Ces travaux de thèse se veulent exploratoires et visent à proposer d’une part une nouvelle approche hybride piézoélectrique-polymère pour le développement de récupérateur d’énergie et d’autre part à développer des méthodes d’actionnement destinée au contrôle de forme structurelle. L’utilisation de polymères diélectriques dans les dispositifs de récupération d’énergie permet de concilier une densité énergétique élevée avec une faible rigidité et une simplicité de mise en œuvre. L’approche hybride proposée dans le cadre de ces travaux permet de s’affranchir de la source de polarisation externe en la substituant par un dispositif piézoélectrique apte à générer, sous l’action d’une contrainte mécanique, le champ électrique nécessaire au fonctionnement du dispositif. L’optimisation du transfert d’énergie entre deux systèmes supposé quelconque a d’abord été généralisée. Les travaux ont ensuite été orientés vers l’investigation de la faisabilité de l’approche hybride piezo-polymère. Les performances des dispositifs hybrides ont été évaluées expérimentalement et comparées à celles obtenues avec des récupérateurs piézoélectriques simples et avec des récupérateurs polymères à polarisation externe. Il est montré que l’utilisation d’un dispositif hybride permet de concilier les qualités des deux approches simples, à savoir la faculté d’initier le processus de conversion d’énergie grâce au champ électrique généré par l’élément piézoélectrique et d’exploiter la haute densité d’énergie des polymères. La deuxième partie de ces travaux porte sur l’utilisation de matériaux électroactifs comme dispositifs d’actionnement destinés au contrôle de forme de structures minces. L’application finale visée ici est le développement de matériau de type peau active. Différents types de polymères ont d’abord été testés et leur performances ont été comparées avec des modèles théoriques spécifiquement développés. Des structures originales ont été proposées pour solutionner certains problèmes liés à l’actionnement par polymères diélectriques. Des prototypes simples ont permis de valider le principe du contrôle de forme des structures à l’aide de polymères diélectriques. / Dielectric polymers have seen their importance grow in the field of electroactive materials because of their undeniable advantages, particularly for potential applications such as energy harvesting, actuation or sensors. The work done in this thesis is exploratory and aims primarily to provide on one hand a new piezoelectric-polymer hybrid approach for the development of energy harvesting systems and secondly to develop operating methods shape control of structures using electroactive polymers. The use of dielectric polymers in energy harvesting devices reconciles a high energy density with low rigidity and simplicity of integration. The main problem which is characteristic of such devices is that they necessarily require the use of an external bias high voltage supply (> 1kV) to achieve significant energy densities. The hybrid approach proposed in the context of this work eliminates this source of external energy by using a piezoelectric device capable of generating, under the action of a mechanical stress, the electric field required to operate the device. The problem of optimization of energy transfer between any two systems was also studied. The work was then directed towards the investigation of the feasibility of the piezo-polymer hybrid approach. Various configurations have been proposed and evaluated in order to deduce their optimal parameters. The performance of hybrid devices was experimentally evaluated and compared with that obtained with simple piezoelectric or electrostatic (using polymers) systems. The second part of this work focuses on the use of electroactive materials as actuators for shape control of thin structures. The final application aimed here is the development of an active skin type material allowing reconfiguration of orbiting satellite antennas. Different types of polymers were first tested and their performance has been compared with the theoretical models developed specifically in this context. Original structures have been proposed to solve some problems related to the actuation using dielectric polymers. Simple prototypes have validated the principle of the structural shape control. If their use brings undeniable advantages over conventional operating techniques, the fact remains that certain specific characteristics of electroactive polymers limit their performance. For example, the square law characteristic of the electroactive polymer control requires the use of particular geometries in order to obtain a symmetrical two-way displacement. This fact complicates the control of such actuators but allows in the end to add new features. Thus the use of a sectored network of polymer actuator is required to obtain a symmetrical movement on a single type of structure blocked blocked-beam, but allows to consider different deformation profiles. Other similar problems have been addressed using different original structures.

