Evolution of an 1 MHz ultrasonic cavitation bubble field in a chopped irradiation mode

In this paper the evolution of an ultrasonic cavitation bubble field is studied by means of the void rate, the cavitation noise power and the electric power that feeds the ultrasonic transducer. The ultrasonic irradiation is performed in chopped mode. It is observed two kinds of evolution that differ respectively by a slow (A regime) and a fast (B regime) void rate increase. They correspond to cavitation regimes that are identified as respectively a stable cavitation and an inertial cavitation field. The beginning of the fast increase of the void rate is delayed from the irradiation start and this delay depends on the chopping frequency of the irradiation mode.