Enhancement and quenching of high-intensity focused ultrasound cavitation activity via short frequency sweep gaps

This letter reports on the use of frequency sweeps to probe acoustic cavitation activity generated by high-intensity focused ultrasound (HIFU). Unprecedented enhancement and quenching of HIFU cavitation activity were observed when short frequency sweep gaps were applied in negative and positive directions, respectively. It was revealed that irrespective of the frequency gap, it is the direction and frequency sweep rate that govern the cavitation activity. These effects are related to the response of bubbles generated by the starting frequency to the direction of the frequency sweep, and the influence of the sweep rate on growth and coalescence of bubbles, which in turn affects the active bubble population. These findings are relevant for the use of HIFU in chemical and therapeutic applications, where greater control of cavitation bubble population is critical.