The modeling, analysis and experimental verification of a two-degree-of-freedom typical aeroelastic section with superelastic shape memory alloy springs are presented. The focus is to investigate the effects of the phase transformation of the shape memory alloy springs on the flutter and post-flutter behaviors of the typical section. The shape memory alloy phase transformation kinetics is described by a modified version of well-known phenomenological models. The shape memory alloy spring model is based on classical spring design (with the pure shear assumption) and modified to account for the nonlinear effects of phase transformation. The cross-section of the shape memory alloy wire is represented by a linear radial distribution of shear strain and nonlinear radial distributions of shear stress and martensitic fraction. The equations of motion of a linear typical section are modified to include the shape memory alloy springs. A linear unsteady aerodynamic model is employed to determine the aerodynamic loads. The proposed model is cast into state-space representation and solved with a Runge-Kutta method. It is numerically and experimentally shown that the phase transformation of shape memory alloy springs can be effectively exploited to enhance the aeroelastic behavior of a typical section by replacing unstable flutter oscillations by stable oscillations of acceptable amplitudes over a range of airflow speeds, providing a useful method of passive aeroelastic control. Since the modified aeroelastic behavior is attractive for wind energy harvesting purposes, electromechanical coupling is also modeled in the plunge degree-of-freedom along with a resistive load in the electrical domain for electrical power estimation. The exploitation of the shape memory alloy phase transformation is more attractive for airfoil-based wind energy harvesting performance than the use of typical concentrated nonlinearities (e.g., hardening steel) in terms of enhanced electrical power output. / A modelagem, análise e verificação experimental de uma seção típica aeroelástica com dois graus de liberdade e molas com memória de forma superelásticas são apresentadas. O foco é investigar os efeitos da histerese pseudoelástica das molas com memória de forma nos comportamentos de flutter e pós-flutter da seção típica. A cinética das transformações de fase nas molas com memória de forma é descrita por uma versão modificada de modelos fenomenológicos amplamente conhecidos. O modelo de molas helicoidais com memória de forma é baseado em teoria clássica de molas (com a hipótese de cisalhamento puro) e modificado para representar os efeitos não lineares de transformação de fase. A seção transversal do fio da mola com memória de forma é representada por uma distribuição radial e linear de deformações de cisalhamento e por distribuições radiais e não lineares de tensões cisalhantes e de frações martensíticas. As equações de movimento de uma seção típica linear são modificadas para incluir as molas com memória de forma. Um modelo aerodinâmico linear não estacionário é utilizado para se determinar as cargas aerodinâmicas. O modelo proposto é representado em espaço de estados e resolvido com um método Runge-Kutta. Mostra-se, numérica e experimentalmente, que a histerese pseudoelástica de molas com memória de forma pode ser efetivamente explorada para melhorar o comportamento aeroelástico de uma seção típica ao transformar oscilações instáveis de flutter em oscilações estáveis e de amplitudes aceitáveis em uma faixa de velocidades do escoamento, provendo um método útil de controle aeroelástico passivo. Como o comportamento aeroelástico modificado (pela histerese pseudoelástica) é atrativo para a coleta de energia do escoamento, um acoplamento eletromecânico é modelado no grau de liberdade de deslocamento linear, juntamente com uma carga resistiva no domínio elétrico do problema para se estimar a potência elétrica gerada. A exploração da histerese pseudoelástica das molas com memória de forma é mais atrativa para a performance da coleta aeroelástica de energia do que o uso de não linearidades concentradas típicas (como o enrijecimento não linear do aço) em termos de melhoria na potência elétrica gerada.

