Development of a High Voltage, 150 ps Pulse Generator for Biological Applications

The use of prolate-spheroidal reflectors as part of a picosecond impulse radiating antenna (IRA) allows us to generate near-field electric fields with high spatial resolution in dielectric and even slightly conductive matter such as biological tissue. In order to achieve spatial resolution on the order of one centimeter, pulses with durations on the order of 100 ps are required. We have developed a pulse generator which provides 150 ps FWHM pulses with an amplitude up to 60 kV into a 50 Omega load with a variation in amplitude of 7%. The pulse generator consists of a four stage Marx bank with a peaking switch and tailcut switch. The rise time of the output pulse from the Marx generator is reduced to 100 ps by means of the adjustable peaking switch. The adjustable tailcut switch, between the inner and outer conductor of the cable, is placed at a distance of 6 cm from the 50 Omega load resistor. This tail-cut switch determines the duration and amplitude of the pulse. The voltage across the load is measured by a capacitive divider probe, placed between the load resistor and the tail-cut switch. By adjusting the input voltage and the gap of the tail-cut switch, it was possible to adjust the pulse width and amplitude. The shortest pulse width recorded was 135 ps at 50 kV. The largest pulse amplitude was recorded at 120 kV with a 185 ps pulse duration.