Simple, high-precision, microliter per minute, fluid-flow sensor

Liquid flow monitoring at μL/min rates is important for many lab-on-a-chip applications. Several technologies have been investigated to achieve this resolution. Most require expensive detection systems and extensive calibration. They also rely on phenomena impacted by diffusion (e.g., heat pulses) that quickly lose accuracy as flow rates decrease. These limitations can be surmounted by using bubbles to mark the flow. A micromachined, bubble time-of-flight device can measure flow rates accurately with minimal calibration. We demonstrate such a device with range from 100 to 2 μL/min and accuracy down to .02 μL/min. A method for detecting sub 100 μL/min is also tested.