Microscale 3D flow mapping with microDDPIV

Three-dimensional (3D) quantitative flow visualization by tracking microscale particles has become an invaluable tool in microfluid mechanics. Defocusing digital particle image velocimetry (DDPIV) can recover spatial coordinates by calculating the separation between defocused images generated by an aperture mask with a plurality of pinholes. In this paper, a high-speed 3D micro-DDPIV (?DDPIV) system was devised based on this technique to achieve microscale velocity field measurements. A micro-volume of 400 × 300 ?m2 with a depth of 150 ?m has been mapped using an inverted microscope equipped with a 20× objective lens. The proposed technique was successfully applied to 3D tracking of 2-?m fluorescent particles inside an evaporating water droplet.