Grâce aux progrès réalisés ces dernières années dans la conception de réseaux intelligents, tels que les réseaux centrés sur la personne (WBAN) ou les réseaux sans fils de proximité (WPAN), de nouveaux types d’applications émergent et utilisent des capteurs d’informations capables de relever les paramètres physiologiques, environnementaux et plus particulièrement le positionnement des personnes. Dans ce cadre, nous nous sommes attachés dans ce travail de recherche à la conception et la réalisation d’antennes en polarisation circulaire pouvant être intégrées dans des vêtements, pour les standards de géolocalisation européen Galiléo et Américain GPS. Nous avons utilisé pour ces antennes des structures métamatériaux de type conducteurs magnétiques artificiels, afin d’augmenter les performances en rayonnement et pour diminuer le couplage avec et le corps humain. Une autre voie explorée est l’utilisation d’antennes patchs qui sont de nature faible encombrement. La bande de fréquence du standard de communications par satellite Iridium étant très proche du standard de géolocalisation GPS, nous avons trouvé intéressant de développer une solution de type patch couvrant les deux bandes GPS (1,575 GHz) et Iridium (1,621 GHz). L’antenne devant être intégrée sur une boite crânienne, les niveaux de débit d’absorption spécifique et les modifications du rayonnement sous conformation de l’antenne ont également été étudiés. L’évolution de ce travail a été ensuite d’étudier le comportement de cette antenne posée sur le dessus d’un casque militaire français. Les performances en rayonnement ont été satisfaisantes et ont montré la possibilité d’une telle application. / Thanks to the progress made in the recent years in the design of smart networks, such as wireless Body Area Network (WBAN), or Wireless Personal Area Network (WPAN), a novel type of emerging applications using smarts sensor measuring physiologic parameters, environmental et more particularly positioning of the persons are nowadays available. In the research presented in this manuscript, we are committed to design and realize antennas that can be possibly integrated into clothes, dedicated to the American GPS (1.227 GHz - 1.575 GHz) and European Galileo (1.180 GHz - 1.575 GHz) global navigation satellite systems. We used for these antennas a type of metamaterial structure named artificial magnetic conductor, to increase and enhance the radiation performance and reduce the coupling between the antenna and the human body. Another way has been explored using patch antenna solutions that are inherently low profile antennas. As the frequency band of the satellite communication system Iridium is close to the GPS one, we developed a dual band antenna solution covering both GPS (1.575 GHz) and Iridium (1.612 GHz) standards. The antenna being dedicated to be integrated over a human skull, the specific absorption rate and the radiation modification was also studied.

In this age of wireless technology, Body Area networks (BAN) is revolutionising the concept of patient care and health monitoring. BAN provides people good assessment of their health status at any time, wherever they are physically. The increased interest in developing effective body (in, on & off) communication systems made phantoms which can mimic the electrical properties of an actual human body necessary. Wearable antennas which are the indispensable part of BAN got to be low pro file and above all influences that human body can make. There should also be a way to reduce the effect of antennas on human body namely specific absorption rate (SAR). In this work effort has been made to develop phantoms suitable for both On body and In body communications. The base materials which are selected for the study are of biological origin (bio ceramics and biopolymers) whose behaviour is closer to that of human tissues. As these phantoms are biocompatible they are essentially non toxic where the conventionally available phantoms are toxic in nature. Different kinds of low profile conformal wearable antennas working at 2.4GHz ISM band were developed and studied in the BAN perspective. Antennas suffer much in terms of matching and efficiency when they are in contact or in the premises of human body. This is a major hurdle in the way to setting up a good body communication network. This work encompasses various techniques adopted to limit the body interferences to an acceptable level. The techniques adopted (Such as Backing Ground Plane, High Impedance Surface & Polymeric Ferrite Sheets) proved to be effective in reducing the sway in antenna characteristics when they are mounted on body. Specific absorption rate is also brought to acceptable levels and thus avoiding the formation of hot spots due to microwave absorption. A safer and cost effective BAN can be set up using this work which will lead to a safer, mobile and healthy future. / Les réseaux BAN (Body Area Network) révolutionnent le concept de la surveillance et de la prise en charge à distance de la santé du patient. Le BAN