No description available.

We tackle the problem of suppressing high-amplitude vibrations of cantilever beams when subjected to either primary external or principal parametric resonances. Guided by results of previous investigations into the nonlinear dynamics of single- and multi-degree-of-freedom structures, we design mechatronic systems of sensors, actuators, and electronic devices and implement nonlinear active feedback control. In the case of external excitation, we devise two vibration absorbers based on either quadratic or cubic feedback. We conduct theoretical analyses and demonstrate that when a two-to-one (one-to-one) internal resonance condition is imposed between the plant and the quadratic (cubic) absorber, there exists a saturation phenomenon. When the plant is forced near its resonant frequency and the forcing amplitude exceeds a certain small threshold, the nonlinear coupling creates an energy-transfer mechanism that limits (saturates) the response of the plant. Our theoretical studies reveal that the cubic absorber creates regimes of high-amplitude quasiperiodic and chaotic responses, thereby limiting its utility. However, we show that superior results can be achieved when the natural frequency of the quadratic absorber is set equal to one-half the excitation frequency. Consequently, we apply the quadratic technique through a variety of linear and nonlinear actuators, sensors, and electronic devices. We design and build second-order analog circuits that emulate the quadratic absorber. Using a DC motor, piezoelectric ceramics, and Terfenol-D struts as actuators and potentiometers, strain gages, and accelerometers as sensors, we demonstrate successful single- and multi-mode vibration control. In order to realize a more versatile implementation of the control strategy, we resort to a digital signal processing (DSP) board. We compose a code in C and design a digital absorber by developing algorithms that, in addition to replacing the analog circuit, automatically detect the amplitude and frequency of oscillation of the plant and fine-tune the absorber parameters. We take advantage of the digital realization, implement a linear absorber, and compare the performance of the quadratic absorber with that of its linear counterpart. In the case of parametric excitation, we investigate two techniques. First, we explore application of the quadratic absorber. We prove theoretically and demonstrate experimentally that this control scheme is not reliable. Then, we propose an alternate approach. We devise a control law based on cubic velocity feedback. We conduct theoretical and experimental investigations and show that the latter strategy leads to effective vibration suppression and bifurcation control. / Ph. D.

No description available.

In most man-made flight, vehicle control is achieved by deflecting flaps. However, in nature, morphing surfaces are found on both flying and swimming creatures. Morphing is used in nature because it is a more efficient form of control. This thesis investigates using morphing flaps to control a class of UAVs known as ducted fan vehicles. Specifically, this thesis discusses both the challenges and benefits of using morphing control surfaces. To achieve morphing, a piezoelectric device known as Macro Fiber Composites is used. These devices are embedded in the skin of the vehicles control surface, and when actuated, they cause the control surface to increase or decrease camber. This thesis describes experiments that were performed to investigate the performance of this type of actuator. Specifically, the actuation bandwidth of these devices is presented and compared to a servo. Results show that the morphing control surfaces can actuate at frequencies twice as high as a servo. / Master of Science

The use of optical fiber sensors is increasing widely in industry, civil, medicine, defense and research. Among different categories of these sensors is the Extrinsic Fabry-Perot interferometer (EFPI) sensor which is inherently simple and requires only modest amount of interface electronics. These advantages make it suitable for many practical applications. Investigating a cost-effective, reliable and repeatable method for optical fiber sensor fabrication is challenging work. In this thesis, a system for controlled fabrication of Fabry-Perot optical fiber sensors is developed and presented as the first attempt for the long-term goal of automated EFPI sensor fabrication. The sensor fabrication control system presented here implements a real-time control of a carbon dioxide (CO₂) laser as sensor bonding power, an optical fiber white light interferometric subsystem for real-time monitoring and measurement of the air gap separation in the Fabry-Perot sensor probe, and real-time control of a piezoelectric (PZT) motion subsystem for sensor alignment. The design of optoelectronic hardware and computer software is included. A large number of sensors are fabricated using this system and are tested under high temperature and high pressure. This system as a prototype system shows the potential in automated sensor fabrication. / Master of Science

