Standard and inverse transducer-plane streaming patterns in resonant acoustofluidic devices: Experiments and simulations

Abstract

• A new transducer-plane streaming pattern is observed and characterised. • A mathematical model is developed for the modelling of transducer-plane streaming patterns. • Modelled standard and inverse transducer-plane streaming patterns are consistent with those observed in experiments. • Physics of standard and inverse transducer-plane streaming patterns have been analysed. • Mathematical model has been verified to show physics of acoustic streaming fields in other acoustofluidic systems. In this paper, we report a new transducer-plane streaming pattern, which we call here inverse four-quadrant transducer-plane streaming , in an ultrasound-excited thin-layer glass capillary device, illustrate the importance of the travelling wave component and emphasize its phase difference with the standing wave component of three-dimensional acoustic fields excited in thin-layer resonant acoustofluidic particle manipulation devices on the formation of transducer-plane streaming patterns through numerical simulations. A mathematical model was created for solving the three-dimensional acoustic streaming fields from limiting velocities derived from predefined acoustic fields, capturing both the standing wave and travelling wave components and their phase relations. This model was then successfully applied to interpret the unusually reversed in-plane streaming patterns seen in a silicon-based fluid channel. It was found that, by tuning the phase difference between the standing and travelling wave components, φ , the transducer-plane streaming vortices could be shifted along the fluid channel and reversed streaming patterns can be excited when φ differ by π, which could provide insights for the control of transducer-plane streaming in thin-layer acoustofluidic devices and may have promising potential for acoustofluidic applications such as nanoscale particle manipulation.