The presented work aims to optimize the performance of piezoresistive cantilevers in cases where the output signal originates either from a static deflection of the cantilever or from the dynamic (resonance) characteristic of the beam. Based on a new stress concentration technique, which utilizes silicon beams and wires embedded in the cantilever, the force sensitivity of the cantilever is increased up to 8 fold with only about a 15% decrease in the cantilever stiffness. Moreover, the developed stress-concentrating cantilevers show almost the same resonance characteristic as conventional cantilevers. The focus of the second part of the present work is to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental and higher flexural resonance at atmospheric pressure. The applied methodology is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the measurement data. To this end, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11 and 17 um and lengths and widths ranging from 70 to 1050 um and 80 to 230 um, respectively, have been fabricated and tested. To better describe the experimental data, modified models for air damping have been developed. Moreover, to better understand the damping mechanisms in a resonant cantilever system, analytical models have been developed to describe the cantilever effective mass in any flexural resonance mode. To be able to extract reliable Q-factor data for low signal-to-noise ratios, a new iterative curve fitting technique is developed and implemented. To address the challenge of frequency drift in (mass-sensitive) resonant sensors, and especially cantilever-based devices, the last part of the research deals with a novel compensation technique to cancel the unwanted environmental effects (e.g., temperature and humidity). This technique is based on exploring the resonance frequency difference of two flexural modes. Experimental data show improvements in temperature and humidity coefficients of frequency from -19.5 to 0.2 ppm/˚C and from 0.7 to -0.03 ppm/%RH, respectively. The last part of the work also aims on techniques to enhance or suppress the flexural vibration amplitude in desired overtones.

Made available in DSpace on 2014-06-11T19:30:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-01-08Bitstream added on 2014-06-13T18:40:52Z : No. of bitstreams: 1 baptista_fg_dr_ilha.pdf: 1105245 bytes, checksum: d9df8c940603a26591e01168eaac4aaa (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A técnica da impedância eletromecânica (E/M) tem sido amplamente pesquisada para o desenvolvimento de sistemas de SHM (Structural Health Monitoring – monitoramento de integridade estrutural) em diversas aplicações. Embora existam muitos trabalhos que indiquem a eficiência e a viabilidade dessa técnica, alguns problemas práticos em aplicações reais ainda precisam ser investigados. A medição da impedância elétrica, etapa básica da técnica, geralmente é realizada por instrumentos comerciais volumosos, pesados e de alto custo, características proibitivas para muitas aplicações. A seleção da faixa de frequência em que a impedância deve ser medida para assegurar boa sensibilidade ao dano é feita por métodos de tentativa e erro ou por metodologias que utilizam dados medidos em uma quantidade considerável de testes. Além disso, o dimensionamento dos transdutores é feito sem um embasamento teórico, independentemente das características da estrutura monitorada. Neste trabalho é proposto um sistema de medição de impedância elétrica rápido, versátil e de baixo custo que substitui com eficiência os instrumentos comerciais. A partir de um circuito eletromecânico equivalente, o efeito de carregamento do transdutor devido à estrutura monitorada foi analisado. A análise do efeito de carregamento permite dimensionar corretamente o transdutor de acordo com a estrutura monitorada e assegurar um bom desempenho do sistema. O circuito eletromecânico também foi utilizado para determinar, teoricamente, as faixas de frequência em que o transdutor tem boa sensibilidade e auxiliar na seleção da faixa de frequência adequada para a detecção de danos estruturais. Todas as metodologias propostas foram verificadas através de experimentos em estruturas de alumínio e houve uma boa concordância entre os resultados teóricos e experimentais / The electromechanical (E/M) impedance technique has been widely studied for the development of Structural Health Monitoring (SHM) systems in various applications. Although there are many studies indicating the effectiveness and feasibility of this technique, some practical issues in real applications yet should be investigated. The electrical impedance measurement, basic stage of the technique, is usually performed by bulky, heavy and expensive instruments; these features are prohibitive for many applications. The selection of the frequency range in which the electrical impedance must be measured to ensure good sensitivity for damage detection is performed by trial and error methods or by