Figure 5.

$R_j^{TMP}$ versus j for TMP electric fields. $R_j^{TMP}$ is the ratio of the mean-squared electric field over the scalp region to that over the brain region for an electric field comprised of a single vector spherical harmonic component indexed by the pair of integers j and m. The index j of the vector spherical representation of the electric field is reciprocally related to spatial scale in the field. Note that $R_j^{TMP}$ is independent of index m for any given value of j. As with TEP the cost of greater electric field focality in the brain is greater mean-squared electric field in the scalp relative to the brain. However that cost is much greater for TEP as compared to TMP.