There is an increasing interest in automated mobile equipment in the construction, agriculture and mining industries to improve productivity, efficiency and operator safety. In general, these machines belong to a class of mobile vehicles with a tool for manipulating its environment to accomplish a repetitive task. Forces and motions are inherently coupled between the tool (<em>e.g.</em> bucket or blade) and the means of vehicle propulsion (<em>e.g</em>. wheels or tracks). Furthermore, they are often operated within uncertain and unstructured environments. A particularly challenging case involves the use of a bulldozer for the removal of excavated material. Modeling and control of mobile robots that interact forcibly with their environment, such as robotic excavation machinery, is a challenging problem that has not been adequately addressed in prior research. This thesis investigates the low-level modeling and control of a 3-DOF robotic bulldozing operation. Motivated by a bulldozing process in an underground mining application, a theoretical nonlinear hybrid dynamic model was developed. The model includes discrete operation modes contained within a hybrid dynamic model framework. The dynamics of the individual modes are represented by a set of linear and nonlinear differential equations. An instrumented scaled-down bulldozer and environment were developed to emulate the full scale operation. Model parameter estimation and validation was completed using experimental data from this system. The model was refined based on a global sensitivity analysis. The refined model was found to be suitable for simulation and design of robotic bulldozing control laws. Optimal blade position control laws were designed based on the hybrid dynamic model to maximize the predicted material removal rate of the bulldozing process. A stability analysis of the underlying deterministic closed-loop process dynamics was performed using Lyapunov’s second method. Monte Carlo simulation was used for further performance and stability analysis of the closed-loop process dynamics including stochastic state disturbances and input constraints. Results of the Monte Carlo simulation were also used for tuning the blade position control laws. Experiments were conducted with the scaled-down robotic bulldozing system. The control laws were implemented with various tuning values. As a comparison, a rule-based blade control algorithm was also designed and implemented. The experimental results with the optimal control laws demonstrated a 33% increase in the average material removal rate compared to the rule-based controller. / Doctor of Philosophy (PhD)

Les nanostructures, et en particulier les nanofils semi-conducteurs, ont suscité ces dernières années un très grand intérêt pour de nombreuses applications comme les systèmes de récupération d'énergie ou les capteurs de très haute précision. Dans de telles structures des expérimentations et des calculs théoriques ab-initio ont mis en évidence des effets de taille, pouvant modifier significativement les propriétés électromécaniques pour des diamètres de fils en dessous de 10 nm. L'objectif de ce travail de thèse est de proposer des modélisations multi échelle des nanostructures électromécaniques, telles que les nanofils ioniques et des nanocomposites stratifiés, permettant de reproduire les effets de taille associés à l'échelle nanométrique dans un cadre continu, en se basant sur des calculs ab-initio pour identifier et valider les modèles. Dans une première partie, les effets de surface dans des nanofils piézoélectriques isolés homogènes sont modélisés. Une approche multi échelle est développée, incluant une modélisation continue des nanofils en prenant en compte une énergie de surface supplémentaire dans un cadre piézoélectrique, dont les paramètres associés sont identifiés par calculs ab-initio. Pour cela, une procédure basée sur un modèle de films minces est développée, permettant au travers de calculs ab-initio sur des films d'épaisseurs successives d'isoler l'énergie volumique et de surface, et d'en déduire les coefficients élastiques et piézoélectriques de surface. Les équations du modèle continu sont ensuite résolues par une méthode d'éléments finis incluant des éléments de surface adaptés. Le modèle multi échelle continu est comparé à des calculs ab-initio impliquant des modèles atomistiques complets de nanofils de différents diamètres (de 0,6 à 3,9 nm) pour valider les effets de taille des propriétés électromécaniques. Dans une deuxième partie, des modèles multi échelles sont construits en vue de modéliser les effets de taille pour des nanostructures hétérogènes. Ces structures