Dissertations / Theses on the topic 'Piezoelectric materials'

Piezoelectric materials find applications in number of devices requiring inter-conversion of mechanical and electrical energy.  These devices include different types of sensors, actuators and energy harvesting devices. A number of lead-based perovskite compositions (PZT, PMN-PT, PZN-PT etc.) have dominated the field in last few decades owing to their giant piezoresponse and convenient application relevant tunability. With increasing environmental concerns, in the last one decade, focus has been shifted towards developing a better understanding of lead-free piezoelectric compositions in order to achieve an improved application relevant performance.  Sodium potassium niobate (KxNa1-xNbO3, abbreviated as KNN) is one of the most interesting candidates in the class of lead-free piezoelectrics. Absence of any poisonous element makes it unique among all the other lead-free candidates having presence of bismuth. Curie temperature of 400"C, even higher than that of PZT is another advantage from the point of view of device applications.
               Present work focuses on the development of fundamental understanding of the crystallographic nature, domain structure and domain dynamics of KNN. Since compositions close to x = 0.5 are of primary interest because of their superior piezoelectric activity among other compositions (0 < x < 1), crystallographic and domain structure studies are focused on this region of the phase diagram. KNN random ceramic, textured ceramic and single crystals were synthesized, which in complement to each other help in understanding the behavior of KNN.
            K0.5Na0.5NbO3 single crystals grown by the flux method were characterized for their ferroelectric and piezoelectric behavior and dynamical scaling analysis was performed to reveal the origin of their moderate piezoelectric performance. Optical birefringence technique used to reveal the macro level crystallographic nature of x = 0.4, 0.5 and 0.6 crystals suggested them to have monoclinic Mc, monoclinic MA/B and orthorhombic structures respectively. Contrary to that, pair distribution function analysis performed on same composition crystals implies them to belonging to monoclinic Mc structure at local scale. Linear birefringence and piezoresponse force microscopy (PFM) were used to reveal the domain structure at macro and micros scales respectively.
                 A noble sintering technique was developed to achieve > 99% density for KNN ceramics. These high density ceramics were characterized for their dielectric, ferroelectric and piezoelectric properties. A significant improvement in different piezoelectric coefficients of these ceramics validates the advantages of this sintering technique. Also lower defect levels in these high density ceramics lead to the superior ferroelectric fatigue behavior as well. To understand the role of seed crystals in switching behavior of textured ceramic, highly textured KNN ceramics (Lotgering factor ~ 88 %) were synthesized using TGG method. A sintering technique similar to one employed for random ceramics, was used to sinter textured KNN ceramics as well. Piezoresponse force microscopy (PFM) study suggested these textured ceramics to have about 6¼m domains as compared to 2¼m domain size for random ceramics.  Local switching behavior studied using switching spectroscopy (SS-PFM) revealed about two and half time improvement of local piezoresponse as compared to random counterpart.

Ph. D.

Piezoelectric composite materials, consisting of a ferroelectric ceramic in an electrically-inactive polymer matrix, have been shown to greatly outperform single phase materials for certain applications. A new assembly technique, which electrically controls the spatial distribution of the ceramic within the polymer, promises to enhance the sensitivity of 0-3 type piezoelectric composites. The materials so-produced have a quasi 1-3 structure and it is intended that they will exhibit some of the advantages of 1- 3 piezoelectric composites, whilst retaining the simplicity of 0-3 manufacturing. The electric field structuring technique exploits the electrokinetic phenomenon of dielectrophoresis, which is responsible for the electrorheological effect. When a suspension of ceramic particles in an insulating fluid is exposed to a moderate AC electric field, the particles polarize and as a result they exhibit a mutually attractive force. Under suitable conditions the particles assemble into 'pearl-chains', 'fibrils' or columns, oriented parallel to the applied field. If the fluid is a resin pre-polymer, this can then be cured and the newly formed structures frozen into place to form a composite material with anisotropic properties. The key process parameters are explored and the implications of employing this method to produce technologically useful materials are discussed. It is demonstrated, for the first time, that dielectrophoresis can be used to induce anisotropic dielectric and piezoelectric properties in 55%vol. fraction ceramic/polymer composites. A model composite system of pure lead titanate in an epoxy resin is considered in basic detail. A method of producing a lead zirconate titanate (PZT) powder with a narrow particle size distribution, by flux growth, has been shown to be effective. New concepts in multiphase composites are introduced, whereby chains are formed within the confines of a second immiscible fluid or where particles of two different materials are mixed in a suspension, each material having its own 'polarization signature'.

This thesis explores local structure variation in (1-x)(Na0.5, Bi0.5)TiO3-xPbTiO3 (NBT-PT) and (Kx, Na1-x)0.5Bi0.5TiO3 (KNBT) around the morphotropic phase boundary (MPB). Local structure alignment or ordering in NBT-PT was achieved through the addition of PbTiO3 (PT), whilst in KNBT local ordering was induced by an applied electric field. Significant emphasis is placed on local structure analysis methods (up to 50 Å length scale) via pair distribution function (PDF) analysis. In situ temperature X-ray diffraction was used to characterise the average structure of NBT-PT. A transition from a rhombohedral structure for x = 0.08 to tetragonal for x = 0.18 was observed (MPB x = 0.13). The ferroelectric-paraelectric transition temperature was corroborated by permittivity measurements which also showed a transition from relaxor to ferroelectric behaviour with increasing x. Whole profile PDF refinement revealed the presence of a monoclinic phase for x = 0.14 acting as a lower symmetry bridge between rhombohedral and tetragonal phases. Range dependent PDF analysis was used to measure the coherence length of nanoscaled regions which decreased in size from 40 to 20 Å with increasing x. These regions persisted at temperatures above the paraelectric transition, though reduced in size across all compositions. The measurements illustrate the order inducing properties of PbTiO3, which suppresses nanoregions and promotes long-range ferroelectric order. PDF analysis of unpoled KNBT at unit-cell length scale distances was used to measure the local Bi off-centre displacement direction. For x = 0.10, a rhombohedral distortion was observed. This transitioned to a monoclinic distortion for x = 0.15, further evolving into a complex mixture of various monoclinic distortions for x = 0.20 (MPB). A tetragonal distortion was observed beyond the MPB (x = 0.30). The improved piezoelectric properties at the MPB are attributed to the greater availability of displacement directions. Under an applied electric field, the suppression in diffuse scattering and sharpening of PDF peaks indicating field induced ordering. Changes in the peak area ratios corresponding to Bi-Ti distances indicate reorientation behaviour along the applied field vector. Local strain analysis was achieved by measuring the PDF peak shift. The onset of linear strain corresponding to piezoelectric response occurred at an electric field (E) ≈ 1000 - 1250 V/mm for x = 0.20 and at E ≈ 2000 – 3000 V/mm for x = 0.15 and 0.18. Non-zero strain below the threshold field indicates the presence of localised strain assumed to be incipient to the macroscopic strain.

This project developed computational tools to analyse and design novel piezoelectric materials that have the potential to be utilised in next-generation electromechanical devices. The thesis demonstrates how such architectured materials can be used in the design of multi-functional robotic ‘pain’ sensors.

