Improve Focalization Using a Conductive Shield Plate 

A new method to improve the focalization and efficiency of the Figure of Eight (F.O.E) coil in rTMS is discussed in this paper. In order to decrease the half width of the distribution curve (H.W.D.C), as well to increase the ratio of positive peak value to negative peak value (R.P.N) of the induced electric field, a shield plate with a window and a ferromagnetic block are assumed to enhance the positive peak value of the induced electrical field. The shield is made of highly conductive copper, and the block is made of highly permeable soft magnetic ferrite.

A computer simulation is conducted on ANSYS® software to conduct the finite element analysis (F.E.A). Two comparing coefficients were set up to optimize the sizes of the shield window and the block. Simulation results show that a shield with a 60 mm × 30 mm sized window, together with a block 40 mm thick can decrease the focal area of a F.O.E coil by 46.7%, while increasing the R.P.N by 135.9%. The block enhances the peak value of the electrical field induced by a shield-F.O.E by 8.4%. Real human head model was occupied in this paper to further verify our method.