incluent des nanofils revêtus, ou des nanocomposites stratifiés. Pour les nanofils avec hétérogénéités radiales, l'approche précédemment développée est étendue au cas des surfaces revêtues, et le modèle continu fait intervenir une énergie de surface incluant les effets du revêtement. Pour les nanocomposites stratifiés AlN/GaN, les effets de taille observés par calculs ab-initio sont dus à des effets d'interface et induisent des propriétés élastiques dépendantes des épaisseurs des couches. Un modèle de matériau homogénéisé continu est proposé, incluant un modèle d'interface imparfaite, permettant d'inclure les effets de taille, identifié par calculs ab-initio. Dans une dernière partie, des applications à des systèmes de nanogénérateurs à base de nanofils sont proposées, faisant intervenir des ensembles de nanofils alignés dans une matrice polymère et surmontés par une feuille de graphène. Les approches précédemment développées sont utilisées pour modéliser ces structures par éléments finis / Nanostructures, and more specifically semiconductor nanowires, have drawn special attention in recent years for many applications such as energy harvesting systems or sensors of very high precision. Many recent experiments and theoretical ab-initio calculations have evidenced size effects, which can significantly modify the electromechanical properties of nanowires for diameters below 10 nm. The objective of this thesis is to provide multi-scale modeling of electromechanical properties of nanostructures, such as ionic nanowires and laminated nanocomposites, to reproduce the size effects associated with nanoscale in a continuum model, based on ab-initio calculations to identify and validate the models. In a first part, the surface effects in isolated homogeneous piezoelectric nanowires are modeled. A multi-scale approach is developed, including continuous nanowires modeling taking into account an additional surface energy in the piezoelectric laminates where the associated parameters are identified by ab-initio calculations. For this, a procedure based on slabs is developed, allowing through first-principles calculations on successive slabs thicknesses to isolate the surface energy and to deduce the surface elastic and piezoelectric coefficients. The equations of the continuous model are then solved by a finite element method including appropriate surface elements. The continuous multi-scale model is compared with ab-initio calculations involving full atomistic models of nanowires with different diameters (from 0.6 to 3.9 nm) to validate model regarding size effects of electromechanical properties. In the second part, multi-scale models are constructed to describe the size effects for heterogeneous nanostructures. These structures include coated nanowires or laminated nanocomposites. For nanowires with radial heterogeneity, the previously developed approach is extended to the case of coated surfaces, and involves a continuous surface energy incorporating the effects of the coating. For laminated AlN/GaN nanocomposites, size effects observed by ab-initio calculations are caused by the presence of the interfaces and induce size-dependent elastic properties with respect to the layer thickness. A continuum model based on an imperfect interface is proposed to describe the size dependent effective elastic properties of the overall composite, which are identified by ab-initio calculations. In the last part, nanogenerators system based on nanowires are modeled, involving nanowires arrays aligned in polymer substrates with graphene electrode. The previously developed finite element models are used to simulate the electromechanical properties of such systems

Le Haut-Parleur Digital Matriciel (HPDM) est un moyen de transduction électroacoustique qui reçoit comme entrée un signal numérique et qui effectue la conversion vers l'analogique directement dans l'air. Il est constitué de plusieurs éléments rayonnants disposés au sein d'une matrice. Ces éléments seront désignés par le terme «speaklet» lorsqu'ils sont de tailles réduites. Le rayonnement acoustique du HPDM est en effet très sensible à la taille de la matrice, ce qui le rend tout particulièrement adapté à la technologie MEMS. Cette thèse porte sur l'étude de HPDM MEMS piézoélectriques. Après une introduction qui débute par certaines généralités jusqu'à se focaliser sur le sujet, la thèse aborde les modélisations multiphysiques des HPDM étudiés, le dimensionnement des speaklets puis les tests expérimentaux. Des modèles analytiques ainsi que des simulations numériques et par éléments finis sont mis en place et permettent de prédire le comportement mécanique des