Abstract
Abstract - Shimming is an important technique in development of nuclear magnetic resonance (NMR) magnets where image resolution is highly dependent on magnetic field homogeneity. Classically, shimming may be categorized into two types: 1) active shimming that incorporates with extra coils and precise tuning of their currents; and 2) passive shimming that incorporates with pieces of steel placed in a bore of a main magnet and their uniform magnetization under homogeneous external fields. Additional magnetic fields, produced by the coils and/or the steel sheets, compensate original magnetic field from the main magnet in such a way that the total field becomes more homogeneous. In this paper, we developed a passive shimming method based on linear programming optimization. Linear programming is well known to be highly efficient to find a global minimum in various linear problems. We firstly confirmed the linearity of magnetization of ferromagnetic pieces under a presence of external magnetic fields. Then, we adopted the linear programming to find optimized allocation of the steel pieces in the inner bore of a main magnet to improve field homogeneity. Key Words : - NMR magnet, Ferromagnetic shimming, Passive shimming, Linear programming †교신저자, 정회원 : 위덕대학교 에너지전기공학부 부교수E-mail : sjlee@uu.ac.kr*정회원:MIT Francis Bitter Magnet Laboratory Research Staff**정 회 원 : 한국전기연구원 초전도연구센터 선임연구원 접수일자 : 2010년 4월 20일 최종완료 : 2010년 5월 13일
Published Version
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