Analysis of Magnetic Characteristics of Permanent Magnet Assembly for MRI Device Taking Account of Minor Loop and Eddy Current

Abstract

The permanent magnet type of MRI for whole body provides a viable alternative to resistive and superconducting MRI. As the permanent magnet assembly contains pole pieces and yokes which are made of steel, the minor loop of B and H of steel due to the pulse excitation and the eddy current induced in the steel affect the magnetic characteristics of permanent magnet assembly.In this paper, the nonlinear iteration method for the analysis considering minor loop is discussed, and also the modeling technique of minor loop using typical major hysteresis loops is shown. The behavior of magnetic characteristics of permanent magnet assembly is examined considering hysteresis and eddy current. It is shown that the selection of time interval is important in the nonlinear analysis taking account of minor loop. The amplitude of residual magnetism is affected by the eddy current and the size of pole piece.