A PDMS-Based Flexible Calorimetric Flow Sensor With Double-Bridge Technology

Flexible flow sensors show potential applications in aerospace, wearable devices, biomedicine, and other fields. In this article, a flexible microelectromechanical system (MEMS) calorimetric flow sensor with high sensitivity is designed and implemented. In the sensor, polydimethylsiloxane (PDMS) is used as the substrate in order to suppress the heat conduction loss in the sensor. The adoption of PDMS substrate can simplify the fabrication process because the technology of etching isolation trench is no longer needed. Additionally, four thermistors are symmetrically placed on both sides of the heater to form the Wheatstone double bridges, resulting in highly sensitive detection in both low- and high-speed ranges. The sensitivity and the range of the flow sensor are significantly improved. The results show that the measurable speed of the sensor can be as high as 50 m/s in a 100 K constant temperature difference (CTD) mode. The sensitivity is 22 mV/(m/s) with the flow rate in the range of 1-50 m/s and up to 3.308 V/(m/s) with the flow rate in the range of 0-0.1 m/s. Compared with the traditional flow sensor in silicon substrate, the sensitivity and the range of the designed sensor are significantly improved. The influences of specific flexible characters on the designed MEMS flow sensor, including the different curvatures and various overheat temperature values, are simulated and analyzed.