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Title: Waveguides in medical ultrasonics
Author: Nicholson, Nicholas C.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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Waveguides occur in a number of areas of medical ultrasonics, one important application being in sonically-sensitive biopsy-needles. The behaviour of the propagation of ultrasound in waveguides is not widely understood. A model of guided sound-wave propagation in the elastic limit, based on Pochhammer's theory, is described. Characteristic equations for both real and imaginary arguments are derived for isotropic solid and hollow cylindrical waveguides and also for transversely-isotropic solid cylindrical waveguides. These equations, which take the form of singular determinants, were solved numerically. The solutions reveal that waveguides are dispersive media and the group and phase velocities of various modes of propagation are presented. In addition, the particle displacements of some of these modes are illustrated. Group velocities of modes in waveguides of different material were measured experimentally using an ultrasound pulse technique and the experimental results are compared with theory. Attenuation of the more dominant modes of propagation was also measured over the frequency range 1.0-5.0 MHz and the phenomenon of selective attenuation is discussed in the light of a number of attenuation models. A systematic study of sound conduction in a variety of waveguides of different radii and material media was undertaken and the effect of heat treatment investigated. The changes in conduction introduced by the latter are explained by changes in the internal grain structure which were observed using methods of metallurgical analysis. Finally, sound propagation was examined for conditions similar to those encountered in biopsy-needle guidance techniques. Other possible applications of waveguides in the field of medical ultrasonics are also considered. These theoretical and experimental studies have provided a fuller understanding of mode propagation in waveguides used in medical ultrasonics.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available