fournit des informations sur l’état de santé du patient en temps réel quelque soit l’endroit où il se trouve. Dans le « télé monitoring », des capteurs de mouvement, de respiration ou du rythme cardiaque placés à l’intérieur ou sur le corps humain transmettent des données via le réseau sans fil constituant le BAN, une antenne étant associée à chaque nœud du réseau. La communication peut être in/on, on/on ou on/off selon que les antennes sont placées à l’intérieur, sur ou à l’extérieur du corps. Le développement des BAN nécessite la réalisation de modèles (ou fantômes) simulant au mieux les propriétés électromagnétiques du corps humain. Des antennes portables, miniaturisées doivent être réalisées avec des contraintes d’intégration d’une part (aux vêtements, à des objets type montre ou badge), des contraintes de résistance ou de prise en compte de l’influence du corps d’autre part. La réduction de l’impact des antennes sur les tissus en terme de SAR (Specific Absorption Rate) doit également être considérée. Dans ce travail, l’objectif est de développer des fantômes valables pour les communications dans et sur le corps. Les matériaux de base sélectionnés sont d’origine biologique (biocéramiques et biopolymères) avec des propriétés proches de celles des tissus humains. Ces fantômes étant biocompatibles, ils sont essentiellement non toxiques alors que les fantômes usuels le sont en général. D’autre part, différents types d’antennes conformables, fonctionnant dans la bande ISM 2.4 GHz ont été développées et étudiées dans la perspective du BAN. Les antennes voient leur adaptation et leur efficacité chuter au contact ou à proximité du corps, ce qui constitue un écueil majeur pour établir une bonne communication. Différentes méthodes permettant de réduire l’influence du corps (plan de masse à l’arrière, surface haute impédance, feuille de ferrite polymère) sont testés et leurs avantages et inconvénients développés. Des mesures de SAR permettent aussi de démontrer l’efficacité de ces méthodes sur la réduction de la puissance absorbée par les tissus. Au final, ce travail apporte une contribution à l’étude théorique et expérimentale de l’interaction entre corps humain et antenne dans le cadre des réseaux BAN appliqués à la télésurveillance de la santé.

L'objectif de cette thèse repose sur le développement et la mise en œuvre des techniques de transmission parallèle (pTx) en Imagerie par Résonance Magnétique pour homogénéiser l’excitation des spins dans le cerveau humain à ultra-haut champ. Afin de permettre des démonstrations in-vivo, un concept de sécurité conservateur mais viable est introduit pour le contrôle de la puissance de la radiofréquence (RF) transmise. Par la suite, de nouvelles méthodes de minimisation du Taux d’Absorption Spécifique local et de conception d’impulsions RF non-sélectives sont investiguées. L’impact de ces impulsions courtes et relativement peu énergétiques, appelées « kT-points », est d'abord démontré dans l’approximation des petits angles de bascule de l’aimantation. Pour cibler un éventail d’applications plus large, la conception de type kT-points est ensuite généralisée en englobant les excitations à grand angle de bascule et les inversions. Cette méthode est appliquée à l'une des séquences pondérées en T1 les plus couramment utilisées en neuro-imagerie. Les résultats ainsi obtenus à 7 Tesla sont comparés à des images acquises avec une configuration clinique à 3 Tesla. Les principes de la méthode sont ainsi validés et démonstration est faite que la transmission parallèle permet aux systèmes à très haut champ d’être aussi compétitifs en imagerie pondérée en T1. Enfin, des simplifications dans la conception globale de la pTx sont étudiées pour un meilleur rapport coût-efficacité des solutions proposées. / The focus of this thesis lies on the development, and implementation, of parallel transmission (pTx) techniques in magnetic resonance imaging for flip-angle homogenization throughout the human brain at ultra-high field. In order to allow in-vivo demonstrations, a conservative yet viable safety concept is introduced to control the absorbed radiofrequency (RF) power . Subsequently, novel methods for local SAR control and non-selective RF pulse-design are investigated. The impact of these short and energy-efficient waveforms, referred to as kT-points, is first demonstrated in the context of the small-tip-angle domain. Targeting a larger scope of applications, the kT-points design is then generalized to encompass large flip angle excitations and inversions. This concept is applied to one of the most commonly used T1-weighted sequences in neuroimaging. Results thus obtained at 7 Tesla are compared to images acquired with a clinical setup at 3 Tesla, validating the principles of the kT-points method and demonstrating that pTx-enabled ultra-high field systems can also be competitive in the context of T1-weighted imaging. Finally, simplifications in the global design of the pTx-implementation are studied in order to obtain a more cost-effective solution.

