Winding-configuration-switching-based field control method and coil design for transcranial magnetic stimulation

Purpose To improve the field-adjustment flexibility of conventional transcranial magnetic stimulation (TMS) coils and reduce the system complexity of multicoil arrays, this study aims to propose a single-coil field-control method based on winding-configuration switching (WCS). Design/methodology/approach An analytical electromagnetic-field calculation model for arbitrarily shaped TMS coils was developed and validated against finite-element simulations. A reconfigurable prototype coil was then fabricated, and its electrical parameters, preliminary high-voltage loading performance and static magnetic-field distributions were experimentally tested. Findings The analytical model agreed well with finite-element results, with maximum errors of 0.83% for the magnetic field and 1.26% for the induced electric field. The calculated results showed quantifiable shifts in the induced electric-field focal positions under two winding configurations. Prototype measurements agreed with analytical predictions, with maximum-field deviations of 0.87% for WC1 and 3.15% for WC2, and peak-normalized errors below 5% along the selected diagonal line. Originality/value The proposed WCS method enables reconfigurable field control by changing the effective turns and current directions within a single coil, providing a new route for low-complexity TMS coil design. This work represents a proof-of-concept study; future work will address automatic high-voltage switching and direct electric-field measurement in conductive phantoms.