Figure 9:

SNR gain relative to the thickness of the HPM layer (ε_r =1000) for a 128-element (A-D) and 32-element (E-H) array of loops fully encircling the spherical sample. The black contour line indicates regions where the SNR remains constant (i.e., ratio equal to one). For both arrays, the performance in the central region is higher when the thickness of the HPM layer corresponds to λ/2 or λ. Array performance increases for all cases near the surface of the sample. Performance at intermediate locations decreases for HPM with thickness equal to λ/4 or 3λ/4, which correspond to the cases that required larger current magnitude to achieve unit signal sensitivity at the intermediate voxel (see Figure 5 and 6).