Objective: Pulse parameter controllable transcranial magnetic stimulation (cTMS) devices with fully-controlled semiconductor switches are increasingly being developed, but the primary waveform they generate is often accompanied by ringing, which is due to the resonance between the stimulation coil inductance and the snubber capacitors paired with the switches at the end of the pulse. This study provides a ringing suppression design method to effectively suppress it and reduce its impact on stimulation efficacy.
Methods: A three-pronged design method is developed to suppress the ringing at its source. Firstly, laminated busbars are designed to connect main components, reducing parasitic inductance and thus decreasing the snubber energy requirement and the energy stored in the snubber capacitors, which is the main source of ringing energy. Secondly, the snubber circuit structure is improved by employing unidirectional snubber circuits to cut off the ringing loop. Lastly, a specially designed converter is used to transfer the energy stored in the snubber circuit, which to some extent represents the energy of the ringing, back to the cTMS storage capacitor.
Results: The suppressed ringing duration has been significantly reduced from around 1000μs to within 30μs.
Conclusion: The proposed method effectively suppresses ringing, making the realized waveform much closer to the ideal waveform, which minimizes the impact of ringing on the stimulation effect and reduces the uncontrollable deviation between the actual activated region and the ideal target activation region.
Significance: The method can be easily transferred to other cTMS devices, enhancing the controllability of stimulation efficacy.
Keywords: Transcranial magnetic stimulation (TMS); pulse parameter controllable TMS (cTMS); pulse waveform; ringing suppression; stimulation selectivity.
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