J. Xie, D. H. Kang, B. C. Woo, J. Y. Lee, Z. H. Sha, and S. D. Zhao, “Optimum Design of Transverse Flux Machine for High Contribution of Permanent Magnet to Torque Using Response Surface Methodology”, J Electr. Eng. Technol., vol. 7, no. 5, pp. 745-752, Sep., 2012.