A Stick on, Film-Like, Split Angle Sensor via Magnetic Induction for Versatile Applications

Foldable structures have been widely employed in industry, consumer electronics, and origami robots. Sensing the angle of foldable structures has been challenging due to the limited high strain area and the impairment of folding movement introduced by sensor integration. Despite extensive research and remarkable progress, strain measurement-based wearable joint angle sensors have been limited in "real-world" applications due to the poor reliability and the strict requirement of sensor placement. In this work, we propose a film-like split angle sensor (FSAS) that operates through ac magnetic field coupling between a soft planar coil and a ferromagnetic or conductive target film. The FSAS has a split configuration in which no electrical or mechanical connection is needed between the sensing film (soft planar coil) and the target film (ferromagnetic or conductive material), overcoming the movement impairment problem presented by the strain sensing approach. Moreover, it inherits the advantages of existing inductive sensors, such as no hysteresis, high sensitivity, and insensitivity to local deformation. The results show that an FPC coil with a copper foil as a sensing target can distinguish a 0.007 degrees angle change when the angle between the sensing film and the target film is 30 degrees. Both finite-element modeling and experimental results indicate that a long rectangular coil or square coil with a small distance between the coil edge and the sensing target film can achieve higher sensitivity and larger effective sensing range. Finally, the FSAS was demonstrated for angle sensing and external force detection of a laptop lid, wearable angle monitoring of elbow, and perception of a pneumatic-driven origami robot, highlighting its high performance, versatility, and extreme easy-to-implementation features