Die wechselhafte Energiebereitstellung für drahtlose Sensorknoten durch Solarzellen stellt das Energiemanagement dieser Systeme vor große Herausforderungen. Bedingt durch saisonale und kurzfristige Effekte treten kontinuierlich Schwankungen in der Eingangsleistung auf, gleichzeitig soll jedoch eine zuverlässige und konstante Systemfunktion realisiert werden. Um dies miteinander zu vereinbaren, wird ein Modell zur Beschreibung der erwarteten Eingangsleistung aufgestellt, mit welchem der planmäßige Energieverlauf bestimmt werden kann. Dieser kann wiederum mit der realen Eingangsleistung verglichen werden, um den tatsächlichen energetischen Zustand des Sensorknotens zu bestimmen. Daraus lassen sich beispielsweise Entscheidungskriterien für die Steuerung der Energieverteilung oder Betriebszustände ableiten. Im Rahmen der Arbeit werden die physikalischen Hintergründe zur Modellierung der eingehenden Sonnenenergie beschrieben, der Stand der Technik zur Modellierung aufgezeigt und ein Modell als Basis für die weiteren Untersuchungen ausgewählt. Dieses wird auf die stark limitierte Hardware von drahtlosen Sensorknoten angepasst. Die Herausforderungen liegen dabei hauptsächlich in der geringen verfügbaren Rechenleistung, wenig Datenspeicher im System und dem Ziel, möglichst wenig Energie für die Berechnung zu verbrauchen. Im Ergebnis zeigt sich, dass ein angepasstes Modell auf drahtlosen Sensorsystemen umgesetzt werden kann und trotz der starken Limitierungen lauffähig ist. Es wird eine deutliche Verbesserung in der Verteilung der Energie über den Tag ermöglicht, wodurch sich trotz wechselhafter Quelle eine konstante Systemfunktion ergibt. Nebenher wird die Zuverlässigkeit und Ausfallsicherheit erhöht und Überdimensionierungen in Energiespeicher und Solarzelle können verringert werden. Das modellbasierte Energiemanagement stellt somit einen wichtigen Baustein für eine gesicherte Energieversorgung drahtloser Sensorsysteme dar. / The volatile energy supply by solar cells for wireless sensor nodes causes vast challenges for the energy management of such systems. Conditioned by seasonal and short time effects, the incoming power continuously varies. Simultaneously a reliable and constant function of the system has to be realized. To reconcile this, a model for the expected incoming solar power has been derived, which enables the estimation of the planned energy curve. This curve can be compared with the real progression of incoming power measured in parallel, to determine the current state of energy of a sensor node. This comparison is used to derive decision criteria for the control of the energy distribution or operating conditions. Within this work, the physical backgrounds for the modelling of the incoming solar energy and the state of the art of modelling solar power are described. A model is chosen as basis for further investigations and adapted to the limited hardware of wireless sensor nodes. The main challenges are the reduced processing power, few data memory in the system and the objective to consume as few energy as possible for the calculation. The results show that an adapted model can be implemented on wireless sensor systems and that it is executable despite the heavy limitations. This enables a distinct improvement of the distribution of energy across the day, which results in a constant systems function, despite the varying incoming power. At the same time the reliability and failure safety are being improved and the oversizing of the solar cell and the storage elements can be reduced. Therefore the model based energy management is an important component for a stable power supply of wireless sensor systems.

Improvements in embedded electronics which have effectively reduced power consumption requirements as well as advancements in IC technology allowing utilization of low power inputs have made Energy Harvesting a popular power solution for low power applications such as WSNs. In many implementation areas, we can see solar, thermal, and vibration energy harvesting techniques have taken the role of batteries as power source. Now that Energy Harvesting is a popular and considerably mature technology, with proper design and installation, any object exposing energy has the ability to be promoted as a power source. We are currently living in Internet age where we connect to the world through network packets. Ethernet, by far, is the most popular LAN technology which allows us to plug and play. Therefore, on an Ethernet link, billions of packets where our data are encapsulated in are traversing every hour. We assume each of these packets exposes some level of energy on an Ethernet link. The challenge here is harvesting the energy available from Ethernet packets and transforming it into useful energy so that it can be used to power devices such as WSNs. In this thesis work, we have revealed how much energy is available from Ethernet packets, and how much of it can be made usable. We have also designed a system where a WSN is generating all of its operating power solely from Ethernet packets and consuming this energy in communication with a base station.

