Wireless powering efficiency assessment for deep-body implantable devices

Several frequency-dependent mechanisms restrict the maximum achievable efficiency for wireless powering implantable bioelectric devices. Similarly, many mathematical formulations have been proposed to evaluate the effect of these mechanisms as well as predict this maximum efficiency and the corresponding optimum frequency. However, most of these methods consider a simplified model, and they cannot tackle some realistic aspects of implantable wireless power transfer. Therefore, this paper proposed a novel approach that can analyze the efficiency in anatomical models and provide insightful information on achieving this optimum operation. First, this approach is validated with a theoretical spherical wave expansion analysis, and the results for a simplified spherical model and a bidimensional human pectoral model are compared. Results have shown that even though a magnetic receiver outperforms an electric one for near-field operation and both sources could be equally employed in far-field range, it is in mid-field that the maximum efficiency is achieved, with an optimum frequency between 1-5 GHz, depending on the implantation depth. In addition, the receiver orientation is another factor that affects the efficiency, with a maximum difference between the best and worst-case scenarios around five times for an electric source and over 13 times for the magnetic one. Finally, this approach is used to analyze the case of a wirelessly powered deep-implanted pacemaker by an on-body transmitter and to establish the parameters that lead to the maximum achievable efficiency

Modeling and Characterization of in-Body Antennas

International audienceEmerging wireless in-body devices pave the way to many breakthroughs in healthcare and clinical research. This technology enables monitoring of physiological parameters while maintaining mobility and freedom of movement of its user. However, establishing reliable communication between an in-body device and external equipment is still a major challenge. The radiation efficiency is constrained by attenuation and reflection losses in tissues. Furthermore, the antennas suffer from impedance detuning issues caused by uncertain electromagnetic properties of body tissues. First, we show that choosing an optimal operating frequency depends on application scenarios and can reduce the losses. Specific designs are then discussed to mitigate the antenna detuning effects due to surrounding biological tissue. Modeling approaches are proposed to lessen the design and optimization complexity. Finally, we present an accurate characterization method of in-body antennas in canonical phantoms using analog fiber optic links