Dans les environnements militaires, et plus particulièrement dans le domaine terrestre, de nombreux systèmes radioélectriques HF (de 3 à 30 MHz), VHF (de 30 à 300 MHz) et UHF (de 300 à 3000 MHz) sont utilisés. Ces systèmes remplissent plusieurs fonctions (communication longue et courte distance, brouillage, radar, etc ...) et peuvent parfois cohabiter sur un même porteur. Ces différentes fonctions utilisent plusieurs antennes et augmentent les risques de surexposition électromagnétique des opérateurs. Des normes civiles et militaires proposent des limites sur les champs électromagnétiques appliqués et sur des grandeurs dosimétriques (débit d'absorption spécifique DAS, densité de courant et champs électriques internes) pour limiter ces risques entre 0 et 300 GHz. Ces travaux de thèse ont deux objectifs principaux. Le premier est d'étudier les normes civiles et militaires afin de comprendre comment elles ont été développées et si elles sont réellement adaptées aux fréquences HF et VHF. Le deuxième est de proposer et valider une nouvelle méthode de validation des produits radio Thales. Pour cela, nous caractérisons numériquement le comportement électromagnétique et thermique du corps humain lors d'une exposition électromagnétique en bandes HF et VHF. L'étude des couplages entre le corps et les champs électromagnétiques externes nous permet de proposer pour la première fois des formules calculant les DAS dans le corps d'un fantôme homogène à partir, soit des courants induits le long du corps pour une exposition quelconque, soit du champ électrique appliqué pour une exposition en onde plane. / In military environments, especially land field, high frequencies (HF, 3 - 30 MHz), very high frequencies (VHF, 30 - 300 MHz) and ultra high frequencies (UHF, 300 - 3000 MHz) have been used for long range and shortrange communications, for communication interference or for detection. To have all those functions on the same carrier, they require many antennas, therefore they are increasing the operator's electromagnetic overexposure risk. Civilian and military standards were published providing limits on external electromagnetic fields and dosimetric quantities (specific absortion rate SAR, current density and internal electric field) to limit this overexposure risk between 0 and 300 GHz. The PhD thesis project has two main objectives. First, civilian and military standards are studied to understand how they were developed and if they are really suited for HF and VHF frequencies. Second, a new validation method of Thales radio product is proposed and validated. This PhD thesis project have characterized numerically the human body electromagnetic and thermal behavior during electromagnetic exposure in HF and VHF. Then, by studying couplings between external electromagnetic fields, induced current and human body, formulas to calculate both whole-body averaged SAR and local SAR 10 g in homogeneous body are proposed for the first time.

