Three-Dimensional Phenomena in Microbubble Acoustic Streaming

Alvaro Marin, Massimiliano Rossi, Bhargav Rallabandi, Cheng Wang, Sascha Hilgenfeldt, Christian J. Kähler

Research output: Contribution to journalArticlepeer-review


Ultrasound-driven oscillating microbubbles are used as active actuators in microfluidic devices to perform manifold tasks such as mixing, sorting, and manipulation of microparticles. A common configuration consists of side bubbles created by trapping air pockets in blind channels perpendicular to the main channel direction. This configuration consists of acoustically excited bubbles with a semicylindrical shape that generate significant streaming flow. Because of the geometry of the channels, such flows are generally considered as quasi-two-dimensional. Similar assumptions are often made in many other microfluidic systems based on flat microchannels. However, in this Letter we show that microparticle trajectories actually present a much richer behavior, with particularly strong out-of-plane dynamics in regions close to the microbubble interface. Using astigmatism particle-tracking velocimetry, we reveal that the apparent planar streamlines are actually projections of a stream surface with a pseudotoroidal shape. We, therefore, show that acoustic streaming cannot generally be assumed as a two-dimensional phenomenon in confined systems. The results have crucial consequences for most of the applications involving acoustic streaming such as particle trapping, sorting, and mixing.

Original languageEnglish (US)
Article number041001
JournalPhysical Review Applied
Issue number4
StatePublished - Apr 14 2015

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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