An H-shaped low-field magnet for NMR spectroscopy designed using the finite element method

Abstract

An H-shaped low-field permanent magnet is presented. It has been designed, simulated and optimized using the finite element method. The magnet mainly consists of two poles, each of which consists of 37 hexagonal magnetic blocks that are magnetically connected by an iron yoke. To achieve the magnetic field homogeneity in the ppm range required for NMR applications, mechanical shimming by a vertical adjustment of the hexagonal magnetic blocks has been applied. Here, the displacement of each block from the initial equidistant symmetric design has been optimized by applying a pattern search method. In addition, two pole pieces made of iron have been added to the magnet to further improve the magnetic field homogeneity. The dimensions of these pole pieces have been optimized using a genetic algorithm. The magnetic field homogeneity of 15 ppm (parts per million) measured inside the manufactured prototype verifies the accuracy of the proposed simulation based design approach.

Keywords

Finite element methods genetic algorithms mobile NMR NMR magnet permanent magnet design pattern search algorithms shimming

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