methodologies that use measured data in a considerable amount of tests. Furthermore, the design of the transducer is done without theoretical basis, regardless the characteristics of the host structure. In this work, a fast, versatile and low-cost electrical impedance measurement system was developed; the proposed system successfully replaces the conventional instruments. From an equivalent electromechanical circuit, the transducer loading effect due to the host structure was analyzed. The analysis of the loading effect allows the correct design of the transducer according to the host structure for ensure a good performance of the system. The electromechanical circuit was also used to theoretically determine the frequency ranges in which the transducer has good sensitivity and assist in the selection of the suitable frequency range for structural damage detection. All proposed methodologies were validated by experimental tests on aluminum structures and there was a good match between the theoretical and practical results

Materiais piezocompósitos laminados são compostos por camadas de material piezelétrico, metálico e compósito (matriz epóxi com fibras de carbono ou de vidro), que possibilitam obter vantagens em relação aos materiais piezelétricos convencionais, permitindo obter características superiores que não podem ser conseguidas pelos seus componentes de forma isolada como, por exemplo, maior flexibilidade e resistência mecânica ou menor peso. Sob esse enfoque, este trabalho tem por objetivo o desenvolvimento de Estruturas Piezocompósitas Laminadas (EPLA) que consistem basicamente em estruturas multicamadas, através do projeto da sua resposta transiente e harmônica visando aplicações dinâmicas. Entre as potenciais aplicações dessas estruturas, tem-se atuadores, motores, sonares e dispositivos de coleta de energia (\"energy harvester\"), sendo de muito interesse a melhora das suas características dinâmicas e o seu desempenho. O projeto dinâmico de uma EPLA é complexo, porém pode ser sistematizado utilizando o Método de Otimização Topológica (MOT). O MOT é um método baseado na distribuição de material num domínio de projeto fixo com o objetivo de extremizar uma função de custo sujeita às restrições inerentes do problema, combinando algoritmos de otimização e de elementos finitos. A formulação de MOT para o projeto dinâmico de EPLA pretende determinar tanto a topologia ótima dos materiais nas diferentes camadas quanto o sinal de polarização do material piezelétrico e o ângulo da fibra na camada compósita, tendo como finalidade a maximização da amplitude de vibração em pontos determinados (em atuadores) ou da geração de energia elétrica a partir de excitações mecânicas (em coletores de energia). Além disso, é formulado um problema combinando os enfoques harmônico e transiente com o intuito de customizar a resposta da EPLA, de modo que, o nível da resposta seja o mesmo perante diferentes tipos de onda de excitação (transdutores multi-entrada). O trabalho inclui as etapas de projeto, simulação, fabricação e caracterização de protótipos. / Laminated piezocomposite materials are composed by layers of piezoelectric, metal and composite material (epoxy matrix with carbon or glass fiber), which have advantages over conventional piezoelectric materials, because of their superior characteristics, which cannot be achieved by any of its components isolated, for example, more flexibility and strength and less weight. Under this approach, this work aims at the development of Laminated Piezocomposite Structures (LAPS) what primarily consist of multi-layer structures, through the transient and harmonic response design aiming at dynamic applications. Among the potential applications of these structures it can be cited actuators, motors, sonar devices and energy harvester, being of great interest the improvement of its dynamic characteristics and performance. The dynamic design of a LAPS is complex however it can be systematized by using the Topology Optimization Method (TOM). The TOM is a method based on the distribution of material in a fixed design domain with the aim of extremizing a cost function subject to constraints inherent to the problem by means of combining the optimization algorithms and the finite element method (FEM). The TOM formulation for the LAPS dynamic project aims to determine together the optimal topology of the materials for different layers, the polarization sign of the piezoelectric material and the fiber angle of the composite layer, in order to maximize the vibration amplitude at certain points (in actuators), or the generation of electrical energy from mechanical excitations (in energy harvesters). In addition, a TOM problem combining harmonic and transient approaches is formulated with the purpose of customizing EPLA response so that the response level is the same for different excitation waveforms (multi-entry transducers). The work includes design, simulation, manufacturing and characterization of prototypes.

