Cavitation in focused ultrasound

  • Bjoern Gerold

    Student thesis: Doctoral ThesisDoctor of Philosophy


    A novel experimental configuration is developed combining a high intensity
    focused ultrasound source and a pulsed-laser, for the study
    of cavitation in a field typical of those used for therapeutic ultrasound.
    The sonoptic chamber is specifically designed to avoid the formation
    of acoustic standing waves, known to have a critical influence
    on cavitation behaviour. A new technique of laser-nucleated acous-
    tic cavitation is presented, whereby a laser-pulse of energy below the
    breakdown threshold for the host medium, acts to nucleate acoustic
    cavitation in a pre-established field. This facilitates the incorporation
    of high-speed cameras for interrogation at unprecedented temporal
    and spatial resolution, combined with acoustic detection directly correlated
    to the observed cavitation activity. A number of cavitation
    phenomena are investigated, including bubble-ensemble oscillations at
    a very early stage of development, in response to the acoustic driving.
    The frequency of oscillation, which bifurcates with increasing intensity,
    is also detected in the acoustic emissions. The application of
    a single-bubble model predicts a source for the acoustic emissions of
    quiescent radius equivalent to the bubble-ensemble observed, for each
    intensity investigated. The physical translation of the ensemble, due
    to the radiation force imposed by the primary field, is also analysed.
    For laser-pulses of energy above the breakdown threshold, applying
    focused ultrasound to the cavity promotes and actuates jet-formation.
    The characteristics of the so formed jets depend on the intensity and
    location of the cavity relative to the ultrasound focus.
    Date of Award2013
    Original languageEnglish
    SupervisorPaul Prentice (Supervisor)

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