Permanet magnet demagnetization test fixture design and validation

This paper investigates demagnetization characteristics of rare-earth permanent magnets 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 2-dimensional flux mapping device. The measurements are compared with 3D 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 guide the selection of magnet grade, shape and dimensions for low cost and robust designs of permanent magnet synchronous machines.