Antennes miniatures pour des applications biomédicales

La télémétrie biomédicale et l’interfaçage neuronal à base de dispositifs miniatures et autonomes sans fil constituent de nouvelles applications en émergence. Elles visent à répondre à de nombreux enjeux y compris dans les domaines de la santé, du sport et bien être, ou encore de la sécurité au travail et de la défense. Parmi les applications typiques de biotélémétrie, nous pouvons citer le monitoring de certains paramètres physiologiques : température corporelle, pression artérielle, rythme cardiaque, taux de glucose et d’anticorps, détection d’agents chimiques, etc. En ce qui concerne l’interfaçage neuronal, il permet de restaurer les informations sensorielles, d’aider à la réadaptation des amputés, des personnes atteintes de paralysie ou des patients atteints de maladies neurodégénératives. L’objectif principal de cette thèse est de contribuer au développement de dispositifs miniaturisés et communicants pour le monitoring, en continu, de variables physiologiques d’humains ainsi que d’animaux. Ces dispositifs innovants nécessitent un système de communication fiable. Plus particulièrement, il s’agit d’analyser le milieu de propagation à l’intérieur des tissus biologiques et de développer des antennes miniatures innovantes ainsi que des méthodes pour leur analyse et leur caractérisation. Le verrou majeur concerne le rendement des antennes miniatures. Les effets de forte hétérogénéité, dispersion, pertes très élevées des milieux biologiques et les contraintes de miniaturisation et d’intégration dans des dispositifs in-body limitent la portée des systèmes existants à quelques dizaines de centimètres. Tout d’abord, des outils spécifiques de modélisation et d’optimisation ont été développés en collaboration avec l’Université de Bohème de l’Ouest. Ces outils sont indispensables pour l’analyse des composants de systèmes antennaires complexes : le code Agros2D (CAO interne) utilise des méthodes entièrement adaptatives. Cette approche permet de réduire la complexité d’optimisation des antennes in-body jusqu’un seul dégrée de liberté. Puis, la limite fondamentale de rendement des antennes pour les applications in-body a été définie ; les liens entre cette limite et la taille de l’antenne, sa fréquence de fonctionnement, la polarisation et les matériaux utilisés (dont hypothétiques) ont été quantifiés pour la première fois. Ce travail fondamental a d’abord pour objectif l’optimisation des performances de l’antenne actuelle de la capsule e-Celsius de l’entreprise BodyCAP pour accroître la portée de la gélule, en prenant en compte les caractéristiques des matériaux et le milieu de propagation que constituent les tissus biologiques. Dans cette étape on inclut également la fabrication des prototypes de gélules télémétriques ainsi que leurs mesures d’impédance. L’antenne optimisée a une portée trois fois plus importante que celle actuelle tout en occupant le même volume. En utilisant ces principes de conception, nous avons développé et caractérisé une antenne à 434 MHz adaptée à une large gamme d'applications in-body. Des dimensions ultra-miniatures, une robustesse et un rendement accrus permettent de l'utiliser à la fois pour des applications des capsules à implanter et à avaler. Enfin, en développant davantage les méthodes de conception et d’optimisation, nous avons conçu une antenne double-bande. Ayant la même robustesse que son équivalent actuel mono-bande, elle présente également un rendement encore plus élevé, permettant ainsi de fonctionner au-delà de 10 m. La caractéristique double-bande permet de concevoir les dispositifs in-body rechargeables sans fil dans le corps. Les antennes proposées contribuent au développement ultérieur d'une nouvelle génération de dispositifs miniatures in-body qui impliquent une intégration complexe et dense des capteurs, de la logique et de la source d'alimentation.Emerging wireless biotelemetry using miniature implantable, ingestible or injectable (in-body) devices allows continuously monitor and yield human or animal physiological parameters while maintaining mobility and quality of life. Recent advances in microelectromechanical systems and microfluidics—along with ongoing miniaturization of electronics—have empowered numerous innovations in biotelemetry devices, creating new applications in medicine, clinical research, wellness, and defense. Among the typical applications, I can mention, for example, the monitoring of physiological variables: body temperature, blood pressure, heart rate, detection of antibodies, chemical, or biological agents. Biotelemetry devices require a reliable communication system: robust, efficient, and versatile. Improving the transmission range of miniature in-body devices remains a major challenge: for the time being, they are able to operate only up to a few meters. Among the main issues to face are low radiation efficiencies (< 0.1%), antenna impedance detuning, and strong coupling to lossy and dispersive biological tissues. Thus, the main goal of the thesis is to conduct a multi-disciplinary study on development, optimization and characterization of antennas for in-body biotelemetry devices. After state-of-the-art and the context, I start with the development on both physical and numerical approaches to account for the effect of human tissues on the antenna. I propose the methodology to achieve given electromagnetic properties at a given frequency based on the full factorial experiment and surface response optimization. In addition, I describe the spherical physical phantom for the far-field characterization along with a combination of feed decoupling techniques. I proceed by reviewing the trough-body propagation mechanisms and deriving the optimal frequency for the in-body devices. I formulate the problem using four phantoms (homogeneous and heterogeneous) and perform full-wave analysis using an in-house hp-FEM code Agros 2D. Next, I study the existing antenna used by the BodyCap Company for its e-Celsius capsule and the ways on how to improve its operating range and robustness under strict integration and material constraints. The mechanisms of antenna–body coupling are analyzed and the found solution improves the antenna IEEE gain by 11 dBi (the operating range is at least tripled). The existing matching circuit and balun are optimized too for the given application reducing its size from eleven to seven discrete elements. In the following chapters, I continue studying the decoupling of antennas from a body using specific microstrip designs and dielectric loading via capsule shell. By applying the developed approaches, a high robustness and radiation efficiency can be achieved. At first, I develop a proof-of-concept antenna that demonstrates that the perfect matching (detuning immunity) is achievable for the operation within all human tissues. Based on these results, I develop a miniature and versatile biotelemetry platform: a 17 mm x 7 mm alumina capsule containing a conformal 434 MHz antenna. The antenna is well matched to 50 Ohm within the majority of human tissues and operates with an arbitrary device circuitry. Like this, one can use it ''as is,'' applying it for a wide range of in-body applications. Then, I develop a low profile conformal dual-band antenna operating in 434 MHz and 2.45 GHz bands. Such antenna can integrate both data transmission and wireless powering functionality increasing the available space inside an in-body device and increasing its scope of applications. Finally, I present the perspective developments including in-body sensing methodology. The obtained results contributes to further development of a new generation of miniature in-body devices that involve complex and dense integration of sensors, logic, and power sources

