As wearable technology and wireless sensor nodes become more and more ubiquitous, the batteries required to power them have become more and more unappealing as they limit lifetime and scalability. Energy harvesting from body heat provides a solution to these limitations. Energy can be harvested from body heat using thermoelectric generators, or TEGs. TEGs provide a continuous, scalable, solid-state energy source ideal for wearable and wireless electronics and sensors. Unfortunately, current TEG technology produces low power (< 1 mW) at a very low voltage (20-90 mV) and require the load to be matched to the TEG internal resistance for maximum power transfer to occur. This thesis research proposes a power management integrated circuit (PMIC) that steps up ultralow voltages generated by TEGs to a regulated 3 V, while matching the internal resistance. The proposed boost converter aims to harvest energy from body heat as efficiently and flexibly as possible by providing a regulated 3 V output that can be used by a variable load. A comparator-based burst mode operation affords the converter a high conversion ratio at high efficiency, while fractional open circuit voltage maximum power point tracking ensures that the controller can be used with a variety of TEGs and TEG setups. This control allows the converter to boost input voltages as low as 50 mV, while matching a range of TEG internal source resistances in one stage. The controller was implemented in 0.25 µm CMOS and taped out in February 2016. Since these fabricated chips will not be completed and delivered until May 2016, functionality has only been verified through simulation. Simulation results are promising and indicate that the peak overall efficiency is 81% and peak low voltage, low power efficiency is 73%. These results demonstrate the the proposed converter can achieve overall efficiencies comparable to current literature and low power efficiencies better than similar wide range converters in literature. / Master of Science

The Internet of Bodies (IoB) is a wireless network of on-body or in-body commu- nication formed by wearable, ingestible, injectable, and implantable smart devices. The vast majority of on-body communications, is typically required to be within <5 cm vicinity of the human body. The radiative nature of currently used RF devices leads to wasted energy that is radiated in unneeded off-body directions. Consequently, it degrades energy efficiency, introduces co-existence and interference problems, and imposes security threats on sensitive data. As an alternative, the capacitive body channel communication (BCC) couples the signal (between 10 kHz-100 MHZ) to the human body, which is more conductive than air. Hence, it provides lower loss, bet- ter privacy and confidentiality, and nJ/bit to pJ/bit energy efficiency. Accordingly, our work investigates orthogonal and non-orthogonal capacitive body channel access schemes for ultralow-power IoB networks with or without cooperation. We derive the closed-form optimal power allocation for uplink and downlink transmissions and the maximum number of IoB nodes satisfying a reliable and feasible network for non- cooperative schemes. The cooperative schemes necessitate joint optimization of both power and phase time allocations. We achieve this by using the Golden-Section search algorithm to minimize the power consumption in both phases.

