Liquid Metal-Filled Polymer Fiber as Wing-Type Inductive Sensors for Deformation and Airflow Sensing

Flexible sensors, as vital components of flexible robots, play significant roles in monitoring the surrounding environment and tracking their own motion states. However, the development of flexible sensors that demonstrate both high sensitivity and reliability while being suitable for integration into actuated parts remains a challenge. In this study, we developed a wing-shaped sensor composed of a hollow fiber polymer structure, into which liquid metal was injected as a flexible conductive material and encapsulated with Ecoflex, which overall presents a cantilever beam structure on both sides. The hollow fiber acts as a natural insulator for the liquid metal coils, while their inner and outer diameters are only 190 and 290 μm, respectively. When both ends of the sensor are deformed by external action, the cantilever beams on both sides will be displaced relative to each other like wings, resulting in a corresponding change in the spatial position of the liquid metal coil, which in turn generates a change in the inductance signal. By leveraging this phenomenon, the wing-type sensor can detect minute displacements at both ends with an accuracy of 5% of their thickness while maintaining excellent stability over 100 cycle tests. This sensor was also able to measure wind speeds in a specific range of 2–10 m/s, with trends that conformed well to both theoretical foundations and simulation results. Further, we have demonstrated several application scenarios for this sensor using this superposition sensing mechanism. Overall, this study elucidates the inductive superposition mechanism of the cantilever beam coils on both sides and offers a strategy for integrating sensing and actuation in flexible robots.