Electromagnetic Field Analysis And Coil Design Based On Real Head Model

The technology of transcranial magnetic stimulation(TMS)was born in 1980s.In clinical application,it has the advantages of noninvasive and painless.But it is too difficult to achieve accurate point stimulation,especially for the depth stimulation.This hinders the popularization and application in the clinic.To solve the problem of site-specific stimulation,this paper proposes a coil array design method.Firstly,the target position is determined.Then,the coil array is designed based on the selected target.The principal work of this paper is to solve the magnetic field generated in the brain by different coils.It is used to evaluate and analyze the performance of coils.Therefore,the method of computing the magnetic field is studied and validated firstly.The software ANSYS is chosen to calculate the magnetic field.It is realized by the finite element method that is a mean of numerical analysis method.The finite element method has three catalogues.They are scalar method,vector method and edge element method.The solutions of these methods are compared with the analytic solution and the experimental measurement data.The results show that the relative error between the solution of edge element method and the analytical solution,experimental measurement value is less than 5%.So,the edge element method will be used to analyze the magnetic field distribution in the brain space.Then,the coil array design method based on the target is proposed.The details of it are described.They are the design idea and calculation method by which the space position parameters of each coil can be calculated.After the real human brain numerical model was got,different coil arrays based on the different targets are designed respectively by the way proposed in this paper.The magnetic field distribution in the 3-D brain space is computed.According to the path distribution where the target at,the magnetic field at the target is higher than the value of non-target.The results show that different coil arrays based on the separate targets both achieve precise magnetic focusing.It verifies the feasibility and flexibility of this method.Finally,this paper proposes a method that is to add the ferrite to further improve the focus of the target.When the cylindrical ferrite is added,the stimulus intensity and focus of the target are both improved.The stimulus intensity of the target is enhanced to 1.73 times.This paper provides a coil array design method for site-specific stimulation in transcranial magnetic stimulation.Another method is put forward to improve the focus of the target.It is expected to promote the further application of transcranial magnetic stimulation in clinical trials.