speaklets présentés, les pressions rayonnées par les HPDM et les puissances électriques consommées. Les speaklets sont ensuite dimensionnés à partir de l'empilement technologique afin de maximiser le niveau de pression qu'ils génèrent. Des tests expérimentaux permettent alors de valider la majorité des modèles ou au contraire de revenir sur certains d'entre eux pour les optimiser ou montrer leurs limitations. Les résultats ont en effet montré l'importance de la prise en compte des contraintes résiduelles, qui provoquent une déformée initiale des speaklets et modifient leurs fréquences propres, rendant alors l'utilisation de grands rayons inefficaces. En accord avec les modèles, les speaklets possèdent un comportement dynamique linéaire, ce qui permet de les caractériser à l'aide de fonctions de transfert. La théorie et les enregistrements sonores montrent alors qu'un HPDM composé de tels speaklets permet dans le meilleur des cas de produire une pression identique à celle générée par la même matrice pilotée en analogique. Dans notre cas, des taux de distorsions supérieurs ont été obtenus lors des reconstructions digitales, à cause des réponses non uniformes des speaklets, dues à des résistances d'accès différentes. Le HPDM présenté possède cependant d'autres avantages, le plus important étant la très faible consommation électrique qu'il est théoriquement possible d'atteindre en utilisant les méthodes de charges et de décharges adiabatiques. Le HPDM piézoélectrique MEMS apparait donc comme étant une technologie prometteuse. L'optimisation de notre premier prototype à l'aide des outils développés doit en effet conduire à un HPDM capable de générer une pression équivalente à celle obtenue en mode analogique, mais avec un rendement électroacoustique beaucoup plus important. Les futurs travaux devront ensuite se concentrer sur la conception de speaklets non-linéaires et sur la forme du pulse de pression qu'ils génèrent, afin de gagner en niveau sonore. / The Digital Loudspeaker Array (DLA) is an electroacoustic transducer which receives as input a digital signal and performs the analog conversion directly into the air. It consists of a plurality of radiating elements arranged in a matrix. These elements will be designated by the term “speaklet” when they are reduced in size. The acoustic radiation of a DLA is indeed very sensitive to the size of the matrix due to differences in path length, which makes it especially suitable for MEMS technology. This thesis is on the study of a piezoelectric MEMS DLA. After an introduction that is increasingly focused on the subject, the thesis addresses the multiphysics modeling of the DLA, dimensioning of the speaklets and experimental tests. Analytical formulas, numerical simulations and finite element models are developed and used to predict the mechanical behavior of the presented speaklets, the pressure radiated by the DLA and the electrical power consumption. The speaklet are then dimensioned from the technological stack (set in advance) in order to maximize the pressure level. Experimental tests involving the use of an anechoic chamber, an optical interferometer, a vibrometer and an impedancemeter validate most of the models. Otherwise, these tests are usefull for improving some of them or for showing their limitations. The results have shown the importance of the residual stresses, which cause an initial deformation of the speaklets and modify their resonance frequencies, thus rendering ineffective the use of large radii. In accordance with the models, the static deflection of the speaklets is nonlinear but their dynamic behavior is linear. This enables characterizations using transfer functions. Theory and sound recordings show that a DLA made of such speaklets can produce in the best case the same pressure to that generated by the same matrix driven in an analog way. In our case, more distortions were obtained in digital reconstructions because of non-uniform responses of the speaklets, due to different access resistances. However, the presented DLA has other advantages, the most important being the very low power consumption it is theoretically possible to achieve using the adiabatic charge principle. The piezoelectric MEMS DLA thus appears as a promising technology. The optimization of our first prototype using the developed tools should indeed lead to a DLA able to generate an equivalent presure to that obtained with analog control, but with a far greater electroacoustic efficiency. Future work should then focus on the design of nonlinear speaklets and on the shaping of the pulse of pressure they generate, in order to increase the total pressure level.