The master’s thesis deals with the piezoelectric coefficients, the resonance frequency and especially the piezoelectric constants verification. With the assistance of several devices, for instance LCR-meter HIOKI 3532, impedance analyzer Agilent 4294A and LCR-meter Agilent E4980A, the resonance and the anti-resonance frequencies as well as impedance and capacitance of samples are measured. The paper opens with the theory of the piezoelectric phenomenon and the difference between direct and indirect piezoelectric phenomenon, it also describes the basic behaviour of a piezoelectric ceramic element during mechanical straining or applied voltage. Further, the paper concerns the description of various piezoelectric constants and their calculations. Subsequent part of the paper is devoted to the temperature dependence of the main piezoelectric parameters of PZT ceramics. The materials coefficients are delineated as a function of temperature of the piezoelectric charge coefficients dij, relative permittivity r, electromechanical coupling factor kij and frequency constants Ni. One of the chapters also determines the piezoelectric charge constant d33 of PZT ceramics by laser interferometer and compares it with the value measured by resonance methods. The surface displacement was measured by a single-beam interferometer Polytec OFV-5000. The results of measurements of piezoelectric charge coefficients d33 acquired by the first and the second method are identical. The last section of the paper is focused on different methods of experimental studies on the characteristics of heat transfer by diffusing heat through conduction between the silver-plated surface of cylinder made of PZT ceramics. The effect on the resonance and the anti-resonance frequencies is monitored. There after, the real heat, determined by thermo camera and the physical model of heat transfer created in program COMSOL Multiphysics, is analysed.

Pour les applications aéronautiques, les fibres en céramique piézoélectrique à âme métallique permettent d'imaginer des solutions pour avoir des dispositifs actifs et des capteurs complétement intégrés dans des structures, telles que les composites renforcés par des fibres.La démarche de cette étude est d'élaborer et de caractériser de telles fibres qui présentent de nombreux avantages : l'activation en mode radial permet d'utiliser de faibles tensions de commandes, l'utilisation d'un cœur et d'une matrice conducteurs permet de s'affranchir du dépôt d'électrodes et de garantir leur continuité, la présence d'un coeur métallique améliore la résistance mécanique de la fibre, l'utilisation sous forme de fibres fines et longues permet de l'intégrer à des profils de formes complexes sur de grandes longueurs. Dans un premier temps, le procédé d'enduction est utilisé pour la réalisation de ces fibres en déposant des particules céramiques à base de titano-zirconate de plomb (PZT) sur des fils de platine. Le développement et l'optimisation d'un procédé multicouche permet de réaliser des fibres avec des épaisseurs parfaitement contrôlées pour obtenir les capacités de déformations optimales en alternant des cycles dépôt/traitement thermique avant une opération de frittage finale. La caractérisation d'échantillons massifs traités dans les mêmes conditions permet de s'assurer des propriétés piézoélectriques atteintes pendant les différents traitements thermiques. Les caractérisations électromécaniques réalisées sur les fibres permettent de vérifier le comportement en tant qu'actionneur et que capteur, bien qu'il s'avère difficile de remonter aux caractéristiques intrinsèques des fibres.Dans un second temps, une réflexion est menée sur les moyens à mettre en oeuvre pour envisager un développement à grande échelle de ce type de fibre. Dans ce sens, des expérimentations sur la mise en place du procédé continu de coextrusion avec un polymère chargé sont menées, de même que sur la réduction de la température de frittage à l'aide d'additifs pour substituer les fils en platine, mais aussi sur la réduction du temps de frittage à l'aide de techniques non conventionnelles comme le frittage laser et le frittage micro-ondes. Ces investigations ouvrent des pistes sérieuses pour imaginer une production continue de fibres piézoélectriques à âme métallique.Enfin, des travaux de modélisation par éléments finis du comportement de ces fibres, intégrées ou non dans une structure, permettent de mettre en évidence l'influence du dimensionnement des fibres sur les déformations résultantes, en fonction notamment de l'épaisseur du matériau actif déposée et des propriétés élastiques des différents éléments. Différentes configurations sont imaginées pour utiliser ces fibres dans des structures en tant qu'actionneur et capteur. / Metal core piezoelectric fibres are suitable for active devices and sensors fully embedded in structuresas fibres reinforced polymers for aeronautic applications.The aim of this study is to develop and characterize such fibres that have many advantages: radial mode activation allows the use of low voltage control, the use of a core and a conductive matrix eliminates the deposition of electrodes and the necessity to maintain their continuity, the presence of a metal core improves the mechanical strength of the fibre, the use of thin and long fibres permits their integration in profiles with complex shapes over long distances.In a first step, a dip-coating process is used to realize such fibres by depositing ceramic particles based on lead zirconium titanate (PZT) on platinum wire. The development and optimization of a multilayer process, by alternating deposition cycles / heat treatment prior to the final sintering step, lead to the production of fibres with perfectly controlled thickness in order to obtain optimal strain capability. Characterization of bulk samples under the same thermal conditions allows to measure equivalent piezoelectric properties as fibres submitted to the same heat treatments. Electromechanical characterizations performed on the fibres confirm their behaviour as actuator and sensor, although it is still difficult to determine the effective piezoelectric properties of the fibres.In a second step, the possibility to develop a large-scale production of this type of fibre is investigated.In this regard, experiments are carried on coextrusion process with a PZT loaded polymer, as well as the reduction of the sintering temperature by using additives to replace the platinum core. In addition, reducing the sintering time using unconventional techniques such as laser sintering and microwave sintering are investigated. It is then open serious leads to imagine a continuous production of metal core piezoelectric fibres.Finally, a finite element modelling approach of the behaviour of these fibres, integrated or not in a structure, allows to highlight the influence of fibre sizing on the resulting strains, in particular according to the thickness of the active deposited material and elastic properties of the individual elements (metal core, matrix). Different configurations are analysed to use these fibres in structures as actuator and sensor.

