Ultrasonically driven antibubbles encapsulated by Newtonian fluids for active leakage detection
Résumé
An antibubble consists of a liquid droplet, surrounded by a gas, often with an encapsulating shell. Antibubbles of microscopic sizes suspended in fluids are acoustically active in the ultrasonic range. In this study, a Rayleigh-Plesset-like model is derived for micron-sized antibubbles encapsulated by Newtonian fluids. The theoretical behaviour of an encapsulated antibubble is compared to that of an antibubble without an encapsulating shell, a free gas bubble, and an encapsulated gas bubble. Antibubbles, with droplet core sizes in the range of 60-90% of the equilibrium antibubble inner radius were studied. Acoustic pressures of 100 kPa and 300 kPa were studied. The antibubble resonance frequency, the phase difference of the radial oscillations with respect to the incident acoustic pulse, and the presence of higher harmonics are strongly dependent of the core droplet size. The contribution to the radial dynamics from a zero-thickness shell is negligible for the bubble size studied, at high acoustic amplitudes, antibubbles oscillate highly nonlinearly independent of core droplet size. This may allow for active leakage detection using harmonic imaging methods.
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