Numerické modelování speciálních antén pro použití v biomedicíně

Výzkum implantovatelné bezdrátové biotelemetrie vyžaduje antény s vysokou účinností, které jsou schopny komunikovat z lidského těla. Práce se zabývá návrhem miniaturních antén, které budou dostatečně robustní vůči okolním biologickým vlivům. Návrh počítá se standardním vstupem o impedanci 50 Ohmů. Anténa je navržena a miniaturizována použitím hybridní analyticko-numerické metody a následně optimalizovány její vnitřní rozměry pro snadné zapouzdření do kapsle. Anténa je dále analyzována s využitím realistického heterogenního fantomu. Zvýšená robusnost umožňuje využití v celé řadě aplikací. Vypočtené radiační obrazce jsou ve velmi dobré shodě s měřením. Navržené antény představují novou generaci miniaturiace těchto zařízení, která umožňuje vysokou integraci senzorů logiky a silových prvků.Neobhájeno2019-07-03Progress in implantable and ingestible wireless biotelemetry requires versatile and efficient antennas to communicate reliably from a body. We propose an miniature antennas immune to impedance detuning caused by varying electromagnetic properties of the surrounding biological environment. It is designed for a standard input impedance of 50 Ohm. The antenna is synthesized and miniaturized using a hybrid analytical-numerical approach, then optimized to conform to the inner surface of long biocompatible encapsulation. The capsule antenna is analyzed both in simplified and anatomically realistic heterogeneous phantoms. Enhanced robustness allows using the antenna for a wide range of in-body applications. Computed reflection coefficients and radiation performance both show good agreement with measurements. The proposed antenna contributes to the further development of a new generation of miniature in-body devices that involve complex and dense integration of sensors, logic, and power source

Stochastic Analysis of WPT Efficiency due to Location Uncertainty of mm-Sized Deep-Implanted Pacemakers

International audienceThe lossy and heterogeneous nature of the body tissues and the significant wave-impedance contrast as the electromagnetic wave propagates inside the body limits the fundamentally achievable efficiency of far- and midfield wireless charging of deep-body implantable devices. In addition, fluctuations in the implant position cause a further variation in the maximum power transfer efficiency. In this work, the analyzed problem consists of a wireless charged deep-implanted pacemaker considering an electric and a magnetic radiation source and a uniform distribution of pacemaker's positions inside the heart. The results show that the optimal frequency remains the same despite the position fluctuations. However, the efficiency bounds are strongly related to the nature of the source. Therefore, the proposed model and the obtained results serve as a gauge for designing implantable wireless power transfer systems and predicting variations in their efficiency

On-Body V-Band Leaky-Wave Antenna for Navigation and Safety Applications

International audienceThe paper discusses an on-body V-band leakywave antenna for navigation and safety applications. The antenna is based on meandering microstrip line operating in V-Band with continuous beam scanning from backward-toforward direction in the elevation plane. The width of the transverse line are alternatively varied to remove the open stop band (OSB) at the broadside frequency. The final antenna shows a scanning range in the elevation direction from -45 degrees to 50 degrees with no impact on performance at broadside direction. The antenna has a gain of more than 11 dB across the operating frequency range. The structure is simulated and the results and compared with the other leaky-wave antenna designs. The performance of the antenna is also verified for on-body conditions. The antenna is self matched at 5011 hence removing the need for matching circuit. The requirements for an on-body antenna are also analysed for the designed structure

Examination of Impedance Response of Capsule-Integrated Antennas Through Gastrointestinal Tract

International audienceThis work focuses on the investigation of the degree of possible detuning that may be observed in the impedance response of ingestible antennas during the transition through the gastrointestinal tract. For this investigation, two fundamental antennas are used: a meandered dipole antenna and a meandered loop antenna. The antennas conform to the inner surface of the biocompatible capsule shell. They are optimized in spherical homogeneous time-averaged gastrointestinal phantoms to operate at 3 different frequencies of interest: 434 MHz, 1.4 GHz, and 2.4 GHz, resulting in 6 different designs in total. Next, the optimized antennas are simulated in 3 different phantoms, each mimicking the electromagnetic properties of one of the tissues in the gastrointestinal tract (stomach, small intestine, and large intestine). The impedance response of each design in 4 different tissues is compared and discussed. The results show that the maximum shift in the operating frequency of the antennas is 7 MHz, indicating that the presence of the encapsulation layer makes the considered antennas robust against the changes in the electromagnetic properties encountered through the gastrointestinal tract