This study presents a method for measurement of whole-body average specific absorption rate (WBSAR) of a millimeter wave (mmWave) antenna in a reverberation chamber. The method takes advantage of multiple radiated power measurements to estimate the power absorbed in a phantom placed in front of the antenna. The first set of measurements is a total radiated power estimation of the antenna. The second set measures the radiated power from the combined antenna and phantom system. By taking the difference between the two measurements, the power absorbed in the phantom and hence WBSAR, which is defined as the total power absorbed in a body divided by the whole-body mass, can be estimated. This method builds on previous reverberation chamber techniques and improves them by isolating only the power absorbed from direct illumination corresponding to a realistic exposure environment of mmWave antennas with high directivity. Verification has been performed by comparing measurements of a horn antenna with a simulation. The difference between measurements and simulation has been found to be less than 1 dB, while the maximum measurement uncertainty was estimated to be 1.1 dB. With the developed method, WBSAR measurements of an Ericsson 5G mmWave base station has been conducted. In 2020 the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published new guidelines for radio frequency electromagnetic fields containing limitations for WBSAR up to 300 GHz. Since these guidelines are new there is currently no standardized measurement method to assess WBSAR in the mmWave frequency ranges. Therefore, the proposed method could be of interest for standardization institutions. / I denna studie presenteras en metod för att i en modväxlande kammare mäta helkroppsbaserad specifik absorptionshastighet (whole-body average specific absorption rate, WBSAR) för en antenn i millimetervågsområdet. Metoden använder mätningar av utstrålad effekt i två situationer, utan och med en helkroppsmodell (fantom). Först mäts den utstrålade effekten från antennen utan fantom, sedan mäts den när fantomen är placerad framför antennen. Differensen mellan de två mätningarna ger den absorberade effekten i fantomen, vilken kan användas för att bestämma WBSAR genom att dela med massan. Metoden bygger på tidigare tekniker för modväxlande kammare och utvecklar dem genom att isolera effekten absorberad från direkt exponering. På så sätt ger metoden realistiska resultat för starkt riktade millimetervågsantenner. Verifikation har utförts genom att jämföra mätningar av en hornantenn med simuleringar vid 28 GHz. Skillnaden mellan de mätta och simulerade värdena var mindre än 1 dB och med en uppskattad maximal mätosäkerhet på 1.1 dB. Med den utvecklade metoden mättes WBSAR för en Ericsson 5G basstation vid frekvensen 28 GHz. År 2020 publicerade ICNIRP nya riktlinjer för exponering för radiofrekventa elektromagnetiska fält som inkluderar begränsningar av WBSAR vid frekvenser upp till 300 GHz. Eftersom dessa riktlinjer är nya finns nuvarande ingen standardiserad metod för att mäta WBSAR i millimetervågsområdet. Metoden kan därför vara av intresse för standardiseringsorganisationer

The objectives of this research work are to investigate, design and implement circularly-polarized antennas to be used for handheld satellite mobile communication and wireless sensor networks. Several antennas such as Quadrifilar Spiral Antennas (QSAs), two arm Square Spiral and stripline or coaxially-fed microstrip patch antennas are developed and tested. These antennas are investigated and discussed to operate at L band (1.61-1.6214GHz) and ISM band (2.4835-2.5GHz) A substantial size reduction was achieved compared to conventional designs by introducing special modifications to the antenna geometries. Most of the antennas are designed to produce circularly-polarized broadside-beam except for wireless sensor network application a circularly-polarized conical-beam is considered. The polarization purity and Specific Absorption Rate (SAR) of two dual-band antennas for satellite-mobile handsets next to the human head are investigated and discussed, using a hybrid computational method. A small distance between the head and the handset is chosen to highlight the effects of the relatively high-radiated power proposed from this particular antenna. A Genetic Algorithm in cooperation with an electromagnetic simulator has been introduced to provide fast, accurate and reliable solutions for antenna design structures. Circularly-polarized quadrifilar helical antenna handset and two air-dielectric microstrip antennas were studied. The capabilities of GA are shown as an efficient optimisation tool for selecting globally optimal parameters to be used in simulations with an electromagnetic antenna design code, seeking convergence to designated specifications. The results in terms of the antenna size and radiation performance are addressed, and compared to measurements and previously published data.

