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Title: Study of piezoelectric transducers in smart structure applications
Authors: Lam, Kwok-ho
Keywords: Hong Kong Polytechnic University -- Dissertations
Piezoelectric transducers
Piezoelectric ceramics
Smart materials
Smart structures
Issue Date: 2005
Publisher: The Hong Kong Polytechnic University
Abstract: To develop a novel smart material in civil engineering applications, cement-based 1-3 composites have been fabricated and characterized. The feasibility of the embedded 1-3 composite transducers in structural monitoring applications have been demonstrated in this project. In the present work, piezoelectric ceramic discs and fibres were fabricated and used as the active phases of the 1-3 composites. Lead zirconate titanate (PZT) ceramic discs were fabricated using a conventional dry pressing method. All the parameters of PZT ceramics have been evaluated by a resonance technique. Crack-free PZT ceramic fibres were fabricated using a simple powder mixing method. The microstructural and electrical characterizations show that performance of the ceramic fibres can be comparable to that of the corresponding bulk ceramics. To study the piezoceramic / cement 1-3 composites, the properties of cement have been studied as a function of water content. The elastic properties of cement with different water / cement ratios were characterized using the ultrasonic immersion method. It was found that the cement paste with water / cement ratio of 0.5 is relatively "soft" to be used as the passive phase of a 1-3 composite. When comparing with the ceramics, the acoustic impedance of cement is much closer to that of concrete.
Piezoelectric PZT / cement 1-3 composites with a wide range of the ceramic volume fraction (ø = 0.25-0.77) have been fabricated successfully using a dice-and-fill technique. Piezoelectric properties of the 1-3 composites were determined by a resonance technique. The characterization showed that the high piezoelectric characteristics of ceramics were maintained and the effective acoustic impedance of composites was reduced as expected. Even the phase matrix is the cement paste, the thickness electromechanical coupling coefficient kt of the 1-3 composites can be enhanced effectively which approaches to the k₃₃ coefficient of the ceramics. The 1-3 composites were found to have reasonable piezoelectric properties that agree quite well with a theoretical modelling. For studying the performance of cement-based 1-3 composites with low ø, composites with low PZT volume fractions ranged from 0.05 to 0.22 have been fabricated by incorporating PZT fibres into the passive cement matrix. It was found that the thickness electromechanical coupling coefficient kt of the composites could reach around 0.5 even the PZT volume fraction is low. The measured parameters are comparable to the analytical approximations of the modified series and parallel model. The measured piezoelectric coefficient of 1-3 composites with very low PZT volume fraction was found to fit the modelling based on an elastic model. The cement-based 1-3 composites have been embedded and evaluated in-situ in the cement paste to study the feasibility of the composites in structural monitoring applications. To compare the performance the embedded 1-3 composite transducer, a ceramic disc was also embedded. Laser vibrometry and acoustic sensing were used to evaluate the performance of the embedded transducers experimentally. With the analysis of finite element modelling, the vibration motion of the host structure was studied. Because of the good piezoelectric performance and the appropriate acoustic impedance of the 1-3 composites, the results have shown that the cement-based 1-3 composites have potential to be used in structural monitoring applications. Original results on the study of PZT cement-based 1-3 composites and embedded composite transducers in smart structure applications have been reported in the thesis.
Description: xxvii, 206, xvi leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P AP 2005 Lam
Rights: All rights reserved.
Appears in Collections:Thesis

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