Bioinspired Graded-Stiffness Strain Sensors for a Broad-Range and Ultra-Sensitive Aerodynamic Perception of Flapping-Wing UAVs

Accurate aerodynamic perception is critical for the autonomous flight of flapping-wing unmanned aerial vehicles (UAVs) in complex, dynamic flow fields. However, conventional sensors suffer from a fundamental trade-off between achieving ultra-high sensitivity to weak micro-disturbances and maintaining a broad operational range without structural or electrical failure. Inspired by the Aedes aegypti antenna, a biomimetic graded-stiffness strain sensor (BGSS) is reported. By programmatically modulating the cross-linking density of a polydimethylsiloxane substrate, we constructed a five-level graded-stiffness PDMS substrate coupled with a surface-modified conductive network. This architecture enables sequential mechanical deformation under loading. The flexible end deforms preferentially to capture weak stimuli, while the rigid end suppresses excessive local strain under high loads to prevent crack saturation within the conductive layer. Consequently, the BGSS provides a more balanced mechanical response than the rigid and flexible counterparts. Benefiting from a high gauge factor of up to 298.6, the BGSS demonstrates a 535.7-fold increase in tensile-force sensitivity over uniform rigid sensors, while simultaneously expanding a high-response force interval to 0.7-6.3 N under uniaxial loading, representing a 215% extension over uniform flexible sensors. As a proof of concept, the conformal integration of the BGSS onto a flapping-wing UAV produced distinguishable resistance responses associated with different wing postures and wing-surface airflow conditions, indicating its potential for aerodynamic-state monitoring.