Le développement de systèmes IRM à plus haut champ magnétique statique s'est accompagné d'une interrogation légitime concernant l'effet des champs électromagnétiques RF sur les patients. L'effet peut être renforcé par l'introduction d'éléments conducteurs à l'intérieur de la bobine RF comme c'est le cas pour les capteurs endoluminaux utilisés pour l'analyse des parois digestives. Ces capteurs entraînent des risques d'échauffements locaux élevés pour le patient en raison du TAS local induit par le champ électrique RF en présence d'un fil conducteur. Ces capteurs ayant le potentiel de présenter un bénéfice pour le patient, il est nécessaire de s'affranchir de ces limitations. Le premier objectif de la thèse est le développement d'un capteur endoluminal à liaisons optiques. Un dispositif de découplage actif optique a été développé et caractérisé. Les images RMN in vitro montrent une distribution du RSB comparable au découplage classique, validant ainsi l'efficacité du découplage optique. Concernant la transmission optique du signal RMN, des travaux ont été réalisés afin de s'affranchir des contraintes liées à l'utilisation d'un guide d'onde pour la conversion électro-optique par effet Pockels. Le capteur a été rendu plus compact. En revanche, l'importance de contrôler le TAS local dans des conditions expérimentales données demeure un besoin ne s'arrêtant pas à ceux des capteurs endoluminaux. Le second objectif est donc la validation expérimentale d'une sonde électro-optique pour la mesure du champ électrique RF durant un examen IRM. Cette sonde a permis d'effectuer des mesures du champ électrique dans l'air et dans différents milieux biologiques à 3 T et 4,7 T et estimer le TAS local / The recent advancement in MRI systems and the increase of the static magnetic field strength were accompanied by a strong concern about the effect of RF electromagnetic fields on patients. The effect can be increased by the use of conductive elements inside the volume coil as in the case of endoluminal coils used to analyze digestive walls. These coils lead to an increase of the local SAR which is induced by RF electric field in the presence of the coaxial cable connecting the coil to the MR system, resulting in strong local heating. Giving that these coils have the potential to present a real benefit to the patient, it worth to overcome these limitations. Accordingly, the first objective of the thesis is the development of a fully optical endoluminal receiver coil. An optical active detuning system has been developed and characterized. The NMR images show a signal-to-noise ratio distribution similar to that obtained with conventional detuning techniques, thus validating the efficiency of the optical detuning. Concerning the electro-optical conversion and the optical transmission of the NMR signal, experiments were performed to overcome constraints related to the use of waveguide for electro-optical conversion by Pockels effect. Moreover, the importance of monitoring global and local SAR during MRI exams remains a need which is not limited only to the endoluminal coils. The second objective of the thesis is then the experimental validation of an electro-optical probe for real-time measurements of RF electric field. This probe can measure the RF electric field in air and in biological media at 3 T and 4.7 T MRI systems and allows the estimation of the local SAR

The main objectives of this research are to investigate and design low profile antennas for mobile handsets applications using the balanced concept. These antennas are considered to cover a wide range of wireless standards such as: DCS (1710¿1880 MHz), PCS (1850¿1990 MHz), UMTS (1920¿2170 MHz), WLAN (2400¿2500 MHz and 5000 ¿ 5800 MHz) and UWB frequency bands. Various antennas are implemented based on built-in planar dipole with a folded arm structure. The performance of several designed antennas in terms of input return loss, radiation patterns, radiation efficiency and power gain are presented and several remarkable results are obtained. The measurements confirm the theoretical design concept and show reasonable agreement with computations. The stability performance of the proposed antenna is also evaluated by analysing the current distribution on the mobile phone ground plane. The specific absorption rate (SAR) performance of the antenna is also studied experimentally by measuring antenna near field exposure. The measurement results are correlated with the calculated ones. A new dual-band balanced antenna using coplanar waveguide structure is also proposed, discussed and tested; this is intended to eliminate the balanced feed network. The predicted and measured results show good agreement, confirming good impedance bandwidth characteristics and excellent dual-band performance. In addition, a hybrid method to model the human body interaction with a dual band balanced antenna structure covering the 2.4 GHz and 5.2 GHz bands is presented. Results for several test cases of antenna locations on the body are presented and discussed. The near and far fields were incorporated to provide a full understanding of the impact on human tissue. The cumulative distribution function of the radiation efficiency and absorbed power are also evaluated. / UK Engineering and Physical Sciences Research Council (EPSRC)