Piezoelectrics present an interactive electromechanical behaviour that, especially in recent years, has generated much interest since it renders these materials adapt for use in a variety of electronic and industrial applications like sensors, actuators, transducers, smart structures. Both mechanical and electric loads are generally applied on these devices and can cause high concentrations of stress, particularly in proximity of defects or inhomogeneities, such as flaws, cavities or included particles. A thorough understanding of their fracture behaviour is crucial in order to improve their performances and avoid unexpected failures. Therefore, a considerable number of research works have addressed this topic in the last decades. Most of the theoretical studies on this subject find their analytical background in the complex variable formulation of plane anisotropic elasticity. This theoretical approach bases its main origins in the pioneering works of Muskelishvili and Lekhnitskii who obtained the solution of the elastic problem in terms of independent analytic functions of complex variables. In the present work, the expressions of stresses and elastic and electric displacements are obtained as functions of complex potentials through an analytical formulation which is the application to the piezoelectric static case of an approach introduced for orthotropic materials to solve elastodynamics problems. This method can be considered an alternative to other formalisms currently used, like the Stroh’s formalism. The equilibrium equations are reduced to a first order system involving a six-dimensional vector field. After that, a similarity transformation is induced to reach three independent Cauchy-Riemann systems, so justifying the introduction of the complex variable notation. Closed form expressions of near tip stress and displacement fields are therefore obtained. In the theoretical study of cracked piezoelectric bodies, the issue of assigning consistent electric boundary conditions on the crack faces is of central importance and has been addressed by many researchers. Three different boundary conditions are commonly accepted in literature: the permeable, the impermeable and the semipermeable (“exact”) crack model. This thesis takes into considerations all the three models, comparing the results obtained and analysing the effects of the boundary condition choice on the solution. The influence of load biaxiality and of the application of a remote electric field has been studied, pointing out that both can affect to a various extent the stress fields and the angle of initial crack extension, especially when non-singular terms are retained in the expressions of the electro-elastic solution. Furthermore, two different fracture criteria are applied to the piezoelectric case, and their outcomes are compared and discussed. The work is organized as follows: Chapter 1 briefly introduces the fundamental concepts of Fracture Mechanics. Chapter 2 describes plane elasticity formalisms for an anisotropic continuum (Eshelby-Read-Shockley and Stroh) and introduces for the simplified orthotropic case the alternative formalism we want to propose. Chapter 3 outlines the Linear Theory of Piezoelectricity, its basic relations and electro-elastic equations. Chapter 4 introduces the proposed method for obtaining the expressions of stresses and elastic and electric displacements, given as functions of complex potentials. The solution is obtained in close form and non-singular terms are retained as well. Chapter 5 presents several numerical applications aimed at estimating the effect of load biaxiality, electric field, considered permittivity of the crack. Through the application of fracture criteria the influence of the above listed conditions on the response of the system and in particular on the direction of crack branching is thoroughly discussed.

Piezoelectrics present an interactive electromechanical behaviour that, especially in recent years, has generated much interest since it renders these materials adapt for use in a variety of electronic and industrial applications like sensors, actuators, transducers, smart structures. Both mechanical and electric loads are generally applied on these devices and can cause high concentrations of stress, particularly in proximity of defects or inhomogeneities, such as flaws, cavities or included particles. A thorough understanding of their fracture behaviour is crucial in order to improve their performances and avoid unexpected failures. Therefore, a considerable number of research works have addressed this topic in the last decades. Most of the theoretical studies on this subject find their analytical background in the complex variable formulation of plane anisotropic elasticity. This theoretical approach bases its main origins in the pioneering works of Muskelishvili and Lekhnitskii who obtained the solution of the elastic problem in terms of independent analytic functions of complex variables. In the present work, the expressions of stresses and elastic and electric displacements are obtained as functions of complex potentials through an analytical formulation which is the application to the piezoelectric static case of an approach introduced for orthotropic materials to solve elastodynamics problems. This method can be considered an alternative to other formalisms currently used, like the Stroh’s formalism. The equilibrium equations are reduced to a first order system involving a six-dimensional vector field. After that, a similarity transformation is induced to reach three independent Cauchy-Riemann systems, so justifying the introduction of the complex variable notation. Closed form expressions of near tip stress and displacement fields are therefore obtained. In the theoretical study of cracked piezoelectric bodies, the issue of assigning consistent electric boundary conditions on the crack faces is of central importance and has been addressed by many researchers. Three different boundary conditions are commonly accepted in literature: the permeable, the impermeable and the semipermeable (“exact”) crack model. This thesis takes into considerations all the three models, comparing the results obtained and analysing the effects of the boundary condition choice on the solution. The influence of load biaxiality and of the application of a remote electric field has been studied, pointing out that both can affect to a various extent the stress fields and the angle of initial crack extension, especially when non-singular terms are retained in the expressions of the electro-elastic solution. Furthermore, two different fracture criteria are applied to the piezoelectric case, and their outcomes are compared and discussed. The work is organized as follows: Chapter 1 briefly introduces the fundamental concepts of Fracture Mechanics. Chapter 2 describes plane elasticity formalisms for an anisotropic continuum (Eshelby-Read-Shockley and Stroh) and introduces for the simplified orthotropic case the alternative formalism we want to propose. Chapter 3 outlines the Linear Theory of Piezoelectricity, its basic relations and electro-elastic equations. Chapter 4 introduces the proposed method for obtaining the expressions of stresses and elastic and electric displacements, given as functions of complex potentials. The solution is obtained in close form and non-singular terms are retained as well. Chapter 5 presents several numerical applications aimed at estimating the effect of load biaxiality, electric field, considered permittivity of the crack. Through the application of fracture criteria the influence of the above listed conditions on the response of the system and in particular on the direction of crack branching is thoroughly discussed.

The objective of this thesis is to present a modelling and simulation study for the mechanics of PNs with an emphasis placed on the unique features of PNs due to the piezoelectric and small scale effects.

Piezoelectric voltage transformers (PTs) can be used to transform an input voltage into a different, required output voltage needed in electronic and electro- mechanical systems, among other varied uses. On the macro scale, they have been commercialized in electronics powering consumer laptop liquid crystal displays, and compete with an older, more prevalent technology, inductive electromagnetic volt- age transformers (EMTs). The present work investigates PTs on smaller size scales that are currently in the academic research sphere, with an eye towards applications including micro-robotics and other small-scale electronic and electromechanical sys- tems. PTs and EMTs are compared on the basis of power and energy density, with PTs trending towards higher values of power and energy density, comparatively, indicating their suitability for small-scale systems. Among PT topologies, bulk disc-type PTs, operating in their fundamental radial extension mode, and free-free beam PTs, operating in their fundamental length extensional mode, are good can- didates for microfabrication and are considered here. Analytical modeling based on the Extended Hamilton Method is used to predict device performance and integrate mechanical tethering as a boundary condition. This model differs from previous PT models in that the electric enthalpy is used to derive constituent equations of motion with Hamilton’s Method, and therefore this approach is also more generally applica- ble to other piezoelectric systems outside of the present work. Prototype devices are microfabricated using a two mask process consisting of traditional photolithography combined with micropowder blasting, and are tested with various output electri- cal loads. 4mm diameter tethered disc PTs on the order of .002cm

3 , two orders smaller than the bulk PT literature, had the followingperformance: a prototype with electrode area ratio (input area / output area) = 1 had peak gain of 2.3 (± 0.1), efficiency of 33 (± 0.1)% and output power density of 51.3 (± 4.0)W cm

-3 (for output power of80 (± 6)mW) at 1M? load, for an input voltage range of 3V-6V (± one standard deviation). The gain results are similar to those of several much larger bulk devices in the literature, but the efficiencies of the present devices are lower. Rectangular topology, free-free beam devices were also microfabricated across 3 or- ders of scale by volume, with the smallest device on the order of .00002cm