Transdutores baseados em cascas piezocompósitas têm uma vasta aplicação no campo de estruturas inteligentes, principalmente como atuadores, sensores e coletores de energia. Essas estruturas piezocompósitas são geralmente compostas por dois ou mais tipos de materiais, como por exemplo materiais piezelétricos, ortotrópicos elásticos (possuem fibras de reforçamento) e isotrópicos (materiais homogêneos). Vários fatores devem ser considerados no projeto de transdutores baseados em cascas piezocompósitas, como o tamanho, a forma, a localização e a polarização do material piezelétrico, bem como a orientação das fibras do material ortotrópico. O projeto desses transdutores é complexo e trabalhos anteriores envolvendo esses tipos de materiais sugerem utilizar Método de Otimização Topológica (MOT) para aprimorar o desempenho dos transdutores distribuindo o material piezelétrico sobre substratos fixos de materiais isotrópicos e ortotrópicos, ou otimizar a orientação das fibras dos materiais ortotrópicos com material piezelétrico com tamanho, forma e localização previamente estabelecidos. Assim, nesta tese, propõe-se o desenvolvimento de uma metodologia baseada no MOT para projetar transdutores piezocompósitos de casca considerando, simultaneamente, a otimização da distribuição e do sentido de polarização do material piezelétrico, e também a otimização da orientação das fibras de materiais ortotrópicos, que é livre para assumir valores diferentes ao longo da mesma camada compósita. Utilizando essa metodologia, são obtidos resultados numéricos para atuadores e sensores em regime estático e para coletores de energia com circuito elétrico acoplado, em regime dinâmico amortecido. Para os casos dos sensores e dos coletores de energia, também são consideradas as tensões mecânicas na estrutura, as quais devem obedecer os critérios de von Mises (para materiais isotrópicos) e de Tsai-Wu (para materiais ortotrópicos) para que não haja falhas na estrutura, que está sujeita a esforços mecânicos. / Transducers based on laminated piezocomposite shell structures have a wide application in the field of smart structures, especially as actuators, sensors and energy harvesting devices. These piezocomposite structures are generally composed by two or more kinds of materials, such as piezoelectric, isotropic, and elastic orthotropic (fiber reinforcement) materials. Several factors must be considered in the design of piezocomposite transducers, such as size, shape, location and polarization of the piezoelectric material and the fiber orientation of the orthotropic material. The design of these transducers is complex and previous studies involving these types of materials suggest using \"Topology Optimization Method\" (TOM) to enhance the performance of piezoelectric transducers by distributing piezoelectric material over fixed isotropic and orthotropic substrate or to optimize the fiber orientation of orthotropic materials with piezoelectric patches previously established. Thus, this thesis proposes the development of a methodology based on the TOM to design laminated piezocomposite shell transducers by considering simultaneously the optimization of distribution and the polarization direction of the piezoelectric material, and also the optimization of the fiber orientation orthotropic material, which is free to assume different values along the same composite layer. By using this methodology, numerical results are obtained for actuators and sensors under static response, and energy harvesting devices with an electrical circuit coupled, in dynamic damped analysis. In the case of sensors and energy harvesting devices, which are subjected to mechanical loads, the mechanical stresses in the structure are also considered, which must satisfy two stress criteria to prevent failure: von Mises for isotropic materials and Tsai-Wu for orthotropic materials.

