A novel magnetic stimulation device with quasi-exponential stimulus currents

Since its invention in 1985, the magnetic stimulator has been based on an oscillating circuit consisting of a capacitor and a coil. Depending on how the energy is switched, different pulse shapes are generated. These play an important role in the activation of nerves. While it is possible to generate nearly arbitrary pulse shapes, this freedom comes with complex and costly power electronics. We present a novel monophasic system that can generate extremely steep edges by inductive intermediate storage of pulse energy. It requires a very simple charging circuit, while the pulse amplitude and pulse duration are controlled by the switching times of two IGBTs. By varying these switching times with an input voltage of 140 VAC, our prototype generates pulses with a pulse length between 155 and 200 μs and a maximum stimulation coil current between 2.1 and 2.8 kA. The total energy in the system (depending on the input voltage and switching time) is limited by exceeding the dielectric strength of the IGBTs due to voltage peaks that occur during switching. These peaks were counteracted to a certain extent using RCD snubbers. Our design enables the development of low-cost and compact monophasic magnetic stimulators and, with its novel topology, opens up further possibilities in generating monophasic pulse shapes.