3 . These devices exhibited higher quality factorsand efficiencies, in some cases, compared to circular devices, but lower peak gain (by roughly 1/2 ). Limitations of the microfab- rication process are determined, and future work is proposed. Overall, the devices fabricated in the present work show promise for integration into small-scale engi- neered systems, but improvements can be made in efficiency, and potentially voltage gain, depending on the application

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A utilização de materiais piezelétricos para transformação de energia mecânica proveniente das vibrações em energia elétrica tem aumentado na última década para tentar suprir a necessidade por fontes alternativas de energia na alimentação de sistemas de monitoramento da condição estrutural (SHM) e dispositivos de aeronaves não tripuladas, tornando estes dispositivos autônomos. Como a energia produzida através da piezoestrutura não é suficiente para alimentar os dispositivos eletrônicos diretamente, técnicas de extração e armazenamento são utilizadas para que a energia produzida seja acumulada até um nível utilizável. Neste sentido, este trabalho apresenta um estudo sobre uma configuração de piezoestrutura capaz de produzir um alto nível de energia mesmo que a frequência de excitação apresente variações. A piezoestrutura proposta é do tipo multifrequência aumentando a largura de banda de operação e podendo produzir um alto nível de energia mesmo que a frequência de excitação apresente alterações. A piezoestrutura multifrequência foi modelada por elementos finitos através do programa ANSYS© e posteriormente comparada com resultados experimentais. Em seguida, a tensão produzida foi extraída através dos circuitos retificador de onda completa em ponte e do dobrador de tensão buscando avaliar o desempenho de ambos na extração da energia produzida para armazenamento em um supercapacitor. Finalmente, a energia armazenada no supercapacitor foi utilizada para alimentar um sistema de monitoramento da temperatura de um ambiente de modo que o sistema passe a operar como um sistema autônomo
The use of piezoelectric materials to transform mechanical energy from the vibrations into electrical energy has increased in the last decade trying to meet the need for alternative sources of energy to power up SHM systems and Unmanned Air Vehicle devices, making these standalone devices. This work presents a study on a configuration of a piezostructure being able to produce a higher energy even if the excitation frequency undergoes changes, and then evaluate two electronic circuit topology as simple interface for extracting the maximum energy produced and store it in a supercapacitor to power a sensor system that monitors the temperature in a room. Initially a brief review of the basics and fundamentals of energy harvesting was presented for better understanding of the development of this work. The proposal is a multifrequency piezostructure type that increases the bandwidth of operation and could produce a high energy value even if the excitation frequency undergoes alterations. The multifrequency piezostructure was modeled by finite element software ANSYS© and then compared with experimental results showing a good correlation between the numerical and experimental models. Then, a parametric study was conducted to determine which geometric parameter from the piezostruture should be varied so that the piezo-beams had their natural frequencies within the specified operating range. The voltage produced was extracted through two types of circuits (full wave rectifier and voltage doubler) trying to evaluate which one is able to extract the maximum possible energy produced for storage in a supercapacitor. Finally, the energy stored in the supercapacitor was used to power a system for monitoring the temperature of an environment so that the system operates as a standalone system

Orientador: João Antônio Pereira
Banca: Samuel da Silva
Banca: Adailton Silva Borges
Resumo: A utilização de materiais piezelétricos para transformação de energia mecânica proveniente das vibrações em energia elétrica tem aumentado na última década para tentar suprir a necessidade por fontes alternativas de energia na alimentação de sistemas de monitoramento da condição estrutural (SHM) e dispositivos de aeronaves não tripuladas, tornando estes dispositivos autônomos. Como a energia produzida através da piezoestrutura não é suficiente para alimentar os dispositivos eletrônicos diretamente, técnicas de extração e armazenamento são utilizadas para que a energia produzida seja acumulada até um nível utilizável. Neste sentido, este trabalho apresenta um estudo sobre uma configuração de piezoestrutura capaz de produzir um alto nível de energia mesmo que a frequência de excitação apresente variações. A piezoestrutura proposta é do tipo multifrequência aumentando a largura de banda de operação e podendo produzir um alto nível de energia mesmo que a frequência de excitação apresente alterações. A piezoestrutura multifrequência foi modelada por elementos finitos através do programa ANSYS© e posteriormente comparada com resultados experimentais. Em seguida, a tensão produzida foi extraída através dos circuitos retificador de onda completa em ponte e do dobrador de tensão buscando avaliar o desempenho de ambos na extração da energia produzida para armazenamento em um supercapacitor. Finalmente, a energia armazenada no supercapacitor foi utilizada para alimentar um sistema de monitoramento da temperatura de um ambiente de modo que o sistema passe a operar como um sistema autônomo
Abstract: The use of piezoelectric materials to transform mechanical energy from the vibrations into electrical energy has increased in the last decade trying to meet the need for alternative sources of energy to power up SHM systems and Unmanned Air Vehicle devices, making these standalone devices. This work presents a study on a configuration of a piezostructure being able to produce a higher energy even if the excitation frequency undergoes changes, and then evaluate two electronic circuit topology as simple interface for extracting the maximum energy produced and store it in a supercapacitor to power a sensor system that monitors the temperature in a room. Initially a brief review of the basics and fundamentals of energy harvesting was presented for better understanding of the development of this work. The proposal is a multifrequency piezostructure type that increases the bandwidth of operation and could produce a high energy value even if the excitation frequency undergoes alterations. The multifrequency piezostructure was modeled by finite element software ANSYS© and then compared with experimental results showing a good correlation between the numerical and experimental models. Then, a parametric study was conducted to determine which geometric parameter from the piezostruture should be varied so that the piezo-beams had their natural frequencies within the specified operating range. The voltage produced was extracted through two types of circuits (full wave rectifier and voltage doubler) trying to evaluate which one is able to extract the maximum possible energy produced for storage in a supercapacitor. Finally, the energy stored in the supercapacitor was used to power a system for monitoring the temperature of an environment so that the system operates as a standalone system
Mestre

Superhydrophobicity refers to surfaces with extremely large water droplet contact angles (usually greater than 150°). This phenomenon requires a hydrophobic material with micro or nano-scale roughness. Superhydrophobic surfaces exist in nature (e.g. the lotus leaf) and can be produced synthetically. This project focuses on the development and characterization of superhydrophobic materials with tunable wettability (i.e. smart superhydrophobic materials). In this study, surfaces were prepared by electrospinning thin, aligned polystyrene fibers onto a piezoelectric unimorph substrate. Results showed electric field induced changes in substrate curvature, which produced corresponding changes in surface wettability. From experiments, an average change in water contact angle of 7.2° ± 1.2° with 90% confidence was observed in ~2μm diameter fiber coatings electrospun for 5 minutes with applied electric field. In addition, fiber coatings electrospun with equivalent deposition showed average electric field induced changes in WCA of 2.5° ± 0.92° for lower diameter fibers (~1μm) and 3.5° ± 1.37° for higher diameter fibers (~2μm) with 90% confidence.