Les systèmes de récupération d’énergies basées sur les vibrations mécaniques environnantes suscitent l’intérêt depuis de nombreuses années. Augmenter l’efficacité de la conversion d'énergie est primordial, mais celle-ci pour être bien maitrisée, passe par la mise au point de modèles précis et notamment par la prise en compte des lois régissant les matériaux piézoélectriques. En effet, ces matériaux sont à la base des couplages mécano/électriques et il est capital de comprendre comment ils fonctionnent quelque soit l'excitation externe. Un modèle précis du matériau ferroélectrique est indispensable pour établir des critères de conception des prototypes et leur optimisation. Dans cette thèse, un modèle précis, temporel, large bande tenant compte de l’ensemble des non-linéarités d’une céramique piézoélectrique a été développé. L’utilisation d’opérateurs fractionnaires a permis d’augmenter fortement la bande de fréquence de validité du modèle. Le modèle permet notamment de prévoir l’évolution de la polarisation diélectrique ainsi que le déplacement mécanique de l’échantillon testé et ceci quelque soit le type de stimulation (contrainte mécanique pure, champ électrique et même excitation hybride électriques/mécaniques). La dérivé fractionnaire a dans un premier temps été utilisée pour l’hystérésis sous excitation électrique pour décrire le comportement dynamique de la polarisation diélectrique. En effet, au delà d’un seuil de fréquence, lorsque l’état du matériau n’est plus quasi-statique, une contribution dynamique apparaît. Cette contribution joue un rôle primordial lorsque les niveaux de fréquence et d’amplitude sont élevés. La même étude a ensuite été menée sous contrainte mécanique, et le même opérateur fractionnaire a été utilisé avec succès. Nous avons entre autre constaté que sur un même échantillon les paramètres de simulation établis sous champ électrique étaient conservés sous contrainte mécanique. Ensuite, un modèle inverse permettant d’imposer la forme d’onde de la polarisation ou du déplacement a été proposé. Pour une polarisation ou un déplacement donné, le modèle inverse permet de déterminer avec précision l’effort mécanique à appliquer sur la céramique piézo-électrique. Ces modèles sont nécessaires pour optimiser une forme d’onde de contrainte mécanique ou électrique et obtenir un rendement supérieur des systèmes récupérateurs d’énergie. En effet, une nouvelle technique couplée champ électrique/contrainte mécanique de récupération d’énergie est présentée à la fin de la thèse, technique qui nous a permis de valider l’utilisation du modèle. L’utilisation du modèle permet d’optimiser la mise au point d’un prototype mais également d’obtenir la valeur exacte du rendement de la méthode en rendant compte notamment des pertes diélectriques. Dans la thèse, le modèle sous ses différentes variantes est décrit de manière exhaustive. / Energy harvesting based on mechanical vibration has been a long time research topic for the last few decades. In addition to enhancing the energy conversion amount, another objective is to master and give a precise model with consideration of the disciplines of piezoelectric material behavior. A precise model for the ferroelectric material is mighty needed in the energy harvesting process, so as to give an instruction to the prototype designing and modelling optimizing. In this thesis, a model working on wide bandwidth considering the nonlinearity of the piezoceramic has been developed. The employment of the fractional derivative has broadened the usage of this model on expanded bandwidth. The model permit to predict the evolution of the dielectric polarization as well as the mechanical displacement, which has been tested on different samples under different kinds of stimulation (pure mechanical, pure electrical and hybrid of electrical and mechanical excitations). This fractional derivative factor has been first developed under electrical excitations to describe the dynamic behavior. In the development of this model to mechanical field, the fractional derivative factor was found available as well under the mechanical excitation in the same value. In the following study, an inverse of mechanical model has been developed as well. In the end, we stimulate the piezoceramic using both electrical and mechanical excitation to augment the energy harvesting amount which could become a promising method in energy harvesting field. Every model has been exhaustively demonstrated and specific measuring benches have been established to validate these models. Experiments results and simulations in different kinds of excitations (amplitudes, frequencies) for every kind of the above models have been compared. Good approximation has been acquired indicating the model has a good accuracy in describing the material property and dynamic behavior.

This thesis focuses on the development of a low power energy harvesting system specifically targeted for wireless sensor nodes (WSN) and wireless body area network (WBAN) applications. The idea for the system is derived from the operation of a micro-grid and therefore is termed as a pico-grid and it is capable of simultaneously delivering power from multiple and multitype energy harvesters to the load at the same time, through the proposed parallel load sharing mechanism achieved by a voltage droop control method. Solar panels and thermoelectric generator (TEG) are demonstrated as the main energy harvesters for the system. Since the magnitude of the output power of the harvesters is time-varying, the droop gain in the droop feedback circuitry should be designed to be dynamic and self-adjusted according to this variation. This ensures that the maximum power is capable to be delivered to the load at all times. To achieve this, the droop gain is integrated with a light dependent resistor (LDR) and thermistor whose resistance varies with the magnitude of the source of energy for the solar panel and TEG, respectively. The experimental results demonstrate a successful variation droop mechanism and all connected sources are able to share equal load demands between them, with a maximum load sharing error of 5 %. The same mechanism is also demonstrated to work for maximum power point tracking (MPPT) functionality. This concept can potentially be extended to any other types of energy harvester. The integration of energy storage elements becomes a necessity in the pico-grid, in order to support the intermittent and sporadic nature of the output power for the harvesters. A rechargeable battery and supercapacitor are integrated in the system, and each is accurately designed to be charged when the loading in the system is low and discharged when the loading in the system is high. The dc bus voltage which indicates the magnitude of the loading in the system is utilised as the signal for the desired mode of operation. The constructed system demonstrates a successful operation of charging and discharging at specific levels of loading in the system. The system is then integrated and the first wearable prototype of the pico-grid is built and tested. A successful operation of the prototype is demonstrated and the load demand is shared equally between the source converters and energy storage. Furthermore, the pico-grid is shown to possess an inherent plug-and-play capability for the source and load converters. Few recommendations are presented in order to further improve the feasibility and reliability of the prototype for real world applications. Next, due to the opportunity of working with a new semiconductor compound and accessibility to the fabrication facilities, a ZnON thin film diode is fabricated and intended to be implemented as a flexible rectifier circuit. The fabrication process can be done at low temperature, hence opening up the possibility of depositing the device on a flexible substrate. From the temperature dependent I-V measurements, a novel method of extracting important parameters such as ideality factor, barrier height, and series resistance of the diode based on a curve fitting method is proposed. It is determined that the ideality factor of the fabricated diode is high (> 2 at RT), due to the existence of other transport mechanism apart from thermionic emission that dominates the conduction process at lower temperature. It is concluded that the high series resistance of the fabricated diode (3.8 kΩ at RT) would mainly hinder the performance of the diode in a rectifier circuit.

