoplada e fracamente acoplada ao problema mecânico do processo de conformação eletromagnética (EMF). Este usa bobina espiral plana, aplicada na deformação de chapas finas e planas para obter geometrias finais rasas. Um método de solução numérica é usado para o problema eletromagnético, o qual foi desenvolvido no software Matlab e utiliza o software Abaqus/Explicit para verificação da geometria deformada após a aplicação da força transiente de origem eletromagnética. O método foca especificamente no cálculo da densidade de fluxo magnético em pontos específicos usando a lei de Biot-Savart e análise do circuito que modela o processo de conformação eletromagnética, sendo que as indutâncias deste circuito são calculadas e fazem o acoplamento entre os fenômenos elétricos e magnéticos. Os cálculos das correntes de descarga e induzidas e perfil da força de origem eletromagnética são realizados para o instante inicial, sem considerar o movimento da chapa. O perfil da força de origem eletromagnética ao longo da chapa é calculado para diversos instantes, sendo este um dos dados de entrada no software Abaqus/Explicit através de uma sub-rotina acessível ao usuário (VDLOAD) obtendo-se a geometria da chapa deformada. A rotina de cálculo discretiza o problema eletromagnético como um sistema de equações diferenciais ordinárias (ODE) para calcular a corrente de descarga da bobina atuadora e as induzidas na chapa metálica. Experimentos, sem chapa acoplada, e com chapa fixa ou deformando foram realizados com a aquisição da corrente de descarga, medição da densidade de fluxo magnético, velocidade de deformação e geometria da chapa deformada, demonstrando uma boa correlação com o método de cálculo proposto. O presente trabalho fornece importantes informações para o projeto de sistemas de conformação eletromagnética sem a necessidade de uma função da corrente de descarga como dado de entrada para solução do problema eletromagnético. / This thesis deals with modeling and numerical simulation electromagnetically coupled and loosely-coupled to the mechanical problem for process of the electromagnetic forming. This uses flat spiral coil, applied to the deformation of thin and flat sheet metal to obtain shallow end geometries. This method uses a numerical solution to the electromagnetic problem, which was developed in the software Matlab and uses the software Abaqus/Explicit for verification of the deformed geometry after applying of the transient force of origin electromagnetic. The method focuses specifically on the calculation of the magnetic flux density at specific points using the Biot-Savart law and circuit analysis that modeling of electromagnetic forming process and the inductances of this circuit are calculated and couple the electric and magnetic phenomena. Calculations of discharge and induced currents, profile force of origin electromagnetic are performed for the initial time, without considering the motion of the sheet metal. The profiles force of origin electromagnetic along the sheet metal is calculated for several instants, which are input data in software Abaqus/Explicit using a user-routine (VDLOAD) obtaining the deformed geometry of the sheet metal. The calculation routine discretizes the electromagnetic problem as a system of ordinary differential equations (ODE) to calculate the discharge current of the actuator coil and induced currents in the metal sheet. Experiments without coupled sheet metal, and fixed or deforming sheet metal were performed with the acquisition of the discharge current, measurement of magnetic flux density, velocity of movement and deformation geometry of the sheet metal, demonstrating a good correlation with the proposed method of calculation. This study provides important information for the design of the electromagnetic forming systems without the need for a function of discharge current as input for solution of the electromagnetic problem.

