Figure 4.

A plot of ratio R^TEP versus electrode separation angle β for four different electrode radii r_e. R^TEP is the ratio of the mean-squared electric field over the scalp region to that of the brain region for the specific electrode system depicted in figure 3. The angle θ_o which subtends the electrode from its center is determined according to ${\theta }_o={\text{cos }}^{-1}\sqrt{1-r_e^2}$. Each plot extends over the range β = [2θ_o, 90] so that the electrodes do not overlap.