Transcranial Magnetic Stimulation Magnetic Field Generator Research

Transcranial magnetic stimulation（TMS）is a non-invasive and painless technology of detection and treatment,and has a wide space for development in the field of biomagnetism,spirit medicine clinical and basic brain research.However,most of the existing magnetic stimulation instruments are single channel,and there are some problems technically,such as the poor focality of the magnetic field,single stimulate target and uncontrollable current pulse parameters.Magnetic field generator is the core of transcranial magnetic stimulation instrument,and directly determines the stimulation mode and application scope of the magnetic stimulator.A multichannel magnetic field generator topology with controllable pulse parameters is proposed,combining with excellent controllability of the Insulated Gate Bipolar Transistor（IGBT）.Firstly,a novel multichannel magnetic field generator topology with controllable pulse parameters is proposed from the point of multiple targets stimulated synchronously and controllable current pulse parameters,based on integrating the merits of different topologies.The new topology uses multichannel structure making each stimulate coils controlled by a special channel,and the parameters of the current pulse in each stimulate coils are adjustable,such as the current amplitude and the pulse width,improving the flexibility of the system.Then,the principle of the new topology structure are analyzed in detail,a circular stimulate coil is actual designed and the parameters of the coil are measured accurately.Based on the measured date,the parameters of the devices which is used in the main circuit were confirmed in accordance with the design principle of TMS.The voltage of the energy storage capacitor and the current of the stimulate coil are simulated by using Matlab.The simulation results prove that the current amplitude and the pulse width is adjustable through control the discharge switch turn ON time.Finally,the actual platform of the single channel system is set up,and the main circuit layout is optimized to reduce the stray inductance effectively.The corresponding snubber circuit is designed to suppress the peak voltage appeared in the switch OFF process.According to the control sequence requirement,a stable and reliable control system is designed and tested with the main circuit.The test results demonstrated that near-triangular current pulses are generated in the stimulate coil,and the parameters of the current amplitude and the pulse width are adjustable by control the discharge switch turn ON time in the range of 5-160 μs.When the pulse width t_pw is 160 μs,the maximum coil current reaching about 941.2 A that was consistent with the calculated result of 950.4 A.