"The recent years have seen the innovative system integration of a great many actuator technologies, such as point force actuators for space vehicle applications and the use of single fire actuators; such as pyrocharges to guide a free falling bomb to it’s target. The inherent limitations of these developments, such as nonlinear behavior under extreme environments and/or prolonged/repeated usage leading to a relaxation time component between firing of actuators and inherent system power limitations, have resulted in greater need for sophisticated control algorithms that allow for optimal switching between various actuators in any given embedded configuration so as to achieve the best possible performance of the system. The objective of this investigation is to offer a proof of concept experimental verification of a real time control algorithm, which switches between online piezoelectric actuators, employed for vibration control in an aluminum beam with fixed boundary conditions. In this investigation at a given interval of time, only one actuator is activated and the rest are kept dormant. The reason is to demonstrate the better vibration alleviation characteristics realized in switching between actuators depending on the state of the system, over the use of a single actuator that is always in fire mode. This effect is particularly pronounced in controlling systems affected by spatiotemporal disturbances. The algorithm can be easily adapted for various design configurations or system requirements. The optimality of switching is with respect to the minimal cost of an LQR performance index that corresponds to each actuator. Computer simulations with repeatable disturbance profiles, revealed that this algorithm offered better performance over the non-switched case. Performance measures employed were the time varying total energy norm of the dynamic system and position traces at any particular location on the beam. This algorithm was incorporated on a dSPACE rapid prototyping platform along with suitable hardware. Experimental and simulation results are discussed. "

Avec le développement des circuits intégrés à très faible consommation d'énergie, la nécessité de réduire les coûts d'exploitation des dispositifs électroniques embarqués et l'utilisation des piles usagées constituant une menace pour l'environnement, le concept de récupération d'énergie a acquis un nouvel intérêt. La récupération d'énergie couvre le piégeage de nombreuses sources d'énergie ambiantes perdues et leur conversion en énergie électrique. Une large gamme de dispositifs de récupération d'énergie des vibrations mécaniques a été développée. Une configuration commune consiste en un système de masse-ressort avec un matériau piézoélectrique en parallèle avec le ressort pour convertir une partie de l'énergie mécanique pendant les oscillations en énergie électrique. Jusqu'à présent, le matériau le plus utilisé pour la récupération d'énergie piézoélectrique est le titano-zirconate de plomb (PbZr1-xTixO3) (PZT). Le PZT est le matériau de référence pour les applications microsystème électromécanique-MEMS (MechanoElectroMechanicalSystems) dans le domaine de la récupération d'énergie. Les matériaux piézoélectriques à base de plomb tels que le PZT et niobate-titanate de plomb-magnésium (PMN-PT) offrent des facteurs de couplage piézoélectriques supérieurs à ceux d'autres matériaux. Cependant, malgré ses excellentes propriétés électriques (diélectriques, ferroélectriques et piézoélectriques), le PZT et d'autres matériaux à base de plomb devraient bientôt être remplacés par des composés sans plomb, à cause des problèmes environnementaux. Notre travail vise à développer des matériaux sans plomb de haute performance pour la récupération d'énergie par vibration mécanique. Nous nous sommes intéressés à la fabrication et la caractérisation des dispositifs MEMS pour la récupération d'énergie en utilisant les matériaux piézoélectriques sans plomb tels que le nitrure d'aluminium (AIN), le titanate de baryum BaTiO3 (BTO) et la ferrite de bismuth BiFeO3 (BFO). Les matériaux piézoélectriques PZT (utilisé comme référence à cause ses coefficients piézoélectriques élevés), BTO, BFO et AIN ont été déposés en utilisant des méthodes de dépôt telles que la pulvérisation cathodique et le dépôt sol-gel, conduisant à des films minces à grande échelle, homogènes et de haute densité, avec une épaisseur contrôlée avec précision. Le dépôt de films de 300 nm d'épaisseur par pulvérisation cathodique ou par Sol-Gel a été réalisé sur du substrat de SrTiO3 (STO) recouvert d'une électrode inférieure de SrRuO3 (SRO), qui est le substrat de référence pour les oxydes fonctionnels (PZT, BTO et BFO), et sur un substrat de silicium recouvert de platine, qui est le modèle industriel classique. Quels que soient les matériaux piézoélectriques, nous avons obtenu des films épitaxiés sur substrat de STO et texturés sur substrat de silicium. Des mesures structurales, électriques et piézoélectriques sur les films de BTO, AIN et PZT montrent qu'ils ont de bonnes propriétés physiques en accord avec la littérature. / With the development of ultra-low-power integrated circuits, the need to reduce operating costs for embedded electronic devices, and since used batteries pose a threat to the environment, the concept of energy harvesting has gained a new relevance. Energy harvesting covers the scavenging of many lost ambient energy sources and their conversion into electrical energy. A broad range of energy harvesting devices has been developed to scavenge energy from mechanical vibrations. A common configuration consists of a spring-mass system with a piezoelectric material in parallel with the spring to convert some of the mechanical energy during oscillations into electrical power. So far the most used material for piezoelectric energy harvesting is the Lead Zirconate Titanate (PbZr1-xTixO3) (PZT). PZT is the reference material for MEMS (MechanoElectroMechanicalSystems) applications in the field of energy harvesting. Lead-based piezoelectric materials such as PZT and lead magnesium niobate-lead titanate (PMN-PT) offer incomparable piezoelectric coupling factors to other materials. However, despite its excellent electrical properties (dielectric, ferroelectric and piezoelectric), PZT and other Lead based materials should be replaced shortly by leadfree compounds, due to environmental issues. Our work aims at developing lead-free high performance vibration energy-harvesting. We focus on the fabrication and characterization of aluminum nitride (AlN), Barium titanate BaTiO3 (BTO) and Bismuth ferrite BiFeO3 (BFO) devices for energy harvesting. PZT (as a reference because it’s high piezoelectric coefficients), BTO, BFO and AlN have been deposited using sputtering methods, leading to high homogeneous, large scale thin films with a precisely controlled thickness. The deposition of 300nm-thick films by sputtering or spin coating was performed on SrTiO3 (STO) substrate with SrRuO3 (SRO) bottom electrode, which is the reference substrate for the functional oxides (PZT, BTO and BFO), and platinum coated silicon substrate, which is the classic industrial template. Whatever the piezoelectric materials, we obtained epitaxial films on STO substrate and textured films on silicon substrate. Structural, electrical and piezoelectric measurements on the BTO, AlN and PZT films show that they have good physical properties in agreement with the literature.

