A new structure of torque sensors using thin pickup head - Use of mutual coupling modulation

A new structure is proposed for the magnetoelastic torque sensors using a pair of figure-eight coils as a pickup. Mutual coupling between two figure-eight coils is used as a measure of torque applied to a shaft. The mutual coupling is governed by torque-induced anisotropic permeability at the surface of the shaft. Basic characteristics of the torque sensor are examined using a tempered steel shaft of 25 mm in diameter and a pair of 25-turn figure-eight coils. Sensitivity was 16 μV/N m and hysteresis was 1.3% at the coil excitation condition of 60 kHz, 0.8 A (RMS). Exciting power needed to reduce hysteresis is much smaller with this structure than with previous methods using self-inductance as a measure of torque.