When Bubbles Are Not Spherical: Artificial Intelligence Analysis of Ultrasonic Cavitation Bubbles in Solutions of Varying Concentrations

Ultrasonic irradiation of liquids, such as water-alcohol solutions, results in cavitation or the formation of smallbubbles. Cavitation bubbles are generated in real solutions withoutthe use of optical traps making our system as close to realconditions as possible. Under the action of the ultrasound, bubblescan grow, oscillate, and eventually collapse or decompose. Weapply the mathematical method of separation of motions tointerpret the acoustic effect on the bubbles. While in mostsituations, the spherical shape of a bubble is the most energeticallyprofitable as it minimizes the surface energy, when the acousticfrequency is in resonance with the natural frequency of the bubble,shapes with the dihedral symmetry emerge. Some of theseresonance shapes turn unstable, so the bubble decomposes. Itturns out that bubbles in the solutions of different concentrations (with different surface energies and densities) attain differentevolution paths. While it is difficult to obtain a deterministic description of how the solution concentration affects bubble dynamics,it is possible to separate images with different concentrations by applying the artificial neural network (ANN) algorithm. An ANNwas trained to detect the concentration of alcohol in a water solution based on the bubble images. This indicates that artificialintelligence (AI) methods can complement deterministic analysis in nonequilibrium, near-unstable situations.