Fig. 3.
a–b) Convergence plot for the two design targets showing penalty values as a function of generation for one run of the genetic algorithm (GA). Both the mean and best penalty values are plotted for the multiple designs produced in each generation. For the homogeneous target design (a), the penalty value is the homogeneity parts per million (ppm) computed from the field range and average field in a 20cm DSV target volume. For the monotonic encoding field target field design (b), the penalty value is computed as a combination of 2 factors: 1) the frequency range over the 20 cm DSV target volume, and 2) the number of non-positive gradient points in the target volume. All designs were constrained to produce a mean field of at least 70 mT. c) Scatter plot of the best off-spring for 100 runs of GA for the homogeneous magnet design. The plot shows field range versus average field in target volume. The color represents the homogeneity ppm. d) Scatter plot of the best off-spring for 100 runs of GA for the monotonic encoding field target. The plot shows average field vs field range in the target volume. The color represents the percentage of non-positive gradient voxels in the volume. The encoding robustness of these 2 designs (Design A and B) are the ones simulated in Fig. 4.