A Method for Predicting Flux Loss of Multipole Magnet and Its Evaluation

The prediction of flux loss due to exposure at an elevated temperature is very important in applications of Nd-Fe-B magnets because of the low Curie temperature of the Nd₂ Fe₁₄ B. Previously, we proposed the prediction method of the initial flux loss, FL_int, from basic magnetic properties of a magnet by taking advantage of the finite element method. The prediction method takes the magnetizing process and the distribution of coercivity into account, and is composed of four steps, 1) simulation of distribution of magnetization under magnetizing filed, 2) determination of demagnetization curves at room and exposure temperatures, 3) simulation of distributions of magnetization at room and exposure temperatures, and finally 4) prediction of distribution of FL_int. We applied this method to a Nd-Fe-B ring magnet with 12 poles, and predicted FL_int due to the exposure at 120^°C. Subsequently, the prediction method was evaluated by comparing the predicted FL_int values with the experimental ones. The predicted FL_int values agreed with those obtained experimentally, which suggests the validity of the proposed method.