Design and Testing of a Novel Transcranial Magnetic Stimulator with Adjustable Pulse Dynamics and High Current Capability (>2 kA) based on a Modular Cascaded H-Bridge Inverter Topology

Transcranial magnetic stimulation (TMS) is an important technology in neurological diagnostics and therapy. The limited output voltage shape of modern TM stimulators constrains the research about the targeted stimulation of individual brain parts. This paper introduces a novel TM stimulator based on a cascaded H-bridge inverter topology. Using a large number of sub-modules (e.g., ten), a nearly arbitrary output voltage waveform can be generated. Within the frame of this paper, the design and testing of an individual H-bridge module, using low-voltage MOSFETs, is explained in detail. To achieve a high current capability, the switching waveforms of the paralleled MOSFETs are synchronized by individual time delays introduced by an integrated CPLD. The H-bridge module is used for different experimental pulse tests. Using a DC link voltage of 180 V a maximum current peak of about 2.1 kA is achieved.