High sensitivity magnetic head for a shaft torque sensor

The structure of a magnetic head used for torque sensing is investigated to seek higher sensitivity with low power consumption. The magnetic head investigated consists of two figure-eight coils embedded in a ferrite core. Torque applied to a magnetostrictive steel shaft makes the magnetic coupling between two coils in the head change positively or negatively depending on the sign and the strength of torque. Two structures, the square shape and the diagonal shape, are analyzed in terms of sensitivity and compared to our previous structure, the circle shape, which is an intermediate of the two in shape. It was found that the diagonal structure is the best choice. With this structure using a 14.6 mm square ferrite core, the applied torque is stably detected with 0.1 W power consumption (excitation condition: 60 kHz, 0.1 A) from a case-hardened steel shaft with an air gap 0.5 mm between head and shaft.