Output characteristics of high power pulsed electromagnetic wave generator for medical applications using water capacitor and water gap switch

Abstract

Nanosecond and sub-nanosecond high voltage pulses can provide new applications. A cancer treatment by an ultra-short pulse high electric field is one of them. High power pulsed electromagnetic wave has been proposed to apply the high electric field for that treatment. This work focuses on the design of a compact high power pulsed electromagnetic wave generator using a nanosecond pulse power generator for the cancer treatment. In this study, a L-C inversion circuit was employed for the pulsed power generator to obtain a voltage waveform with a single frequency for applying an antenna. A water gap switch and a water capacitor were used for L-C inversion circuit to obtain the frequency of hundreds MHz, because the water gap switch has a low inductance property and the loop inductance of the circuit can be made small using the same medium for the capacitor and the switch. By using the water gap switch and the water capacitor for the L-C inversion circuit, the pulsed voltage had the frequency element of 250 MHz. The electromagnetic wave was radiated underwater by the loop antenna in this experiment. Water was used for a simplest phantom of tissues because tissues have much water inside. A measuring antenna put at 0.15 and 0.3 m from the radiating antenna caught the electric field intensities of 112 kV/m and 49 kV/m, respectively. A focusing bowl was equipped on the radiating antenna to obtain higher electric field. The electric field intensity by the radiating antenna with the focusing bowl, 300 kV/m, is 6 times higher than that without the focusing bowl.