Abstract: A permanent magnet magnetic circuit comprises a main magnet block having a pair of opposite outer surfaces. A pair of main magnetic poles of opposite polarities are disposed on the respective outer surfaces of the main magnet block. The main magnet block is provided with a channel defined between the pair of outer surfaces and the channel has a pair of inner surfaces corresponding to the respective outer surfaces of the main magnet block. The main magnet block is also provided with a pair of oppositely polarized compensating magnetic poles arranged on the respective inner surfaces for controlling any vector of the magnetic field directed from one of the main magnetic pole to the other main magnetic pole. A pair of adjusting magnet blocks are arranged on the respective inner surfaces to adjust the magnetic field directed from one of the main magnetic poles to the other magnetic pole.