Ultrasonic cleaning using oscillating microbubbles

Microbubbles subjected to acoustic waves are used in the ultrasonic cleaning of dental implants, medical instruments, and semiconductors. Recently, experimental results have shown that the shape oscillation of bubbles can remove harmful bacterial biofilms from wounds and other affected surfaces without damaging those surfaces.

The mechanism of the cleaning effects resulting from bubble movement has previously been studied in an infinite field rather than within boundaries created by real-life situations. Corbett et al. studied the shape mode oscillations of microbubbles over rigid boundaries using the boundary integral method, the viscous potential flow theory, and the weakly compressible theory.

“A bubble oscillates at a frequency dependent on factors such as its size, the properties of the surrounding fluid, and the bubble’s proximity to a nearby structure,” said author Callan Corbett. “Certain frequencies of bubble oscillation can lead to different types of resonant oscillation, called shape modes, which will each exert a different amount of force on the boundary.”

The team numerically modeled oscillating bubbles near a wall and determined the specific frequency and force generated by each. The results showed significant shear stress, at least twenty times higher than volume oscillation, near the contact line among the liquid, gas, and solid as the bubbles approached and touched a boundary. The model was validated through comparison with theoretical results.

“We hope that this work will lead to further advances in the efficacy of ultrasonic cleaning,” said Corbett.

Source: “Cleaning effects due to shape oscillation of bubbles over a rigid boundary,” by Callan Corbett, Qianxi Wang, Warren Smith, Wenke Liu, and A. Damien Walmsley, Physics of Fluids (2023). This article can be accessed at https://doi.org/10.1063/5.0173730 .