Artificiels structurés, présentent des propriétés inédites et des aptitudes uniques pour la manipulation d’ondes en général. L’avènement de ces nouveaux matériaux a permis de dépasser les limites classiques dans tout le domaine de l’acoustique-physique, et d’élargir l’horizon des recherches fondamentales. Plus récemment, une nouvelle classe de structures artificielles, les métasurfaces acoustiques, présentant une valeur ajoutée par rapport aux métamatériaux, avec des avantages en termes de flexibilité, de finesse et de légèreté de structures, a émergé. Inspirés par ces propriétés et fonctionnalités sans précédent, des concepts innovants pour la collecte d’énergie acoustique avec ces deux types de structures artificielles ont été réalisés dans le cadre de cette thèse. Tout d’abord, nous avons développé un concept à base d’un métamatériau en plaque en se basant sur le de l’approche de bande interdite et des modes de défaut permis par le mécanisme de Bragg. Dans la deuxième partie de cette thèse, des métasurfaces d’épaisseur sublongueur d’onde et ultra-minces composées d’unités labyrinthiques ou de résonateurs de Helmholtz ont été conçues et étudiées pour s’atteler à la focalisation et au confinement de l’énergie acoustique. Cette thèse propose un nouveau paradigme de collecte d’énergie des ondes acoustiques à base des métamatériaux et métasurfaces. La collecte de cette énergie acoustique renouvelable, très abondante et actuellement perdue, pourrait particulièrement être utile pour l’industrie de l’aéronautique, de l’automobile, du spatial, de l’urbanisme / Phononic crystals (PCs) and acoustic metamaterials (AMMs), well-known as artificially engineered materials, demonstrate anomalous properties and fascinating capabilities in various kinds of wave manipulations, which have breached the classical barriers and significantly broaden the horizon of the whole acoustics field. As a novel category of AMMs, acoustic metasurfaces share the functionalities of AMMs in exotic yet compelling wave tailoring. Inspired by these extraordinary capabilities, innovative concepts of scavenging acoustic energy with AMMs are primarily conceived and sufficiently explored in this thesis. Generally, a planar AMM acoustic energy harvesting (AEH) system and acoustic metasurfaces AEH systems are theoretically and numerically proposed and analyzed in this dissertation. At first, taking advantage of the properties of band gap and wave localization of defect mode, the AEH system based on planar AMM composed of a defected AMM and a structured piezoelectric material has been proposed and sufficiently analyzed. Secondly, subwavelength (λ/8) and ultrathin (λ/15) metasurfaces with various lateral configurations, composed of labyrinthine and Helmholtz-like elements, respectively, are designed and analyzed to effectively realize the acoustic focusing and AEH. This thesis provides new paradigms of AEH with AMMs and acoustic metasurfaces, which would contribute to the industries of micro electronic devices and noise abatement as well

