Design of gradient coil system by 3DFEM with implemented simplex optimization method

Abstract

This investigation uses three-dimensional finite element package MagNum3D and design strategy, based on the simplex optimization method, to obtain required field strength and linearity within a region of interest (ROI) for electron paramagnetic resonance (EPR) measurements. While the design of Z-gradient coils can be realized on axisymmetrical model, the accurate design of the two transverse (X- and Y-) gradient coils, should be constructed on the basis of a 3D numerical analysis. Proposed technique for designing gradient coils assumes that each coil consists of a finite number of polygonal turns, each carrying an identical current. Coordinates of this turns must be determined to minimize the deviation of the actual magnetic flux density from the ideal linear distribution. Predefined design conditions include: allowable spatial range for coil location, cross section area of coils, required multilayer configuration of coils (for cooling operations) with a gap of 2 mm between the coil layers, size of ROI. The routine chosen to locate optimal coil coordinates was the simplex minimization technique. We initialized the searching routine by choosing a set of random coordinates within a range of given geometrical parameters for initial guess.