3D measurement and simulation of surface acoustic wave driven fluid motion: a comparison

Abstract

The characterisation of the fluid motion induced by the acoustic streaming effect is of paramount interest for novel microfluidic devices based on surface acoustic waves (SAWs), e.g. for a detailed description of the achievable mixing efficiency and thus the design of such devices. Here, we present for the first time a quantitative 3D comparison between experimental measurements and numerical simulations of the acoustic streaming induced fluid flow inside a microchannel originating from a SAW. On the one hand, we performed fully three-dimensional velocity measurements using the astigmatism particle tracking velocimetry. On the other hand, we derived a novel streaming force approach solving the damped wave equation, which allows fast and easy 3D simulations of the acoustic streaming induced fluid flow. Furthermore, measurements of the SAW amplitude profile inside the fluid filled microchannel were performed. Based on these results, we obtained a very good agreement between the velocity measurements and the simulations of the fluid flow demonstrating the importance of comprising the actual shape of the SAW amplitude profile for quantitatively reliable simulations. It is shown that the novel streaming force approach is a valid approximation for the simulation of the acoustic streaming induced fluid flow, allowing a rapid and simple estimation of the flow field of SAW based microfluidic devices.

Microfluidic flow switching via localized acoustic streaming controlled by surface acoustic waves

“…The experimental results suggested that the uid streams rotated in the clockwise direction within the microchannel cross-section which is consistent with the direction of the acoustic streaming ow eld produced by a SAW. 39 As the uid streams owed from the b 2 -b 2 0 to the b 3 -b 3 0 congurations, the IPA and FC-40 streams owed into the le and right ow paths, respectively. The two uid streams were completely altered and clearly separated from one another.…”

Frequency dependence of microflows upon acoustic interactions with fluids

“…Here we take into consideration the whole volume of the fluid, including microstructures (such as an anechoic corner, shown in Fig 1 A), enabling us to build an accurate description of an acoustically pumped microfluidic system. 15 We do not consider the reflections off the walls of the microchannels (which are most often made of elastomeric materials with a low acoustic impedance, and which do not generate significant reflections). It is important to note that, where other materials are used in the construction of the microfluidic network (such as glass or silicon for example), the contribution of such reflections will be significant and will need to be considered systematically.…”

“…When a channel is smaller than the attenuation length of the SAW, the magnitude of streaming flows is significantly decreased. Recent advances have taken the so-called 'anechoic corner' into account and shown good agreement between simulation and experiment, 15,16 but only over a limited range of frequencies, preventing the generation of significant insight into the interplay between acoustic frequency and streaming efficiency.…”

“…In this work, we now expand upon the approaches for modelling the acoustic field in microfluidics channels 10,14,15 and build a simple expression of the body force, taking into account the anechoic corner and the damping coefficients of both the SAW wave and the viscous damping of the fluid. We demonstrate, for the first time, how these expressions can be used to fully analyse the scaling of SAW induced acoustic streaming with the acoustic frequency.…”

Surface acoustic wave electric field effect on acoustic streaming: Numerical analysis

“…First of all, this is 3D-simulation. 50,51 In principle, the 3D scattering problem can also be solved using FEM and PML but not on ordinary personal computers.…”