The Design And Simulation Of Focused Magnetic Field For Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation(TMS) is an non-invasive technology used tostimulate Central Nervous System，which takes advantage of time-varying magneticfield and produces induced current to change the potential difference between theinside and outside of the cell and then excite the cell. Due to the permeability of theskull, magnetic field can stimulate nerve tissue inside the scalp and skull. Comparedwith traditional electrode stimulation, TMS have more advantages for its non-invasive,security, convenience and easy-to-repeat, and this method is being used in more andmore filed. However, nowadays TMS has some issues to solve, such as the bulky size,expensive cost and bad focused magnetic field of the stimulating coils.So as to realize magnetic focus, this paper introduce two new coil array modelsrespectively with8coils and20coils. In consideration of that many facts caninfluence the magnetic focus and the solution space is very large, we introduce theswarm intelligence method to improve the coil former. On the basis of Particle SwarmOptimization (PSO) algorithm and Standard Genetic Algorithm (SGA), we come outwith an improved hybrid Genetic-Particle Swarm Optimization (GA-PSO) algorithm,and then we use specific test function to measure GA-PSO algorithm’s efficiency andsuccess rate to get the global optimal solution. The results show that this improvedalgorithm has good performance, and that it has obvious advantage in convergencetime and convergence rate. At last we use this algorithm to get the optimal solution ofthe parameters of the sub-coil of the coil array model, and induce magnetic fieldaround the coil array and focus it in designated area. Compared with the traditional8shaped coil, this two models both have better magnetic focusing, and the model with20coils realizes point focusing.Besides, this paper introduce the Physiological basis and Physical principles ofTMS in details, the principles of the TMS excitation source system, and analyses thefacts affect the induced magnetic field, and then we come to a conclusion that the change rate and the strength of the current influence the strength of the inducedmagnetic field and the induced electric field. Then we design and complete the circuitboard which includes “Main circuit of high pressure”,“Rectified filter circuit”,“driving circuit”. We tell the parameters of the circuit and its influence to the systemsecurity, stability and magnetic field energy, and then we improved the circuit board.Now we generate320A,400us high pulse current in the stimulate circuit under180Vpower supply. The frequency analysis shows that the main energy is concentrated inthe0-20kHz.This article introduces some solutions to improve the disadvantages of thenowadays Transcranial Magnetic stimulation system, and can help to the developmentof this system.