Color-Coded Three-Dimensional Micro Particle Tracking Velocimetry and Its Applications

Abstract

A color-coded three-dimensional particle image velocimetry is successfully adapted into a microscopic setup using a 10X objective lens. A three-pinhole plate, color-coded by color filters of different wavelengths, is utilized to create a triangular triple exposure pattern on the image sensor plane for each tracer particle in the flow. The 3-D physical location of the particle can then be calculated from the size of the triangle pattern with micrometer accuracy. Light sources of different wavelengths are aligned with the corresponding pinholes, and a color separation algorithm based on principal component transformation (PCT) is developed to account for the signal crosstalk issues caused by the color filters. A particle identification method modified from cascade correlation method is used to resolve the peak locations of heavily overlapped particle images, and the triplet exposures are matched to reconstruct the 3D particle locations with a calibration-based epi-polar line search method. The velocity field is resolved by a vision-based particle tracking algorithm to track the individual particle movement between the reconstructed particle fields from each image pair. The experimental uncertainties of the system verified with experiments shows that the location uncertainties are less than 0.10µm and 0.08µm for the in-plane, and less than 0.82µm for the out-of-plane components, respectively. The displacement uncertainties are 0.62 µm and 0.63µm for the in-plane, and 0.77µm for the out-of-plane components, respectively. With the ability to tack particles in higher particle densities, the experimental setup is used to image a 600 µm × 600 µm × 600 µm volume of a backward-facing step micro-channel flow. Both results of steady flow and decelerating flow are presented, ranging from Reynolds number 0.825 to 0.033.