Microdispositivos piezelétricos tem uma vasta aplicação em mecânica de precisão, como, por exemplo, manipulação de células, microcirurgias, equipamentos de nanotecnologia e principalmente em microeletromecanismos (MEMS). Os microdispositivos piezelétricos considerados nesta tese essencialmente consistem de uma estrutura multi-flexível atuada por duas ou mais piezocerâmicas, que geram deslocamentos e forças em direções e regiões pré-determinadas do domínio, ou seja, a estrutura multi-flexível atua como um transformador mecânico amplificando e alterando os deslocamentos gerados pelas piezocerâmicas nos movimentos de atuação. O desenvolvimento destes microdispositivos piezelétricos em sua grande maioria não utiliza ferramentas sistemáticas e genéricas. A complexidade dos movimentos de atuação torna o desenvolvimento dos microdispositivos piezelétricos complexo, principalmente devido ao surgimento de movimentos indesejados ou acoplados durante a sua atuação. Portanto, é necessário um método sistemático e eficiente como o método de otimização topológica (MOT), que incorpore na sua formulação as principais exigências de projeto dos microdispositivos, como apresentado nesse trabalho. O MOT implementado é baseado na abordagem CAMD (Distribuição Contínua da Distribuição de Material), onde as pseudo-densidades são interpoladas nos nós de cada elemento finito, resultando numa distribuição contínua de material no domínio. Um método adjunto foi implementado para o cálculo das sensibilidades. São consideradas três formulações. A primeira denominada de MAPs (Multi-Atuadores Piezelétricos) considera as regiões piezocerâmicas fixas, otimizando apenas a estrutura multi-flexível no domínio de projeto. Nesta formulação materiais não-piezelétricos (como, por exemplo, Alumínio) e vazio são distribuídos no domínio de projeto, mantendo as regiões piezocerâmicas fixas e homogêneas. Para validar os resultados obtidos com essa formulação foram fabricados protótipos de nanoposicionadores $XY$, que foram caracterizados experimentalmente utilizando técnicas de interferometria laser, considerando excitação quasi-estática. No entanto, essa primeira formulação impõe restrições no problema, limitando a optimalidade da solução obtida pela otimização topológica. Assim, surgiu a necessidade de desenvolver uma segunda formulação, que permite distribuir simultaneamente material não-piezelétrico, piezelétrico e vazio no domínio de projeto, denominada de LOMPs (Localização Ótima do Material Piezelétrico). A formulação dos LOMPs obtém simultaneamente a localização do material piezelétrico na estrutura flexível otimizada pela OT, e inclui também uma variável de projeto para determinar o ângulo ótimo entre as direções de polarização e do campo elétrico. Nesta formulação como as posições dos eletrodos não são conhecidas, ``a priori\'\', é utilizado como abordagem aplicar um campo elétrico constante para determinar a localização do material piezelétrico e conseqüentemente dos eletrodos. Finalmente, foi explorado o conceito de materiais com gradação funcional (MGFs) no projeto dos MAPs. Os MGFs apresentam uma distribuição contínua de materiais na sua microestrutura, não possuindo interface entre os materiais distribuídos, o que possibilita aumentar a vida útil do dispositivo piezelétrico. Assim, foi implementado uma terceira formulação denominada de MAPs MGFs, que permite obter a gradação ótima de materiais piezelétricos e não-piezelétricos no domínio piezocerâmico dos MAPs, conjuntamente com a topologia da estrutura multi-flexível. Essa formulação foi estendida para projetar atuadores bilaminares MGFs. Todas as formulações desenvolvidas utilizam uma função multi-objetivo, que permite controlar a rigidez e a flexibilidade minimizando o movimento acoplado, de cada movimento de atuação. Os exemplos numéricos são limitados a modelos bi-dimensionais, utilizando o estado plano de tensões e deformações mecânicas e elétricas, uma vez que a grande maioria das aplicações dos microdispositivos piezelétricos são bi-dimensionais. / Microtools offer significant promise in a wide range of applications such as cell manipulation, microsurgery, nanotechnology processes, and many other fields. The microtools considered in this doctoral thesis essentially consist of a multi-flexible structure actuated by two or more piezoceramic devices that when each piezoceramic is actuated, it generates an output displacement and force at a specified point of the domain and direction. The multi-flexible structure acts as a mechanical transformer by amplifying and changing the direction of the piezoceramic output displacements. Thus, the development of microtools requires the design of actuated flexible structures that can perform complex movements. The development of these microtools is still in the beginning and it can be strongly enhanced by using design tools. In addition, when multiple piezoceramic devices are involved, coupling effects in their movements become critical, especially the appearance of