<div>My dissertation research is in the field of plasmonics. Specifically, my focus is on the use of plasmonics for various applications such as solar energy harvesting and optically addressable magnetic memory devices. Plasmonics is the study of collective oscillations of free electrons in a metal coupled to an electromagnetic field. Such oscillations are characterized by large electromagnetic field intensities confined in nanoscale volumes and are called plasmons. Plasmons can be excited on a thin metal film, in which case they are called surface plasmon polaritons or in nanoscale metallic particles, in which case they are called localized surface plasmon resonances. Researchers have taken advantage of this electromagnetic field enhancement resulting from the excitation of plasmons in metallic structures and demonstrated phenomenon such as plasmon-assisted photocatalysis, plasmon-induced local heating, plasmon-enhanced chemical sensing, optical modulators, nanolasers, etc.</div><div>In the first half of my dissertation, I study the role of plasmonics in hydrogen production from water using solar energy. Hydrogen is believed to be a very viable source of alternative green fuel to meet the growing energy demands of the world. There are significant efforts in government and private sectors worldwide to implement hydrogen fuel cells as the future of the automotive and transportation industry. In this regard, water splitting using solar energy to produce hydrogen is a widely researched topic. It is believed that a Solar-to-Hydrogen (STH) conversion efficiency of 10% is good enough to be considered for practical applications. Iron oxide (alpha-Fe2O3) or hematite is one of the candidate materials for hydrogen generation by water splitting with a theoretical STH efficiency of about 15%. In this work, I experimentally show that through metallic gold nanostructures we can enhance the water oxidation photocurrent in hematite by two times for above bandgap wavelengths, thereby increasing hydrogen production. Moreover, I also show that gold nanostructures can result in a hematite photocurrent enhancement of six times for below bandgap wavelengths. The latter, I believe, is due to the excitation of plasmons in the gold nanostructures and their subsequent decay into hot holes which are harvested by hematite.</div><div>The second part of my dissertation involves data storage in magnetic media. Memory devices based on magnetic media have been widely investigated as a compact information storage platform with bit densities exceeding 1Tb/in2. As the size of nanomagnets continue to reduce to achieve higher bit densities, the magnetic fields required to write information in these bits increases. To counter this, the field of heat-assisted magnetic recording (HAMR) was developed where a laser is used to locally heat up a magnet and make it susceptible to smaller magnetic switching fields. About two decades ago, it was realized that a single femtosecond laser pulse can switch magnetic media and therefore could be used to write information in magnetic bits. This field is now known as All-Optical Magnetic Switching (AOMS). My research aims to bring together the two fields of HAMR and AOMS to create optically addressable nanomagnets for information storage. Specifically, I want to show that plasmonic resonators can couple the laser field to nanomagnets more efficiently. This can therefore be used not only to heat the nanomagnets but also switch them with lower optical energy compared to free-standing nanomagnets without any plasmonic resonator. The results of my research show that by coupling metallic resonators, supporting surface plasmons, to nanomagnets, one can reduce the light intensity required for laser induced magnetization reversal.</div>

Energiskördning är idag ett växande område och är framstående sett till hållbarhetsaspekterna. Vibrationsbaserad sådan har blivit allt populärare där man kan utnyttja mekanisk energi från olika källor till att generera elektrisk energi. Piezoelektricitet fungerar enligt denna princip och piezoelektrisk energiskördning har varit ett område som fler och fler utnyttjar på grund av dess effektivitet, exempelvis till trådlösa sensornätverk. Ett krav på att piezoelektrisk energiskördning ska fungera optimalt är att vibrationerna sker med en satt frekvens utan större variation, ofta i väldigt höga frekvenser. Syftet med detta projekt är att anpassa denna teknik till mänskliga rörelser vilket kan göra den mer användbar och ett tänkt ändamål kan vara ett demonstrationsexempel för oregelbundna