Objetivo: Desenvolver um modelo experimental de aneurisma cerebral em artéria de suínos. Secundariamente, avaliar o processo de organização do trombo e de formação de tecido fibrocelular dentro do aneurisma com o tratamento endovascular utilizando molas revestidas (Matrix) comparadas às sem revestimento (GDC). Materiais e Métodos: Em 10 suínos sadios, com peso variando entre 16 e 20 kg, sendo 6 machos e 4 fêmeas, foi realizada a cirurgia de formação de aneurisma nas carótidas bilateralmente, através de arteriotomia e anastomose término-lateral com segmento de veia jugular. O diâmetro médio dos aneurismas era de 3 mm (variação de 2 a 4mm). Procedia-se então ao tratamento endovascular dos aneurismas divididos do seguinte modo: grupo I, embolização do aneurisma da carótida esquerda com mola de platina (GDC); grupo II, embolização do aneurisma da carótida direita com mola de platina revestida com copolímero - PGLA 90/10 (Matrix). Após 14 dias, eram retiradas as lesões e analisadas microscopicamente, comparando-se a formação de trombo recente ou trombo organizado no interior de cada aneurisma. Para isso, foi criada uma escala de caracterização das fases do processo de trombose (Escores de 1 a 4). O Escore 1 era definido como a presença de trombo inicial ou recente; o Escore 2 era categorizado como a presença de leucócitos em diferenciação contendo fibrina e absorção das hemácias e plaquetas, porém intercalados com zonas contendo trombo recente. No Escore 3, observavase a presença de leucócitos em diferenciação contendo fibrina e no Escore 4, a presença de tecido fibrocelular contendo fibras de colágeno. A análise estatística foi realizada de modo pareado, através do Teste de Wilcoxon, sendo os dados processados no programa SPSS 12.0. O nível de significância mínimo adotado foi de 5%. Resultados: Um animal (macho) foi excluído do estudo devido à formação de abscesso cervical, restando, portanto, 9 animais (18 aneurismas para avaliação). Na análise do processo de organização do trombo, utilizou-se a graduação por escores, obtendo-se no grupo I, 88,8% de casos de trombo recente (Escore 1) e 11,1% de casos de trombo em organização ainda contendo coágulo (Escore 2). No grupo II, obteve-se 11,1% de casos com escore 1 , 11,1% com escore 2, 55,5% de casos de trombo organizado com tecido fibrocelular frouxo (Escore 3) e 22,2% de casos de tecido fibrocelular denso contendo colágeno (Escore 4). Houve diferença estatística a favor do grupo II, por meio do Teste de Wilcoxon (p=0,008). Conclusão: O modelo experimental de aneurisma de pequenas dimensões utilizado neste estudo foi adequado e permitiu a realização do tratamento endovascular testando dois tipos de molas. Por meio da análise histológica baseada em escala criada para avaliar a organização do trombo, pôde-se verificar diferença significativa a favor das molas com revestimento de copolímero. / Background and Objectives: To develop an experimental model in a pig that could be used for analysis of patency of cerebral aneurysms is the goal of this study. Adictionaly, it aims to evaluate the degree of thrombosis after embolization with two types of coils: copolymer-coated coils (Matrix) and uncoated platinum coils (GDC). Method: In a total of 10 Large-White pigs, small aneurysms (with a mean diameter of 3 mm) were created in both carotid arteries (6 males and 4 females) weighing 16 to 20 kg (mean: 18 kg). Embolization was performed with GDC platinum coils on the left side and with a coil coated with Matrix polymer on the right side. After 14 days, angiography was performed to confirm exclusion of the aneurysm. Before euthanasia with a lethal dose of potassium chloride, the carotid artery was removed in one piece, including the aneurysm. The specimens were cut into sections, including the mid portion of the aneurysm and the artery above and below the aneurysm, and stained with hematoxylin- eosin for histological analysis. A graduated scale with progressive scores ranging from 1 to 4 was used to evaluate the organization of the thrombus. Score 1 indicated clusters of platelets, white blood cells, and red blood cells; Score 2 showed the presence of differentiating white blood cells containing fibrin and absorption of red blood cells and platelets, interspersed with zones containing a recent thrombus; Score 3 corresponded to the presence of differentiating white blood cells containing fibrin, which characterized a loose fibrocellular tissue; and Score 4 indicated the presence of fibrocellular tissue containing collagen fibers, which characterized an incipient dense fibrocellular tissue The data were described as frequency and percentage using the Wilcoxon test for findings involving thrombosis scores. The data were analyzed using the SPSS 12.0 software, and the minimum significance level was set at 5%. Results: One animal (male) was excluded from the study due to abscess formation near the anastomosis. Therefore, 9 animals (18 aneurysms) were assessed. A score was used for analyzing the organization of the thrombus. In group I, 88.8% had score 1, 11.1% score 2, but no cases showed scores 3 and 4. In group II, 11.1% had score 1, 11.1% score 2, 55.5% score 3, and 22.2% score 4. The Wilcoxon test was applied, revealing a significant difference (p=0.008) between the scores for group I and group II in the course of 14 days. Conclusion: The experimental aneurysm developed in this study was suitable for assessing the patency of small aneurysms (measuring, on average, 3 mm) after coil embolization. The organization of the intra-aneurysmal thrombus after 14 days was verified using the progressive score, which indicated a significant difference between the group treated with the Matrix coil and that treated with GDC.