Conformal airborne antennas have several advantages compared to externally mounted antennas, and they will play an important role in future aircrafts. However, they are subjected to vibration induced deformations which degrade their electromagnetic performances. With the motivation of suppressing such vibrations, use of active vibration control techniques with piezoelectric actuators is investigated in this study. At first, it is aimed to control the first three bending modes of a cantilever beam. In this scope, four different modal controllers / positive position feedback (PPF), resonant control (RC), integral resonant control (IRC) and positive position feedback with feed-through (PPFFT) are designed based on both reduced order finite element model and the system identification model. PPFFT, is a modified version of PPF which is proposed as a new controller in this study. Results of real- time control experiments show that PPFFT presents superior performance compared to its predecessor, PPF, and other two methods. In the second part of the study, it is focused on controlling the first three modes of a rectangular plate with four clamped edges. Best location alternatives for three piezoelectric actuators are determined with modal strain energy method. Based on the reduced order finite element model, three PPFFT controllers are designed for three collocated transfer functions. Disturbance rejection performances show the convenience of PPFFT in multi-input multi-output control systems. Performance of the control system is also verified by discrete-time simulations for a random disturbance representing the in-flight aircraft vibration characteristics.

Confinement effect on semiconductor nanowires properties. Alexis Nduwimana 100 pages Directed by Dr. Mei-Yin Chou We study the effect of confinement on various properties of semiconductor nanowires. First, we study the size and direction dependence of the band gap of germanium nanowires. We use the density functional theory in the local density approximation. Results shows that the band gap decreases with the diameter The susceptibility of these nanowires is also computed. Second, we look at the confinement effect on the piezoelectric coefficients of ZnO and AlN nanowires. The Berry phase method is used. It is found that depending on passivation, thepiezoelectric effect can decrease or increase. Finally, we study the size and direction dependence of the melting temperature of silicon nanowires. We use the molecular dynamics with the Stillinger Weber potential. Results indicate that the melting temperature increases with the nanowire diameter and that it is direction dependent.

In this thesis, an attitude control system based on Linear Quadratic Regulator (LQR) technique is developed for a hypothetical Earth observation satellite with a long flexible boom. To improve pointing performance of the satellite, the piezoelectric actuators are used as well. The boom is rectangular made of aluminum with the surface bonded piezoelectric layers on all four surfaces. The boom is modeled using finite elements. The pointing performance of the satellite using various metrics is evaluated through simulations. Effectiveness of the piezoelectric actuators is demonstrated.