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, Cape Town, 2002
Distributed Piezoelectric Actuator (DPA) is one kind of actuator in the smart technology field. Firstly, DPA is one kind of solid-state actuator, and can be embedded in the structure. Secondly, it can be controlled by the electrical signal with high bandwidth and high precision. So it can be applied in the many different fields, such as high-resolution positioning, noise and vibration detection and shape control. Up to now, all of the DPA theory investigations and the product designs are based on applying the approximate electrical field. And only the rectangular shape DPA has been studied. The accurate distribution and intensity of electrical and mechanics field, and the numerical imitation for the DPA products with rectangular and other shapes have never been discussed and studied. Therefore, the development of DPA to be used in the micro application, such as in the Micro Electro-Mechanical System (MEMS), has been limited. This thesis has developed the analytical analysis models for two types of DPA elements and the part circular shape DPA element. The MathCAD and MATLAB program have been used to develop the analytical models. The ABAQUS program has also been used to compare the results between the analytical models and Finite Element Method (FEM). Finally, the accuracy and reliability of analytical models have been proved by results comparison between the analytical models, FEM and the product testing data from the industry. This thesis consists of five chapters. Chapter 1 is the introduction of smart structure. The characterizations of constituent materials, including the piezoelectric material and matrix epoxy material have been discussed in Chapter 2. In Chapter 3, the analytical models for two type of DPA element have been developed and the comparisons have also been completed. The analytical models for part circular shape DPA element have been developed in Chapter 4. The conclusions and recommendations are included in Chapter 5.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 1990.
Thesis Advisor(s): Panholzer, R. Second Reader: Neighbours, J.R. "June 1990." Description based on signature page. DTIC Identifiers(s): Nonvolitile memories, ferroelectric materials. Author(s) subject terms: Ferrorelectric, nonvolatile memory, radiation hard. Includes bibliographical references (p. 80-86). Also available online.

Dissertation (Ph.D. in Aeronautical and Astronautical Engineering) Naval Postgraduate School, September 1996.
Dissertation supervisor(s): B.N. Agrawal. "September 1996." Includes bibliographical references (p. 111-118). Also available online.

The work of this thesis concerns to study of a particular technique related to the treatment of generated voltage by the piezoelectric elements. This nonlinear technique increases the effect of electromechanical conversion of piezoelectric materials considerably. This technique called Synchronized Switching Damping (SSD) has been developed in laboratory of electrical engineering and ferroelectricity of INSA-Lyon. The advantage of these techniques is that can be self-powered by using the converted electrical energy by piezoelectric elements. The presented work propose a new approach of control for the SSD techniques that allowing to increase of damping in the case of complex vibration such as random excitations. This new approach is the statistical approach on the sliding time window of the piezoelectric voltage or displacement of structure. Numerical as well as the experimental results have been presented for a cantilever beam. These results show the ability of the piezoelectric patches with passive shunting to damp out the structural vibration and also show that this new strategy of control is very efficient. The effect of the size of piezoelectric patches on the vibration damping and their damping sensibility to the variations of the excitation force parameters have been presented as well. Finally, it shows the effect of boundary conditions on the SSDI technique
Les travaux de cette thèse concernent l'étude d'une technique particulière se rapportant au traitement de la tension générée par les éléments piézoélectriques. Cette technique non linéaire augmente considérablement l'effet de la conversion électromécanique des matériaux piézoélectriques. Cette technique appelée synchronise switch damping (SSD) a été mis au point en laboratoire de génie électrique et férroélectricite de l'INSA-Lyon. L’un des avantages de ces techniques est la possibilité d’être autoalimenté par la conversion de l’énergie électrique par des éléments piézoélectriques. Le présent travail propose une nouvelle approche du contrôle pour les techniques SSD permettant l'augmentation de l'amortissement dans le cas de vibrations complexes tels que les excitations aléatoires. Cette nouvelle approche est l'approche statistique sur fenêtre glissante dans le temps par rapport à la tension piézo-électrique ou le déplacement de l'ouvrage. Les résultats numériques et expérimentaux ont été présentés pour une poutre encastrée libre. Ces résultats montrent l’efficacité de cette nouvelle stratégie de contrôle, avec la capacité des patchs piézoélectrique pour amortir les vibrations de la structure. L'effet de la taille des patchs piézo-électrique sur l’amortissement des vibrations et leur sensibilité aux variations de la force d'excitation sont aussi présentées. Enfin, il montre l'effet des conditions aux limites sur la technique SSDI

Thèse doctorat : Génie Electrique.Energie et Système : Villeurbanne, INSA : 2008.
Thèse rédigée en anglais. Résumé étendu en français. Titre provenant de l'écran-titre. Bibliogr. p. [142]-151.

This thesis has dealt with the preparation and the characterization of piezoelectric 0-3 composite materials. The technological aim is to evaluate a material potentially suitable for the development of a sensitive skin for human robotics. As secondary objectives this material should be cheap (relatively) and easy processable in order to make it possibly adaptable for industrial production. For these reasons, 0-3 composites were prepared and characterized. Raw materials were selected among the most commonly used for piezoelectric applications. PVDF is the most widely used ferroelectric polymer. It was used along with two of its copolymers: PVDF-HeFP, developed to have improved flexibility but no piezoelectricity and PVDF-TrFE, developed to obtain the crystalline piezoelectric phase whatever the process. PMMA was also studied. Barium titanate submicron-powder was chosen as piezo-active filler. Composites were prepared with increasing volume percentages of fillers. Two different processing methods were explored in order to evaluate their effect on the microstructure and the piezoelectric response

Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2008
In recent years, due to rapid advances in technology there has been an increasingly high demand for large displacement and large force, precise positioning, fast response, low power consuming miniature piezoelectric actuators. In certain smart structure applications, the use of curved piezoelectric actuators is necessary. The present work extends the earlier investigations on the C- shape actuator by providing a detailed investigation on the influence of geometric and material properties of the individual layers of the C-shape piezocomposite for its optimal performance as an actuator. Analytical models have. been used to optimize the geometry of the actuator. Experimental and finite element analyses (using general purpose finite element software i.e. CoventerWare and MSC. Marc) have been used for validation. The present work has established that, by maintaining the thickness of the substrate and piezoceramic layers constant; changing the external radius, for example increasing it, the stiffness of the structure decreases and thus yielding large displacement This has a negative effect on the force produced by the actuator. With fixed thickness of the substrate and varying the thickness of the piezoceramic (for fixed external radius) the result is as follows: Increasing the thickness of the piezoceramic layer has the effect of decreasing the displacement while the force increases. With fixed PZT thickness as well as the external radius, varying the substrate thickness has the following effect: As the thickness of the substrate increases the displacement increases reaching a maximum. Subsequent increase in the thickness of the substrate the displacement is reduced. The force continues increasing at least for the ratios up to 1.0, further increase of the substrate, subsequent decrease of force is also noted. In addition to changing the thickness of the substrate, the choice of different material for the substrate has the following effect: For substrate/PZT ratios of up to 0.6. an actuator with substrate material having higher elastic modulus will produce larger displacement while for ratios beyond this ratio the situation is reversed. The causes for this kind of behaviour have been addressed. In all cases both force and displacement are found to be directly proportional to applied voltage.

