“…Since then, several papers have been published in this field, for example, Takahashi et al proposed a topology optimization using ON/OFF method (3) , Okamoto et al proposed a genetic algorithm (GA) and design space reduction (4) , and Sato et al proposed topology optimization using normalized network (5) . The authors also proposed a topology optimization method to optimize the material distribution of electrical machines using the GA (6)- (8) . In the method, the concept of the cluster of material and cleaning procedure has been proposed, which can remove small pieces of iron scattered in the air and in the permanent magnet (PM), and remove small structural spots in the iron and in the PM.…”