No description available.

A procedure for computational dosimetry to verify safety standards compliance of mobile communications base stations is presented. Compared with the traditional power density method, a procedure based on more rigorous physics was devised, requiring computation or measurement of the specific absorption rate (SAR) within the biological tissue of a person at an arbitrary distance. This uses a hybrid methd of moments/finite difference time domain (MoM/FDTD) numerical method in order to determine the field or SAR distribution in complex penetrable media, without the computational penalties that would result from a wholly FDTD simulation. It is shown that the transmitted power allowed by the more precise SAR method is, in many cases, between two and five times greater than that allowed by standards implementing the power flux density method.

The main goals of this thesis are to design and examine heterogeneous antennas for different wireless applications of a wide variety of EM spectrum requirements: which includes WLAN 5.0 GHz, WLAN (2.45 GHz), UMTS (1.92-2.17 GHz), 2G, UMTS, LTE, ultra-wideband (UWB) applications, and MBAN applications (2.4 GHz). Various techniques for expanding bandwidth, enhancing performance, and balancing the operation have been examined through comprehensive simulated and physically fabricated models. Thereafter, a compact DRA, for UWB applications is examined. The combined resultant effects of asymmetric positioning of DRs (2, 3 and 4 Cylindrical elements), defected ground technique, dimensions, and profile of the aperture give RF designers detailed scope of the optimization process. More resonances are achieved, and the bandwidth is improved. The obtained results show that, an impedance bandwidth of 133.0%, which covers the Ultra­ Wideband band (3.6GHz - 18.0GHz), with a maximum power gain of 9dBi attained. In addition, a compact conformal wearable CPW antenna using EBG-FSS for MBAN applications at 2.4GHz is proposed. They are designed using fabric materials suitable for daily clothing. The performance of the antenna is investigated in free space, on a layered biological tissue model, and on a real human body to evaluate SAR. When the antenna is combined with an EBG-FSS structure, isolation between the antenna and the human body is introduced. The results show that the FBR is enhanced by 13 dB, the gain by 6.55dBi, and the SAR is lowered by more than 94%. The CPW antenna demonstrated here is appropriate for future MBAN wearable systems. The design, investigation, and application of water level monitoring utilizing subsurface wireless sensor are covered in this thesis. A wideband double inverted-F antenna is designed and examined to overcome signal attenuation issues. The obtained result is feasible, which has an operating bandwidth of 0.8 to 2.17GHz, with a reflection coefficient better than 10 dB. Moreover, a field trial is conducted to evaluate the robustness of the antenna under extreme conditions. A very good efficiency was also demonstrated, with losses of under 20%. Further, the results from the field experiment established that the antenna is a reliable contender for wireless communication in such challenging environments. / Libyan Ministry of Higher Education / The full text will be available at the end of the embargo: 25th May 2025

The objectives of this research work are to investigate, design and implement circularly-polarized antennas to be used for handheld satellite mobile communication and wireless sensor networks. Several antennas such as Quadrifilar Spiral Antennas (QSAs), two arm Square Spiral and stripline or coaxially-fed microstrip patch antennas are developed and tested. These antennas are investigated and discussed to operate at L band (1.61-1.6214GHz) and ISM band (2.4835-2.5GHz) A substantial size reduction was achieved compared to conventional designs by introducing special modifications to the antenna geometries. Most of the antennas are designed to produce circularly-polarized broadside-beam except for wireless sensor network application a circularly-polarized conical-beam is considered. The polarization purity and Specific Absorption Rate (SAR) of two dual-band antennas for satellite-mobile handsets next to the human head are investigated and discussed, using a hybrid computational method. A small distance between the head and the handset is chosen to highlight the effects of the relatively high-radiated power proposed from this particular antenna. A Genetic Algorithm in cooperation with an electromagnetic simulator has been introduced to provide fast, accurate and reliable solutions for antenna design structures. Circularly-polarized quadrifilar helical antenna handset and two air-dielectric microstrip antennas were studied. The capabilities of GA are shown as an efficient optimisation tool for selecting globally optimal parameters to be used in simulations with an electromagnetic antenna design code, seeking convergence to designated specifications. The results in terms of the antenna size and radiation performance are addressed, and compared to measurements and previously published data.

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.