Objective To design a new type of coil for transcranial magnetic stimulation (TMS),which can stimulate the cerebral cortex on multipoint with good focusing property and is simple to make and convenient to use. Methods Circular coils and figure-8 coils were simulated using electromagnetic simulation methods. The distribution of the coil-induced electric field in homogeneous phantom was computed. The impact of coil size and winding on the focusability and stimulation depth of TMS coils were analyzed. On this basis,a new type of coil named multi-circle tangent coil (MTC) was designed,and the distribution of MTC-induced electric field in homogeneous phantom model and realistic human head model was computed. Results With the increase of stimulation depth,there was an exponential decay in the intensity of the induced electric field. Smaller circular coils produced higher focusability and lower intensity of induced electric field. The focusability of figure-8 coils was higher than that of circular coils. The comprehensive effect of multi-layer winding method was preferable. MTC supported multipoint stimulation in addition to owning the advantages of figure-8 coils. Conclusions Factors such as size and winding have a big influence on the focusability and stimulation depth of coils. MTC has an exciting application prospect in TMS. Simulation on realistic human head model is of great significance for coil design and target location.
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