undesired movements, which makes the design task very complex. One way to avoid such undesirable effects is the use of a systematic design method, such as topology optimization, with appropriate formulation of the optimization problem. The topology optimization method implemented is based on the CAMD (Continuous Approximation of Material Distribution) approach where fictitious densities are interpolated at each finite element, providing a continuum material distribution in the domain. The corresponding sensitivity analysis is presented using the adjoint method. Three formulations are considered. The first formulation, called Piezoelectric Multi-Actuators (PMAs), keeps fixed piezoceramic positions in the design domain and only the flexible structure is designed by distributing some non-piezoelectric material (Aluminum, for example). $XY$ Piezoelectric Nanopositioner are manufactured and experimentally analyzed to validate the results of the topology optimization obtained using this formulation. Experimental analyses are conducted using laser interferometry to measure displacement, while considering a quasi-static excitation. However, this first formulation imposes a constraint to the position of piezoelectric material in the optimization problem limiting the optimality of the solution. Thus, the second formulation presented, called LOMPs, allows the simultaneous distribution of non-piezoelectric and piezoelectric material in the design domain, to achieve certain specified actuation movements. The optimization problem is posed as the simultaneous search for an optimal topology of a flexible structure as well as the optimal position of piezoceramics in the design domain and optimal rotation angle of piezoceramic material axes that maximize output displacements or output forces at a specified point of the domain and direction. When the distribution of a non-piezoelectric conductor material and a piezoceramic material is considered in the design domain, the electrode positions are not known ``a priori\'\'. To circumvent this problem, an electric field is applied as electrical excitation. Finally, the concept of functionally graded materials (FGM) is applied to PMAs design. FGMs are special materials that possess continuously graded properties without interfaces which can increase lifetime of piezoelectric devices. Thus, a third formulation is implemented to find the optimum gradation and polarization sign variation of piezoceramic FGMs, while simultaneously optimizing the multi-flexible structural configuration. This formulation is extended to design bimorph type FGM actuators. For all developed formulations, a multi-objective function is defined that controls the stiffness and flexibility, minimizing the coupling movement of each actuated movement. The present examples are limited to two-dimensional models because most part of the applications for such micro-tools are planar devices.

This thesis presents a real-time autonomous guidance and control method for a quadrotor in a GPS-denied environment. The quadrotor autonomously seeks a destination while it avoids obstacles whose shape and position are initially unknown. We implement the obstacle avoidance and destination seeking methods using off-the-shelf sensors, including a vision-sensing camera. The vision-sensing camera detects the positions of points on the surface of obstacles. We use this obstacle position data and a potential-field method to generate velocity commands. We present a backstepping controller that uses the velocity commands to generate the quadrotor's control inputs. In indoor experiments, we demonstrate that the guidance and control methods provide the quadrotor with sufficient autonomy to fly point to point, while avoiding obstacles.

The effects of system pressure on the performance stability of flow-through capacitive deionization (CDI) cells was investigated. Initial data showed that the highly porous carbon electrodes possessed air/oxygen in the micropores, and the increased system pressure boosts the gases solubility in saline solution and carries them out of the cell in the effluent. Upon applying a potential difference to the electrodes, capacitive-based ion adsorption occurs in competition with faradaic reactions that consume oxygen. Through the addition of backpressure, the rate of degradation decreases, allowing the cell to maintain its salt adsorption capacity (SAC) longer. The removal of oxygen from the pore space of the electrodes makes it no longer immediately accessible to faradaic reactions, thus hindering the rate of reactions and giving the competing ion adsorption an advantage that is progressively seen throughout the life of the cell. A quick calculation shows that the energy penalty to power the pump is fairly insignificant, especially in comparison to the cost of replacing the electrodes in the cell. Thus, operating at elevated pressures is shown to be cost effective for continuous operation through the reduced electrode replenishment costs.