L'Internet des objets (IoT) est annoncé comme la prochaine grande révolution technologique où des milliards d'appareils s'interconnecteront en utilisant les technologies d’Internet et permettront aux utilisateurs d'interagir avec le monde physique, permettant Smart Home, Smart Cities, tout intelligent. Les réseaux de capteurs sans fil (WSN) sont cruciales pour tourner la vision de l'IoT dans une réalité, mais pour que cela devienne réalité, beaucoup de ces dispositifs doivent être autonomes en énergie. Par conséquent, un défi majeur est de fournir une durée de vie de plusieurs années tout en alimentant les nœuds par batteries ou en utilisant l'énergie récoltée. Bluetooth Low Energy (BLE) a montré une efficacité énergétique et une robustesse supérieures à celles d'autres protocoles WSN bien connus, ce qui fait BLE un candidat solide pour la mise en œuvre dans des scénarios IoT. En outre, BLE est présent dans presque tous les smartphones, ce qui en fait une télécommande universelle omniprésente pour les maisons intelligentes, les bâtiments ou les villes. Néanmoins, l'amélioration de la performance BLE pour les cas typiques d'utilisation de l'IoT, où la durée de vie de la batterie de nombreuses années, est toujours nécessaire.Dans ce travail, nous avons évalué les performances de BLE en termes de latence et de consommation d'énergie sur la base de modèles analytiques afin d'optimiser ses performances et d'obtenir son niveau maximal d'efficacité énergétique sans modification de la spécification en premier lieu. À cette fin, nous avons proposé une classification des scénarios ainsi que des modes de fonctionnement pour chaque scénario. L'efficacité énergétique est atteinte pour chaque mode de fonctionnement en optimisant les paramètres qui sont affectés aux nœuds BLE pendant la phase de découverte du voisin. Cette optimisation des paramètres a été réalisée à partir d'un modèle énergétique extrait de l'état de la technique. Le modèle, à son tour, a été optimisé pour obtenir une latence et une consommation d'énergie quel que soit le comportement des nœuds à différents niveaux: application et communication. Puisqu'un nœud peut être le périphérique central à un niveau, alors qu'il peut être le périphérique à l'autre niveau en même temps, ce qui affecte la performance finale des nœuds.En outre, un nouveau modèle d'estimation de la durée de vie de la batterie a été présenté pour montrer l'impact réel de l'optimisation de la consommation énergétique sur la durée de vie des nœuds, de façon rapide (en termes de temps de simulation) et réaliste (en tenant compte des données empiriques). Les résultats de performance ont été obtenus dans notre simulateur Matlab basé sur le paradigme OOP, à travers l'utilisation de plusieurs cas de test IoT. En outre, le modèle de latence utilisé pour notre étude a été validé expérimentalement ainsi que l'optimisation des paramètres proposée, montrant une grande précision.Après avoir obtenu les meilleures performances possibles de BLE sans modification de la spécification, nous avons évalué les performances du protocole en implémentant le concept de Wake-Up radio (WuR), qui est un récepteur d’ultra-faible consommation et qui est en charge de détecter le canal de communication, en attente d'un signal adressé au nœud, puis réveiller la radio principale. Ainsi, la radio principale, qui consomme beaucoup plus d'énergie, peut rester en mode veille pendant de longues périodes et passer en mode actif uniquement pour la réception de paquets, économisant ainsi une quantité d'énergie considérable. Nous avons démontré que la durée de vie de BLE peut être significativement augmentée en implémentant une WuR et nous proposons une modification du protocole afin de rendre ce protocole compatible avec un mode de fonctionnement qui inclut une WuR. Pour cela, nous avons étudié l'état de l'art de la WuR et évalué la durée de vie des périphériques BLE lorsqu'une WuR sélectionnée est implémentée du côté master. / The Internet of Things (IoT) is announced as the next big technological revolution where billions of devices will interconnect using Internet technologies and let users interact with the physical world, allowing Smart Home, Smart Cities, smart everything. Wireless Sensor Network (WSN) are crucial for turning the vision of IoT into a reality, but for this to come true, many of these devices need to be autonomous in energy. Hence, one major challenge is to provide multi-year lifetime while powered on batteries or using harvested energy. Bluetooth Low Energy (BLE) has shown higher energy efficiency and robustness than other well known WSN protocols, making it a strong candidate for implementation in IoT scenarios. Additionally, BLE is present in almost every smartphone, turning it into perfect ubiquitous remote control for smart homes, buildings or cities. Nevertheless, BLE performance improvement for typical IoT use cases, where battery lifetime should reach many years, is still necessary.In this work we evaluated BLE performance in terms of latency and energy consumption based on analytical models in order to optimize its performance and obtain its maximum level of energy efficiency without modification of the specification in a first place. For this purpose, we proposed a scenarios classification as well as modes of operation for each scenario. Energy efficiency is achieved for each mode of operation by optimizing the parameters that are assigned to the BLE nodes during the neighbor discovery phase. This optimization of the parameters was made based on an energy model extracted from the state of the art. The model, in turn, has been optimized to obtain latency and energy consumption regardless of the behavior of the nodes at different levels: application and communication. Since a node can be the central device at one level, while it can be the peripheral device at the other level at the same time, which affects the final performance of the nodes.In addition, a novel battery lifetime estimation model was presented to show the actual impact that energy consumption optimization have on nodes lifetime in a fast (in terms of simulation time) and realistic way (by taking into account empirical data). Performance results were obtained in our Matlab based simulator based on OOP paradigm, through the use of several IoT test cases. In addition, the latency model used for our investigation was experimentally validated as well as the proposed parameter optimization, showing a high accuracy.After obtaining the best performance possible of BLE without modification of the specification, we evaluated the protocol performance when implementing the concept of Wake-Up radio, which is an ultra low power receiver in charge on sensing the communication channel, waiting for a signal addressed to the node and then wake the main radio up. Thus, the main radio which consumes higher energy, can remain in sleep mode for long periods of time and switch to an active mode only for packet reception, therefore saving considerable amount of energy. We demonstrated that BLE lifetime can be significantly increased by implementing a Wake-Up radio and we propose a modification of the protocol in order to render this protocol compatible with an operating mode which includes a Wake-Up radio. For this, we studied the Wake-Up radio state of the art and evaluated BLE devices lifetime when a selected Wake-Up radio is implemented at the master side.

Ultra low power wireless sensors and sensor systems are of increasing interest in a variety of applications ranging from structural health monitoring to industrial process control. Electrochemical batteries have thus far remained the primary energy sources for such systems despite the finite associated lifetimes imposed due to limitations associated with energy density. However, certain applications (such as implantable biomedical electronic devices and tire pressure sensors) require the operation of sensors and sensor systems over significant periods of time, where battery usage may be impractical and add cost due to the requirement for periodic re-charging and/or replacement. In order to address this challenge and extend the operational lifetime of wireless sensors, there has been an emerging research interest on harvesting ambient vibration energy. Vibration energy harvesting is a technology that generates electrical energy from ambient kinetic energy. Despite numerous research publications in this field over the past decade, low power density and variable ambient conditions remain as the key limitations of vibration energy harvesting. In terms of the piezoelectric transducers, the open-circuit voltage is usually low, which limits its power while extracted by a full-bridge rectifier. In terms of the interface circuits, most reported circuits are limited by the power efficiency, suitability to real-world vibration conditions and system volume due to large off-chip components required. The research reported in this thesis is focused on increasing power output of piezoelectric transducers and power extraction efficiency of interface circuits. There are five main chapters describing two new design topologies of piezoelectric transducers and three novel active interface circuits implemented with CMOS technology. In order to improve the power output of a piezoelectric transducer, a series connection configuration scheme is proposed, which splits the electrode of a harvester into multiple equal regions connected in series to inherently increase the open-circuit voltage generated by the harvester. This topology passively increases the rectified power while using a full-bridge rectifier. While most of piezoelectric transducers are designed with piezoelectric layers fully covered by electrodes, this thesis proposes a new electrode design topology, which maximizes the raw AC output power of a piezoelectric harvester by finding an optimal electrode coverage. In order to extract power from a piezoelectric harvester, three active interface circuits are proposed in this thesis. The first one improves the conventional SSHI (synchronized switch harvesting on inductor) by employing a startup circuitry to enable the system to start operating under much lower vibration excitation levels. The second one dynamically configures the connection of the two regions of a piezoelectric transducer to increase the operational range and output power under a variety of excitation levels. The third one is a novel SSH architecture which employs capacitors instead of inductors to perform synchronous voltage flip. This new architecture is named as SSHC (synchronized switch harvesting on capacitors) to distinguish from SSHI rectifiers and indicate its inductorless architecture.