Bio-inspired Flexible Airflow Sensor with Self-bended 3D Hair-like Configurations

This paper presents a novel flexible airflow sensor based on four curved microcantilevers arranged in a cross-form configuration. A self-bending method based on MEMS technology has been used to fabricate the curved microcantilevers structure, and this method can transfer a 2D plane structure into a 3D structure with good consistency in the morphology. The curved microcantilever consists of a polyimide (PI) top layer, silicon (Si) bottom layer, and platinum (Pt) piezoresistor at the root of the cantilever. The difference in the in-plane residual stress between the PI and Si layers bent the microcantilever upward. The curved-up microcantilever transfers the fluidic momentum that acts on it to drag force, which deflects the curved-up microcantilever and changes the resistance of the piezoresistor. To realize temperature compensation and decrease the noise, a reference resistor and an ambient temperature detector were integrated for the Wheatstone half-bridge measurement and temperature monitoring, respectively. The cross-form configuration of the curved-up cantilevers has high sensitivity advantages and possesses direction-sensing ability. Experimental results show that the sensitivity of the sensors increased as a function of the airflow velocity, and the sensors exhibited a maximum resolution of 4 mm⋅s⁻¹ and a maximum sensitivity of 60.35 mV⋅(ms⁻¹) ⁻¹ when the airflow velocity was larger than 38.5 m⋅s⁻¹.