rörelser vid låga frekvenser, precis som mänskliga rörelser. Utmaningen lägger därmed i att utveckla en piezoelektrisk energiskördare som har ett frekvensområde inom mänskliga rörelsers frekvenser på 4 till 7 Hertz, där effektiviteten fortfarande kan vara hög. Detta har beprövats med vibrationsplatta. Vad som observerades var att med flera piezoelektriska material på konsolbalkar i kolfiber av olika dimensioner med olika vikter längst ut, uppstod ett frekvensområde inom mänskliga området med höga spänningar. För att göra det möjligt behövdes vikterna ha en stor massa av upp till hundratals gram så att resonansfrekvenserna kunde vara inom nämnt frekvensområde. Då piezoelektriska material ger en växelspänning, måste spänningen likriktas. Detta gjordes med två olika gränssnitt med ett mönsterkort tillverkat för vardera. Dessa gränssnitt är ett klassiskt som helt enkelt likriktar spänningen, medan den andra, Parallel Synchronized Switch Harvesting on the Inductor (P-SSHI), ska maximera spänningen och effekten. Det visade sig att det inte blev lika lyckat som planerat. Det klassiska gränssnittet gav en likspänning som var nästan lika hög som den inmatade växelspänningen medan det inte gällde för P-SSHI. / Today energy harvesting is an area on the rise and is outstanding in regards to the environmental aspects. Vibration based energy harvesting has become popular where it uses mechanical energy from different sources to produce electrical energy. Piezoelectricity operates according to this principle and piezoelectric energy harvesting has been an area more are using because of its efficiency, with applications such as wireless sensor networks. One demand for piezoelectric energy harvesting to work optimally is that the vibration source must have a well known frequency with minor deviations and this in usually very high frequencies. The purpose of this thesis is to adapt this technology to human motions which could make it even more useful and a proposed usage is a demo product for irregular motions of low frequency, just like human motions. The challenge is hence to create a piezoelectric energy harvester which has a frequency range within the human motions’ frequencies of 4 to 7 Hertz, where the efficiency still could be high. This has been tested using a vibration exciter. What was noticed was that with multiple piezoelectric materials on cantilever beams of carbon fibre with different dimensions and tip masses, a frequency range within human range with high voltages could be created. To make this possible, the masses needed to have a significant mass of up towards hundreds of grams in order for the resonance frequencies to be within the stated frequency range. As the piezoelectric materials provide an AC voltage, the voltage needs to be rectified. This was done with two different interfaces with a PCB created for each. These interfaces are a classic one which simply rectifies the voltage, while the other, Parallel Synchronized Switch Harvesting on the Inductor (PSSHI), is supposed to maximize the voltage and power. This did not turn out to be as successful as predicted. The classical interface delivered a DC voltage almost as much as the provided AC voltage while the P-SSHI interface did not.

Electromagnetic based energy harvesting systems such as Variable reluctance energy harvesting systems (VREH) have shown to be an effective way of extracting the energy of rotating parts. The transducer can provide enough power to run an electronic sensing system, but the problem arises in finding an efficient way of rectifying that power to generate a stable energy supply to run a system, which this report will investigate. Active and passive voltage doublers have proven to be a suitable candidate in solving this issue due to the simplicity and the small footprint. This thesis will aim to compare active and passive voltage doublers under various scenarios in order to understand under which circumstances are active or passive voltage doublers to be preferred. From the conducted experimental measurements, this thesis concluded that active voltage doublers are recommended during high RPMs (&gt;10 RPM) while passive voltage doublers (especially fullwave voltage doubler) is recommended at lower RPMs. Quality of power also plays a significant role in this study. Therefore, measurements have also been done for ripple and rise time. From the measurements, this thesis can conclude that the overall power quality was the best in Full-wave voltage doublers, while Active-voltage doublers had lower ripple than FWVDs at higher current loads.