La mesure des champs électromagnétiques très basses fréquences en mer est utilisée pour de nombreuses applications, dont les principales sont militaires et géophysiques. Les besoins pour ces applications sont des capteurs capables d'effectuer des mesures à très basses fréquences avec un niveau de bruit inférieur au nV.m^(-1).Hz^(-1/2).Les électromètres commerciaux et académiques utilisés actuellement pour la mesure des champs électriques en mer sont à mesure de tension. Leur inconvénient majeur est une remontée de bruit aux basses fréquences, due à l'électronique d'amplification du signal. Une autre méthode de mesure des champs électriques en mer consiste à mesurer le courant traversant un dispositif de faible impédance. Nous avons conçu un électromètre à mesure de courant et magnétomètre au sein du même capteur, en essayant de pallier les défauts des électromètres passés et actuels.Dans un premier temps, nous décrivons le milieu dans lequel le capteur sera amené à fonctionner, puis les applications auxquelles il est destiné, et enfin l'état de l'art des capteurs existant et leurs limites.Nous décrivons ensuite de manière détaillée le comportement du capteur. En particulier, nous déterminons par simulation et de manière expérimentale les différentes fonctions de transfert du capteur, en fonction de ses caractéristiques géométriques et de son environnement.Après avoir présenté plusieurs architectures possibles d'électromètres répondant aux objectifs fixés, nous utilisons les résultats obtenus au chapitre précédent pour dimensionner un électromètre dont la conductivité équivalente n'est pas forcément égale à celle de l'eau de mer. Ce degré de liberté supplémentaire par rapport aux contraintes de conception des électromètres à mesure de courant passés permet d'améliorer les performances du capteur. Enfin nous proposons deux méthodes de calibration de l'électromètre, sans connaissance a priori de son environnement.Enfin nous caractérisons les différents éléments d'un prototype de laboratoire, et nous présentons les résultats des tests de ce prototype complet. / The measurement of electric and magnetic fields at sea is of great interest for many applications (geophysics, oil prospection, vessels detection, etc.) In all cases, measurements at very low frequency with a very low noise are required.Most marine electrometers measure the potential difference between two separated electrodes. Their noise level is very good but increases when frequency decreases, due to amplification electronics. Another type of electrometers is based on a low impedance current measurement system. We designed a current based electrometer, which is as well able to simultaneously measure the magnetic field, trying to solve the problems of former devices.First, we describe the medium in which the sensor will be used, the applications for which it is intended, and the state of the art of existing sensors and their defects.We then describe in detail the behavior of the sensor. In particular, we determine by simulation and experimentally the different transfer functions of the sensor, depending on its geometrical characteristics and its environment.After presenting several potential architectures of electrometers meeting the targets, we use the results obtained in the previous chapter to scale an electrometer, whose equivalent conductivity is not necessarily equal to that of seawater. This additional degree of freedom in comparison with the design constraints of the former current measurement electrometers enables us to improve the performance of the sensor. Finally we propose two calibration methods of the electrometer, without prior knowledge of its environment.Finally we characterize the different elements of a laboratory prototype, and we present the results of the tests of the complete prototype.