Frequency dependence of microflows upon acoustic interactions with fluids

Abstract

Rayleigh surface acoustic waves (SAWs), generated on piezoelectric substrates, can interact with liquids to generate fast streaming flows. Although studied extensively, mainly phenomenologically, the effect of the SAW frequency on streaming in fluids in constrained volumes is not fully understood, resulting in sub-optimal correlations between models and experimental observations. Using microfluidic structures to reproducibly define the fluid volume, we use recent advances modeling the body force generated by SAWs to develop a deeper understanding of the effect of acoustic frequency on the magnitude of streaming flows. We implement this as a new predictive tool using a finite element model of fluid motion to establish optimized conditions for streaming. The model is corroborated experimentally over a range of different acoustic excitation frequencies enabling us to validate a design tool, linking microfluidic channel dimensions with frequencies and streaming efficiencies. We show that in typical microfluidic chambers, the length and height of the chamber are critical in determining the optimum frequency, with smaller geometries requiring higher frequencies

Coalescence of Surfactant-Stabilized Adjacent Droplets Using Surface Acoustic Waves

“…The acoustic streaming velocity is aected by the SAW frequency and amplitude, attenuation length of the SAW beam, channel height and PDMS thickness as shown before with µ-PIV measurements and simulation studies. 71,72 We will discuss how this might play a role in the merging mechanism in Results & Discussion.…”

Effect of Liquid Crystalline Host on Structural Changes in Magnetosomes Based Ferronematics

“…Chains composed of several particles are clearly visible. The size distribution of magnetosome particles that was studied using the procedure published previously [ 32 ], led to the following mean size: 43 ± 12 nm. Magnetization measurements of the prepared isolated magnetosomes in the powder form were carried out by a Vibrating Sample Magnetometer installed on a cryogen-free superconducting magnet (Cryogenic Ltd., London, UK).…”

Acoustic fields and microfluidic patterning around embedded micro-structures subject to surface acoustic waves

“…The particular fluid velocities that result, however, are a function of the channel geometry; the relationship between this geometry, actuation mode, frequency, streaming velocity and their effects on particle migration have been discussed in detail elsewhere 14,32,43,56,59,66 . In the systems considered here, the acoustic radiation forces necessarily exceed those arising from fluid drag for particle patterning in acoustic fringes to be observed.…”

“…The physics of these systems have been extensively explored, where the effects of acoustic streaming [31][32][33][34][35] and acoustic radiation forces arising from standing waves [36][37][38][39] and travelling waves [40][41][42] have been well accounted for. These models, however, are largely predicated on the existence of spatially periodic acoustic fields along the propagation direction without accounting for the effect of channel elements in the SAW path.…”