A Thermal Microfluidic Flow Sensor Screen-Printed onto an Ultrathin PMMA Foil

This paper reports on the devised fabrication procedure and experimental investigation and characterization of a thermal based flow sensor for microfluidic systems based on polymer technology. The sensor itself is screen-printed onto a self-fabricated ultrathin polymethylmethacrylate (PMMA) foil, which minimizes the heat capacity and therefore yields fast response times of integrated thermal transducers. Integrating the foil-based sensor into the center of a PMMA stack consisting of a substrate and a top plate (both preprocessed to form a microfluidic channel) enables a suitable material compatibility and a low-cost fabrication procedure. Using the well-known evaluation principles of thermal anemometers, the four-wire sensor can be used for accurate flow measurements in such polymer-based microfluidic systems, where the measurement range of the sensor is easily adaptable by changing the channel's height. Currently, it is possible to measure flows starting in the range of $10\ \mu\mathrm{l}$ per minute up to $1000\ \mu\mathrm{l}$ per minute.