Modern 3D printing technology is becoming a more viable option for use in industrial manufacturing. As the speed and precision of rapid prototyping technology improves, so too must the 3D scanning and verification technology. Current 3D scanning technology (such as CT Scanners) produce the resolution needed for micron precision inspection. However, the method lacks in speed. Some scans can be multiple gigabytes in size taking several minutes to acquire and process. Especially in high volume manufacturing of 3D printed parts, such delays prohibit the widespread adaptation of 3D scanning technology for quality control. The limiting factors of current technology boil down to computational and processing power along with available sensor resolution and operational frequency. Realizing a 3D scanning system that produces micron precision results within a single minute promises to revolutionize the quality control industry. The specific 3D scanning method considered in this thesis utilizes a line profile triangulation sensor with high operational frequency, and a high-precision mechanical actuation apparatus for controlling the scan. By syncing the operational frequency of the sensor to the actuation velocity of the apparatus, a 3D point cloud is rapidly acquired. Processing of the data is then performed using MATLAB on contemporary computing hardware, which includes proper point cloud formatting and implementation of the Iterative Closest Point (ICP) algorithm for point cloud stitching. Theoretical and physical experiments are performed to demonstrate the validity of the method. The prototyped system is shown to produce multiple loosely-registered micron precision point clouds of a 3D printed object that are then stitched together to form a full point cloud representative of the original part. This prototype produces micron precision results in approximately 130 seconds, but the experiments illuminate upon the additional investments by which this time could be further reduced to approach the revolutionizing one-minute milestone.

Depuis quelques années on s'intéresse aux actionneurs base polymères, souvent appelés polymères électroactifs électroniques (EAPS) pour intégrer dans des microsystèmes électromécaniques (MEMS). Trois mécanismes sont à l'origine du couplage électromécanique : (i) la piézoélectricité qui apparait dans certaines phases cristallines, (ii) la force "de Maxwell" lorsqu'un champ électrique aux bornes du condensateur constitué d'un polymère souples placé entre deux électrodes, et (iii) l'électrostriction, phénomène intrinsèque aux matériaux polaires, mal connu. Les deux derniers se traduisent par une dépendance quadratique de la déformation macroscopique avec le champ électrique appliqué. Parmi les EAPs électrostrictifs, on cite souvent certains polyuréthanes (PU) qui a conduit à ce choix pour ce travail de thèse. Une première partie a consisté à analyser en détail l'électrostriction de 3 PUs, copolymères à blocs de deux types d'unités de répétition, les unes conduisant à des segments rigides très polaires, les autres à des segments souples peu polaires. La séparation de phase qui apparait lors de la mise en œuvre de ces PUs (contenant des fractions différentes de segments souples et rigides) semble propice à l'apparition de leur électrostriction. C'est ce qu'indique une modélisation récemment proposée qui prédit un facteur de près de 1000 entre forces de Maxwell (ici négligeables) et électrostriction. Le comportement des matériaux résultent clairement de la compétition entre contraintes d'origine électrostatique (dipôles des phases polaires dans un gradient de champ électrique) et contraintes mécaniques liées à la rigidité des phases. L’influence systématique de l'épaisseur des films sur leur activité électromagnétique a été rendue compte: les films minces présentent une plus faible déformation à champ électrique donné que les films plus épais. Les films obtenus par évaporation du solvant utilisé pour dissoudre les PU présentent