Cavitation in focused ultrasound

A novel experimental configuration is developed combining a high intensity<br/>focused ultrasound source and a pulsed-laser, for the study<br/>of cavitation in a field typical of those used for therapeutic ultrasound.<br/>The sonoptic chamber is specifically designed to avoid the formation<br/>of acoustic standing waves, known to have a critical influence<br/>on cavitation behaviour. A new technique of laser-nucleated acous-<br/>tic cavitation is presented, whereby a laser-pulse of energy below the<br/>breakdown threshold for the host medium, acts to nucleate acoustic<br/>cavitation in a pre-established field. This facilitates the incorporation<br/>of high-speed cameras for interrogation at unprecedented temporal<br/>and spatial resolution, combined with acoustic detection directly correlated<br/>to the observed cavitation activity. A number of cavitation<br/>phenomena are investigated, including bubble-ensemble oscillations at<br/>a very early stage of development, in response to the acoustic driving.<br/>The frequency of oscillation, which bifurcates with increasing intensity,<br/>is also detected in the acoustic emissions. The application of<br/>a single-bubble model predicts a source for the acoustic emissions of<br/>quiescent radius equivalent to the bubble-ensemble observed, for each<br/>intensity investigated. The physical translation of the ensemble, due<br/>to the radiation force imposed by the primary field, is also analysed.<br/>For laser-pulses of energy above the breakdown threshold, applying<br/>focused ultrasound to the cavity promotes and actuates jet-formation.<br/>The characteristics of the so formed jets depend on the intensity and<br/>location of the cavity relative to the ultrasound focus.

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

University of Dundee

Year dc:date.issued

2013

Author dc:creator

• Gerold, Bjoern

Language dc:language

eng

Identifier

oai:discovery.dundee.ac.uk:studenttheses/f41bf6b9-ae59-4a41-ba29-d5873821418b

OAI identifier oai:identifier

oai:discovery.dundee.ac.uk:studenttheses/f41bf6b9-ae59-4a41-ba29-d5873821418b