The interaction of complex harmonic elastic waves with periodically corrugated surfaces and with anisotropic viscoelastic and/or piezoelectric layered media

CHAPTER II: Introduction Chapter II Introduction My admiration for waves originates from the observation of sea waves in Sri Lanka in June 1997. Nevertheless, the destructive power of waves on that same spot on December 26, 2004, when a tsunami hit, destroying the lives of too many people, has uncovered the dark side of the sea. The message of the tsunami was loud and clear : “Nature gives and Nature takes! Scientists can only observe and attempt to understand.” This dissertation is the result of my research that started in October 2001. Prior to October 2001, I have written a Master’s thesis under the supervision of Rudy Briers and Oswald Leroy, entitled “A theoretical treatment of the diffraction of linear and circular polarized ultrasonic plane waves at a periodically rough solid-liquid interface” (Institute of Astronomy, Department of Physics, KU Leuven, 2000). After my graduation in the summer of 2000, I have developed my background in acoustics as a volunteer researcher in the Research Group on Physical Acoustics and Acousto-Optics (KU Leuven Campus Kortrijk) of Oswald Leroy, under Leroy’s promotership and the co-promotership of Rudy Briers and Joris Degrieck. After Leroy’s retirement, I have joined the research team of Joris Degrieck (Department of Mechanical Construction and Production, Ghent University), under Degrieck’s promotership and the co- promotership of Oswald Leroy. My salary has been paid since October 2001 by the IWT, for which I’m very grateful! So far, my work has resulted in 25 published/accepted papers in international journals of Thomson’s science citation index. Furthermore, I’ve had the pleasure to make over 40 presentations at congresses all over the world. Professionally, this output is mainly the result of a motivation, coming from the collegial atmosphere at international conferences (following strict deadlines), as well as from the mutual respect for my promoters and colleagues. Each chapter of this dissertation contains a number of sections. I have intended to make every section self-contained. This means that there are no cross references between different sections and it also means that, from time to time, short explanations or one or two figures are repeated. The reason for this is the ease to read the dissertation in relative short portions, which is a necessary requirement in nowadays academic world, overloaded by meetings and administration. The sequence of chapters does not necessarily reflect the temporal development. Nevertheless, it is attempted to follow a constructive series, in which each chapter makes the consecutive pieces better understandable and each chapter makes the preceding portions better understood. - 49 -