Figure 1.

(a) Illustration of side-view for the proposed angle-tuned TMS coil with five winding layers located above a homogenous and spherical head model, (b) The definitions of the half-value depth (d_1/2), half-value volume (V_1/2), and half-value spread (S_1/2) used for the estimation of the depth-spread characteristics for the proposed coils; The cerebral cortex is defined 1.5 cm below the surface of the head model. The half-value depth is defined as the radial distance from the cortical surface to the deepest point where the electric field strength is half of the maximum field strength on the cortical surface, (c) Induced electric field in the head model. The volume and depth of the electric field define half-value depth, half-value volume, and half-value spread, (d) A plan view of the definition of the footprint. For the figure-8 coil (shown in blue), the footprint involves two circular coils with an outer diameter of 8.7 cm for each and is around 120 cm² (dotted blue lines). In contrast, for the AT coil (shown in red), this value is calculated by multiplying the coil’s surface area by the cosine of the tilting angle. The footprint for a single 4.5 cm outer diameter is around 5.5 cm² (dotted red lines), (e) Fabricated angle-tuned coil for experimental measurements with nine winding layers wrapped over a 3D printed coil holder. The fabricated coil has an inner and outer diameter of 1 cm and 3 cm, respectively, with a tilting angle of 20°.