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Title: Modeling of ultrasonic guided wave field generated by piezoelectric transducers
Author: Marty, Pierre Noel
ISNI:       0000 0001 3620 4388
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2002
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The thesis investigates some aspects of the fundamental science necessary for the development of piezoelectric sensors for use in integral structural inspection systems based on ultrasonic Lamb waves. It is particularly concerned with the analysis of the electromechanical interaction, the process of generation of Lamb wave modes and the design of permanently attached transducers such as PVDF-based interdigital transducers (IDT) or ceramic-based piezoelectric strips. Interdigital transducers developed for use in smart structures are now at the stage where practical applications on plate and pipe structures are being considered. For such a transducer to be used, it is necessary to understand exactly the electromechanical interaction and the internal scattering phenomena governing their performance. An analytical investigation into the interactions that occur between mechanical fields and electric quantities is presented. This model is developed for a simple transducer design, a single-strip transducer under plane strain conditions. A computer model for predicting the acoustic field generated by a given voltage applied to the transducer and vice-versa is presented. This model is developed on the basis of normal mode theory and perturbation methods, providing flexibility and physical insight. Intermediate calculations as well as final results are validated using the finite element model developed in parallel with this work. Since the analytical model is based on assumptions mainly related to the perturbation methods, these are discussed and limits of the model as well as its eventual extensions are drawn. The thesis is also concerned with a numerical analysis based on the finite element method. A finite element formulation that includes the piezoelectric or electroelastic effect alongside the dynamic matrix equation of electroelasticity and its reduction to the well-known equation of structural dynamics, based on a strong analogy between electric and elastic variables, is presented. It is shown how these equations were incorporated in an already existing finite element code. In parallel with validation, results are produced to identify several important features that are not taken into account in the analytic model. Results are presented for IDTs and checked against experimental data when measuring displacement field amplitudes using a laser probe.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available