O titanato e zirconato de chumbo \'PB\'(\'ZR\'1-y\'TI\'y)\'O IND.3\' é um material ferroelétrico de estrutura perovskita que tem sido aplicado como transdutores, amplificadores, sensores piezoelétricos, piroelétricos e memórias ferroelétricas. É bem estabelecido que a incorporação de íons de \'LA POT.3+\' ou \'BA POT.2+\' nos sítios ocupados pelo \'PB\' no sistema \'PB\'(\'ZR\'1-y\'TI\'y)\'O\' (PZT), formando os sistemas \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) e \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT), provoca mudanças significativas nas suas propriedades. No entanto, poucos trabalhos tem sido dedicados a esses sistemas contendo altas concentrações de \'TI\', principalmente no que se refere à estrutura desses materiais. Assim, este trabalho teve por objetivo analisar as propriedades estruturais e suas correlações com as propriedades dielétricas dos sistemas \'PB\'1-x\'LA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PLZT100x) e \'PB\'1-x\'BA\'x\'ZR\'0,40\'TI\'0,60\'O IND.3\' (PBZT100x) em função da composição e da temperatura. Foram preparadas amostras cerâmicas por meio de sinterização convencional com x variando entre 0,05 e 0,21 para o sistema PLZT e entre 0,10 e 0,50 para o sistema PBZT. Em relação à estrutura a longa distância, medidas de difração de raios X mostraram uma diminuição no grau de tetragonalidade com o aumento da concentração dos cátions substituintes, que foi atribuída à formação de vacâncias no sítio A (caso do \'LA\') e diferença entre o raio iônico (caso do \'BA\'). Estas alterações estruturais em função da composição foram também responsáveis pelo aumento do grau de difusidade das curvas de permissividade dielétrica e pela observação de um estado ferroelétrico relaxor nas amostras contendo altas concentrações de \'LA\' e \'BA\'. Em relação à estrutural local, os resultados obtidos através da técnica de espectroscopia de absorção de raios X (XAS) nas bordas \'K\' do \'TI\' e LIII do \'PB\' mostraram que a incorporação de átomos de \'LA\' ou \'BA\' à estrutura do PZT leva a uma redução no deslocamento do átomo de \'TI\' em relação ao centro do octaedro \'TI\'O IND.6\' e mudanças na ordem local do átomo de \'PB\'. No que tange as composições contendo 21% at. de \'LA\' e 50% at. de \'BA\', diferentemente dos resultados de DRX que mostraram uma simetria cúbica, a técnica de XAS mostrou uma simetria local tetragonal. Em bom acordo com os resultados obtidos pela técnica de espectroscopia Raman, espectros EXAFS medidos em altas temperaturas mostraram também que a estrutura local não é compatível com uma estrutura de simetria cúbica. Espectros XANES medidos na borda \'K\' do oxigênio revelaram uma redução no grau de hibridização entre os estados 2p do \'O\' com 6sp do \'PB\' à medida que a concentração de \'LA\' ou \'BA\' aumenta, que estaria relacionada com o surgimento de comportamento relaxor. Amostras cerâmicas densas nanoestruturadas de composição PZT, PLZT11 e PBZT10 foram preparadas pelo método de spark plasma sintering (SPS) a fim de analisar a influência do tamanho de grão. Foi verificado que as amostras sinterizadas por SPS apresentam tamanho de grão em torno de 60 nm. A caracterização dielétrica destas amostras mostra que a redução do tamanho de grão causa uma redução no valor de máximo da permissividade dielétrica e características difusas da permissividade em função da temperatura devido ao aumento das regiões de contorno de grão. / Lead titanate zirconate (\'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\') are ferroelectric materials with perovskite structure which has been used as transducers, capacitors, piezoelectric and pyroelectric sensors and ferroelectric memories. The substitution of \'PB POT.+2\' ions by \'LA POT.+3\' or \'BA POT.+2\' ions in the \'PB\'(\'ZR\'1-x\'TI\'x)\'O IND.3\' (PZT) system, which leads to the formation of the \'PB\'1-x\'LA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PLZT) and the \'PB\'1-x\'BA\'x\'ZR\'1-y\'TI\'y\'O IND.3\' (PBZT) systems, induces several changes in the electric and structural properties of these materials. However, PLZT or PBZT systems based on \'TI\'-rich compositions have not been thoroughly investigated and the literature contains few reports concerning their structure. Thus, the main objectives of this doctoral thesis were the synthesis and structural characterization of \'PB\'1-x\'R\'x\'ZR\'0.40\'TI\'0.60\'O IND.3\' ferroelectric ceramic samples, with R = \'BA\' and \'LA\' and x between 0.00 to 0.50 (PLZT100x and PBZT100x). The characterization with X-ray diffraction technique of these samples showed a decrease of the tetragonality degree with increase of the doping cation concentration, which was related to the appearance of defects caused by the incorporation of \'LA\' or \'BA\' cations. These structural modifications were also responsible by the increase of the diffuseness at the dielectric permittivity and a relaxor behavior as a function of the \'LA\' or \'BA\' concentration. Concerning the local structure, XANES spectra in the absorption edge of various elements in PLZT and PBZT samples were performed. In the cases of \'TI\' \'K\'-edge absorption, the doping of \'LA\' and \'BA\' atoms in the PZT structure leads to a reduction of the displacement of \'TI\' atom in the center of the \'TI\'O IND.6\' octahedron. However, even when the crystal structure is cubic, a local octahedron distortion remains. EXAFS measurements in \'PB\' LIII-edge and \'ZR\' \'K\'-edge were performed and also indicate that local structure around lead or zirconium atoms is also affected by the introduction of \'LA\' and \'BA\' atoms in the PZT structure. In addition, XANES spectra measured at \'O\' \'K\'-edge revealed a reduction in the hybridization degree between \'O\' 2p and \'PB\' 6sp states with the addition of \'LA\' or \'BA\' atoms to the structure of PZT. It has been shown that hybridization between these states is essential to ferroelectricity and this reduction would be related to the relaxor behavior. PLZT and PBZT systems were also studied depending on the size of particle size in a nanometer scale. Thus samples PZT, PLZT11 and PBZT10 compositions were prepared using the synthesis method of precursor polymers and the process of sintering by spark plasma. A pronounced decrease in the values of maximum permittivity was observed and the dielectric curve as a function of the temperature exhibits a diffuse behavior. This size-induced diffuse phase transition and the reduction of the permittivity magnitude could be related to the differences between the core grain and the grain boundaries.

