Complete Micro-PIV Characterisation of Microfluidic Devices

Microfluidic devices can take advantage of novel physics only available at the micro-scale. As a result, new physical models for the flow behaviour within these devices are required. In recent years micron resolution particle image velocimetry (Micro-PIV) has established itself as a reliable verification tool for these models. Micro-PIV measures the velocity profile across a single 2D plane within a microfluidic device. Here, Micro-PIV data is obtained from several planes within a device to create a complete mapping of the flow field. Combination of the data from all the planes allows the flow profile on the plane perpendicular to the original images to be studied and the volumetric flowrate through the device to be measured. By fitting the measured velocities to known flow profiles, the width and depth of the device can also be measured with sub micron precision. The technique is applied to an isotropically etched microchannel, where the results are compared to an independent computational fluid dynamics solution. Good agreement is found between the two data sets. The technique is then demonstrated in a more complex flow in a mixing channel device. In order to image an entire device a large field of view may be required. This dictates the use of low magnification lenses, which in turn have a large depth of field. A theoretical model for the measured Micro-PIV velocity demonstrates that, if care is taken when measuring near to curved walls, the use of these low magnification lenses does not significantly reduce the quality of the data obtained.