3-D optimal shape design of pole piece in permanent magnet MRI using parameterized nonlinear design sensitivity analysis

The pole piece of a permanent magnet magnetic resonance imaging (MRI) is optimally designed in three-dimensional (3-D) space, taking into account the nonlinearity of materials to get high homogeneous magnetic fields in the working region. The pole face is parameterized using a B-spline surface and optimized using 3-D nonlinear design sensitivity analysis based on the 3-D finite-element method. An optimal design result shows how the nonlinear magnetic property of the yoke and column, as well as the pole piece, affect the magnetic-field homogeneity in the working region, although the MRI system has a large air gap.