Orientador: Eduardo Tavares Costa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-11T02:41:16Z (GMT). No. of bitstreams: 1 Zanella_FabioPieroni_M.pdf: 8365446 bytes, checksum: c1fa57572fdaf7e48b08a6a5fb58a524 (MD5) Previous issue date: 2006 / Resumo: O ultra-som na medicina tem passado por enorme evolução nas últimas décadas e ocupado posição de destaque cada vez maior como ferramenta para terapia e diagnóstico. Isso é devido principalmente ao fato de que os equipamentos de diagnóstico por ultra-som são de relativo baixo custo, o ultra-som é uma radiação não-ionizante e permite realização de exame por método não-invasivo e as imagens são geradas e visualizadas em tempo real. Na geração de imagens deste tipo, é comum a utilização de transdutores matriciais. Entretanto, o Brasil apresenta defasagem tecnológica com respeito à construção destes transdutores e à eletrônica envolvida em sua operação. O objetivo deste trabalho consistiu no desenvolvimento de circuitos eletrônicos com 12 canais de geração e de recepção de ondas ultra-sônicas para operação com transdutor matricial linear. O sistema é capaz de excitar transdutores piezoelétricos e receber ecos ultra-sônicos na faixa de 0,5 a 30 MHz e tem seus circuitos de recepção protegidos contra a alta tensão dos pulsos gerados para a excitação do transdutor. Os disparos dos elementos do transdutor e o tempo de corte dos sinais nos circuitos de recepção, para evitar receber sinais indesejáveis referentes ao período inicial de oscilação do transdutor, são controlados via circuito com microcontrolador PIC 16F877 que, juntamente com o programa de controle, foram desenvolvidos para conectar o sistema a um microcomputador. Os 12 canais foram caracterizados eletricamente e verificou-se seu funcionamento utilizando um transdutor piezoelétrico linear de 12 elementos com 1 MHz de freqüência central, especialmente desenvolvido para este trabalho. Os resultados mostraram que o sistema funciona adequadamente, gerando imagem de um phantom construído em nosso laboratório / Abstract: Ultrasound in medicine has gone through great evolution in the last few decades and has occupied important position as a tool for therapy and diagnosis. This is due to the ultrasound equipment be of relatively low-cost, ultrasound is a non-ionizing radiation, is a non-invasive imaging method, and the images are created and seen in real time. It is common the use of transducer arrays in order to generate this kind of image. There is a lack of know how in Brazil relative to the construction of these transducers and the involved electronics in their operation. The objective of this work was the development of a multi-purpose 12 channel pulser/receiver electronic circuitry to operate with linear transducer arrays. The system is able to fire ultrasound piezoelectric transducers and to receive ultrasound echo signals in the range 0.5-30 MHz. The system has reception circuits with protection against high voltage pulses. The firing of transducer elements and cutting time of the reception circuits, to avoid unwanted signals of natural initial transducer oscillations, can be controlled via PIC 16F877 hardware and software designed to connect the system to a microcomputer. The electrical characteristics of the 12 channel pulser/receiver and its use in firing a specially constructed 1 MHz 12 element PZT transducer array has been carried out and the images of a specially constructed phantom showed that it can be used in laboratory conditions / Mestrado / Engenharia Biomedica / Mestre em Engenharia Elétrica

Orientador: Eurípedes Guilherme de Oliveira Nóbrega / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T01:49:32Z (GMT). No. of bitstreams: 1 Souza_PabloRodrigode_D.pdf: 10455045 bytes, checksum: b8461069008fc0a12ec07525f9bd8d2e (MD5) Previous issue date: 2013 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The abstract is available with the full electronic document / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

Contactless ultrasonic power transfer (UPT), using piezoelectric transducers, is based on transferring energy using acoustic waves, in which the waves are generated by an acoustic source or transmitter and then transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver then converts the mechanical strain induced by the incident acoustic waves to electricity and delivers to an electrical load, in which the electrical power output of the system can be determined. The execution and efficiency of this technology can be significantly enhanced through patterning, focusing, and localization of the transmitted acoustic energy in space to simultaneously power pre-determined distributed sensors or devices. A passive 3D-printed acoustic hologram plate alongside a single transducer can generate arbitrary and pre-designed ultrasound fields in a particular distance from the hologram mounted on the transmitter, i.e., a target plane. This dissertation presents the use of these simple, cost-effective, and high-fidelity acoustic holograms in UPT systems to selectively enhance and pattern the electrical power output from the receivers. Different holograms are numerically designed to create single and multi-focal pressure patterns in a target plane where an array of receivers are placed. The incident sound wave from a transmitter, after passing through the hologram, is manipulated, hence, the output field is the desired pressure field, which excites the receivers located at the pre-determined