Theoretical and experimental validation of a dual-frequency excitation method for spatial control of cavitation.

Inertial cavitation has been implicated as the primary mechanism for a host of emerging applications. In all these applications, the main concern is to induce cavitation in perfectly controlled locations in the field; this means specifically to be able to achieve the cavitation threshold at the geometrical focus of the transducer without stimulating its near field. In this study, we develop dual-frequency methods to preferentially lower the cavitation threshold at the focus relative to the rest of the field. Two families of dual-frequency driving waveforms are evaluated in a bubble model incorporating rectified diffusion. Results are then verified by experiment. Finally, the performance of the rest of acoustic field in suppressing cavitation when cavitation is induced at the focus is investigated theoretically and checked experimentally. This study shows that dual-frequency phased arrays could be used to precisely control cavitation. The cavitation threshold is proved to be 1.2 times higher in the near field than at the focus. The concept of cavitation field is introduced and complements cavitation studies concentrating on the focal behaviour only.