The fifth-generation (5G) wireless network has received a lot of attention from both academia and industry with many reported efforts. Multiple-input-multiple-output (MIMO) is the most promising wireless access technology for next-generation networks to provide high spectral and energy efficiency. For handheld devices such as smartphones, 2×2 MIMO antennas are currently employed in 4G systems and it is expected to employ a larger number of elements for 5G mobile terminals. Placing multiple antennas in the limited space of a smartphone PCB poses a significant challenge. Therefore, a new design technique using dual-polarized antenna resonators for 8×8 MIMO configuration is proposed for sub 6 GHz 5G applications. The proposed MIMO configuration could improve the channel capacity, diversity function, and multiplexing gain of the smartphone antenna system which makes it suitable for 5G applications. Different types of new and compact diversity MIMO antennas with Patch, Slot, and Planar inverted F antenna (PIFA) resonators are studied for different candidate bands of sub 6 GHz spectrum such as 2.6, 3.6, and 5.8 GHz. Unlike the reported MIMO antennas, the proposed designs provide full radiation coverage and polarization diversity with sufficient gain and efficiency values supporting different sides of the mainboard. Apart from the sub 6 GHz frequencies, 5G devices are also expected to support the higher bands at the centimeter/millimeter-wave spectrums. Compact antennas can be employed at different portions of a smartphone board to form linear phased arrays. Here, we propose new linear phased arrays with compact elements such as Dipole and Quasi Yagi resonators for 5G smartphones. Compared with the recently reported designs, the proposed phased arrays exhibit satisfactory features such as compact size, wide beam steering, broad bandwidth, end-fire radiation, high gain, and efficiency characteristics. The proposed 5G antennas can provide single-band, multi-band, and broad-band characteristics with reduced mutual coupling function. The fundamental characteristics of the 5G antennas are examined using both simulations and measurements and good agreement is observed. Furthermore, due to compact size and better placement of elements, quite good characteristics are observed in the presence of the user and the smartphone components. These advantages make the proposed antennas highly suitable for use in 5G smartphone applications. / European Union Horizon 2020 Research and Innovation Programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424

The fifth generation (5G) has developed a lot of interest, and there have been many reported initiatives in both industry and academics. Multiple-input-multiple-output (MIMO) is the most promising wireless access technique for next-generation networks in terms of spectral and energy efficiency (MIMO). In 4G systems, 2-Element MIMO antennas are already used, while 5G mobile terminals for smartphone hand-held devices are projected to use a bigger number of elements. The placement of many antennas in the restricted space of a smartphone PCB is one of the most critical challenges. As a result, for sub-6 GHz 5G applications, a new design technique based on dual-polarised antenna resonators for 6-Element, 8-Element MIMO configuration is proposed. The proposed MIMO design could improve the smartphone antenna system's chan-nel capacity, diversity function, and multiplexing gain, making it appropriate for 5G applica-tions. For distinct prospective bands of the sub-6 GHz spectrum, such as 2.6, 3.6, and 5.8 GHz, different types of novel and compact diversity MIMO antennas using Patch, Slot, and Planar inverted F antenna (PIFA) resonators are examined. Unlike previously reported MIMO antennas, the proposed designs provide full radiation coverage and polarisation diversity, as well as adequate gain and efficiency values to support several mainboard sides. Apart from sub-6 GHz frequencies, 5G devices are projected to support the centimetre/milli-metre wave spectrum's higher bands. To create linear phased arrays, small antennas can be placed at various locations on a smartphone board. For 5G smartphones, we propose novel linear phased arrays with tiny parts like Dipole and Quasi-Yagi resonators. In comparison to previously published designs, the suggested phased arrays have desirable qualities such as compact size, wide beam-steering, broad bandwidth, end-fire radiation, high gain, and efficiency. With a reduced mutual coupling function, the suggested 5G antennas can provide single-band, multi-band, and broad-band characteristics. Both models and measurements are used to an-alyse the fundamental features of 5G antennas, and good agreement is found. Furthermore, in the presence of the user and the smartphone components, good features are seen due to the small size and superior arrangement of elements. Because of these benefits, the sug-gested antennas are well-suited for usage in 5G smartphone applications.

