Mathematics

Measuring the velocity of fluids confined in microscopic devices is a challenging task. The small dimensions involved prevent the use of conventional probes such as hot wire anemometers or pitot tubes. A microscopic adaptation of the particle-image-velocimetry (PIV) technique, namely micro-PIV, has been for the past decades the gold-standard in this domain. The limitations of micro-PIV are mainly two: It gives a two-dimensional measurement of the velocity field, and it suffers for errors in the depth direction in case of large velocity gradients.  A way to overcome these problems is to use 3D-particle-tracking methods. However, a major constraint in this case is that multi-camera approaches are often not possible and only one optical access, usually through a microscope objective, is allowed. In this talk, the basics of micro-PIV and the recent advancements in 3D-particle-tracking methods for micro-flows based on defocusing will be presented and discussed. Furthermore, a couple of applications will be shown in which the astigmatic-particle-tracking-velocimetry (APTV) technique was used to measure complex three-dimensional flows in microfluidic devices with sub-micrometric resolution.