Detailed measurement and simulation of FeNdB permanent magnet used for magnetic spring

The ring shaped rare earth permanent magnets are tested in conditions corresponding to the magnetic spring, where two magnets acts in repulsive direction. The mathematical model based on the surface bounded currents was used for calculation of external field and spring forces. The magnet polarization uniformity was measured from external flux density close to magnet surface. The measurement was designed to distinguish the experimental errors from the magnet polarization errors. The agreement between experiment and model was good in all cases. The flux density scatter on the concentric circle close to magnet surface vary from 3.2 to 12.8 % on one magnet sample and the average value vary about 14 % between samples. The crank mechanism was used to simulate the magnet aging in a real condition of the magnetic spring. The repulsive force was periodically monitored during more than 120 millions of spring cycles. The observed force decrease was 2 % at the spring working point at a distance of 1 mm.