This paper focuses on the anisotropy constant K_u that is required for the long-term stability of information stored when recording at a high areal density of, for example, 4 Tbpsi. To estimate the required K_u, we introduced a bit error rate (bER) derived from the Arrhenius-Néel statistical switching model of the thermal fluctuation in grain magnetization, which includes grain size and K_u distributions, and a weak inter-grain exchange coupling e. A smaller grain size and/or K_u distributions can reduce the required K_u and a further reduction can be expected as a result of inter-grain exchange coupling. We found that reducing the grain size distribution is more effective than reducing the K_u distribution. Moreover, the K_u reduction caused by inter-grain exchange coupling will be larger than 1/(mean e), suggesting that coupling between grains can be an effective way to reduce K_u.

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  The magnetic properties of non-oriented electrical steel sheets are known to deteriorate from punching stress. This phenomenon should be considered when designing electrical machines such as motors and actuators in order to obtain precision. However, very little research exists on the estimation of deteriorated magnetic properties using the measured data of punched specimens having various widths that can be applied to an actual design. We report here on a method to estimate the deterioration in the magnetic properties of non-oriented electrical steel sheets caused by cutting stress. The magnetic properties of single sheet specimens punched in various widths were measured using a newly developed single sheet tester (SST) that can measure up to 2T. It is shown that the magnetic field intensity and core loss increase due to the cutting stress. The detailed behavior of the deterioration of B-H curves and iron loss is illustrated. The dependences of magnetic properties on cutting size are estimated from the measured data. It is shown that the stress dependences can be modeled by an energy impulse function. Moreover, the estimated magnetic properties that deteriorate by the cutting stress are useful in the design of highly efficient electrical machines.

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  Technology for wireless power transmission via electromagnetic induction is expected to be useful for many kinds of electric equipment. In this technology, an alternating magnetic field shared between the primary and secondary coils is necessary. However, the leakage magnetic field caused by this linkage may negatively affect electronic circuits and other devices near the wireless power transmission unit. This paper describes a wireless power transmission coil shape that has high efficiency and a restraining leakage magnetic field. The main result is that a figure-8 coil with a ferrite plate reduces leakage magnetic field strength while maintaining efficiency of wireless power transmission.

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  Axial-gap permanent magnet (PM) motors have an air gap in the axial direction and produce more torque than conventional radial-gap motors, especially with flat structures. However, eddy-current loss in the magnets cannot be disregarded since axial-gap PM motors generally have a surface permanent magnet (SPM) rotor and an open slot structure. Furthermore, the open slot structure causes large amounts of torque ripple. We report here a method for decreasing the eddy-current loss by mounting a soft magnetic composite (SMC) onto the magnets. We also propose a method for reducing the torque ripple by adjusting both the pole arc angle of the magnets and the spatial phase difference between the two rotors.

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