Electrical detection of the ultrasonic cavitation onset.

We propose a new technique for the study of ultrasonic cavitation. This method is based on the quantification of the electrical admittance variations of the emitter in a range around the resonance frequency at different excitation levels. As the cavitation threshold is reached, the state of the fluid is changing; we evaluate these changes. The high-power piezoelectric transducer is modelled through an analytical model, which is used to relate the characteristics of the fluid domain (bubble density, extent) to the electrical admittance (peak value, resonance frequency, and bandwidth). Thus, the admittance we measure allows us to determine the characteristics of the bubbly liquid. The procedure is applied to the inertial cavitation field generated at 24kHz at very high amplitudes. The results obtained show that a very high bubble density layer is formed at the surface of the sonotrode.