focal points more significantly. Furthermore, multi-functional holograms are designed to generate multiple images at different target planes and driving frequencies, called, respectively, multi-image-plane and multi-frequency patterning holograms. The multiple desired pressure distributions are encoded on the single hologram plate and each is reconstructed by changing the axial distance and by switching the frequency. Several proof-of-concept experiments are performed to verify the functionality of the computationally designed holograms, which are fabricated using modern 3D-printers, i.e., the desired wavefronts are encoded in the hologram plates' thickness profile, being input to the 3D-printer. The experiments include measurement of output pressure fields in water using needle hydrophones and acquisition of receivers' voltage output in UPT systems. Another technique investigated in this dissertation is the implementation of acoustic impedance matching layers deposited on the front leading surface of the transmitter and receiver transducers. Current UPT systems suffer from significant acoustic losses through the transmission line from a piezoelectric transmitter to an acoustic medium and then to a piezoelectric receiver. This is due to the unfavorable acoustic impedance mismatch between the transducers and the medium, which causes a narrow transducer bandwidth and a considerable reflection of the acoustic pressure waves at the boundary layers. Using matching layers enhance the acoustic power transmission into the medium and then reinforce the input as an excitation into the receiver. Experiments are performed to identify the input acoustic pressure from a cylindrical transmitter to a receiver disk operating in the 33-mode of piezoelectricity. Significant enhancements are obtained in terms of the receiver's electrical power output when implementing a two-layer matching structure. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a high-intensity focused ultrasound (HIFU)-excited microbubble or stable acoustic cavitation, which includes the effects of acoustic nonlinearity, diffraction, and absorption of the medium, and entails the problem of several biomedical ultrasound applications. Finally, the design and use of acoustic holograms in microfluidic channels are addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems. / Doctor of Philosophy / This dissertation presents several techniques to enhance the wireless transfer of ultrasonic energy in which the sound wave is generated by an acoustic source or transmitter, transferred through an acoustic medium such as water or human tissue to a sensor or receiver. The receiver transducer then converts the vibrational energy into electricity and delivers to an electrical load in which the electrical power output from the system can be determined. The first enhancement technique presented in this dissertation is using a pre-designed and simple structured plate called an acoustic hologram in conjunction with a transmitter transducer to arbitrarily pattern and shape ultrasound fields at a particular distance from the hologram mounted on the transmitter. The desired wavefront such as single or multi-focal pressure fields or an arbitrary image such as a VT image pattern can simply be encoded in the thickness profile of this hologram plate by removing some of the hologram material based on the desired shape. When the sound wave from the transmitter passes this structured plate, it is locally delayed in proportion to the hologram thickness due to the different speed of sound in the hologram material compared to water. In this dissertation, various hologram types are designed numerically to implement in the ultrasonic power transfer (UPT) systems for powering receivers located at the predetermined focal points more significantly and finally, their functionality and performances are verified in several experiments. Current UPT systems suffer from significant acoustic losses through the transmission from a transmitter to an acoustic medium and then to a receiver due to the different acoustic impedance (defined as the product of density and sound speed) between the medium and transducers material, which reflects most of the incident pressure wave at the boundary layers. The second enhancement technology addressed in this dissertation is using intermediate materials, called acoustic impedance matching layers, bonded to the front side of the transmitter and receiver face to alleviate the acoustic impedance mismatch. Experiments are performed to identify the input acoustic pressure from a transmitter to a receiver. Using a two-layer matching structure, significant enhancements are observed in terms of the receiver's electrical power output. A design platform is also developed that can facilitate the construction of high-fidelity acoustically matched transducers, that is, the material layers' selection and determination of their thicknesses. Furthermore, this dissertation presents a numerical analysis for the dynamical motions of a microbubble exposed to a high-intensity focused ultrasound (HIFU) field, which entails the problem of several biomedical ultrasound applications such as microbubble-mediated ultrasound therapy or targeted drug delivery. Finally, an enhancement technique involving the design and use of acoustic holograms in microfluidic channels is addressed which opens the door of acoustic patterning in particle and cell sorting for medical ultrasound systems.