probablement un gradient de microstructure : en surface, l'évaporation rapide limite la séparation de phase, alors qu'elle est plus avancée à cœur. C’est cohérent avec la modélisation reposant sur la présence de gradient de constante diélectrique au sein des films. Dans une dernière partie, on a cherché à augmenter encore l'électrostriction de ces matériaux en dispersant des particules conductrices à conduction électronique, de taille nanométrique (noir de carbone et nanotubes de carbone). On observe trois effets, l'un correspondant à l'augmentation de la constante diélectrique apparente (celle diverge au seuil de percolation), et un deuxième effet à une augmentation des forces d'attraction locales. En revanche, le troisième effet qui contrecarre les forces d'origine électrostatique puisqu'il résulte de l'augmentation de la rigidité dû à la présence des particules rigides. Là encore, la compétition entre contraintes électrostatique et mécanique conduit à un optimum en termes de fraction volumique de particules renforçantes. / Piezoelectric ceramics are commonly used for actuation applications. However, they suffer from several drawbacks particularly such low electric field-induced strains and difficult implementation inside microelectromechanical systems (MEMS). Recently, electroactive polymers (EAPs) have attracted considerable interest, especially following the publication of elevated electric field-induced strain values. The results have rendered EAPs very attractive for replacing the lead-based ceramics. Three mechanisms are responsible for the electromechanical coupling in electronic EAPs: (i) The piezoelectricity that appears in some crystalline phases, (ii) The “Maxwell” forces when applying an electric field through a capacitor which consists of a flexible polymer film placed between two electrodes, and (iii) The electrostriction, an intrinsic phenomenon related to polar materials, which is still poorly understood. The last two mechanisms result in a quadratic dependence of the deformation with the applied electric field. Among the electrostrictive EAPs, some polyurethanes (PU) have been often cited, and have therefore guided the choice of the materials for this work. The first part was to analyze the electrostrictive behavior of three PUs, made of two partially miscible types of repeating units: the high polar hard segments and the low polar soft segments. The phase separation occurred during the elaboration process of these PU films seems favorable to the emergence of electrostrictive behavior. A model predicted recently an almost 1000 factor between the electrostriction and the Maxwell stress (here negligible). This is clearly related to the competition between the electrostatic strains (polar phases dipoles in a field gradient) and the mechanical stresses. The thickness of films was found to have a strong influence on electromechanical activity: thin films present a lower strain for a given electric field compared to thick films. Depending on the solvent evaporation during the film elaboration, the films exhibit a thickness gradient in the microstructure: Fast evaporation on the surface inhibits the phase separation, whereas it is more favored in the core. This is consistent with the modeling based on the gradient of dielectric constant in PU. In the last part, we aimed to further increase the electrostriction of PU by filling with nanoscale conductive particles (carbon black or carbon nanotubes). This normally results three effects, one corresponding to the increase of the dielectric constant in the vicinity of the percolation threshold, a second effect relates to an increase in local attractive forces which behave as internal constraints. In contrast, the third effect counteracts the electrostatic forces since it results from the increased stiffness due to the hard particles. Again, the competition between electrostatic and mechanical stress leads to an optimum induced-deformation associated to a fraction of reinforcing particles.

