Figure 8.

Three hexagonal sensors were manufactured on a 4-layer PCB. (a) The reference coil a has a diagonal, $D_{out}$, of 3 $\mathrm{cm}$ and 30 turns per layer. (b) Another version with 15 turns, and (c) a smaller coil with $D_{out}=2\mathrm{cm}$, were manufactured to validate the formulas used in the coil design procedure.