A sobreposição de frequências ultrassônicas a uma ferramenta em operações de perfuração, utilizando transdutores piezelétricos, resulta em melhorias na usinagem de metais, garantindo melhor acabamento (ausência de rebarba), redução do tamanho do cavaco e menor desgaste ferramental. A utilização desse tipo de técnica na perfuração de rochas reduz a carga axial e aumenta a velocidade do processo, possibilitando maior profundidade de perfuração, podendo vir a ser muito útil em pesquisas aplicadas à perfuração de reservas petrolíferas e exploração mineral. Este trabalho teve como objetivo simular e aplicar um transdutor piezelétrico ultrassônico de potência para perfuração de rochas e metais. Para as simulações numéricas duas técnicas foram utilizadas: o método dos elementos finitos (MEF) e o método das matrizes em cadeia (MMC). O MEF permitiu análises harmônicas e modais de forma rápida e precisa enquanto o MMC resultou em expressão analítica, possibilitando melhor compreensão dos parâmetros físicos e geométricos envolvidos na performance do transdutor. Ambos os métodos nortearam o projeto do protótipo a ser usado em ensaios de perfuração. Para a construção do protótipo, foi projetado um mandril para a fixação da broca, que foi adaptado a um transdutor de potência de 20 kHz. Ensaios de perfuração de rochas e de discos de alumínio foram realizados com o protótipo. A aplicação do protótipo à perfuração de rochas carbonáticas demonstrou redução no tempo de furação, quando comparada ao método convencional (sem aplicação de ultrassom). Na furação de discos de alumínio, a redução de rebarbas, quebra do cavaco durante a operação e melhor acabamento da peça, são conclusões evidentes das melhorias proporcionadas pela sobreposição de frequências ultrassônicas à broca. / Superposition of high frequency vibration in the tool, driven by a piezoelectric actuator, in a drilling machining process of metals results in some improvements such as finishing quality (without burr), reduction of tool wear and chip dimensions. Similar techniques applied in rock perforation reduce the axial load in the tool, which enhances the process velocity, resulting in deeper perforation. This might be useful in oil and mineral exploration, opening the feasibility of researches in this field. The aim of this work is to simulate and implement an ultrasonic piezoelectric transducer to perforate rocks and metals. Concerning numerical simulation, two techniques were performed: finite element method (FEM) and chain matrix method (CMM). FEM simulations provide fast and effective modal and harmonic analysis. CMM provide mathematical expressions, analytically exposing geometrical and physical parameters involved in the transducer performance. Both methods were the guide and basement for the prototype project, able to perform perforation experiments. For the construction of the prototype, a drill chuck were designed and adapted for a 20 kHz power ultrasonic transducer. Aluminum drilling and rock perforation experiments were carried out with this prototype. A lower perforation time was achieved in carbonate rocks when the ultrasound-aided method was used as opposed to the conventional method. Results in aluminum disks presented burr reduction, better part finishing and breakage of chips during operation. Those results evidently appoint some improvements due to the power ultrasonic superposition in the drilling process.

