title: Bubble-based acoustic micropropulsors: active surfaces and mixers.
abstract: Acoustic micropropulsors present great potential for microfluidic applications. The propulsion is based on encapsulated 20 μm bubbles excited by a contacless ultrasonic transducer. The vibrating bubbles then generate a powerful streaming flow, with speeds 1-100 mm s-1in water, through the action of viscous stresses. In this paper we introduce a full toolbox of micropropulsors using a versatile three-dimensional (3D) microfabrication setup. Doublets and triplets of propulsors are introduced, and the flows they generate are predicted by a theoretical hydrodynamic model. We then introduce whole surfaces covered with propulsors, which we term active surfaces. These surfaces are excited by a single ultrasonic wave, can generate collective flows and may be harnessed for mixing purposes. Several patterns of propulsors are tested, and the flows produced by the two most efficient mixers are predicted by a simple theoretical model based on flow singularities. In particular, the vortices generated by the most efficient pattern, an L-shaped mixer, are analysed in detail.
authors.affiliation: Univ. Grenoble Alpes and CNRS, UMR 5588 LIPhy, F-38402 Grenoble, France. n.m.bertin@gmail.com.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bertin
authors.forename: Tamsin A
authors.initials: TA
authors.lastname: Spelman
authors.forename: Thomas
authors.initials: T
authors.lastname: Combriat
authors.forename: Hervé
authors.initials: H
authors.lastname: Hue
authors.forename: Olivier
authors.initials: O
authors.lastname: Stéphan
authors.forename: Eric
authors.initials: E
authors.lastname: Lauga
authors.forename: Philippe
authors.initials: P
authors.lastname: Marmottant