Multiferroics (MF) have attracted much research attention due to the coexistence of ferroelectric and magnetic ordering as well as magnetoelectric (ME) coupling. At present there are very few room temperature single phase MF except BiFeO3. Multiferroic properties of Aurivillius compound Bi5FeTi3O15 were reported at 80 K. The at 80 K. The at 80 K. The at 80 K. The at 80 K. The magnetization of Bi5FeTi3O15 was significantly improved by substituting parts of Fe cations by Co cations. Bi5FeTi3O15 showed ferromagnetic order above room temperature. The magnetic cations Fe/Co in B-site contribute to the both ferroelectric and ferromagnetic properties, which could possibly induce strong magnetoelectric effect. Aurivillius materials are layered structured materials with formula (Bi (Bi2O2)2+ (A m-1BmO3m+1 )2-. The polarization of Aurivillius materials is mainly in a-b plane . High dense and textured ceramics were fabricated by a two-step spark plasma sintering (SPS) method to improve the polarization of ceramics. The multiferroic properties of of Aurivillius materials with different octahedral layers (m=2, 3, 4 and 5) were investigated. All these materials showed ferroelectric and ferromagnetic order at room temperature except Bi 3Nb 1.1251.1251.1251.1251.125Fe 0.1250.1250.1250.1250.125Co 0.1250.1250.1250.1250.125Ti 0.750.750.750.75O9 (m = 2). (m = 2). (m = 2). (m = 2). (m = 2). Bi 3.253.253.253.25La 0.750.750.750.75Nb 0.250.250.250.25Fe 0.1250.1250.1250.1250.125Co 0.1250.1250.1250.1250.125Ti 2.52.52.5O12 (m = 3) was identified to be single phase. (m = 3) was identified to be single phase. Although a small amount of secondary phase (CoFe (CoFe2O4/Co /Co2FeOFeOFeO4) were found in Bi 4.254.254.254.25La 0.750.750.750.75Fe 0.50.50.5Co 0.50.50.5Ti 3O15 (m = 4) and Bi 5.25.25.25La 0.750.750.750.75FeCoTiFeCoTiFeCoTiFeCoTi FeCoTi3O18 (m = 5), ), the intrinsic multiferroicity of the main Aurivillius phase was confirmed by the magnetic controlled ferroelectric domain switching. Clear ME couplings were observed in these materials.

No description available.

Introducing the notion of transformational silicon electronics has paved the way for integrating various applications with silicon-based, modern, high-performance electronic circuits that are mechanically flexible and optically semitransparent. While maintaining large-scale production and prototyping rapidity, this flexible and translucent scheme demonstrates the potential to transform conventionally stiff electronic devices into thin and foldable ones without compromising long-term performance and reliability. In this work, we report on the fabrication and characterization of reversibly bistable flexible electronic switches that utilize flexible n-channel metal-oxide-semiconductor field-effect transistors. The transistors are fabricated initially on rigid (100) silicon substrates before they are peeled off. They can be used to control flexible batches of light-emitting diodes, demonstrating both the relative ease of scaling at minimum cost and maximum reliability and the feasibility of integration. The peeled-off silicon fabric is about 25 µm thick. The fabricated devices are transferred to a reversibly bistable flexible platform through which, for example, a flexible smartphone can be wrapped around a user’s wrist and can also be set back to its original mechanical position. Buckling and cyclic bending of such host platforms brings a completely new dimension to the development of flexible electronics, especially rollable displays.

