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Cogging torque exhibits a strong correlation with manufacturing tolerances. Aiming for robust design of the mass-produced surface-mounted permanent magnet motors, an analytical solution for the estimation of cogging torque is presented, which considers the magnet imperfections and the rotor eccentricity. In addition, the analytical solution is based on the exact subdomain model and accurate modified magnetization intensity, which takes magnet misplacement, remanence variation, magnetization direction error, pole-arc deviation, thickness error, and recoil permeability variation into consideration. Furthermore, the perturbation method is introduced into the model to describe the effect of rotor eccentricity. The spatial change of magnets and slots resulting from eccentricity is also considered in this paper, which effectively facilitates the calculation precision of cogging torque. Magnetic field distributions and cogging torque calculation by the proposed analytical solution are found to be consistent with the finite-element and experimental results.

Using ab initio methods, we have calculated the characteristic inverse length scale for spin polarized tunneling in Langmuir-Blodgett (LB) films contacted by Fe electrodes. As a function of energy, the scale is found to vary significantly around its mean value, and the variation is much more drastic in parallel configuration than that of anti-parallel configuration. This unusual behavior can be understood from the point of view of interface resonance, which shows very sharp features in the k-space resolved transmission probability.