Typescript / 141 leaves : ill., appendix in end pocket / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Experimental determination of the dispersion of Rayleigh waves across Australia has provided information about the earth's crust in this region. This technique is particularly useful in Australia, where in many areas the low level of natural seismicity prohibits the use of more conventional methods of investigation of the crust. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1967

This research studies higher harmonics of Rayleigh surface waves propagating in nickel base superalloys. Rayleigh waves are used because they carry most of the energy and travel along the surface of a specimen where fatigue damage is typically initiated. The energy concentration near the free surface leads to stronger nonlinear effects compared to bulk waves. An ultrasonic piezoelectric transducer together with a plastic wedge is used for the experimental generation of the Rayleigh wave. The detection system consists of a laser heterodyne interferometer. Measurements are performed to detect the fundamental wave as well as the second harmonic. The amplitude ratio is related to the nonlinearity parameter beta which is typically used to describe changes in microstructure and investigate fatigue damage.

Thesis (M.S. in E.S.M.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2004. Directed by Laurence Jacobs and Jianmin Qu. / Includes bibliographical references (leaves 113-117).

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This dissertation descibes the development and the application of a planar acoustic microscope lens. The prototype lens consists of a pair of concentric circular metal electrodes plated on the interface between a piezoelectric solid and a liquid medium. These two circular electrodes excite Rayleigh waves of velocity V(,R) which are converging towards the common centre but which are phase matched to the compressional waves of the velocity V(,c) in the liquid in a very narrow range of zenith angle about a value given by (phi)(,m) = sin('-1)V(,c)/V(,R). The waves radiated into the liquid are thus in the form of a hollow cone converging onto a common focal spot on the lens axis at a distance determined by this zenith angle and the radius of the electrodes. This planar acoustic microscope lens is called the Rayleigh-to-Compressional Conversion (RCC) lens. / Since the lens behavior is determined by the geometry of the electrodes and because of the simplicity of the photolithographic fabrication process of the RCC lens, more complicated configurations can be made as easily as the prototype; for example, semicircular lenses have been produced and analyzed. / A mathematical analysis based on a spatial impulse of stress applied on the solid/liquid boundary has been used to calculate the focussing characteristics of the RCC lens. For isotropic solid not only the particle displacements of the compressional wave in the liquid have been computed, but also that of the waves radiated into the solid. For anisotropic solids only the radiation pattern of the compressional wave in the liquid, which is the one of most interesting, has been investigated using an isotropic equivalent model. In the model the circular shape of the electrodes has been considered to consist of many line segments and it has been used to analyze the focal properties of partial circles and anisotropic substrate. / This planar acoustic microscope lens has been employed in standard transmission and reflection imaging experiments to demonstrate the structure of its focal spot and in particular the lack of spherical aberration when traversing a metal surface. Because of the hollow conical nature of the beam away from the focal region the RCC lens is inherently adapted to dark field microscopy. Some properties of semicircular lens are also given as examples in linear and nonlinear operation. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

This dissertation addresses forward and inverse modeling of Rayleigh waves for near surface investigation. Results were obtained by imaging abandoned mine openings using Rayleigh waves in the laterally inhomogeneous medium. The efficient staggered grid stencil method to solve elastic wave equations using 2-D finite difference technique is presented. This numerical scheme is used to conduct a series of parametric studies on the propagation of Rayleigh waves. The first parametric study was conducted on a flat layered model of increasing and decreasing velocity with depth. A Rayleigh waves dispersion curve is found to be sensitive on a layer’s depth up to half of the minimum wavelength of Rayleigh waves. The phase velocity in the dispersion curve of Rayleigh waves is inversely and directly proportional to the frequency, depending on velocity increase or decrease with depth. The parametric study was carried out by introducing dipping layers in the model with increasing dip. The front (near the shot point) and back (at the end of receiver line) shot records are different if the subsurface contains dip. Dispersion is observed in near offset for down dip and in the far offset for up dip, computed from front and back shots respectively. Finally, a parametric study looked at subsurface anomalies with different shapes and sizes as well as their material properties. A Rayleigh wave is sensitive to very high material contrast and very low material contrast of the anomaly from it surrounding medium. The presence of a low material contrast anomaly from the surrounding medium traps the energy which causes reverberation. A Rayleigh wave is sensitive to an anomaly which is placed within the depth between one-third to half of minimum wavelength of Rayleigh wave from the surface. In order to resolve lateral heterogeneity, a new method is developed in this research which allows localization of the multichannel record in different panels. The dispersion curve of Rayleigh waves is computed in each panel using the slant stack technique. On the basis of parametric studies, an innovative inversion algorithm has been developed to minimize the error norm; ”the sum of the squares of the difference of reference and model dispersion curves” in an iterative way using a Very Fast Simulated Re-annealing (VFSR) technique.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics, 1967. / Typescript.

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published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy