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Title: Stable-inertial cavitation
Author: Johansen, Kristoffer
ISNI:       0000 0004 7654 9024
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2018
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Research and development of applications utilising acoustic cavitation, particularly medical therapy, is often based on the spectrum of the scattered emissions collected during the cavitation occurrence. There is, however, limited understanding as to how driven bubble behaviour is related to the myriad of non-linear features that can exist within the cavitation noise spectrum, including those commonly reported. Moreover, there is an enduring tendency to classify cavitation activity as either stable or inertial, with no clear delineation between the two categories in terms of associated emissions. The work described in this thesis is dedicated to reconciling bubble dynamics driven by focused ultrasound, and resolved with ultra-high speed shadowgraphic imaging, to the acoustic emissions simultaneously detected via a broadband calibrated needle hydrophone system. Specifically, the role of periodic bubble collapse shock waves are experimentally investigated, supported by bubble oscillation models and spectral analysis. First, hydrophone-deconvolution for restoring an approximation to physical pressure data is demonstrated, through laser-plasma mediated bubble detection. Subsequent application to precision measurements of an acoustically driven cavitation bubble, verifies a contribution from periodic shock waves to all features within the emission spectrum, including the sub-harmonics. Moreover, complete spectral peak suppression at the sub-harmonic is demonstrated for a specific two-bubble configuration. Finally, the design of a bespoke passive cavitation detector, optimised for shock wave detection is described, and its performance evaluated against a comparable, commercially available device. Implications for cavitation detection and detector characterisation are discussed, as is the conventional classification of activity as stable or inertial, with reference to the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Q Science (General) ; QC Physics