O presente trabalho teve como objetivo a modelagem de células solares MOS operando em regime de inversão controlado por centros positivamente carregados na interface SiNxOy/Si. Este tipo de célula solar foi recentemente fabricada pela primeira vez no âmbito dos trabalhos desenvolvidos no grupo de Superfícies, Interfaces e Deposição Eletroquímica (GSIDE) do LSI/PSI/EPUSP utilizando dielétricos de porta ultra-finos (~2nm). A receita de crescimento de dielétrico ultra-fino desenvolvida foi no sentido de assegurar reprodutibilidade e uniformidade da espessura do dielétrico ao longo de áreas extensas de alguns cm2. Baseado nas curvas experimentais CxVg, GxVg e IxVg das células solares fabricadas, foi mostrado para as células fabricadas em substrato tipo P que existem os centros K predominantemente preenchidos com cargas positivas em todos os regimes de operação (acumulação, depleção e inversão). A densidade de cargas positivas (Qiq) na interface SiNxOy/Si além de ter resultado positivo, apresentou um comportamento linear com o potencial de superfície (ys) ou com a tensão de porta Vg de acordo com os resultados obtidos através de um simulador numérico desenvolvido para esta aplicação específica. Tal comportamento consistiu no acomodamento das cargas positivas na interface de forma que uma região de depleção profunda (Wd) é formada sem a presença da camada de inversão na condição sem iluminação. Para as células MOS submetidas a diferentes níveis de iluminação, tanto para os dielétricos crescidos a 850oC como também para aqueles que foram crescidos a 700oC, foi constatado que os centros K na interface funcionam como uma região de armazenamento de cargas positivas a medida em que os elétrons tunelam em direção à porta metálica da estrutura MOS. Como resultado, este tipo de comportamento significa uma nova forma de implementar o efeito fotovoltáico. / The goal of the present work was the modeling of MOS solar cells operating in an inversion regime controlled by positively charged centers at the SiNxOy interface. This type of solar cell was recently manufactured for the first time in the activities developed in the group of Surfaces, Interfaces and Electrochemical Deposition (GSIDE) from LSI/PSI/EPUSP using ultra-thin gate dielectrics (~2nm). The recipe for the growth of ultra-thin dielectrics was developed to ensure reproducibility and uniformity of the dielectrics thickness over large areas of few square centimeters. Based on the experimental curves CxVg, GxVg e IxVg of the manufactured MOS solar cells, it was shown for cells manufactured in P-type substrate that there are K centers dominantly filled with positive charges in all operating regimes (accumulation, depletion and inversion). The positive charge density (Qiq) at the SiNxOy/Si interface, in addition to having a positive charge, presented a linear behaviour with the surface potential (ys) or with the gate voltage (Vg) according to the results obtained from a numerical simulator developed for this application. Such behavior consisted of accommodating the positive charges at the SiNxOy/Si interface so that a deep depletion region (Wd) is formed without the presence of the inversion layer in the condition without illumination. For MOS cells subjected to different levels of illumination, both for dielectrics grown at 850oC as well as for those grown at 700oC, it was found that the K centers at the SiNxOy/Si interface work as a region of positive charge storage as the electrons tunnel from the interface towards the metal gate of the MOS cells. As a result, this type of behaviour means a new way of implementing the photovoltaic effect.

