Computation of fields in periodic permanent magnet structures with undercut pole diameters

The field analysis procedure described by Sterzer and Seikanowicz (S&S) gives accurate predictions of the axial field in periodic permanent magnet structures subject to the restrictions that the outer diameters of the poles must be the same as the magnets, and the flux in the poles must be below saturation. Simple physical reasoning can be used to derive a modification of the S&S analysis to give accurate predictions of the field in a structure with undercut pole diameters, and thus determine the optimum pole diameter. The algorithm for including this in a computer code for computation of the fields is described in this paper. Field computations using this code, results obtained using the standard S&S analysis, and results obtained using another code were evaluated by comparison with computations using the "Pandira" finite element analysis code.