The growing need and desire for the harvesting of energy from everyday mechanical interactions impose a challenge on the current design of such systems. Often their nature indicates slow response times and unsteady AC voltages. The objective of this work is to present a new method of designing and controlling an oscillating energy harvesting system using a cutting-edge algorithm for fast determination of the optimal operating condition. In this thesis, an energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is being introduced. The new control strategy, Maximum Energy Harvesting Control (MEHC), is developed and applied to the aforementioned system to evaluate its improvement over the basic Maximum Power Point Tracking (MPPT) algorithm. MEHC algorithm can also be used in many different applications, ranging from ocean wave to sports shoes energy harvesting.

Dans les dernières années, l'utilisation intensive des combustibles fossiles a déclenché une crise mondiale due à la forte production de polluants et à la réduction des stocks, en raison de sa nature de source d'énergie non renouvelable. Parce que l'utilisation généralisée des combustibles fossiles a entraîné la production de grandes quantités de CO2, ce qui est un facteur aggravant du réchauffement de la planète. Les piles à combustible microbiennes (MFC) représentent une technique de récupération d'énergie qui convertit l'énergie chimique des composés organiques en énergie électrique par le biais de réactions catalytiques de micro-organismes. La MFC peut être considérée comme un archétypique de système microbien bioélectrochimique (BES), qui exploite l’activité bio-électrocatalytique de micro-organismes vivants pour la génération de courant électrique. Durant la dernière décennie, l’évolution de l’électronique de faible consommation a rendu la technologie des MFC plus attrayante, car elle commence à pouvoir fournir une énergie comparable à celle consommée par des périphériques dit à faible consommation, comme un nœud de réseau de capteurs sans fil (WSN). En plus, les MFC ont gagné en intérêt car elles peuvent générer de l'énergie électrique tout en traitant des déchets. Contrairement aux autres piles à combustible, les MFC peuvent générer en permanence une énergie propre à une température ambiante, à la pression atmosphérique et à un pH neutre, sans entretien supplémentaire. Les seuls sous-produits sont le CO2 et H2O, qui ne nécessitent aucune manipulation supplémentaire, car le CO2 produit est biogénique, ce qui est inclus dans le cycle du carbone biogéochimique, évitant l'émission nette de carbone dans l'atmosphère. Ce manuscrit examine certains aspects liés à la technologie des piles à combustible microbiennes, depuis les réactions chimiques jusqu’aux systèmes de gestion de l'énergie requis pour exploiter la puissance fournie par les MFC. Une campagne expérimentale a été menée sur les MFCs concernant la caractérisation électrique, la connexion multiple des MFCs et l’influence des principaux paramètres qui affectent les performances de conversion de l’énergie. Le contexte de la pile à biocarburant est introduit et les principes de base de fonctionnement et les applications principales sont expliqués. L'enquête comprend une évaluation de l'impact des différents matériaux d'électrode, du substrat utilisé et des bactéries impliquées dans le processus chimique. Une perspective consiste à ajuster les paramètres afin de maximiser la production d'électricité. La conception spécifique de nos MFC de laboratoire est également présentée. Les essais expérimentaux ont été effectués sur deux types de réacteurs : la pile à combustible microbienne terrestre et la pile à combustible microbienne à eau usée. Un système de mesure approprié est présenté, il est spécialement conçu pour les tests sur les MFC. Il est capable d'assurer une mesure précise de toutes les valeurs et paramètres électriques nécessaires à la caractérisation électrique des réacteurs dans une configuration unique ou dans une connexion multiple. Les solutions utilisées pour alimenter les WWMFC étaient différentes et dans certains cas, on utilisait de vraies eaux usées, alors que dans d'autres, des solutions synthétisées appropriées étaient conçues à cet effet. Les méthodes de synthèse des solutions sont décrites. L'influence des principaux paramètres tels que le pH et la température a été analysée pour les deux types de cellules. La campagne expérimentale comprend des mesures de réacteurs en configuration unique ou disposées dans des connexions en série ou en parallèle. Les résultats confirment l'augmentation de la tension dans le cas de connexions en série et l'augmentation de la puissance dans le cas de connexions en parallèle. [...] / In recent years, the extensive use of fossil fuels has triggered into a global crisis due to high pollution and stock reduction, because of its nature of non-renewable source of energy. Because the wide use of fossil fuels has led to the production of high amounts of CO2, as a result is a trigger of the global warming issue. Microbial fuel cells (MFCs) is an energy harvesting technique that converts chemical energy from organic compounds to electrical energy through catalytic actions of microorganisms. MFC can be considered as archetypical microbial Bioelectrochemical Systems (BESs), that exploit the bio-electrocatalytic activity of living microorganisms for the generation of electric current. In the past decade, the evolution of low power electronics has made MFCs technology more attractive, because it has begun to be able to power low-power devices forming complete systems, such as the nodes of a wireless sensor network (WSN). Moreover, MFCs gained more interest because they can generate electric power while treating wastes. Unlike other fuel cells, MFCs can continuously generate clean energy at normal temperature, atmospheric pressure, and neutral pH value without any supplementary maintenance. The only by-products are CO2 and H2O, which do not require additional handling. The production of CO2 is part of a short duration carbon cycle. The CO2 produced is biogenic, which is included in the biogeochemical carbon cycle, avoiding net carbon emission into atmosphere. This manuscript examines many aspects related to microbial fuel cell technology from chemical reactions inside the cells to the energy management systems required to exploit energy delivered from MFCs for practical usage in autonomous sensors. Experimental campaign was performed on MFCs regarding electrical characterization, multiple connections of MFCs and influence of main parameters that affect energy conversion performances. The experimental tests were performed on two different lab-scale reactor typologies: terrestrial microbial fuel cell and waste water microbial fuel cell. A survey is presented about different proposed energy management systems and other devices able to build a node of a WSN powered by MFCs.

