Nanosecond biphasic pulse generators for biomedical applications

In the research of bioelectrics, bipolar pulses appear to enhance the membrane effects by creating anode on both sides of the cell sequentially. On the other hand, the membrane charging resulted from the first part of the pulse may be removed by the following pulse of opposite polarity. To explore the biological effects of bipolar pusles on cells, we have constructed several types of nanosecond bipolar pulse generators, which can drive low-impedance loads of, for example, 10 Ω. They have been used for loads of electroporation cuvettes. The pulses were generated by means of five, 50 Ω transmission lines connected in parallel which were then switched on by a single spark gap switch, or a RLC circuit charged by a Marx generator. The pulse waveforms are symmetrical for long pulses, such as 600 ns, but for short pulses, such as 10 ns, an apparent asymmetry was observed. We suggest several causes for the deviation of the theoretical pulse-duration prediction.