Piezoelectric materials are widely used for sensors, actuators and trasducers. Traditionally, piezoelectric applications are dominated by multicomponent oxide ferroelectrics such as lead zirconate titanate (PZT), which have the advantage of high piezoelectric coefficients. Recently, one-dimensional piezoelectric nanostructures such as nanowires of zinc oxide (ZnO) and gallium nitride (GaN) has gained a lot of attention due to their combined piezoelectric and semiconducting properties. The focus of this thesis is to study the processing and electric properties of such piezoelectric thin films and nanostructures for various applications. There is an increasing interest to form thin films of multicomponent ferroelectric oxides such as PZT on three-dimensional structures for charge storage and MEMS applications. Traditional vapor phase deposition techniques of PZT offer poor conformality over threedimensional surfaces due to their reactant transport mechanisms. As an alternative, solgel synthesis may provide new process possibilities to overcome this hurdle but the film quality is usually inferior, and the yield data was usually reported for small device areas. The first part of this study is dedicated to the characterization of the electric properties and yield of PZT thin film derived from the sol-gel process. PZT thin films with good electric property and high yield over a large area have been fabricated. La doping was found to double the breakdown field due to donor doping effect. LaNiO3 thin films that can be coated on a three-dimensional surface have been synthesized by an all-nitrate based sol-gel route, and the feasibility to form a conformal coating over a three-dimensional surface by solution coating techniques has been demonstrated. ZnO and GaN micro/nanowires are promising piezoelectric materials for energy harvesting and piezotronic device applications. The second part of this study is focused on the growth of ZnO and GaN micro/nanowires by physical vapor deposition techniques. The morphology and chemical compositions are revealed by electron microscopy. Utilizing the as-grown ZnO nanowires, single nanowire based photocell has been fabricated, and its performance was studied in terms of its response time, repeatability, excitation position and polarization dependence upon He-Cd UV-laser illumination. The excitation position dependence was attributed to the competition of two opposite photo- and thermoelectric currents originated from the two junctions. The excitation polarization dependence was attributed to the difference in optical properties due to crystallographic anisotropy. Employing the as-grown GaN nanowires, single nanowire based strain sensor is demonstrated, and its behavior is discussed in terms of the effect of strain-induced piezopotential on the Schottky barrier height.

The @lab is a group dedicated to the research and development of electronic textiles for architectural applications; this thesis presents the structural analyses performed by the author to improve the @lab’s projects. Also included are three investigations performed by the author that pertain to smart material applications in responsive architecture and textiles. The first investigation evaluated the feasibility of using piezoelectric materials to harvest power from human foot traffic; overall, it was determined to not be feasible. The second investigation experimentally tested how six parameters of shape memory alloy spring actuators affect their reaction times and stroke; all six parameters affected the reaction times and/or stroke. The third investigation experimentally tested how three parameters of superelastic SMA springs influence their stiffness and resonant frequencies; overall, it was found that traditional spring mechanics can be used to predict their behavior providing the internal stress does not reach the upper plateau stress.

The requirements of the consumer market on high frequency devices have been more and more demanding over the last decades. Thus, a continuing enhancement of the devices’ performance is required in order to meet these demands. In a macro view, changing the design of the device can result in an improvement of its performance. In a micro view, the physical properties of the device materials have a strong influence on its final performance. In the case of high frequency devices based on piezoelectric materials, a natural way to improve their performance is through the improvement of the properties of the piezoelectric layer. The piezoelectric material studied in this work is AlN, which is an outstanding material among other piezoelectric materials due to its unique combination of material properties. This thesis presents results from experimental studies on the synthesis of AlN thin films in view of telecom, microelectronic and sensor applications. The main objective of the thesis is to custom design the functional properties of AlN to best suit these for the specific application in mind. This is achieved through careful control of the crystallographic structure and texture as well as film composition. The piezoelectric properties of AlN films were enhanced by doping with Sc. Films with different Sc concentrations were fabricated and analyzed, and the coupling coefficient (kt2) was enhanced a factor of two by adding 15% of Sc to the AlN films. The enhancement of kt2 is of interest since it can contribute to a more relaxed design of high frequency devices. Further, in order to obtain better deposition control of c-axis tilted AlN films, a new experimental setup were proposed. When this novel setup was used, films with well-defined thicknesses and tilt uniformity were achieved. Films with such characteristics are very favorable to use in sensors based on electroacoustic devices operating in viscous media. Studies were also performed in order to obtain c-axis oriented AlN films deposited directly on Si substrates at reduced temperatures. The deposition technique used was HiPIMS, and the results indicated significant improvements in the film texture when comparing to the conventional Pulsed DC deposition process.