Electron emission from ferroelectric materials is initiated by a variation of the spontaneous polarization. It is the main focus of this work to develop ferroelectric cathodes, which are characterized by a significantly decreased excitation voltage required to initiate the electron emission process. Particular attention is paid to the impact of the polarization on the emission process. Two materials are investigated. Firstly, relaxor ferroelectric lead magnesium niobate - lead titanate (PMN-PT) single crystals are chosen because of their low intrinsic coercive field. Electron emission current densities up to 5 · 10^(−5) A/cm² are achieved for excitation voltages of 160 V. A strong enhancement of the emission current is revealed for the onset of a complete polarization reversal. Secondly, lead zirconate titanate (PZT) thin films are investigated. A new method to prepare top electrodes with sub-micrometer sized, regularly patterned apertures is introduced and a stable electron emission signal is measured from these structures for switching voltages < 20 V. Furthermore, a detailed analysis of the polarization switching process in the PMN-PT samples is given, revealing a spatial rotation of the polarization vector into crystallographic easy axes, as well as the nucleation of reversed nano-domains. Both processes are initiated at field strengths well below the coercive field. The dynamics of the polarization reversal are correlated to the electron emission measurements, thus making it possible to optimize the efficiency of the investigated cathodes. / Die Ursache für Elektronenemission aus ferroelektrischen Materialien ist eine Veränderung des Zustandes der spontanen Polarisation. Gegenstand der vorliegenden Arbeit ist eine Verringerung der dafür nötigen Anregungsspannung, wobei besonderes Augenmerk auf die Rolle der ferroelektrischen Polarisation innerhalb des Emissionsprozesses gelegt wird. Es werden zwei verschiedene Materialien untersucht. Das Relaxor-Ferroelektrikum Bleimagnesiumniobat - Bleititanat (PMN-PT) wurde aufgrund seines geringen Koerzitivfeldes ausgewählt. Es konnten Emissionsstromdichten von bis zu 5·10^(−5) A/cm² bei einer Anregungsspannung von 160 V erreicht werden. Bei Einsetzen eines vollständigen Umschaltens der Polarisation wurde eine deutliche Verstärkung des Emissionsstromes festgestellt. Desweiteren werden Untersuchungen an Bleizirkoniumtitanat (PZT) Dünnfilmen gezeigt. Eine neue Methode, eine Elektrode mit periodisch angeordneten Aperturen im Submikrometerbereich zu präparieren, wird vorgestellt. Diese Strukturen liefern ein stabiles Emissionssignal für Anregungsspannungen < 20 V. Eine detailierte Analyse des Schaltverhaltens der Polarisation der PMN-PT Proben zeigt sowohl eine Rotation des Polarisationsvektors als auch eine Nukleation umgeschaltener Nanodomänen. Beide Prozesse starten bei Feldstärken unterhalb des Koerzitivfeldes. Die ermittelte Zeitabhängigkeit des Schaltprozesses erlaubt Rückschlüsse auf den Emissionsprozess und erlaubt es, die Effizienz der untersuchten Kathoden weiter zu optimieren.