The main objectives of this research are to investigate and design low profile antennas for mobile handsets applications using the balanced concept. These antennas are considered to cover a wide range of wireless standards such as: DCS (1710-1880 MHz), PCS (1850-1990 MHz), UMTS (1920-2170 MHz), WLAN (2400-2500 MHz and 5000-5800 MHz) and UWB frequency bands. Various antennas are implemented based on built-in planar dipole with a folded arm structure. The performance of several designed antennas in terms of input return loss, radiation patterns, radiation efficiency and power gain are presented and several remarkable results are obtained. The measurements confirm the theoretical design concept and show reasonable agreement with computations. The stability performance of the proposed antenna is also evaluated by analysing the current distribution on the mobile phone ground plane. The specific absorption rate (SAR) performance of the antenna is also studied experimentally by measuring antenna near field exposure. The measurement results are correlated with the calculated ones. A new dual-band balanced antenna using coplanar waveguide structure is also proposed, discussed and tested; this is intended to eliminate the balanced feed network. The predicted and measured results show good agreement, confirming good impedance bandwidth characteristics and excellent dual-band performance. In addition, a hybrid method to model the human body interaction with a dual band balanced antenna structure covering the 2.4 GHz and 5.2 GHz bands is presented. Results for several test cases of antenna locations on the body are presented and discussed. The near and far fields were incorporated to provide a full understanding of the impact on human tissue. The cumulative distribution function of the radiation efficiency and absorbed power are also evaluated.

This dissertation develops adaptive hp-Finite Element (FE) technology and a parallel sparse direct solver enabling the accurate modeling of the absorption of Electro-Magnetic (EM) energy in the human head. With a large and growing number of cell phone users, the adverse health effects of EM fields have raised public concerns. Most research that attempts to explain the relationship between exposure to EM fields and its harmful effects on the human body identifies temperature changes due to the EM energy as the dominant source of possible harm. The research presented here focuses on determining the temperature distribution within the human body exposed to EM fields with an emphasis on the human head. Major challenges in accurately determining the temperature changes lie in the dependence of EM material properties on the temperature. This leads to a formulation that couples the BioHeat Transfer (BHT) and Maxwell equations. The mathematical model is formed by the time-harmonic Maxwell equations weakly coupled with the transient BHT equation. This choice of equations reflects the relevant time scales. With a mobile device operating at a single frequency, EM fields arrive at a steady-state in the micro-second range. The heat sources induced by EM fields produce a transient temperature field converging to a steady-state distribution on a time scale ranging from seconds to minutes; this necessitates the transient formulation. Since the EM material properties depend upon the temperature, the equations are fully coupled; however, the coupling is realized weakly due to the different time scales for Maxwell and BHT equations. The BHT equation is discretized in time with a time step reflecting the thermal scales. After multiple time steps, the temperature field is used to determine the EM material properties and the time-harmonic Maxwell equations are solved. The resulting heat sources are recalculated and the process continued. Due to the weak coupling of the problems, the corresponding numerical models are established separately. The BHT equation is discretized with H¹ conforming elements, and Maxwell equations are discretized with H(curl) conforming elements. The complexity of the human head geometry naturally leads to the use of tetrahedral elements, which are commonly employed by unstructured mesh generators. The EM domain, including the head and a radiating source, is terminated by a Perfectly Matched Layer (PML), which is discretized with prismatic elements. The use of high order elements of different shapes and discretization types has motivated the development of a general 3D hp-FE code. In this work, we present new generic data structures and algorithms to perform adaptive local refinements on a hybrid mesh composed of different shaped elements. A variety of isotropic and anisotropic refinements that preserve conformity of discretization are designed. The refinement algorithms support one- irregular meshes with the constrained approximation technique. The algorithms are experimentally proven to be deadlock free. A second contribution of this dissertation lies with a new parallel sparse direct solver that targets linear systems arising from hp-FE methods. The new solver interfaces to the hierarchy of a locally refined mesh to build an elimination ordering for the factorization that reflects the h-refinements. By following mesh refinements, not only the computation of element matrices but also their factorization is restricted to new elements and their ancestors. The solver is parallelized by exploiting two-level task parallelism: tasks are first generated from a parallel post-order tree traversal on the assembly tree; next, those tasks are further refined by using algorithms-by-blocks to gain fine-grained parallelism. The resulting fine-grained tasks are asynchronously executed after their dependencies are analyzed. This approach effectively reduces scheduling overhead and increases flexibility to handle irregular tasks. The solver outperforms the conventional general sparse direct solver for a class of problems formulated by high order FEs. Finally, numerical results for a 3D coupled BHT with Maxwell equations are presented. The solutions of this Maxwell code have been verified using the analytic Mie series solutions. Starting with simple spherical geometry, parametric studies are conducted on realistic head models for a typical frequency band (900 MHz) of mobile phones. / text