Permanent-Magnet Demagnetization Design and Validation

This paper investigates demagnetization characteristics of rare-earth permanent magnets (PMs) used in electric machines. A test fixture was designed and built to induce controllable local demagnetization in the magnet sample under test. A range of demagnetizing magnetomotive force (MMF) was applied to force the magnet samples to operate at various points along their B-H curves. The degree of demagnetization in the magnet samples was measured with a computer-controlled two-dimensional (2-D) flux mapping device. The measurements are compared with three-dimensional (3-D) finite-element analysis (FEA) simulations. This study results in greater insight into the capability of magnets to withstand various demagnetization forces and how spatially varying material properties affect this capability. The understanding gained from this study can be applied to the test and validation of the magnetic properties of the PMs used in the electric machines.