Cavitation Bubbles are Micromachines for Wet Physical Processing

Small bubbles in liquids can be resonantly driven with ultrasound. These so called cavitation bubbles then perform volume oscillations, develop non-spherical modes and create fast and directed flows. In several critical industrial processes ultrasound driven cavitation bubbles are already utilized. The acoustic field not only supplies energy for the oscillations, but also creates forces on the bubbles. As a result the bubbles move along gradients of the sound field, move towards boundaries and interact which each other. Here, clever designs allow the steering of the bubbles to the locations of interest. In the first part of the presentation I’ll introduce the physics of ultrasound driven bubbles. In the second part I’ll discuss four selected processes, namely cleaning of surfaces from water filtration membranes to semiconductors, the emulsification of immiscible liquids, the extraction of biological cell content, and the material erosion and nanoparticle generation.  I’ll conclude with an outlook how acoustic cavitation bubbles i future could be controlled as microscopic steerable robots.