Le projet présenté dans ce mémoire a pour objectif de développer un système de récupération d’énergie des gaz d’échappement d’un véhicule à essence. Constitué de piles à combustible à oxyde solide (SOFC) en configuration monochambre, le dispositif doit convertir l’énergie chimique des gaz imbrûlés en électricité. Son fonctionnement en aval du catalyseur trois voies permettrait de compléter son action dépolluante tout en améliorant l’efficacité énergétique du véhicule. Par opposition aux piles SOFC dites conventionnelles, les piles SOFC monochambres ne nécessitent pas de scellement étanche entre les compartiments et fonctionnent sous un mélange gazeux composé d’hydrocarbures et d’oxygène. L’empilement en stack de plusieurs cellules est simplifié et plus compact, son intégration au cœur du pot d’échappement est donc plus simple. Ce concept a été précédemment étudié dans la littérature et le présent projet a pour but d’améliorer les performances délivrées en optimisant certains paramètres : la géométrie de pile et les matériaux d’électrodes et d’électrolyte. De plus, un mélange gazeux plus représentatif des conditions réelles a été défini et utilisé tout au long du projet. Une étude préliminaire sur les matériaux sous forme de poudre a permis de réaliser un premier choix parmi quatre matériaux de cathode et de définir les conditions de fonctionnement théoriques des cellules. Ensuite, les cellules complètes ont été mises en forme puis étudiées sous mélange gazeux. Une densité maximale de puissance de 25 mW.cm-2 à 550°C pour une cellule Ni-CGO/CGO/LSCF-CGO a ainsi pu être obtenue. / This study aims at developing a system able to recover energy from exhaust gases of a thermal engine. Composed of Solid Oxide Fuel Cells (SOFC) in a single chamber configuration, the device has to convert chemical energy of gases into electricity. Embedded in the exhaust line at the exit of the three-way catalyst, the stack of single chamber SOFC will complete the reduction of toxic gases emissions with an improvement of the vehicle energy efficiency.Unlike conventional SOFC, single chamber SOFC do not require any gastight sealing between compartments and work in a mixed atmosphere composed of hydrocarbon and oxygen. Stack assembly is thus simplified and more compact; insertion into the exhaust line is therefore easier. This concept has been previously studied in the literature and this work aims at enhancing performances through the optimisation of some parameters such as cell geometry and cell components materials.Moreover, a more representative gas mixture of actual compositions in the exhaust line has been defined and used all along this project. A preliminary study on the raw materials has allowed to make a first selection among four cathode materials and to define theoretical working conditions of our cells. Afterwards, cells have been elaborated and then studied in the selected gas mixture. A maximum power density of 25 mW.cm-2 has been obtained at 550°C for a Ni-CGO/CGO/LSCF-CGO cell.

La récupération d'énergie ambiante permet d’alimenter de manière autonome des systèmes de petite taille tels que des neouds de capteurs ou des objets connectés à internet (IoT) en remplacement des batteries. Les sources d’énergie ambiante sont par exemple, l’énergie solaire, le gradient thermique, les forces mécaniques, le rayonnement électromagnétique et la pile microbienne. Les matériaux piézoélectriques permettent de valoriser électriquement l’énergie mécanique de vibration en la convertissant directement en énergie électrique. Les niveaux de puissance assez faible (de quelques μW au mW) ont amené à développer des interfaces électriques de récupération afin d’extraire le maximum d'énergie en améliorant le couplage électromécanique. Dans ce travail, nous nous intéressons à l’amélioration de dispositif de récupération d’énergie. Deux aspects sont abordés : dans un premier temps l’étude d’un commutateur hybride synchrone électrique-mécanique est faite pour remplacer le transistor MOSFET couramment utilisé, afin de réduire sa consommation d’énergie ; dans un deuxième temps, un travail est mené sur une nouvelle structure mécanique à base de poutres reliées entre elle par des forces de répulsion magnétique. La structure obtenue par cet ensemble de poutres et de type non-linéaire à plusieurs degrés de liberté (MDOF) ce qui permet augmenter la bande passante. / The future trend of Internet of Things (IoT) is bringing energy harvesting in to the core technique due to its requirement of self-power supplying. For best customer interface and eco-friendly issues, additional sensing systems are to be designed small, wireless and self-powering. Energy harvesting provides a way to realize the wireless self-powered system, it enables the device itself to obtain its own energy from their environment. Solar energy, thermal gradient, mechanical forces, are some commonly seen methods to obtain energy from the environment. The piezoelectric energy harvester is chosen to harvest vibrational energy in this study. In this work, a simple model of the original electrical smart switch driven under ultra-low power is proposed. By using the miniature device to drive the smart switch, the efficiency when low power is provided was examined. To construct an energy harvesting system in a more complete aspect, two newly proposed methods are as below: First, the hybrid-electrical-mechanical switches were utilized to replace the commonly seen electrical smart switches, to reduce its energy consumption such as threshold loss. Secondly, we designed a new mechanical structure for the cantilever array by connecting the beams using magnetic repelling force. In this way, the beams within the array were connected physically, forming a nonlinear multi-degree of freedom (MDOF) -like result.