Die Weiterentwicklung klassischer, elektronischer Identifikationstechnologien leistet einen wichtigen Beitrag zum technischen Fortschritt in Industrie, Logistik und Gesundheitswesen. Die vorliegende Dissertationsschrift beschreibt die Entwicklung eines Dual-Feed-Antennendesigns für passive UHF-RFID-Transponder auf kritischen Oberflächen. Die zu Grunde liegende Antennenstruktur besteht aus einem Microstrip-Patch unter Verwendung eines verlustarmen Substratmaterials. Dieser erfährt eine Optimierung hinsichtlich seiner Lesereichweite, insbesondere auf kritischen Oberflächen. Ein Zwei-Port-Konzept mit gekoppeltem Feed-Line-Anpassnetzwerk reduziert die Anzahl benötigter, diskreter Komponenten und ermöglicht eine kostengünstige Herstellung mittels klassischer Ätzverfahren. Verschiedene Ansätze zur Modellierung und zur analytischen Berechnung der Antennenparameter werden dargestellt. Des Weiteren erfolgt eine Verifikation der Antennenstruktur anhand eines Konzepts für einen passiven Energy-Harvesting-RFID-Transponder, der zur Temperaturüberwachung in den genannten Branchen eingesetzt werden kann. Dieses Konzept schließt ein effizientes Energiemanagement mittels eines Ultra-Low-Power-Mikrocontrollers sowie Ansätze zur Energiegewinnung und -speicherung mit ein und stellt die Wahl wichtiger Systemparameter und Bauelemente anhand anwendungsspezifischer Abschätzungen dar.

With higher frequencies now being used in RFID systems, antennas are becoming much smaller resulting in more space on tags that can be used for innovative array designs to harvest more wireless energy. This master's thesis outlines and details a new methodology for designing and simulating the staggered pattern charge collector, a technique to improve harvesting wireless energy. Staggered pattern charge collectors enable RFID tag's to produce a higher DC voltage from a charge pump circuit by creatively using multiple arrays to increase the antenna power conversion gain without limiting the half power beamwidth. This thesis discusses the basics of patch antennas and charge pumps as well as an optimization technique for the staggered pattern array by maximizing integrated power conversion gain (IPCG). An example of a staggered pattern charge collector is fully specified from design through simulation, in preparation for fabrication. This methodology allows for the staggered pattern charge collectors to be designed, simulated, and fabricated quickly and effectively.

