Acoustofluidics 14: Applications of acoustic streaming in microfluidic devices

Abstract

In part 14 of the tutorial series "Acoustofluidics--exploiting ultrasonic standing wave forces and acoustic streaming in microfluidic systems for cell and particle manipulation", we provide a qualitative description of acoustic streaming and review its applications in lab-on-a-chip devices. The paper covers boundary layer driven streaming, including Schlichting and Rayleigh streaming, Eckart streaming in the bulk fluid, cavitation microstreaming and surface-acoustic-wave-driven streaming.

Acoustic streaming in the transducer plane in ultrasonic particle manipulation devices

“…However experimental observations in planar microfluidic resonators have described streaming patterns with vortices flowing parallel to the transducer plane 16,22 . Similar vortices had previously been described by Spengler et al 23 and later work from Kuznetsova and Coakley 9 also discusses 'unexpected wall-independent' suspension vortices with circulation planes parallel to the transducer radiating surface.…”

Ultrasound assisted particle and cell manipulation on-chip

“…The two main sources of streaming are: i) due to acoustic energy dissipation into the bulk of a fluid, and ii) due to energy dissipation from the interaction of an acoustic field with a boundary. The first of these mechanisms, also known as "Eckart streaming", or the "quartz wind", is caused by attenuative loss over a number of wavelengths so is typically only an issue in microfluidic devices when high frequency waves propagate along the length of a channel [21]. It is also less likely to be observed in standing wave systems in which the forces leading to Eckart streaming from counter-propagating waves tend to cancel each other out.…”

Acoustofluidics 23: acoustic manipulation combined with other force fields

“…Due to boundary and bulk losses, acoustic streaming flow fields are almost universally present in acoustic radiation force devices 6 . The hydrodynamic drag force resulting from this streaming often acts in competition with the radiation force.…”

“…This series of tutorial articles has explored the theory underlying acoustic radiation forces 1 and acoustically-induced streaming 2 , has described experimental techniques for evaluating these effects 3,4 and has discussed a variety of applications [5][6][7][8] based on both bulk acoustic waves 9 and surface acoustic waves 10 . It has become apparent that the acoustic phenomena employed have a potentially large scale of action 11 , can trap and manipulate relatively large particles and agglomerates 8 , are appropriate for biological use 12 , and are suitable for integration with many microfluidic fabrication techniques 13 .…”