Effects of acoustic parameters on acoustically-vaporized droplets under dynamics flow conditions

This study investigated the effects of varying acoustic parameters on the temporal evolution of the population of acoustic droplet vaporization (ADV) bubbles under flowing conditions. The experiments were conducted in an integrated acousto-optical system. A 2-MHz high intensity focus ultrasound (HIFU) transducer was used to transmit acoustic pulses to vaporize the per fluoropentane (PFP) droplets. High-speed photography was conducted to monitor the ADV bubbles at up to 1.2 s after the onset of ADV. The results show that the mean size of ADV bubbles gradually increased and reached a plateau at 0.7 s after HIFU irradiation. No significant change was found in the trend of bubble growth and maximum size when the flow velocity were altered from 21.4 to 44.1 mm/s. Varying the acoustic pressure resulted in no significant effects on the temporal evolution of the bubble population when the acoustic pressure exceeded the ADV threshold pressure. Increasing both pulse duration and PRF resulted in the increase but great decrease in the size and number of bubbles, respectively. This study suggests that the control of the size and number of ADV bubbles may be achieved by using different HIFU pulse sequences. Future work includes the investigation of ADV bubbles under flow conditions in in vivo models.