Doppler-Based Flow Rate Sensing in Microfluidic Channels

We design, fabricate and experimentally demonstrate a novel generic method to detect flow rates and precise changes of flow velocity in microfluidic devices. Using our method we can measure flow rates of similar to 2 mm/s with a resolution of 0.08 mm/s. The operation principle is based on the Doppler shifting of light diffracted from a self-generated periodic array of bubbles within the channel and using self-heterodyne detection to analyze the diffracted light. As such, the device is appealing for variety of lab on chip bio-applications where a simple and accurate speed measurement is needed, e. g., for flow-cytometry and cell sorting.