published_or_final_version / Chemistry / Master / Master of Philosophy

Thesis (Ph.D.)--Drexel University, 2009. / Includes abstract and vita. Includes bibliographical references (leaves 234-251).

Thesis (Ph.D.)--Drexel University, 2009. / Includes abstract and vita. Includes bibliographical references (leaves 183-192).

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 135-155).

Thesis (Ph.D.) - Simon Fraser University, 2005. / Theses (Dept. of Chemistry) / Simon Fraser University.

Thesis (Ph.D.) - Simon Fraser University, 2005. / Theses (Dept. of Chemistry) / Simon Fraser University.

Thesis (M.S. in Materials Science and Engineering)--Washington State University. / Includes bibliographical references.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Actuator placement algorithm; piezoelectric actuators; LQR; Galerkin; supervisory control; active vibration control; FEA; switching policy; dSPACE. Includes bibliographical references (p. 58-64).

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-12-14Bitstream added on 2014-06-13T20:16:16Z : No. of bitstreams: 1 camara_fho_me_ilha.pdf: 1061097 bytes, checksum: dd65d1481cdc65c74077f24ca53e3b77 (MD5) / 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

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.