Piezokeramischen Werkstoffe auf der Basis von Bleizirkonat - Titanat (PZT) zeigen Extremwerte der elektromechanischen Eigenschaften im morphotropen Phasenübergangsbereich. Durch Modifikation des Verhältnisses von rhomboedrischer und tetragonaler Phase im Gefüge können die piezoelektrischen Eigenschaften des Werkstoffs entsprechend den jeweiligen Anforderungen angepasst werden. Es wurde eine Methode vorgestellt, einen mathematisch kohärenten Satz piezoelektrischer Kleinsignalkoeffizienten vollständig und mit hoher Genauigkeit über einen breiten Temperatur-(-200°C...+200°C) und Zusammensetzungsbereich (0...1 rh/tet) zu bestimmen. Desweiteren wurden die piezoelektrischen Eigenschaften dem Phasenanteil im Gefüge zugeordnet. / Piezoceramic materials based on Lead- Zirconate- Titanate (PZT) show extreme electromechanic properties in the area of morphotropic phase transition. PZT materials can be tailored to specific demands by modifying the ratio of volume of the rhombohedral and tetragonal phase within the micro structure. A method was introduced to accurately determine a complete and mathematically coherent set of piezoelectric small signal coefficients. This was done over a wide range of temperature (-200°C…+200°C) and phase composition (0…1 rh/tet). Additionally, the piezoelectric properties were correlated to the ratio of rhombohedral and tetragonal phases.