Investigation and characterization of a planar figure-of-eight coil as a curvature sensor

A novel inductive curvature sensor has been fabricated for the purpose of monitoring angular joint movements of the finger. The sensor is a planar figure-of-eight coil sandwiched between a flexible polyester film and a Metglas magnetostrictive ribbon. The coil and its flexible substrate measures 7.5 mm wide, 50 mm long, and 110 μm thick, with the Metglas ribbon and bonding layer contributing an additional 50 μm, approximately. Inductance changes were measured as a function of sensor bending induced through uniaxial displacements. Bending the sensor exerts stresses on the magnetostrictive ribbon and, due to the Villari effect, leads to changes in permeability and therefore inductance. Inductance changes up to 350 nH, a 20 % decrease of the initial inductance value, were recorded. The main advantages of this sensor are ease of use, small size profile, flexibility, and simplicity. The results indicate great potential for measuring the angular articulation of human joints.