Ces travaux portent sur la question de l’autonomie énergétiquedes capteurs sans fil dans un contexte aéronautique, à laquelle la récupérationet le stockage d’énergie ambiante sont susceptibles d’apporter uneréponse. Nous étudions dans un premier temps la génération thermoélectrique,destinée à être appliquée au suivi du vieillissement structurelprès de la zone moteur, et débouchant sur la réalisation d’un démonstrateur.Nous proposons ensuite une architecture de stockage capacitif qui,en s’adaptant à son état de charge, vise à améliorer la performance de cettesolution de stockage en termes de temps de démarrage, de taux d’utilisationd’énergie et sous certaines conditions, de transfert d’énergie. Finalement,nous rapportons les résultats d’une étude prospective sur la récupérationd’énergie du vent relatif grâce au phénomène aéroacoustique. Nousmontrons que cette méthode présente un potentiel énergétique intéressant,puis nous présentons la conception et la réalisation d’un circuit optimiséde gestion de l’énergie, permettant d’alimenter grâce à cette technique uncapteur sans fil de température / This work adresses the issue of energy autonomy within wirelesssensor networks embedded in aircrafts, which may be solved throughambient energy harvesting and storage. In a first study, we develop a demonstratorbased on thermal gradients energy harvesting, which is designedto supply power to a structural health monitoring system implementednear the engine zone. Thereafter, we introduce a capacitive storagearchitecture which self-adapts to its own state of charge, aiming at improvingits performance in terms of startup time, the energy utilization ratioand under some conditions, the energy transfer. Finally, we report the resultsof a prospective study on aeroacoustic energy harvesting appliedto the relative wind. It is shown that this method exhibits an interestingpotential in terms of generated power, then we introduce the design andthe realization of an optimized energy management circuit, allowing ourtechnique to supply power to a wireless temperature sensor

L'électronique a connu une évolution incontestable ces dernières années. Les progrès réalisés, notamment dans l'électronique numérique et l'intégration des circuits, ont abouti à des systèmes plus performants, miniatures et à faible consommation énergétique. Les évolutions technologiques, alliant les avancées de l'informatique et des technologies numériques et leur intégration de plus en plus poussée au sein d'objets multiples, ont permis le développement d'un nouveau paradigme de systèmes qualifiés de systèmes cyber-physiques. Ces systèmes sont massivement déployés de nos jours grâce à l'expansion des applications liées à l'Internet Des Objets (IDO). Les systèmes cyber-physiques s'appuient, entre autre, sur le déploiement massif de capteurs communicants sans fil autonomes, ceux-ci présentent plusieurs avantages : * Flexibilité dans le choix de l'emplacement. Ils permettent l'accès à des zones dangereuses ou difficiles d'accès. * Affranchissement des câbles qui présentent un poids, un encombrement et un coût supplémentaire. * Elimination des problèmes relatifs aux câbles (usure, étanchéité...) * Facilité de déploiement de réseaux de capteurs Cependant, ces capteurs sans fils nécessitent une autonomie énergétique afin de fonctionner. Les techniques conventionnelles telles que les batteries ou les piles, n'assurent le fonctionnement des capteurs que pour une durée limitée et nécessitent un changement périodique. Ceci présente un obstacle dans le cas où les capteurs sans fils sont placés dans un endroit où l'accès est impossible. Il est donc nécessaire de trouver un autre moyen d'approvisionner l'énergie de façon permanente à ces réseaux de capteurs sans fil. L'intégration et la miniaturisation des systèmes électroniques ont permis la réalisation de systèmes à faible consommation, ce qui a fait apparaître d'autres techniques en termes d'apports énergétiques. Parmi ces possibilités se trouvent la récupération d'énergie électromagnétique et le transfert d'énergie sans fil (TESF). En effet, l'énergie électromagnétique est de nos jours, omniprésente sur notre planète, l'utiliser donc comme source d'énergie pour les systèmes électroniques semble être une idée plausible et réalisable. Cette thèse s'inscrit dans ce cadre, elle a pour objectif la conception et la fabrication de systèmes de récupération d'énergie électromagnétique pour l'alimentation de réseaux de capteurs sans fil. Le circuit de récupération d'énergie électromagnétique est appelé " Rectenna ", ce mot est l'association de deux entités qui sont " antenne " et " rectifier " qui désigne en anglais le " redresseur ". L'antenne permet de récupérer l'énergie électromagnétique ambiante et le redresseur la convertit en un signal continu (DC) qui servira par la suite à alimenter les capteurs sans fil. Dans ce manuscrit, plusieurs rectennas seront présentées, pour des fréquences