Automated and temperature-controlled micro-PIV measurements enabling long-term-stable microchannel acoustophoresis characterization

Abstract

We present a platform for micro particle image velocimetry (μPIV), capable of carrying out full-channel, temperature-controlled, long-term-stable, and automated μPIV-measurement of microchannel acoustophoresis with uncertainties below 5% and a spatial resolution in the order of 20 μm. A method to determine optimal μPIV-settings for obtaining high-quality results of the spatially inhomogeneous acoustophoretic velocity fields of large dynamical range is presented. In particular we study the dependence of the results on the μPIV interrogation window size and the number of repeated experiments. The μPIV-method was further verified by comparing it with our previously published particle tracking method. Using the μPIV platform we present a series of high-resolution measurements of the acoustophoretic velocity field as a function of the driving frequency, the driving voltage, and the resonator temperature. Finally, we establish a direct and consistent connection between the obtained acoustophoretic velocity fields, and continuous flow mode acoustophoresis, commonly used in applications.

Acoustic streaming in the transducer plane in ultrasonic particle manipulation devices

“…For beads of this size streaming effects were not in evidence due to the much larger radiation forces. While temperature effects are known to have an influence on the resonances in devices such as this 34 , the streaming pattern was found to be reliably present at this frequency and the streaming magnitude similar and within the level of accuracy resulting from the approximations made in the modelling below.…”

“…As described above, the voltage-drop method of pressure measurement is subject to significant errors. Other methods involving PIV based bead tracking 4 have been shown much more accurate, although this method would be hard to apply in this case due to the radiation force being in line with the viewing direction. 2.…”

“…The temperature of the device has not been stabilised. Experiments 4 have shown that self-heating of the transducer and attached structures at higher drive levels can cause a shift in the resonant frequency of the system. We hypothesise that this is the cause for the small steepening of the experimental results with frequency (ie the curve is steeper than a quadratic one).…”

“…We hypothesise that this is the cause for the small steepening of the experimental results with frequency (ie the curve is steeper than a quadratic one). Temperature stabilisation in this system is not straightforward (compared to the silicon devices presented by Augustsson et al 4 ) as the air boundaries of the device are an integral part of the design, and do not allow for thermal connections. 4.…”

Acoustofluidics 23: acoustic manipulation combined with other force fields

“…However this experiment is prone to high measurement errors due to the difficulty in distinguishing a particle in equilibrium from one that is slowly dropping, and the uncertainty in material properties for the bead. Much more accurate measurements can be produced in lateral aspect devices using PIV based methods 23 . The general presence of the earth's gravitational field makes it a particularly simple field to use yet its relative weakness compared to the acoustic forces in microfluidic systems means that time must be allowed when equilibrium situations have to be reached.…”