The purpose of this research is to identify the configurations of several mechanism classes which result in bistable behavior. Bistable mechanisms have use in many applications, such as switches, clasps, closures, hinges, and so on. A powerful method for the design of such mechanisms would allow the realization of working designs much more easily than has been possible in the past. A method for the design of bistable mechanisms is especially needed for micro-electro-mechanical systems (MEMS) because fabrication and material constraints often prevent the use of simple, well-known bistable mechanism configurations. In addition, this knowledge allows designers to take advantage of the many benefits of compliant echanisms, especially their ability to store and release energy in their moving segments. Therefore, an analysis of a variety of mechanism classes has been performed to determine the configurations of compliant segments or rigid-body springs in a mechanism which result in bistable behavior. The analysis revealed a relationship between the placement of compliant segments and the stability characteristics of the mechanism which allows either analysis or synthesis of bistable mechanisms to be performed very easily. Using this knowledge, a method of type synthesis for bistable mechanisms has been developed which allows bistable mechanisms to be easily synthesized. Several design examples have been presented which demonstrate the method. The theory has also been applied to the design of several bistable micromechanisms. In the process of searching for usable designs for micro-bistable mechanisms, a mechanism class was defined, known as "Young" mechanisms, which represent a feasible and useful way of achieving micro-mechanism motion similar to that of any four-bar mechanism. Based on this class, several bistable micro-mechanisms were designed and fabricated. Testing demonstrated the ability of the mechanisms to snap between the two stable states. In addition, the mechanisms showed a high degree of repeatability in their stable positions.

This thesis presents novel research in the area of energy harvesting from broadband vibra-tions. The aim of energy harvesting is to recover energy wasted or unused in the environmentto power low-consumption devices on the order of hundreds of microwatts to milliwatts. The motivation is twofold. In providing a localized, self-contained power source, device reliability, flexibility of installation location can be improved, and maintenance costs can be reduced. Furthermore, reduced reliance on batteries will mitigate the environmental impact associated with resource extraction, and disposal. To this end, this thesis investigates bistable laminates with piezoelectric transduction as broadband energy harvesters. Hitherto, a wealth of literature exists in which narrowband energy harvesters have been studied and optimized to operate over a small frequency interval. While these have been successful to the point of having devices commercially available, many situations exist where the dominant frequencies from which energy is to be harvested change with respect to time, or may be dominated by noise, thus not having a truly dominating frequency. Energy harvesters with nonlinear frequency responses have attracted substantial research interest because of their ability to respond over a broaderfrequency band. Due to complexities of the response of these harvesters, particularly when the intensity of the vibrational input is high, modeling their behavior is difficult. Designing these harvesters is therefore challenging as the relationships between the various design parameters and power output can be highly involved, or require numerical solutions as analytical solutions may not be possible. This thesis helps to address this knowledge gap. Bistable laminates ofboth cantilever and plate configuration are studied. Parametric studies are undertaken to empirically demonstrate the relationship between power output and parameters such as resistance load, proof mass addition, operation orientation, different shapes, ply angles, and introduction of adjustable magnetic compression. Modeling work is also undertaken to capture the mainfeatures of the nonlinear response such as subharmonics, superharmonics, and snap-through. A study is also carried out to quantify the differences of performance between a linear harvester and an equivalent bistable counterpart. As a practical demonstration, some plate-type harvesters are subjected to excitation patterns based on measured train data. Ultimately, thisthesis provides an in depth understanding of bistable shape, layup, and design on harvesting performance.

Compliant bistable mechanisms are mechanisms that have two stable equilibrium positions within their range of motion. Their bistability is mainly due to the elasticity of their members. This thesis introduces a new type of bistable micromechanisms, the Bistable, Spherical, Compliant, four-bar Micromechanism (BSCM). Theory to predict bistable positions and configurations is also developed. Bistabilty was demonstrated through testing done on micro-prototypes. Compared to the mathematical model of the BSCM, Finite element models of the BSCM indicated important qualitative differences in the mechanism's stability behavior and its input-angle-input torque relation. The BSCM has many valuable features, such as: Two stable positions that require power only when moving from one stable position to the other, accurate and repeatable out-of-plane motion with resistance to small perturbations. The BSCM may be useful in several applications such as active Braille systems and Digital Light Processing (DLP) chips.

No description available.

No description available.

