Multi-parametric defocusing particle tracking velocimetry (PTV) for micro-fluidic channels

A 3D particle model based on defocusing effect is proposed for 3-dimensional 3-component particle tracking velocimetry measurements in microfluidic systems. The model parameters describing the particle behavior are used directly as tracking features in the multi-parametric PTV. Micro-fluidic channels are mounted on a nano-positioning piezo stage which sweeps periodically in the out-of-plane direction, and a high-speed camera is synchronized to take two-dimensional microscopy images. Particles identification from the intensity volume is achieved by a combination of a 3D Hessian filter and a dynamic thresholding segmentation. Estimation of the measurement uncertainties over a large dynamic range is performed by artificial images based on direct numerical simulations of flow through porous media, and shows improvement over other PTV methods. A proof-of-concept experiment is performed by measuring the steady-state flow through a refractive-index-matched randomly packed glass bead channel. This experimental method doesn’t require calibration since the out-of-plane position of each image is recorded from the piezo stage position feedback, and thus eliminates any uncertainties associated with the calibration required by other PTV methods for micro-fluidics.