Numerical Investigation of the Magnetic and Electric Field Distributions Produced by Biconical Transcranial Magnetic Stimulation Coil for Optimal Design

Transcranial magnetic stimulation (TMS) is a powerful tool for investigating the physiology of the human brain. Recently, the application of TMS in brain therapy has also received great interest. In this paper, a finite-element method is employed to investigate the distributions of magnetic and electric fields induced by the biconical stimulation coil in the two-shell spherical human head model. The structure and electrical parameters are optimized to achieve deep and accurate stimulation. The simulation results indicate that high stimulation current frequency can produce great electric field strength, with which a deep position in the brain can be stimulated. When the distance between two cones increases, the magnetic field distribution in the tissue fluid becomes less focusing and the stimulation depth decreases. In addition, reducing the intersection angle between the two parts of the biconical coil can lead to deeper and more focused stimulation. These results can be used for guiding the TMS design.