Propagation of ultrasound in inhomogeneous viscoelastic media.

In this thesis an investigation was centered on models of inhomogeneous viscoelastic media, which consisted of glass beads (lead and soda glass) embedded in a silicone rubber matrix (RTV-602). The specimens were classified into groups according to the nominal size of the glass beads content (mean diameter ranging from 63.8 pm to 582 pm) in a range of concentrations (up to 5% volume). Ultrasonic velocity and attenuation as a function of frequency were measured by transmission techniques in the range of 0 to 10 MHz. An extended investigation was centered on the effects of diffraction on velocity and attenuation measurements. The effects of diffraction in distilled water were found to be in good agreement with modified mathematical transducer models. The measured velocity and attenuation in the specimens were compared with theoretical predictions based on the multiple scattering of waves formulation of Waterman and Truell (1961) in combination with the Kramers-Kronig relationship between absorption coefficient and phase-velocity dispersion in the constituent materials of the specimens. Good agreement was obtained between the experimental and the theoretical approaches used, which suggest their applicability for inhomogeneous viscoelastic materials. From the attenuation coefficient and velocity, the composition of materials can be determined. The attenuation coefficient was shown to be a more reliable acoustic parameter than velocity, although both are necessary for a complete characterization of composite materials