Low-power requirements of contemporary sensing technology attract research on alternate power sources that can replace batteries. Energy harvesters function as power sources for sensors and other low-power devices by transducing the ambient energy into usable electrical form. Energy harvesters absorbing the ambient vibrations that have potential to deliver uninterrupted power to sensing nodes installed in remote and vibration rich environments motivate the research in vibrational energy harvesting. Piezoelectric bimorphs have been demonstrating a pre-eminence in converting the mechanical energy in ambient vibrations into electrical energy. Improving the performance of these harvesters is pivotal as the energy in ambient vibrations is innately low. The present work is organized in three major sections: firstly, audit of the energy available in a vibrating source and design for effective transfer of the energy to harvesters, secondly, design of vibration energy harvesters with a focus to enhance their performance, and lastly, identification of key performance metrics influencing conversion efficiencies and scaling analysis for MEMS harvesters. Typical vibration levels in stationary installations such as surfaces of blowers and ducts, and in mobile platforms such as light and heavy transport vehicles, are determined by measuring the acceleration signal. The frequency content in the signal is determined from the Fast Fourier Transform. A method of determining the energy associated with the vibrating source and the associated power using power spectral density of the signal is proposed. Power requirements of typical sensing nodes are listed with an intent to determine the adequacy of energy harvesting. Effective transfer of energy from a given vibration source is addressed through the concept of dynamic vibration absorption, which is a passive technique for suppressing unintended vibrations. Optimal absorption of energy from a vibration source entails the determination of absorber parameters such as resonant frequency and damping. We propose an iterative method to obtain these parameters for a generic case of large number of identical vibration absorbers resembling harvesters by minimizing the total energy absorbed by the system. The proposed method is verified by analysing the response of a set of cantilever absorber beams placed on a vibrating cantilever plate. We find, using our method, the values of the absorber mass, resonant frequency and damping of the absorber at which significant amount of energy supplied to the system flows into the absorber, a scenario which is favourable for energy harvesting. We emphasize through our work that monitoring energies in the system and optimizing their flow is both rational and vital for designing multiple harvesters that absorb energy from a given vibration source optimally. Enhancing the performance of piezoelectric energy harvesters through a multilayer and, in particular, a multistep configuration is presented. Partial coverage of piezoelectric material in steps along the length of a cantilever beam results in a multistep piezoelectric energy harvester. We find that the power generated by a multistep beam is almost twice of that generated by a multilayer harvester made out of the same volume of polyviny-lidine fluoride (PVDF), further corroborated experimentally. Improvements observed in the power generated prove to be a boon for weakly coupled, low pro le, piezoelectric materials. Thus, in spite of the weak piezoelectric coupling observed in PVDF, its energy harvesting capability can be improved significantly by using it in a multistep piezoelectric beam configuration. Besides, the effect of piezoelectric step length and thickness in a piezoelectric unimorph harvester and performance metrics such as piezoelectric coupling factor and efficiency of conversion are presented. Modeling of a hybrid energy harvester composed of piezoelectric and electromagnetic mechanisms of energy conversion motivated by the need to determine the contribution of each domain to the power generated by the harvester is presented, particularly, when multiple domains exist in a single harvester. Two exclusive schemes of energy transduction are represented using equivalent circuits, which allow modeling any additional transduction scheme employed in the hybrid harvester with relative ease. Furthermore, a method of determining optimal loads in the respective domains using the equivalent circuit of the hybrid harvester is presented. Four different hybrid energy harvesters were fabricated and evaluated for their performance in comparison with that estimated from the proposed models. Additionally, scaling laws for hybrid energy harvesters are presented. The power developed by both piezoelectric and electromagnetic domains is observed to decrease with width and length cubed. Power indices and figures of merit in a hybrid harvester are proposed and are used to estimate the efficiencies of the four fabricated hybrid harvesters. The important design parameters for micro scale harvesting are identified by performing scaling analysis on MEMS piezoelectric harvesters. Performance of energy harvesters is directly related to the harvester attributes, viz., size, material, and end-mass. Depending on the contribution from each attribute, the power developed by MEMS harvesters can vary widely. A novel method of delineating the power developed by a harvester using five exclusive factors representing scaling, composition, inertia, material, and power (SCIMP) factors is presented. Although the proposed method can be extended to bi-morph and multilayer harvesters, in the present work, we elucidate it by applying it to a MEMS unimorph. We also present a unique coupling factor that ensures maximum power factor in a harvester. As any tiny increment in the power generated would considerably improve the power densities of MEMS harvesters, we focus on enhancing the power developed by maximizing each of the five exclusive factors irrespective of material and size. Furthermore, we demonstrate the competence of the proposed method by applying it on nine different MEMS harvesters reported in the literature. Considering the close match between the reported and predicted performance, we emphasize that monitoring the proposed factors is sufficient to attain the best performance from a harvester.

Die wechselhafte Energiebereitstellung für drahtlose Sensorknoten durch Solarzellen stellt das Energiemanagement dieser Systeme vor große Herausforderungen. Bedingt durch saisonale und kurzfristige Effekte treten kontinuierlich Schwankungen in der Eingangsleistung auf, gleichzeitig soll jedoch eine zuverlässige und konstante Systemfunktion realisiert werden. Um dies miteinander zu vereinbaren, wird ein Modell zur Beschreibung der erwarteten Eingangsleistung aufgestellt, mit welchem der planmäßige Energieverlauf bestimmt werden kann. Dieser kann wiederum mit der realen Eingangsleistung verglichen werden, um den tatsächlichen energetischen Zustand des Sensorknotens zu bestimmen. Daraus lassen sich beispielsweise Entscheidungskriterien für die Steuerung der Energieverteilung oder Betriebszustände ableiten. Im Rahmen der Arbeit werden die physikalischen Hintergründe zur Modellierung der eingehenden Sonnenenergie beschrieben, der Stand der Technik zur Modellierung aufgezeigt und ein Modell als Basis für die weiteren Untersuchungen ausgewählt. Dieses wird auf die stark limitierte Hardware von drahtlosen Sensorknoten angepasst. Die Herausforderungen liegen dabei hauptsächlich in der geringen verfügbaren Rechenleistung, wenig Datenspeicher im System und dem Ziel, möglichst wenig Energie für die Berechnung zu verbrauchen. Im Ergebnis zeigt sich, dass ein angepasstes Modell auf drahtlosen Sensorsystemen umgesetzt werden kann und trotz der starken Limitierungen lauffähig ist. Es wird eine deutliche Verbesserung in der Verteilung der Energie über den Tag ermöglicht, wodurch sich trotz wechselhafter Quelle eine konstante Systemfunktion ergibt. Nebenher wird die Zuverlässigkeit und Ausfallsicherheit erhöht und Überdimensionierungen in Energiespeicher und Solarzelle können verringert werden. Das modellbasierte Energiemanagement stellt somit einen wichtigen Baustein für eine gesicherte Energieversorgung drahtloser Sensorsysteme dar. / The volatile energy supply by solar cells for wireless sensor nodes causes vast challenges for the energy management of such systems. Conditioned by seasonal and short time effects, the incoming power continuously varies. Simultaneously a reliable and constant function of the system has to be realized. To reconcile this, a model for the expected incoming solar power has been derived, which enables the estimation of the planned energy curve. This curve can be compared with the real progression of incoming power measured in parallel, to determine the current state of energy of a sensor node. This comparison is used to derive decision criteria for the control of the energy distribution or operating conditions. Within this work, the physical backgrounds for the modelling of the incoming solar energy and the state of the art of modelling solar power are described. A model is chosen as basis for further investigations and adapted to the limited hardware of wireless sensor nodes. The main challenges are the reduced processing power, few data memory in the system and the objective to consume as few energy as possible for the calculation. The results show that an adapted model can be implemented on wireless sensor systems and that it is executable despite the heavy limitations. This enables a distinct improvement of the distribution of energy across the day, which results in a constant systems function, despite the varying incoming power. At the same time the reliability and failure safety are being improved and the oversizing of the solar cell and the storage elements can be reduced. Therefore the model based energy management is an important component for a stable power supply of wireless sensor systems.

Energy harvesting is identified as a promising alternative solution for powering implantable biosensors. It can completely replace the batteries, which are introducing many limitations, and it enables the development of self-powered implantable biosensors. An interface circuit is necessary to correct for differences in the voltage and power levels provided by an energy harvesting device from one side, and required by biosensor circuits from another. This thesis investigates the available energy harvesting sources within the human body, selects the most suitable one and proposes the power management unit (PMU), which serves as an interface between a harvester and biosensor circuits. The PMU targets the efficient power transfer from the selected source to the implantable biosensor circuits. Based on the investigation of potential energy harvesting sources, a thermoelectric energy harvester is selected. It can provide relatively high power density of 100 μW/cm2 at very low temperature difference available in the human body. Additionally, a thermoelectric energy harvester is miniature, biocompatible, and it has an unlimited lifetime. A power management system architecture for thermoelectric energy harvesters is proposed. The input converter, which is the critical block of the PMU, is implemented as a boost converter with an external inductor. A detailed analysis of all potential losses within the boost converter is conducted to estimate their influence on the conversion efficiency. The analysis showed that the inevitable conduction and switching losses can be reduced by the proper sizing of the converter’s switches and that the synchronization losses can be almost completely eliminated by an efficient control circuit. Additionally, usually neglected dead time losses are proved to have a significant impact in implantable applications, in which they can reduce the efficiency with more than 2%. An ultra low power control circuit for the boost converter is proposed. The control is utilizing zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques to eliminate the synchronization losses and enhance the efficiency of the boost converter. The control circuit consumes an average power of only 620 nW. The boost converter driven by the proposed control achieves the peak efficiency higher than 80% and can operate with harvested power below 5 μW. For high voltage conversion ratios, the proposed boost converter/control combination demonstrates significant efficiency improvement compared to state-of-the-art solutions. / <p>QC 20150413</p>

This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.