Due to decreasing power requirements for wireless networks and other microwatt devices, energy harvesting from ambient vibrations has become a realized power source. Piezoelectric cantilevers are a viable option as the transducer element for converting mechanical to electrical energy. Being able to accurately model piezoelectric cantilevers is important in designing efficient converters needed in the power management circuitry. In this thesis a method is outlined that enables the modeling of the physical behaviour of piezoelectric cantilevers with an equivalent circuit model comprised of RLC circuits. A MatLab model of piezoelectric cantilevers is developed and verified via literature comparisons. The equivalent circuit model, which is particularly important in electrical engineering of power management circuity, is demonstrated with a proof-of-concept harvester unit design. In the process and for a fraction of the traditional cost, the accuracy and usability of a low-cost vibration shaker is shown. The design is tested on two real-world applications. The first application is a transformer that has regular vibrations with low harmonic content. The second application are industrial fans with high harmonic content vibrations. The results of both applications show that energy harvesting is possible with a simplistic approach as presented. Further it is shown that high harmonic content, such as was found in the fans, can interfere with energy harvesting in both a constructive and destructive manner leading to further analysis. These findings have implications in designing vibrational energy harvester units as discussed.

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Esta dissertação aborda fundamentalmente a formação de eletretos de Teflon FEP em múltiplas camadas com carregamento por descargas impulsivas de alta tensão. Devido a suas excelentes qualidades piezoelétricas, eles serão destinados a sensores de pressão em múltiplas aplicações. Este tipo de eletreto foi escolhido por se utilizar materiais com grande disponibilidade no mercado e de custo bastante reduzido. O processo de carregamento por altas tensões impulsivas também foi escolhido devido à sua simplicidade, segurança e tempo reduzido. Para se obter maior valor de constantes piezoelétricas foi utilizado o processo de formação de eletretos por multicamadas, e a metodologia empregada utiliza verniz tanto na união das folhas de Teflon FEP quanto na junção dos eletrodos de alumínio. Dessa forma, microbolhas de ar são criadas entre os materiais, que carregadas eletricamente, formando o eletreto. Com tal artifício, é possível obter coeficientes piezoelétricos d33 elevados sem o uso de materiais de alta tecnologia ou de restrita tecnologia. O método de obtenção do eletreto apresenta um custo extremamente reduzido - pelo emprego de materiais simples e de fácil obtenção - e a diversidade de possibilidades de aplicações, o que torna o método bastante atraente, podendo, ainda, tornar o país independente de tecnologia importada. / This dissertation approaches fundamentally the formation of electrets of Teflon FEP in multiple layers by impulsive discharges. Due to their excellent piezoelectric qualities, they will be destined to sensors of pressure in multiple applications. This electret type was chosen due to its easiness of obtaining, by using low-cost common materials easily found in the market. The process of loading by high impulsive tensions was chosen due to its simplicity, safety and reduced necessary time. To reach higher values of piezoelectrics constant the process of electrets formation in multilayers was used, and the methodology employed varnish in the union of both FEP Teflon films and aluminum electrodes. In this way, micro bulbs of air is created among the materials, which were later loaded electrically, forming the electret. With such artifice, it is possible to obtain high piezoelectrics d33 coefficients without using materials of high or restricted technology. The simplicity of the method of electret obtaining, the extremely reduced cost - by the use of simple and easy - of - obtaining materials - and the diversity of application possibilities, make the method quite attractive. By using such method, the country may even become independent of imported technology.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 140-141). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 140-141). Also available on the Internet.

Thesis (Ph.D.)--Drexel University, 2010. / Includes abstract. Includes bibliographical references (leaves 225-236).

a b s t r a c t A study concerning the propagation of free non-axisymmetric waves in a homogeneous piezoelectric cylinder of transversely isotropic material with axial polarization is carried out on the basis of the linear theory of elasticity and linear electro-mechanical coupling. The solution of the three dimensional equations of motion and quasi-electrostatic equation is given in terms of seven mechanical and three electric potentials. The characteristic equations are obtained by the application of the mechanical and two types of electric boundary conditions at the surface of the piezoelectric cylinder. A novel method of displaying dispersion curves is described in the paper and the resulting dispersion curves are presented for propagating and evanescent waves for PZT-4 and PZT-7A piezoelectric ceramics for circumferential wave numbers m = 1, 2, and 3. It is observed that the dispersion curves are sensitive to the type of the imposed boundary conditions as well as to the measure of the electro-mechanical coupling of the material.

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