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Master's Dissertation
DOI
https://doi.org/10.11606/D.76.1998.tde-08042014-151001
Document
Author
Full name
Flávio Pandur Albuquerque Cabral
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1998
Supervisor
Committee
Alves, Neri (President)
Altafim, Ruy Alberto Corrêa
Tannus, Alberto
Title in Portuguese
Medidas das constantes dielétricas e deslocamento elétrico em dielétricos: desenvolvimento da técnica e metodologia
Keywords in Portuguese
Constante dielétrica
Efeitos não-lineares
Histerese
Polímeros ferroelétricos
Abstract in Portuguese
Desenvolveu-se um sistema para medir a constante dielétrica complexa de amostras dielétricas, de construção simples, versátil e de baixo custo. A medida é feita aplicando-se uma tensão senoidal e fazendo-se a aquisição do sinal aplicado e do sinal da resposta elétrica (carga elétrica). Emprega-se uma placa A/D para a aquisição de dados com taxa de amostragem de 100 Ksamples/seg e através da transformada de Fourier discreta destes sinais determina-se a impedância complexa da amostra, a partir da qual calcula-se a constante dielétrica complexa. A placa utilizada e o circuito de medida da carga elétrica introduzem defasagens indesejáveis nos sinais, cujas correções são feitas através de programa no computador usado para aquisição dos sinais. O sistema mostra um desempenho similar àqueles dos equipamentos comerciais para freqüências no intervalo de 0,1H.z a 1KHz, sendo testado com componentes resistivos e capacitivos e posteriormente em amostras de Teflon FEP, poli(fluoreto de vinilideno) e seus copolímeros com trifluoretileno. O sistema também foi utilizado para medir o deslocamento elétrico nos polímeros ferroelétricos sob a aplicação de campos elevados. Neste caso determinaram-se as curvas de histerese dielétrica e os deslocamentos de primeira, segunda e terceira ordem.
Title in English
Measurements of dielectric constant and dielectric displacement: development of technique and methodology
Keywords in English
Dielectric constant
Ferroelectric polymers
Hysteresis
Nonlinear dielectric constant
Abstract in English
A low cost and a simple experimental system for measuring the complex dielectric constant of dielectric samples were developed. Measurements were performed measuring the electric charge response resulting from the application of a sinusoidal voltage. The system was based on an A/D acquisition board with sampling rate of 100 Ksamples/sec. The complex impedance was calculated using the discrete Fourier transform from which the complex dielectric constant was found. The phase differences introduced by the A/D board and the amplifiers circuits were connected by software. The setup showed that the results are comparable to that ones obtained with commercial impedance analyzers in the range of frequencies between 0.1 Hz and 1 KHz. Such measurements were obtained using resistors and/or capacitors and also using samples of Teflon FEP, PVDF and its copolymers with trifluorethylene. The setup was also capable to measure the electric displacement in ferroelectric polymers submitted to high fields. Hysteresis loops and the nonlinear electric displacement of first, second and third order were measured.
 
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Publishing Date
2014-04-09
 
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