Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation presents the development of a system for converting the mechanical energy from vibrations into electrical energy. The conversion is performed in a low-cost piezoelectric transducer, commonly known as buzzer. The main purpose of this system is to charge, or to extend the time between charges, of chargeable batteries up to 2V. In order to control the charging process, an integrated energy processor was also designed. Processor design is presented from its specification, followed by circuit topology definition, electric simulation, layout, extraction of circuit from layout and a final simulation including layout effects. The main contribution of the investigation is to show how much energy could be obtained from vibrations with a low-cost transducer, comparing its performance to full custom generators. The final system implementation is very simple, composed by a generator (a buzzer with a steel ball glued onto its center) and an integrated circuit that controls the charge delivered to the battery, sensing the voltage across its terminals. An efficiency of 55% is expected, being comparable to results published by other researchers. / Esta dissertação apresenta o desenvolvimento de um sistema para converter energia mecânica de vibrações em energia elétrica. A conversão é realizada através de um transdutor de baixo custo comumente chamado de buzzer. O principal objetivo deste sistema é carregar ou estender o tempo entre cargas de baterias recarregáveis de até 2 V. Para o controle do processo de carga, um processador de energia integrado também foi desenvolvido. O projeto do processador de energia é apresentado segundo especificações como definição de topologia, simulação elétrica, layout, extração elétrica do circuito através do layout e a simulação final incluindo os efeitos do layout. A principal contribuição desta dissertação é mostrar como muita energia poderia ser obtida de vibrações com um transdutor de baixo custo, comparando sua performance a outros microgeradores. O sistema final implementado é muito simples, composto por um microgerador (buzzer com uma esfera de aço colada no centro) e um circuito integrado que controla a carga da bateria, através da monitoração da tensão da mesma. Uma eficiência de 55% é esperada, sendo comparável com os resultados obtidos por outros pesquisadores.

Bismuth layer-structured ferroelectrics have received significant attention recently due to their fairly high TC and good fatigue endurance which make them important candidates for non-volatile ferroelectric random access memories (Fe-RAMs) as well as for the piezoelectric device applications at high temperatures. Structure of these compounds is generally described as the pseudo-perovskite block (An-1BnO3n+1)2- sandwiched between the bismuth oxide layers (Bi2O2)2+ along the c-axis, where n represents the number of corner sharing BO6 octahedra forming the perovskite-like slabs. Only a few compounds belonging to this family show relaxor behavior (frequency dependent diffuse phase transition). Relaxor ferroelectrics are very attractive for a variety of applications, such as capacitors, sensors, actuators, and integrated electromechanical systems. The present work attempts to understand the mechanism of relaxor behavior in Aurivillius oxides as well as to improve the piezoelectric and ferroelectric properties of some of the known phases. Details pertaining to the fabrication and characterization of BaBi4Ti4O15 (n = 4 member of Aurivillius family of oxides) ceramics are presented. X-ray diffraction, Raman spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were employed to probe the structural and microstructural details. The contribution of irreversible domain wall movement to the room temperature dielectric constant and polarization was quantitatively evaluated using the nonlinear dielectric response. Dielectric dispersion and conduction mechanism of these ceramics are also explicated using the complex impedance spectroscopy. The effects of La3+ and Ca2+ doping on the phase transition behavior and other properties of BaBi4Ti4O15 are investigated. La3+ doping for Bi3+ was found to strengthen the relaxor behavior. New compounds such as CaNaBi2Nb3O12, SrNaBi2Nb3O12, Na0.5La0.5Bi4Ti4O12, etc. belonging to the Aurivillius family of oxides have been synthesized and investigations concerning their structural, dielectric and ferroelectric properties are presented. Rietveld refinement of room temperature X-ray powder data suggested that CaNaBi2Nb3O12 and SrNaBi2Nb3O12crystallize in the orthorhombic space group B2cb. SrNaBi2Nb3O12 ceramics exhibited frequency-dependent Tm which follows the Vogel-Fulcher relation implying a relaxor nature. No frequency dependence of Tm was observed for CaNaBi2Nb3O12 ceramics. Polarization - electric field hysteresis loops recorded well above Tm confirmed the coexistence of polar and non-polar domains in SrNaBi2Nb3O12 ceramics. Dielectric anomaly observed around 675 K for CNBN corresponds to the ferroelectric to paraelectric phase transition which is accompanied by the change in crystal structure from orthorhombic to tetragonal. Fe and Nb co-doped Bi4Ti3O12 ceramics were fabricated and characterized for their structural, electrical and magnetic properties.