Orientador: Jozué Vieira Filho / Banca: Vicente Lopes Junior / Banca: Carlos Antonio. Barros Alves / Banca: Carlos de Marqui Junior / Banca: Washington Luiz de Melo / Resumo: A técnica da impedância eletromecânica (E/M) tem sido amplamente pesquisada para o desenvolvimento de sistemas de SHM (Structural Health Monitoring - monitoramento de integridade estrutural) em diversas aplicações. Embora existam muitos trabalhos que indiquem a eficiência e a viabilidade dessa técnica, alguns problemas práticos em aplicações reais ainda precisam ser investigados. A medição da impedância elétrica, etapa básica da técnica, geralmente é realizada por instrumentos comerciais volumosos, pesados e de alto custo, características proibitivas para muitas aplicações. A seleção da faixa de frequência em que a impedância deve ser medida para assegurar boa sensibilidade ao dano é feita por métodos de tentativa e erro ou por metodologias que utilizam dados medidos em uma quantidade considerável de testes. Além disso, o dimensionamento dos transdutores é feito sem um embasamento teórico, independentemente das características da estrutura monitorada. Neste trabalho é proposto um sistema de medição de impedância elétrica rápido, versátil e de baixo custo que substitui com eficiência os instrumentos comerciais. A partir de um circuito eletromecânico equivalente, o efeito de carregamento do transdutor devido à estrutura monitorada foi analisado. A análise do efeito de carregamento permite dimensionar corretamente o transdutor de acordo com a estrutura monitorada e assegurar um bom desempenho do sistema. O circuito eletromecânico também foi utilizado para determinar, teoricamente, as faixas de frequência em que o transdutor tem boa sensibilidade e auxiliar na seleção da faixa de frequência adequada para a detecção de danos estruturais. Todas as metodologias propostas foram verificadas através de experimentos em estruturas de alumínio e houve uma boa concordância entre os resultados teóricos e experimentais / Abstract: The electromechanical (E/M) impedance technique has been widely studied for the development of Structural Health Monitoring (SHM) systems in various applications. Although there are many studies indicating the effectiveness and feasibility of this technique, some practical issues in real applications yet should be investigated. The electrical impedance measurement, basic stage of the technique, is usually performed by bulky, heavy and expensive instruments; these features are prohibitive for many applications. The selection of the frequency range in which the electrical impedance must be measured to ensure good sensitivity for damage detection is performed by trial and error methods or by methodologies that use measured data in a considerable amount of tests. Furthermore, the design of the transducer is done without theoretical basis, regardless the characteristics of the host structure. In this work, a fast, versatile and low-cost electrical impedance measurement system was developed; the proposed system successfully replaces the conventional instruments. From an equivalent electromechanical circuit, the transducer loading effect due to the host structure was analyzed. The analysis of the loading effect allows the correct design of the transducer according to the host structure for ensure a good performance of the system. The electromechanical circuit was also used to theoretically determine the frequency ranges in which the transducer has good sensitivity and assist in the selection of the suitable frequency range for structural damage detection. All proposed methodologies were validated by experimental tests on aluminum structures and there was a good match between the theoretical and practical results / Doutor

In this work passive piezoelectric devices for vibration damping are studied. It is developed the basic idea of synthesizing electrical wave guides to obtain an optimal electro-mechanical energy exchange and therefore to dissipate the mechanical vibrational energy in the electric form. Modular PiezoElectroMechanical (PEM) structures are constituted by continuous elastic beams (or bars) coupled, by means of an array of PZT transducers, to lumped dissipative electric networks. Both refined and homogenized models of those periodic systems are derived by an energetic approach based on the principle of virtual powers. Weak and strong formulation of the dynamical problem are presented having in mind future studies involving the determination of numerical solutions. In this framework the effectiveness of the proposed devices for the suppression of mechanical vibrations is investigated by a wave approach, considering both the extensional and flexural oscillations. The optimal values of the electric parameters for a fixed network topology are derived analytically by a pole placement technique. Their sensitivities on the dimensions of the basic cell of the periodic system and on the design frequency are studied. Moreover the dependence of damping performances on the frequency is analyzed. Comparing the performances of different network topological configurations, the advantages of controlling a mechanical structure with an electric analog are shown. As a consequence of those results, new interconnections of PZT transducers are proposed. An experimental setup for the validation of the analytical and numerical results is proposed and tested. A classical experience on resonant shunted PZT is reproduced. Future experimental work is programmed.