<p>U disertaciji je opisan namenski projektovan bežični senzorski čvor namenjen za praćenje parametara životne sredine. Razvijeno rešenje se odlikuje malom cenom i dimenzijama, širokom primenom i minimalnim utocajem na životnu sredinu u poređenju sa primerima iz literature. Koristi se prikupljanje energije sunca iz okoline i superkondenzator za napajanje, što utiče na povećanje životnog veka i smanjivanje troškova održavanja. Izvršena testiranja su potvrdila funkcionalnost predloženog rešenja i mogućnost praćenja različitih parametara korišćenjem komercijalnih i namenski projektovanih senzora. Unapređeno, modularno, rešenje rešava uočena ograničenja i povećava broj parametara životne sredine koji se mogu pratiti.</p> / <p>The dissertation describes a specially designed WSN node for application in<br />environmental monitoring. The developed solution is characterized by low price and<br />dimensions, wide application and minimal environmental impact compared to<br />example in literature. Solar energy harvesting and supercapacitor are used as power<br />supply, which increase node lifetime and reduce maintenance costs. The performed<br />tests confirmed the functionality of the proposed solution and the ability to monitor<br />various environmental parameters using commercial and specially designed sensors.<br />The new enhanced solution, with modular design, solves the observed limitations and<br />increases the number of environment parameters that can be monitored.</p>

Cal Poly’s ongoing Energy Harvesting from Exercise Machines (EHFEM) project is a very convenient and cost-effective way for generating DC power from physical exercise and sending it back to the electrical grid as AC power, providing a renewable energy source for the future. The EHFEM project consists of numerous subprojects involving converting different types of exercise machines for power generation. This project is a continuation of one of the previous subprojects, specifically involving an elliptical machine, and focuses on improving system functionality at different machine settings without altering the elliptical user’s experience by selecting a new DC-DC converter design, while keeping the other system components intact. The new proposed DC-DC converter design is based on a non-isolated, PWM-switching single-ended primary inductor converter (SEPIC) topology, as opposed to the resonant zero-current switching/zero-voltage switching (ZCS/ZVS) topology-based off-the-shelf DC-DC converter that the previous project utilized, which had poor system functionality at high physical input levels (greater than 30V input) from the elliptical trainer. This project proves that a PWM-switching SEPIC topology provides a functional DC-DC converter design for DC power generation and inverter interfacing from a dynamic input voltage generator because of its wide input voltage range, high power driving capability and inherent voltage step-up and step-down functions. The proposed DC-DC converter supplies up to 288 watts of power and outputs 36 volts, and simultaneously takes 5-65 volts from its input depending on the elliptical user’s physical input level. This project details the new DC-DC converter’s design and construction processes, compares its topology to other existing DC-DC converter topologies and analyzes unfeasible designs as well as the overall system’s performance when converting the generated DC power to AC power, and documents any potential problems when used for this specific application.

L'avènement de l'Internet des Objets a permis de déployer de nombreux réseaux de capteurs sans-fil. Ces réseaux sont utilisés dans des domaines aussi variés que l'agriculture, l'industrie ou la ville intelligente, où ils permettent d'optimiser finement les processus. Ces appareils sont le plus souvent alimentés par des piles ou batteries, ce qui limite leur autonomie. De plus, il n'est pas toujours possible ou financièrement viable de changer ou recharger les batteries. Une solution possible est d'alimenter ces capteurs en récupérant l'énergie présente dans l'environnement alentour. Ces sources d'énergie sont cependant peu fiables, et le capteur doit être capable d'éviter de vider complètement sa réserve d'énergie. Afin de moduler sa consommation d'énergie, le capteur peut adapter sa qualité de service à ses capacités énergétiques. L'appareil peut ainsi fonctionner en continu sans interruption de service. Cette thèse présente les méthodes utilisées pour la conception d'un capteur entièrement autonome alimenté par récupération d'énergie ambiante, communiquant sur un réseau longue portée LoRa. Afin d'assurer l'alimentation électrique, une carte permettant de récupérer de l'énergie depuis plusieurs sources d'énergie simultanément a été conçue. Un module logiciel de gestion d'énergie a ensuite été développé afin de calculer un budget énergétique que le capteur peut dépenser, et choisir la meilleure manière de dépenser ce budget pour exécuter une ou plusieurs tâches. Ce travail a ainsi permis le développement d'un prototype de produit industriel entièrement autonome en énergie. / The advent of the Internet of Things has enabled the roll-out of a multitude of Wireless Sensor Networks. These networks can be used in various fields, such as agriculture, industry or the smart city, where they facilitate fine optimization of processes. These devices are often powered by primary or rechargeable batteries, which limits their battery life. Moreover, it is sometimes not possible or financially viable to change and/or recharge these batteries. A possible solution is to harvest energy from the environment to power these sensors. But these energy sources are unreliable, and the sensor must be able to prevent the complete depletion of its energy storage. In order to adapt its energy consumption, the node can match its quality of service to its energetical capabilities. Thus, the device can continuously operate without any service interruption. This thesis presents the methods used for the conception of a completely autonomous sensor, powered by energy harvesting and communicating through a long range LoRa network. In order to ensure its power supply, a board has been designed to harvest energy from multiple energy sources simultaneously. A power management software module has then been developed to calculate an energy budget the sensor can use, and to choose the best way to spend this budget over one or multiple tasks. This work has enabled the development of an energy autonomous industrial sensor prototype.