In recent years, vibration-based energy harvesting technologies have gained great importance because of reduced power requirement of small electronic components. External power source and maintenance requirement can be minimized by employment of mechanical vibration energy harvesters. Power sources that harvest energy from the environment have the main advantages of high safety, long shell life and low cost compared to chemical batteries. Electromagnetic, electrostatic and piezoelectric transduction mechanisms are the three main energy harvesting methods. In this thesis, it is aimed to apply the piezoelectric elements technology to develop means for energy storage in munitions launch. The practical problems encountered in the design of piezoelectric energy harvesters are investigated. The applicability of energy harvesting to high power needs are studied. The experience compiled in the study is to be exploited in designing piezoelectric energy harvesters for munitions applications. Piezoelectric energy harvesters for harmonic and mechanical shock loading conditions with different types of piezoelectric materials are designed and tested. The test results are compared with both responses from analytical models generated in MATLAB®
and ORCAD PSPICE®
, and finite element method models generated in ATILA®
. Optimum energy storage methods are considered.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Esse trabalho discute o uso dos materiais piezelétricos, mais especificamente, o Polyvinylidene Fluoride (PVDF) e o Lead Zirconate Titatane (PZT) na análise modal experimental (AME) de estruturas mecânicas. Materiais piezelétricos, também chamados de materiais inteligentes, têm se consolidado como uma nova tecnologia que mostra um grande potencial de aplicação em diferentes áreas da engenharia. Esse tipo de material exibe um acoplamento entre multi-domínios físicos, como por exemplo o acoplamento eletro-mecânico, o térmo-magnético, etc. O acoplamento eletro-mecânico produz um deslocamento elétrico quando o material é sujeito a uma tensão mecânica (efeito direto) e um deformação mecânica quando esse material é submetido a um campo elétrico (efeito inverso). Assim, principalmente por conta desses efeitos, seu uso no campo da análise modal experimental torna-se uma interessante questão a ser investigada. A incorporação de novas tecnologias nos testes estruturais pode agregar novos conhecimentos e avanços tanto na análise modal baseada na relação entrada-saída da estrutura, quanto na mais recente técnica, a análise modal baseada apenas na resposta das mesmas. Os conceitos teóricos para o desenvolvimento são apresentados e discutidos neste trabalho, onde é mostrada a análise modal de uma viga utilizando tanto sensores e atuadores convencionais quanto os produzidos com materiais inteligentes. Os testes de análise modal da viga foram feitos utilizando diferentes combinações de sensores e atuadores e isso pode mostrar as diferenças da estimativa de modos utilizando materiais piezelétricos. Também é apresentada a formulação da relação entre os modos em deslocamento e os modos com diferença de inclinação obtidos com materiais piezelétricos e, finalmente, uma comparação dos resultados obtidos pelas diferentes técnicas. Os testes apresentados mostram...
This work discusses the use of piezoelectric materials, more specifically, Polyvinylidene Fluoride (PVDF) and Lead Zirconate Titanate (PZT) for experimental modal analysis (EMA) of mechanical structures. Piezoelectric materials also called smart materials have becoming a consolidated new technology that shows a large potential of application for different engineering areas. These materials exhibit a multi physics domain field coupling like mechanical and electrical coupling domains, thermal and magnetic coupling and etc. The electro-mechanical coupling domains of the material produces an electric displacement when the material is subject to a mechanical stress (direct-effect) and a mechanical strain when the material is submitted to an electric field (inverse effect). So, mainly due to these effects, the use in the experimental modal analysis field appears to be an interesting issue to be investigated. The incorporation of this new technology in the structural tests might aggregate new acknowledgments and advances in the well consolidated input-output based modal analysis techniques as well as in the more recent output only-based modal analysis. This work aims to present some contribution in this area by using piezoelectric sensors, instead of the conventional ones like accelerometers for modal analysis of mechanical structures. The theoretical concepts and background for the developing of the work are presented and discussed, it is also presented the modal analysis of a beam like structure using conventional sensors/actuators and piezoelectric materials. The modal analysis tests of the beam are conducted using different kinds of sensors/actuator and they give some insight of the difference of the estimated modes shapes by using piezoelectric materials. It is also presented a formulation that shows the relation between... (Complete abstract click electronic access below)

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The military’s dependence on fossil fuels for electric power production in isolated settings is both logistically and monetarily expen-sive. Currently, the Department of Defense is actively seeking alternative methods to produce electricity, thus decreasing dependence on fossil fuels and increasing combat power.We believe piezoelectric generators have the ability to contribute to military applications of alternative electrical power generation in isolated and austere conditions. In this paper, we use three and six variable mathemat-ical models to analyze piezoelectric generator power generation capabilities. Using mk factorial sampling, nearly orthogonal and balanced Latin hypercube (NOBLH) design, and NOBLH iterative methods, we find optimal solutions to maximize piezoelectric gen-erator power output. We further analyze our optimal results using robustness analysis techniques to determine the sensitivity of our models to variable precision. With our results, we provide analysts and engineers the optimal designs involving material parameters in the piezoelectric generator, as well as the generator’s environment, in order to maximize electric output.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003.
Includes bibliographical references (p. 93-95).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Ferroelectric materials are key to many modem technologies, in particular piezoelectric actuators and electro-optic modulators. BaTiO₃ is one of the most extensively studied ferroelectric materials. The use of BaTiO₃ for piezoelectric applications is, however, limited due to the small piezoelectric coefficient of the room temperature-stable tetragonal phase. Furthermore, research on BaTiO₃ for integrated optics applications remains sparse. In this work Zr-, Hf-, and KNb- doped BaTiO₃ materials were prepared in a composition range that stabilizes the rhombohedral phase. These materials were prepared as bulk polycrystals using a standard solid-state reaction technique in order to test the piezoelectric and dielectric properties. Some compositions were then chosen for thin film deposition. The films were deposited using pulsed laser deposition on MgO and SOI substrates. Growth orientation, remnant strain and optical properties were then measured. X-ray diffraction was used to confirm the existence of a stable rhombohedral phase. Dielectric measurements confirmed the expected phase transition temperatures. A piezoelectric coefficient of d₃₃=290-470pc/N was measured for Zr- and Hf- doped BaTiO₃, compared with d₃₃=75pC/N for pure BaTiO₃. The electrostrictive coefficient of the KNb-doped material, was measured as Q33=0.37m⁴/C², compared with Q33=0.11m⁴/C² for pure BaTiO₃. The maximum strain measured for the doped samples was 5-10 times higher then that of pure BaTiO₃. The effect of growth conditions on the orientation and strain of BaTiO₃ thin films was studied. As the substrate temperature and laser fluency were increased the film orientation varied from (111) to (110), then to (100). Zr- and Hf- doping helped lower the forming temperature for the
(cont.) orientations. The index of refraction for the thin films was measured and a model based on the Clausius-Mossotti relation was used to explain the data. The refractive index for BaTiO₃ films was extracted from the model, giving n=2.334 and n,=2.163.
by Ytshak Avrahami.
Ph.D.

Une analyse exhaustive de la piézoélectricité a été réalisée par la modélisation moléculaire basée sur l'application des principes de la mécanique quantique. La calibration de la méthode et des paramètres du calcul est d'abord examinée en comparant les résultats calculés concernant les oxydes de silicium et de Germanium à leurs homologues expérimentaux. Ensuite, les paramètres microscopiques qui influencent chaque contribution de cette propriété macroscopique de réponse sont distinctement rationalisés. Enfin, après la rationalisation de la propriété piézoélectrique, la conception de matériaux montrant un effet piézoélectrique élevé a été tentée. Nous avons montré que la grande piézoélectricité induite par un dopage dans le plan du graphène tendra vers une valeur unique, ni nulle ni infinie, et de façon indépendante de la nature physique ou chimique particulière du défaut. L'induction d'une piézoélectricité hors du plan du graphène en brisant sa planéité selon la direction-z est également étudiée. La réponse piézoélectrique obtenue est largement améliorée par rapport à la limite finie de la piézoélectricité dans le plan, mais aux grandes concentrations du défaut seulement. En effet, contrairement à la composante dans le plan de la piézoélectricité, la composante hors du plan, dépend de la nature du défaut et diminue jusqu'à tendre vers zéro à dilution infinie
An exhaustive analysis of the technologically important piezoelectric phenomena is here done by applying quantum chemical simulations. At first, the calibration of the assumed computational scheme is examined by comparing our calculated piezoelectric properties of the well-known piezoelectric quartz to their experimental counterparts. Secondly, the microscopic parameters that influence each contribution of piezoelectric macroscopic property are distinctly rationalized. After the rationalization of the piezoelectric property, the design of materials that exhibiting a high piezoelectric effect has been attempted. It has been shown that a large in-plane piezoelectricity induced in graphene by doping can be acquired by including any in-plane defect(s). Moreover, in the limit of vanishing defect concentration, the piezoelectric response tends toward a unique value, neither null nor infinite, regardless of the particular chemical or physical nature of the defect. The induction of an out-of-plane piezoelectricity in graphene by breaking its planarity through the non-periodic z-direction is stated, where the obtained piezoelectric response is largely improved compared to the finite in-plane piezoelectric limit, at however higher concentration of the defect. Contrarily to what has been discussed for the in-plane piezoelectric effect, the out-of-plane one eventually vanishes as far as the limit of infinite defect dilution is reached, and so it relies ultimately on the nature of the defect

