(A) design of magnetic field gradient coil using target field methodTarget field method를 이용한 경사자계 코일의 설계

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The gradient coil makes the linear gradient magnetic field, which encodes spins with linearly increasing frequency in special domain. As one of many existing design methods of the gradient coil, the target field method has given a desirable result, good linearity and small inductance. We have developed two design methods using target field method. One is an analytic analysis which gives a complete closed solution, and the other is a numerical finite element method, which gives a numerical interpolated solution. For the analytic solution, we constraints a geometry to two planar surfaces, whereas any arbitrary geometry could be applied for the numerical approach. A new design method of a planar gradient coil is proposed, which has a minimum inductance with the presence of a pole piece around the gradient coil. In MRI (Magnetic Resonance Imaging) systems using permanent magnets, magnetic materials of high permeability are used for the pole piece so that the magnetic field can be as uniform as possible within the imaging region. Due to the high permeability of the pole piece, the gradient field produced by the conventional planar gradient coil deviates from the desired one. We have modeled the pole piece effects as a mirror current for design of minimum-inductance gradient coil. A finite element method is applied to find the optimum amplitude of the mirror current that makes the magnetic field most similar to the real field. With the mirror current model, we have derived the current density function that gives minimum inductance with the presence of the pole piece and the coil performance is compared to the conventional result. A numerical design method is applied to the design of the parabolic curved two sheet surfaces in the prolate spheroidal coordinate. This geometry can give more efficient gradient coil than conventional flat plane. Especially the requirement for interventional MRI increases for the real-time imaging and operation of patient, and the accessi...
Advisors
Park, Hyun-Wookresearcher박현욱researcher
Description
한국과학기술원 : 전기및전자공학전공,
Publisher
한국과학기술원
Issue Date
2000
Identifier
157647/325007 / 000959009
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 전기및전자공학전공, 2000.2, [ xv, 116 p. ]

URI
http://hdl.handle.net/10203/35853
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=157647&flag=dissertation
Appears in Collection
EE-Theses_Ph.D.(박사논문)
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