Ce travail de thèse s'inscrit dans le cadre général du développement de micro-actionneurs MEMS, à bas coût et de technologie simple, pour de futures applications dans le domaine de la microfluidique, notamment. La motivation de ce travail est d'évaluer la faisabilité d'un micro-actionneur électrostricitf à base de film mince polymère électroactif nanocomposite. Le polyuréthane, chargé en nanoparticules de carbone ou carbure de fer, encore peu étudié mais aux propriétés électrostrictives prometteuses, est choisi comme matériau à intégrer dans une filière MEMS silicium classique. Le premier chapitre dresse un état de l'art sur les actionneurs MEMS, présente les différentes familles de polymères électroactifs et définit ce qu'est l'électrostriction. Le second chapitre est consacré à l'intégration sur silicium de films minces de polyuréthane et au développement de différentes structures de tests. L'accent est mis sur la levée de plusieurs verrous technologiques. Le chapitre trois présente les méthodes de caractérisations mécaniques et électriques et les résultats obtenus sur films purs et nanocomposites. Le quatrième et dernier chapitre concerne la réalisation et la caractérisation de premiers démonstrateurs MEMS. Ces micro-actionneurs sont caractérisés de manière statique et dynamique. / This thesis is part of the general development of MEMS microactuators, low cost and simple technology for future applications in the domain of microfluidics. The motivation of this work is to evaluate the feasibility of an electrostrictive microactuator based on electroactive nanocomposite polymer thin films. Polyurethane, loaded with carbon or iron carbide nanoparticles is chosen to be integrated in a conventional silicon MEMS process. The first chapter provides a state of the art of MEMS actuators, presents the different families of electroactive polymers and defines what is electrostriction. The second chapter is devoted to the integration of polyurethane thin films on silicon and to the development of different mechanical and electrical test structures. The emphasis is on identifying and overcoming technological barriers. Chapter three presents the mechanical and electrical characterization methods and the obtained results for pure and nanocomposites films. The fourth and final chapter concerns the realization and the static and dynamic characterizations of first MEMS demonstrators.

Hypersonic flow is both fascinating and intriguing mainly because of presence of strong entropy and viscous interactions in the flow field. Notwithstanding the tremendous advancements in numerical modeling in the last decade separated hypersonic flow still remains an area where considerable differences are observed between experiments and numerical results. Lack of reliable data base of surface static pressures with good spatial resolution in hypersonic separated flow field is one of the main motivations for the present study. The experiments in hypersonic shock tunnels has an advantage compared to wind tunnels for simulating the total energy content of the flow in addition to the Mach and Reynolds numbers. However the useful test time in shock tunnels is of the order of few milliseconds. Hence in shock tunnel experiments it is essential to have pressure measurement devices which has special features such as small in size, faster response time and the sensors in array form with improved spatial resolutions. Micro Electro Mechanical Systems (MEMS) is an emerging technology, which holds lot of promise in these types of applications. In view of the above requirement, MEMS based pressure sensor array was developed to measure the static pressure distribution. The study is comprised of two parts: one is on the development of MEMS based pressure sensor array, which can be used for hypersonic application and other is on experimental static pressure measurement using MEMS based sensors in separated hypersonic flow over a backward facing step model. Initially a static pressure sensor array with 25 sensors was developed. The static calibration of sensor array was carried out to characterize the sensor array for various characteristic parameters. The preliminary experimental study with cluster of 25 MEMS sensor array mounted on the flat plate did not provide reliable and repeatable results, but gave valuable inputs on the typical problems of using MEMS sensors in short duration hypersonic ground test facilities like shock tunnels. Incidentally, to the best of our knowledge this is first report on use of MEMS based pressure sensors in hypersonic shock tunnel. Later cluster of 5 sensor array was developed with improved electronic packaging and surface finish. The experiments were conducted with flat plate by mounting 5 sensor array shows good agreement in static pressure measurement compared with standard sensors. In the second part of the study a backward facing step model, which simulates the typical gasdynamic flow features associated with hypersonic flow separation is designed. Backward facing step model with step height of 3 mm was mounted with sensor array along the length of model. Just after the step, static pressure measurements were carried out with MEMS sensors. It is important to note that, in the space available in backward facing step model we could mount only one conventional Kulite pressure transducer. The experiments were conducted at Mach number of 6.3 and at stagnation enthalpy of 1.5 MJ/kg in hypersonic shock tunnel (HST-5) at IISc. Based on the static pressure measurement on backward facing step, the location of separation and reattachment points were clearly identified. The static pressure values show that reattachment of flow takes place at about 7 step heights. Numerical simulations were carried out using commercial CFD code, FLUENT for flat plate and backward facing step models to compliment the experiments. The experimental tests results match well with the illustrative numerical simulations results.