Piezoelectric materials find applications in multitude of devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based systems which are becoming serious problem owing to the restrictions imposed by regulatory agencies across the globe. In the functional ceramics community, currently there is no problem more important than to find a replacement for lead-based piezoelectrics used for actuators. The electromechanical properties required for actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are, however, far inferior to those of lead-based systems. There are three lines of research for addressing this fundamental problem "C (i) search for new systems through a combination of theory-based prediction followed by experimental effort (doping, solid solutions having a morphotropic (M) or polymorphic (P) phase boundary (PB), (iii) stabilization of metastable phases or finding the high temperature triclinic systems, and (iii) improving the properties of known compositions through microstructure optimization, domain engineering and multilayering. All these approaches are challenging and require innovation to make a significant impact on the current state-of-the-art. In this thesis, the later line of research was focused which is promising for near future applications, as it builds upon the known material systems with high depoling temperatures that have demonstrated the potential to be practical.

In the first chapter, a novel method for the synthesis of lead-free (1-x)(Na0.5Bi0.5)TiO3 "C xBaTiO3 piezoelectric ceramics was investigated. Initially, multiple compositions around morphotrpic phase boundary (MPB) were synthesized to identify the optimum composition 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) for electromechanical effect. The new synthesis method starts with the synthesis of Na2Ti6O13 (NTO) whiskers which are then transformed into lead-free NBT-BT ceramics. Synthesis of NTO whiskers was performed using molten salt synthesis (MSS) method. Tape casting method was used to align the whiskers in base matrix powder and subjected to various processing temperatures to elucidate the microstructure and texture evolution. For this, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis were used as principal tools. The sintering process can be understood by dividing it into three stages, namely (i) transformation of monoclinic whiskers in to NBT-BT perovskite phase through topochemical reaction (<800oC), (ii) localized sintering confined on single whisker (800-1050oC), and (iii) liquid phase sintering as densification and grain growth occurs in the whole matrix (>1050oC). The concentric growth ledges observed on grain surfaces were found to be preferably confined on the corners of cubical grains indicating <111> growth direction. The Lotgering factor (f100) for the sintered matrix was found to decrease with increase in sintering temperature. The longitudinal piezoelectric constant (d33) of samples sintered for 20h at 1175oC, 1200oC and 1225oC was measured to be ~153 pC/N, ~216 pC/N and ~180 pC/N, respectively.
Next, a novel method was developed for the synthesis of nanostructured lead-free ferroelectric NBT-BT whiskers with high aspect ratio using NTO as a host structure. High energy x-ray diffraction coupled with atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of lead-free NBT-BT whiskers as rhombohedral, i.e. a ferroelectricity enabling type. The HRTEM analysis revealed local monoclinic-type structural distortions indicating a modulated structure at the nanoscale in the MPB composition of lead-free NBT-BT whiskers. The structural rearrangement during the synthesis of lead-free NBT-BT whiskers was found to occur via translation of edge shared octahedra of NTO into a corner sharing coordination. The high temperature morphological changes depicting disintegration of isolated whiskers into individual grains due to higher grain boundary energy have been found to occur in a close analogy with Rayleigh-type instability.
In lead-based ABO3 compounds, with B-site disorder, the origin of enhancement of piezoelectric properties near MPB has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. In this thesis, a microscopic model derived from comparative analyses of HR-TEM and neutron diffraction was developed that explains the origin of high piezoelectric response in lead "C free MPB compositions of NBT-BT. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase were attributed to localized displacements of atoms along the non-polar directions. These results provide new insight towards design of high performance lead "C free piezoelectric materials.
Microstructure and domain structure play dominant role towards controlling the magnitude of piezoelectric coefficient and hysteretic losses in perovskites. Brick-wall like microstructure with large grain size and small domain size can provide significant enhancement in the magnitude of piezoelectric coefficient. A synthesis technique for lead-free piezoelectric NBT-BT system that can provide [001]pc/[012]Rh grain oriented ceramics with large grain size and an electrical poling technique that results in smaller domain size will have significant impact on the electromechanical response. In this research, a synthesis technique was developed and the processing variables that play deterministic role in achieving the large grain brick-wall like microstructure were expplained. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with applied electric field. The piezoelectric response was found to increase monotonously with the incease in the degree of texturing and optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient as compared to its random form.
In order to understand mechanim of enhanced piezoelectric response in textured NBT-BT, in-situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly-oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nano regions and internal stresses induced by domain switching.
In conjunction to focus on NBT-BT, new lead-free piezoelectric materials with enhanced piezoelectric response were synthesized. This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO3-xA(Cu1/3Nb2/3)O3 (A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large d33 of ~330 pC/N and electromechanical planar coupling constant (kp)~ 46% at room temperature. The piezoelectric instability in these compositions was found to increase with x despite monotonous decrease in the long range polar ordering. High energy X-ray diffraction coupled with PDFs indicated increase in local polarization. Raman scattering analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. These localized polar distortions were found to persist much above the Curie temperature (Tc). Polarization "C electric field (P-E) hysteresis loop analysis indicated presence of the internal bias that was found to be correlated with the formation of polar defects. This defect structure was found to modulate the domain structure resulting in nano domains and broad domain walls with higher mobility as revealed through analysis from HR-TEM and piezoresponse force microscopy (PFM). The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The electron paramagnetic resonance (EPR) investigations revealed that substitution of Cu2+ takes place on octahedral sites that are distorted due to Jahn-Teller effect. The A-sites were distorted by substitution of Sr and Ca on Ba-site possessing different ionic radii and electronegativity. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions.
As an application, the solid solution with nominal composition of (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (BCN) (x = 0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO3 "C 0.025 Ba(Cu1/3Nb2/3)O3 (y = 0.05, 0.06, 0.075, 0.1). Room temperature XRD patterns showed decrease in tetragonality of BT after modifying with BCN (BT-BCN). Modifications with Sn lead to further decrement in tetragonality and the room temperature structure became cubic at 6.0 at% doping level. The decrement in tetragonality was accompanied by lowering of Tc.  BT-BCN doped with 6 and 7.5 at% Sn were found to exhibit diffuse phase transition accompanied by high dielectric constant "Ý 7000, low loss tangent "Ü 1% and grain size in the submicron regime ("Ü 1 "Ìm). These compositions were found to be promising for Y5V type multilayer ceramic capacitors (MLCCs).
Lastly, the dielectric and ferroelectric responses of compositionally graded bilayer and trilayer composites consisting of BT and 0.975BaTiO3-0.025Ba(Cu1/3Nb2/3)O3 (BT-BCN) were investigated. Two types of graded bilayer samples were synthesized, one with same thickness of BT and BT-BCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BT-BCN layers of equal thickness. SEM and TEM images showed a sharp interface with needle-shape domains across the interface. The domain size on BT-side was found to be larger than that on BT-BCN-side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting of characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BT-BCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from P"CE field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area , Pr and EC decreased with increasing frequency due to delayed response, but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations.