Progress in energy harvesting technology and the increasing need for the energy efficient and environmentally friendly applications have called for reconsideration of communication systems. This reconsideration results in new problem formulations regarding the recent developments on energy harvesting systems. Recently, optimal strategies for various types of energy harvesting networks have been developed based on different harvesting models. This thesis reports the results of our research to develop the optimal scheduling structures on an energy harvesting broadcast and fading channels, and to devise online implementable algorithms for a point-to-point communication system. Particularly, structural properties of an optimal offline schedule in, (1) an energy harvesting broadcast channel with one transmitter two receivers, (2) a single user communication system under fading conditions, are investigated. Moreover, an online algorithm is proposed for a single-user energy harvesting communication system considering the physical constraints and necessities regarding implementation. The proposed scheme is implemented through GNU Radio framework on a USRP device.

Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT) thin films are of interest for their large dielectric permittivity, ferroelectric, and piezoelectric properties. The material has been widely studied for use in high frequency transducers, multi-layered capacitors, and ferroelectric random access memory. Copper foils are an inexpensive, flexible substrate with a low resistivity which makes them ideal for many transducer and capacitor applications. PZT thin films on copper foils were produced by RF sputtering and crystallized under reducing conditions. Causes and prevention of a cuprous oxide interlayer are discussed. The film structure was characterized by XRD, SEM, and AFM. The permittivity was low, but remanent polarization increased to as high as ~40 μC/cm² as film thickness and crystallization temperature increased. Residual stresses were measured by x-ray diffraction using the sin²ψ method. The relative permittivity of the PZT/Cu films was measured as a function of applied AC electric field. By performing a Rayleigh analysis on this data one can determine the relative contributions of the intrinsic, reversible, and irreversible components to the permittivity. The residual stress could be correlated to the reversible part of the permittivity. The first order reversal curves (FORCs), which characterize the ferroelectric switching, give indications of the defect state of the film. Cantilever energy harvesters were fabricated. Large electrodes were able to be evaporated onto the films after oxidizing pinholes and cracks on a hot plate. Devices were tested on a shaker table at < 100 Hz. A dynamic model based on Euler-Bernoulli beam equations was used to predict power output of the fabricated devices. The observed output was comparable to model predictions. Resonant frequency calculations were in line with observed first and second resonances at ~17 Hz and ~35 Hz which were also close to those predicted by the dynamic model. / Graduation date: 2013

This thesis presents various studies on energy efficient design of wireless networks. It starts with a survey on recent shortest path based energy efficient routing algorithms developed for ad hoc and sensor networks, making a comprehensive classification for these algorithms. In addition to energy efficient design, sustainable and environmentally friendly deployment of wireless networks demands increased use of renewable energy. However, this calls for novel design principles to efficiently utilize the variation in the availability of the energy. The thesis continues with an investigation of state-of-the-art resource management and scheduling algorithms developed for energy harvesting wireless sensor networks. Building on the stateof- the-art, the main contribution of this thesis is to formulate and solve a utility maximizing scheduling problem in a multiuser broadcast channel with an energy harvesting transmitter. The goal is to determine the optimal power and time allocations to users between energy arrivals. The structural properties of the problem are analyzed, and its biconvexity is proved. A Block Coordinate Descent (BCD) based algorithm is developed to obtain the optimal solution. Two simple and computationally scalable heuristics, PTF and ProNTO, which mimic the characteristics of the optimal policy, are proposed. Finally, an online algorithm, PTF-On,that will bypass the need for offline knowledge about the energy harvesting statistics, is developed. PTF-On uses a Kalman filter based energy harvesting prediction algorithm, developed in this thesis, to predict the energy that will arrive in the future.