Figure 13
From: A compact theory of magnetic nerve stimulation: predicting how to aim
Joint B-fields of figure of 8 coils (top) and bowl metaphor (bottom). Figure of eight coils with counter-rotating currents are aligned with the x-axis. B-fields from the two coils and their time derivatives are opposite in sign. As they rise and fall in time counter-rotating eddy currents are induced in underlying tissue which reinforce at points near the z-axis.