Ce travail de thèse décrit l'utilisation de complexes de platine(II) dans les diodes électroluminescentes organiques (OLEDs). Ces complexes ([Pt(II) (tetra-tert-butylSalophen)] et [Pt(II) Salophen]) ont été caractérisés par les méthodes usuelles (1H RMN, spectroscopie UV-visible, électrochimie, diffraction des rayons X pour le [Pt(II) (tetra-tert-butylSalophen)]). Des calculs DFT ont corroboré les données expérimentales qui ont guidé le choix du Tris(8-hydroxyquinolinato) aluminum (Alq3) en tant que matrice. Des dispositifs bistables, susceptibles d'être utilisés en tant que mémoires, ont été obtenus lors du dopage, à 5%, d'OLEDs monocouches. La modulation de ce phénomène par l'ajout d'une couche de N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD) d'épaisseur contrôlée, a été mis en évidence. Des OLEDs bicouches (NPD/Alq3:Pt) émettant dans la gamme spectrale 640-750 nm (rouge profond), et présentant des rendements supérieurs à 20 %, ont ainsi été réalisées. En dopant la couche de NPD, des OLED jaunes présentant un comportement électro-chromatique ont été élaborées. Sous l'effet du dopage par ces complexes, l'augmentation de la durée de vie des OLEDs a aussi été démontrée. / This thesis describes the integration of platinum(II) complexes within organic light emitting diodes (OLEDs). These complexes ([Pt(II) (tetra-tert-butylSalophen)] and [Pt(II) Salophen]) were characterized by the usual methods ( 1H NMR, UV-Vis spectroscopy, electrochemistry and X-ray diffraction for [Pt(II) (tetra-tert-butylSalophen)]). DFT calculations support the experimental data which guided the selection of Tris(8-hydroxyquinolinato) aluminum (Alq3)as host. 5% doping in monolayer OLEDs gave bistable devices which may be used as memory. Modulation of this phenomenon was allowed by adding a controlled layer of N,N'-Di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD). Bilayer OLEDs (NPD/Alq3:Pt) were shown to emit in the deep-red range between 640-750nm with efficiencies higher than 20%. Upon doping with complexes, an enhancement in the lifetime of OLEDs was highlighted.