Ph. D.

This work examines a novel concept and design of simultaneous energy harvesting and vibration control on the same host structure. The motivating application is a multifunctional composite sandwich wing spar for a small Unmanned Aerial Vehicle (UAV) with the goal of providing self-contained gust alleviation. The basic idea is that the wing itself is able to harvest energy from the ambient vibrations along with available sunlight during normal flight. If the wing experiences any strong wind gust, it will sense the increased vibration levels and provide vibration control to maintain its stability. This work holds promise for improving performance of small UAVs in wind gusts. The proposed multifunctional wing spar integrates a flexible solar cell array, flexible piezoelectric wafers, a thin film battery and an electronic module into a composite sandwich structure. The basic design factors are discussed for a beam-like multifunctional wing spar with load-bearing energy harvesting, strain sensing and self-controlling functions. Three-point bending tests are performed on the composite sandwich structure for bending strength analysis and bending stiffness prediction under a given safety factor. Additional design factors such as the configuration, location and actuation type of each piezoelectric transducer are investigated for optimal power generation. The equivalent electromechanical representations of a multifunctional wing spar is derived theoretically, simulated numerically and validated experimentally. Special attention is given to the development of a reduced energy control (REC) law, aiming to minimize the actuation energy and the dissipated heat. The REC law integrates a nonlinear switching algorithm with a positive strain feedback controller, and is represented by a positive feedback operation amplifier (op-amp) and a voltage buffer op-amp for each mode. Experimental results exhibit that the use of nonlinear REC law requires 67.3 % less power than a conventional nonlinear controller to have the same settling time under free vibrations. Nonlinearity in the electromechanical coupling coefficient of the piezoelectric transducer is also observed, arising from the piezoelectric hysteresis in the constitutive equations coupling the strain field and the electric field. If a constant and voltage-independent electromechanical coupling coefficient is assumed, this nonlinearity results in considerable discrepancies between experimental measurements and simulation results. The voltage-dependent coupling coefficient function is identified experimentally, and a real time adaptive control algorithm is developed to account for the nonlinear coupling behavior, allowing for more accurate numerical simulations. Experimental validations build upon recent advances in harvester, sensor and actuator technology that have resulted in thin, light-weight multilayered composite sandwich wing spars. These multifunctional wing spars are designed and validated to able to alleviate wind gust of small UAVs using the harvested energy. Experimental results are presented for cantilever wing spars with micro-fiber composite transducers controlled by reduced energy controllers with a focus on two vibration modes. A reduction of 11dB and 7dB is obtained for the first and the second mode using the harvested ambient energy. This work demonstrates the use of reduced energy control laws for solving gust alleviation problems in small UAVs, provides the experimental verification details, and focuses on applications to autonomous light-weight aerospace systems.
Ph. D.

With piezoceramic materials, it is possible to harvest power from vibrating structures. It has been proven that micro- to milliwatts of power can be generated from vibrating systems. We develop definitive, analytical models to predict the power generated from a cantilever beam and cantilever plate. Harmonic oscillations and random noise will be the two different forcing functions used to drive each system. The predictive models are validated by being compared to experimental data. A parametric study is also performed in an attempt to optimize the cantilever beam systemâ s power generation capability.
Master of Science

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 132-137). Also available in electronic version. Access restricted to campus users.

O objetivo deste trabalho é analisar materiais piezelétricos compósitos com conectividade 1-3 e 2-2 para aplicações em transdutores de ultra-som na faixa de MHz utilizando modelos matemáticos e verificações experimentais. O estudo de um material piezelétrico compósito pode ser feito através de seus três principais tipos de modos de vibração: modo planar, modo de espessura e modo lateral. Neste trabalho, é utilizado o método dos elementos finitos para modelar os modos planares, de espessura e laterais de um compósito, e modelos analíticos para modelar o modo de espessura e o modo lateral. A modelagem do modo de espessura de um transdutor de ultra-som é feita a partir de um modelo analítico unidimensional. A modelagem unidimensional de um transdutor de ultra-som é feita através do cálculo das propriedades efetivas do material piezelétrico compósito. Essas propriedades são utilizadas no modelo da matriz distribuída para prever a impedância elétrica de um compósito e a resposta impulsiva de um transdutor de ultra-som. Com o objetivo de validar os modelos, foram construídos um material piezelétrico compósito com conectividade 1-3 e outro com conectividade 2-2 através da técnica “dice-and-fill”, utilizando cerâmica de PZT-5A e resina epóxi. O compósito com conectividade 1-3 foi utilizado na construção de um transdutor de ultra-som. Os resultados teóricos da impedância elétrica e da resposta impulsiva são comparados com os obtidos experimentalmente. A impedância elétrica experimental é obtida através de um analisador de impedâncias, enquanto que a resposta impulsiva experimental do eco do transdutor é medida acoplando o protótipo do transdutor a um tarugo de acrílico. Devido à periodicidade do compósito foi feito um estudo teórico da propagação de ondas mecânicas em meios periódicos, mostrando que existem determinadas faixas de freqüências que não se propagam no material. Foi verificado que esta periodicidade é responsável pela diminuição das amplitudes dos modos radiais de um material piezelétrico compósito quando comparados com os modos radiais de um disco de cerâmica piezelétrica. Também foram feitos ensaios em tanque de imersão para determinar as propriedades mecânicas de amostras de epóxi e amostras de tungstênio e epóxi em função da fração de volume de tungstênio na amostra.
The objective of this work is to analyze piezoelectric composite materials with 1-3 and 2-2 connectivity for applications in ultrasonic transducers in the megahertz frequency range. The analysis is done through mathematical models and experimental validation. The analysis of piezoelectric composite materials can be done through the study of its three main vibrational modes: planar mode, thickness mode, and the lateral mode. In this work, it is used the Finite Element Method to model the planar, thickness and the lateral modes of the composite, and it is used analytical models to model the thickness and the lateral modes. The modeling of the thickness mode of an ultrasonic transducer is obtained through an unidimensional analytical model. The unidimensional modeling of the transducer is done by calculating the effective properties of the piezoelectric composite material. The effective properties are used in a distributed matrix model to calculate the electrical impedance of the composite and the impulse response of an ultrasonic transducer. To validate the models, a 1-3 and a 2-2 piezoelectric composite were built using the “dice-and-fill” technique. These composite were constructed using a piezoelectric ceramic of PZT-5A and epoxy. The piezoelectric composite with 1-3 connectivity was used in the fabrication of an ultrasonic transducer. The theoretical results of the electrical impedance and the impulse response are compared with the experimental results. The experimental electrical impedance is measured by using an impedance analyzer, and the experimental impulse response is measured by coupling the ultrasonic transducer prototype to an acrylic block. Due to the periodicity of the composite, it was analyzed the behaviour of mechanical waves in periodic media, showing that there are frequency ranges that the waves cannot propagate. It was verified that the periodicity is responsible for the suppression of the radial modes in a piezoelectric composite when compared with the radial modes of a disk of piezoelectric ceramic. It is also conducted measurements in a water filled tank to determine the mechanical properties of samples of epoxy, and Tungsten/epoxy composites as a function of the volume fraction of Tungsten.