allant des bandes GSM 868MHz, 915MHz, passant par l'UMTS à 2GHZ et WIFI à 2,45GHz, et allant jusqu'aux bandes Ku et Ka. / The electronic domain has known a significant expansion the last decades, all the advancements made has led to the development of miniature and efficient electronic devices used in many applications such as cyber physical systems. These systems use low-power wireless sensors for: detection, monitoring and so on. The use of wireless sensors has many advantages: * The flexibility of their location, they allow the access to hazardous areas. * The realization of lighter system, less expensive and less cumbersome. * The elimination of all the problems associated to the cables (erosion, impermeability...) * The deployment of sensor arrays. Therefore, these wireless sensors need to be supplied somehow with energy to be able to function properly. The classic ways of supplying energy such as batteries have some drawbacks, they are limited in energy and must be replaced periodically, and this is not conceivable for applications where the wireless sensor is placed in hazardous places or in places where the access is impossible. So, it is necessary to find another way to permanently provide energy to these wireless sensors. The integration and miniaturization of the electronic devices has led to low power consumption systems, which opens a way to another techniques in terms of providing energy. Amongst the possibilities, we can find the Wireless Power Transfer (WPT) and Energy Harvesting (EH). In fact, the electromagnetic energy is nowadays highly available in our planet thanks to all the applications that use wireless systems. We can take advantage of this massive available quantity of energy and use it to power-up the low power wireless sensors. This thesis is incorporated within the framework of WPT and EH. Its objective is the conception and realization of electromagnetic energy harvesters called "Rectenna" in order to supply energy to low power wireless sensors. The term "rectenna" is the combination of two words: Antenna and Rectifier. The Antenna is the module that captures the electromagnetic ambient energy and converts it to a RF signal, the rectifier is the RF circuit that converts this RF signal into a continuous (DC) signal that is used to supply the wireless sensors. In this manuscript, several rectennas will be presented, for different frequencies going from the GSM frequencies (868 MHz, 915 MHz) to the Ku/Ka bands.

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This thesis is based around the use of energy harvesting in systems, specifically for a Bluetooth Low Energy (BLE) mesh testbed. This BLE mesh is located in a well lit lab and is currently powered by mains electricity. Systems such as the BLE mesh are considered Internet of Things (IoT). The market for these systems is rapidly expanding and in turn so is the energy use. Many systems are powered by battery, and the need to replace a battery with an energy harvesting system has arisen. This thesis will explore the possibilities to power a node in this mesh and introduce a level of intelligence to allow the system to better predict available energy to harvest. The lab the BLE mesh is in is characterised for potential energy sources. Light is chosen to be an exceptional power source, from here a lux metre is created from a photovoltaic (PV) cell. This PV cell would function as both the power for the system and provide a method to measure the current light intensity. This would help add a layer of intelligence to the system to allow future systems to better understand how much energy is available. This idea can be implemented in other harvesters as well. / Denna avhandling är baserad på användningen av energiskördning i ett system, specifikt i en Bluetooth Low Energy (BLE)-mesh. Denna BLE-mesh befinner sig i ett väl upplyst labb och är för närvarande strömdrivet genom huvudström. System som BLE-mesh anses vara en del av Internet of Things (IoT). Marknaden för dessa system expanderar snabbt och därmed ökar också energiförbrukningen. Många system är batteridrivna och det har uppstått ett växande behov av att ersätta batteriet med ett energiskördsystem. Denna avhandling kommer att utforska möjligheterna att strömförsörja en nod i denna mesh och införa en intelligensnivå för att förbättra systemets möjlighet att förutspå energi som är tillgänglig för att skördas. Labbet där BLE-meshen befinner sig karakteriseras för potentiella energikällor. Ljus valdes som en exceptionell kraftkälla, och därifrån skapas en luxmeter från en fotovoltaisk (PV) cell. Denna PV-cell ska fungera både som strömkälla för systemet och utgöra en metod för att mäta nuvarande ljusintensitet. Detta skulle bidra till att lägga till ett skikt av intelligens i systemet för att göra det möjligt för framtida system att bättre förutspå tillgänglig skördbar energi. Denna idé kan även implementeras i andra energiskördsystem.