La récupération d'énergie à partir des sources de vibration est une des stratégies développées pour l'alimentation de capteurs autonomes communicants. La variabilité des gisements vibratoires dans l'environnement constitue un défi notable pour l'obtention de performances satisfaisantes et appelle au développement de dispositifs de récupération d'énergie à large bande passante. Les générateurs basés sur des oscillateurs mécaniques non linéaires bistables ont démontré des performances particulièrement intéressantes. Grâce à l'effet de conversion fréquentielle notamment, la plage de fonctionnement est considérablement augmentée. Une nouvelle architecture de générateur bistable basée sur un oscillateur non linéaire et des composants piézoélectriques est proposé dans la thèse. Ce générateur possède des caractéristiques particulièrement favorables en termes de compacité et de simplicité. Des études théoriques et expérimentales ont été menées. En utilisant les excitations canoniques dans le cas de systèmes dynamiques non linéaires (balayage fréquentiel et bruit blanc), les gains obtenus par rapport à des générateurs linéaires ont été quantifiés. Les performances du générateur proposé sont également supérieures à celles des générateurs bistables de la littérature. Une attention particulières a été portée à l'étude des réponses dynamiques non linéaires complexes révélant la présence d'attracteurs étranges et l'influence des conditions initiales. Une analyse spectrale est également utilisée pour améliorer la compréhension du comportement du générateur. L'adimensionnement des équations d'équilibres donne à ces analyses une portée générique. Selon le modèle normalisé développé, la performance d'un générateur bistable est liée à quatre paramètres critiques: l'amortissement structurel, le niveau de couplage électromécanique, le niveau de flambement et la fréquence caractéristique. Un facteur de mérite est proposé et constitue un élément de comparaison pertinent entre générateurs. Une stratégie de conception optimale a été élaborée et mise en œuvre pour la réalisation d'un générateur miniaturisée. Après une caractérisation expérimentale complète utilisant les signaux canoniques, son potentiel d'application à des cas plus proches des environnements réels a été étudié en répliquant en laboratoire l'excitation mesurée sur un véhicule en roulage. L'association du générateur bistable avec une technique d'extraction d'énergie non linéaire a été réalisée : la technique OSECE (Optimized Synchronous Electric Charge Extraction) est choisie. Les gains de performances obtenus pour différents niveaux de couplage électromécanique dans le cas des excitations canoniques sont étudiés. L'énergie récupérée est considérablement augmentée en cas de faibles couplages électromécaniques. Lorsque celui-ci est plus élevé, les performances sont comparables à celles obtenues avec un simple pont redresseur, mais l'indépendance à l'impédance d'entrée du circuit alimenté dans le cas de la technique OSECE peut être un avantage déterminant pour des applications réelles. Finalement, compte tenu des gains attendus par l'approche combinée oscillateur bistable et technique OSECE, l'auto-alimentation du circuit actif OSECE est réalisée dans le cas d'un oscillateur bistable par des moyens mécaniques. La complexité du générateur est légèrement augmentée dans la mesure où des butées mécaniques et un système de contacteurs électriques sont ajoutés. Les résultats démontrent le potentiel de l'approche qui capitalise les bénéfices de l'oscillateur bistable et du circuit d'extraction non linéaire. / As scavenging the energy from the vibration sources has the wide adaptability and the easy feasibility of integration with other sources, it becomes one of the hottest topic in the energy harvesting field. Numerous works have been done to enhance the harvested power by optimizing the interface circuit and the mechanical structure. The variability of the environmental vibrations introduces a challenge to the conventional linear harvesters and calls for the development of wideband vibration generators. Plenty of approaches have been proposed. Bistable generators have shown some of the best properties of the frequency-up-conversion effect at the low frequency range and the bandwidth increase from the nonlinear backbone response. A novel bistable generator with a BSM (Buckled-Spring-Mass) architecture is proposed in the thesis. This BSM generator possesses some especially desired properties of compactness and simplicity. Utilizing the chirp and noise excitations, experimental and numerical investigations have shown that it effectively extends the operation bandwidth compared with linear generators. The performance is also demonstrated to be better than most of the reported bistable generators. The complex nonlinear dynamics have been studied, including the strange attractor and the influence of the initial condition. A spectrum method is also used to give more details about the motion of the BSM generator. According to the developed normalized model, the BSM generator's performance is related to four critical parameters: structural damping, electromechanical coupling level, buckled position and characteristic frequency. Applying the concluded optimization and design procedures, a miniaturized BSM generator of the millimeter scale has been produced and tested. The application potential is further investigated with a replicated realistic excitation from the wheel of a driving car. Moreover, a wireless demonstration platform has been constructed to exhibit the wideband operation ability.A figure of merit is proposed to make fair comparisons between the literature nonlinear wideband generator and the BSM generators. Chapter 4 presents a novel energy harvesting solution which combines the BSM generator with a nonlinear extraction technique: the OSECE (Optimized Synchronous Electric Charge Extraction) technique is used along with the BSM bistable generator.The performances of the proposed solution for different levels of electromechanical coupling coefficients in the cases of chirp and noise excitations are compared against the performance of the BSM generator with the standard technique. It is shown that the harvested energy is drastically increased for all excitations in the case of low electromechanical coupling coefficients. When the electromechanical coupling coefficient is high, the performance of the OSECE technique is not as good as the standard circuit for forward sweeps, but superior for the reverse sweep and band-limited noise cases in the tested range. Finally, a self-powered approach for the combination of the BSM generator and the OSECE circuit is realized by replacing the electronic switches with mechanical switches and introducing additional stoppers. It allows wideband harvesting capability, high harvested power and autonomous features. A model of this novel generator is detailed and experimentally validated. Discussions and optimizations are performed to find the optimal parameters and fully investigate the performance of the proposed generator. It shows that introducing the stoppers and the self-powered OSECE circuit using mechanical switches can substantially enhance the harvested power with moderate additional complexity.