A Real-Time Microscopic PIV System Using Frame Straddling High-Frame-Rate Vision

Abstract

In this paper, we propose a novel concept of realtime microscopic particle image velocimetry (PIV) for apparent high-speed microchannel flows in lab-on-achip (LOC). We introduce a frame-straddling dualcamera high-speed vision system that synchronizes two different camera inputs for the same camera view with a submicrosecond time delay. In order to improve upper and lower limits of measurable velocity in microchannel flow observation, we designed an improved gradient-based optical flow algorithm that adaptively selects a pair of images in the optimal frame-straddling time between the two camera inputs based on the amplitude of the estimated optical flow. This avoids large image displacement between frames that often generates serious errors in optical flow estimation. Our method is implemented using software on a frame-straddling dual-camera high-speed vision platform that captures real-time video and processes 512 × 512 pixel images at 2000 fps for the two camera heads and controls the frame-straddling time delay between them from 0 to 0.25 ms with 9.9 ns step. Our microscopic PIV system with frame-straddling dualcamera high-speed vision simultaneously estimates the velocity distribution of high-speed microchannel flow at 1 × 108pixel/s or more. Results of experiments using real microscopic flows on microchannels thousands of µm wide on LOCs verify the performance of the real-time microscopic PIV system we developed.