Orientadores: Niederauer Mastelari, Carlos Alberto Cimini Júnior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: A utilização de materiais compósitos na indústria tem crescido cada vez mais e se firmou como uma tendência para os próximos anos. Seja nos ramos automotivo, náutico, aeroespacial ou de defesa, as aplicações são as mais diversas, tendo em comum o usufruto da excelente relação de resistência por peso oferecida por este tipo de material. Em certos ramos, entretanto, como o aeroespacial, a utilização de materiais compósitos requer atenção especial, por ser característico destes materiais a ocorrência de tipos de falha próprios como delaminações, rupturas de fibra e de matriz, descolamentos, perfuração parcial ou total, alguns dos quais não observáveis a olho nu. O presente trabalho se debruça sobre esta problemática, visando o desenvolvimento de um método de apoio a técnicas de monitoramento de integridade estrutural por meio da localização de impactos com uso de sensores piezelétricos, implantado em peças sobretudo da indústria aeroespacial, permita catalogar regiões que hajam sofrido impactos importantes e possam apresentar falhas. Para conduzir o presente trabalho, foi feita uma revisão bibliográfica de técnicas de localização de impactos ou falhas em placas presentes no estado da arte, com análise e proposta de um método que se preste a este mesmo propósito inclusive para placas anisotrópicas. Foi estudado e desenvolvido um método a base de funções de erro, associando através de uma função pertinente cada ponto do domínio da placa a um valor de erro tanto menor quanto sua distância ao ponto de impacto real. O local de impacto estará associado ao ponto de menor erro. O método proposto, que já havia sido testado em simulações e experimentalmente em placas isotrópicas, forneceu resultados promissores também em placas anisotrópicas, apresentando estimativas com erro médio inferior a 2,0 cm
Abstract: The use of composite materials in industry has been increasing and establishing itself as a tendency for the next years. Be it in automotive, nautical, aerospace or defense, applications are many, all of which have in common taking advantage of the excellent relationship amongst resistance and weight offered by this kind of material. In certain areas, however, such as in aerospace, use of composite materials demands special attention, due to being characteristic of these materials the occurrence of certain proper types of damage such as delamination, fiber or matrix ruptures, debondings or partial or total perforation, some of which aren't even observable to naked eye. The present works focus in these problematics, aiming to develop a structural health monitoring supportive method via impact localization with low cost piezoelectric sensors that, embedded in parts primarily from the aerospace industry, allows to catalogue regions that have suffered significant impact and may have been damaged. In order to conduct the present work, a bibliographic revision was made of current state-of-the-art impact and damage localization techniques, with analysis and proposal of an innovative method for the same purpose. With that in mind, an error function method was studied and developed that associates through a pertinent function to each point in the plate an error value that is as small as its distance to real point of impact. This way, the point of impact will be related to the point of smaller error. The proposed method, which has already been tested in simulations and isotropic plates, presented interesting results also in anisotropic plates, with average estimative errors of less than 2.0 cm
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

This dissertation examines the response of piezoelectric material strain to electron flux influence. A plate of PZT5h is prepared as the specimen. The positive electrode is removed, and the negative electrode is connected to a power amplifier. Sixteen strain gages are attached as the strain sensor. The specimen is placed in a vacuum chamber, then the positive side is illuminated by electron beam. The characteristic of the static strain response is predicted by deriving the equation strain/deflection of the plate. Two methods are used, the Electro-Mechanical Equations and numerical analysis using Finite Element Method. The settings of the electron gun system (energy and emission current), along with the electric potential of the negative electrode (back-pressure), are varied to examine piezoelectric material responses under various conditions. Several material characteristics are examined: current flow to and from the material, time response of material strain, charge and strain distribution, and blooming. Results from these experiments suggest several conditions control the strain development in piezoelectric material. The current flow and strain on the material is stable if the backpressure voltage is positive. As a comparison, the current flow is small and the strain drifts down if the backpressure voltage is significantly negative. The material needs only 1 second to follow a positive step in backpressure voltage, but needs almost 1 minute to respond to a negative step backpressure change. This phenomenon is a result of secondary electron emission change and the energy transfer from the primary electrons to the local electrons on the material. The time needed to achieve steady state condition is also a dependent of emission current. After a period of time the primary electron incidence induces strain throughout the 7.5-cm-by-5-cm plate despite the fact that the beam diameter is only 1 cm2. One possibility is blooming due to electron movement under intense electric fields in the dielectric material.

Piezoelectric materials in the forms of both bulk and thin-film have been widely used as actuators and sensors due to their electromechanical coupling. The characterization of piezoelectric materials plays an important role in determining device performance and reliability. Instrumented indentation is a promising method for probing mechanical as well as electrical properties of piezoelectric materials. The use of instrumented indentation to characterize the properties of piezoelectric materials requires analytical relations. Finite element methods are used to analyze the indentation of piezoelectric materials under different mechanical and electrical boundary conditions. For indentation of a piezoelectric half space, a three-dimensional finite element model is used due to the anisotropy and geometric nonlinearity. The analysis is focused on the effect of angle between poling direction and indentation-loading direction on indentation responses. For the indentation by a flat-ended cylindrical indenter, both insulating indenter and conducting indenter without a prescribed electric potential are considered. The results reveal that both the indentation load and the magnitude of the indentation-induced potential at the contact center increase linearly with the indentation depth. For the indentation by an insulating Berkovich indenter, both frictionless and frictional contact between the indenter and indented surface are considered. The results show the indentation load is proportional to the square of the indentation depth, while the indentation-induced potential at the contact center is proportional to the indentation depth. Spherical indentation of piezoelectric thin films is analyzed in an axisymmetric finite element model, in which the poling direction is anti-parallel to the indentation-loading direction. Six different combinations of electrical boundary conditions are considered for a thin film perfectly bonded to a rigid substrate under the condition of the contact radius being much larger than the film thickness. The indentation load is found to be proportional to the square of the indentation depth. To analyze the decohesion problem between a piezoelectric film and an elastic substrate, a traction-separation law is used to control the interfacial behavior between a thin film and an electrically grounded elastic substrate. The discontinuous responses at the initiation of interfacial decohesion are found to depend on interface and substrate properties.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39).
The goal of this thesis is to explore ways of harvesting energy from a building. To be more specific, the conversion of mechanical energy into electrical energy using piezoelectric materials is studied. Applications of piezoelectric materials as actuators are also explored, with particular interest in the question: what is the maximum moment that an actuator, whose energy comes from piezoelectricity, can develop when attached to a beam. As a piezoelectric material cannot generate much energy, and often requires amplification, the goal is to optimize the circuit linked to the piezoelectric material to obtain as much power as possible.
by Antoine Ledoux.
M.Eng.

Following the studies of natural frequency based damage detection methods, an advanced technique for damage detection and localization in beam-type structures using a vibration characteristic tuning procedure is developed by an optimal design of piezoelectric materials. Piezoelectric sensors and actuators are mounted on the surface of the host beam to generate excitations for the tuning via a feedback process. The excitations induced by the piezoelectric effect are used to magnify the effect of the damage on the change of the natural frequencies of the damaged structure to realize the high detection sensitivity. Based on the vibration characteristic tuning procedure, a scan-tuning methodology for damage detection and localization is proposed. From analytical simulations, both crack and delamination damage in the beams are detected and located with over 20% change in the natural frequencies. Finite element method (FEM) simulations are conducted to verify the effectiveness of the proposed methodology.
October 2016