A microfluidic flow meter with micromachined thermal sensing elements

The design, fabrication, operation, calibration, and performance of a microfluidic flow meter utilizing a micromachined (MEMS) thermal time-of-flight sensing chip are presented. The MEMS sensing chip integrates multiple sensing elements (thermistors) on a silicon substrate. This sensing chip works on the principle of thermal excitation with a modulated power source from the microheater while the responses of the sensing elements at both upstream and downstream of the modulated thermal source are processed for both the time differences and the amplitudes of the heat transfer in the microfluidic flow. Unlike most of the current flow meter products based on the thermal sensing principle that only offer the calorimetric mass flow rates, this flow meter can measure not only the mass flow rate but also the flow media properties. Experimental results for water and isopropyl alcohol are discussed, which demonstrate the capability and performance of the novel microfluidic flow meter.