I. Introduction
TO perform efficient functional magnetic stimulation or to localize the stimulation sites precisely in brain studies, magnetic stimulations are often used. Brain stimulation with transcranial magnetic stimulation (TMS) is achieved from the outside of the head using pulses of electromagnetic field to induce an electric field in the brain [1]. TMS has numerous applications in the study, diagnosis, and therapy of the brain. It is well known that TMS can either excite the cortex or disturb its function. Intense current pulses are driven through a stimulating coil placed above the head, generating a time-varying magnetic field. The poor linkage between the coil and the tissue however limits the efficacy of TMS: only about 10%–30% of the magnetic energy in the coils is transmitted into the nervous tissues. Optimization of the magnetic coil design is therefore necessary in order to improve and optimize TMS. Recent advances in MC configuration have improved the focality (the ability for a coil to stimulate a small target area of the tissue) significantly.