A study on asymmetric current in plasma-mediated electrosurgery

• In spite of the installation of a blocking capacitor, asymmetric RF currents are observed during the plasma knife discharge.
• The origin of the asymmetric current is the different secondary electron emission coefficients of the metal and the tissue.
• Changing the condition for ionization, the current was maintained symmetric for a short time which we called ‘delay time’.
• Changing gas species, input voltage, and knife speed reduces the asymmetric peaks with longer delay time.

Electrosurgery using a radio frequency (RF) plasma knife is a new medical technique that enhances the coagulation effect and reduces skin damage. It uses a high current density and ohmic heat to vaporize tissue at the cutting point. In spite of the installation of a blocking capacitor, asymmetric RF currents are observed. These asymmetric currents induce a direct current (DC) in the tissue, which can cause muscular stimulation during a medical operation; for medical applications of a plasma knife, the unexpected damage that can occur due to these asymmetric currents needs to be prevented. A study is performed to find the origin of the asymmetric current and to reduce the electrical damage to biological tissue during plasma-mediated electrosurgery. One of the main causes of an asymmetric current is differences in the secondary electron emissions from the tissue and metal. The difference in the secondary electron emission from the tissue and metal, and the resulting asymmetric current peaks can be reduced by (1) using argon or helium gas, (2) using a lower voltage range, and (3) decreasing the knife speed. The physics revealed in this article should provide insight for a safety window for plasma-mediated electrosurgery devices during the plasma surgical operations.