Prediction and verification of the magnetic orientation pattern in motor magnets

The magnetic orientation pattern of the permanent magnet in a spindle motor has a significant impact on its torque output. Determining the spatial dis tribution of magnetization vectors throughout the magnet volume, however, i s difficult. This paper describes a simple method for direct visual verific ation of magnetic orientation patterns in bonded neodymium magnets by using a ferrofluid decoration scheme. A simple theory for the appearance of the pattern is presented, and an algorithm to numerically extract a magnetizati on pattern from the developed image is proposed.