Journal of the Magnetics Society of Japan

A quick response and robust torque sensor is presented for a carbon steel shaft on which a pair of magnetostrictive layers are formed and a pair of twin-coils are set. Sensitive and reliable magnetostrictive layer of Fe₄₀Ni₅₆Cr₄ was formed using a low-pressure plasma spray method. A magnetic field perpendicular to the magnetostrictive layer plane is generated by a current flowing through a twin-coil, which magnetizes the steel shaft in a radial direction (difficult magnetization direction). Linear characteristics of the sensor output for applied torque (－40～40 N・m) were obtained using these twin-coils with exciting frequencies up to 600 kHz. Variations of sensor output of the zero-output and the sensitivity for temperature variation of the steel shaft were compensated for using newly constituted non-induction coils which detected the temperature of λ-layers.

View full abstract

Show abstractHide abstract

Study on the magnetic microstructures was made for CoNiPt thin film media with different coercive force ranging from 800 Oe to 1800 Oe through rotational hysteresis loss analysis. In order to investigate the mechanism for the increase of coercive force, H_c was analyzed as a function of H_k (2θ), H_k^grain and H_p, determined by magnetic torque measurements. Here, H_k (2θ) is macroscopically induced uniaxial anisotropy field in film plane, H_k^grain is the magnetic field where rotational hysteresis loss W_r vanishes in high magnetic field region and H_p is the magnetic field where W_r reaches its maximum. According to the results, H_c increased as H_p increased, keeping a slightly higher value than H_p, while H_k (2θ) and H_k^grain showed no systematic change and remained almost constant. These experimental facts suggest that H_c for these samples is mainly determined by magnetization reversal of exchange-coupled crystallites, and H_c increased as a consequence of the reduction of intergranular exchange coupling. These trends were in good accord with the improvement in media noise.

View full abstract

Download PDF (779K)

Register with J-STAGE for free!