Microwave Plasma Pencil for Surface Treatment: Numerical Study of Electromagnetic Radiation and Experimental Verification.

An atmospheric pressure plasma source of the microwave plasma pencil type utilizing a coaxial line is presented. The generated plasma takes the form of a cylinder up to about 30 mm long and up to 5 mm in diameter. It is suitable for surface sterilization, surface treatment, and material processing. This study numerically analyzes the electromagnetic radiation emitted by the plasma pencil, which compromises performance and poses safety risks. Electric field distributions, radiation patterns, the ratio of the power entering the discharge to the incident wave power, and the ratio of radiated power to entering power were numerically investigated for different plasma parameters and pencil lengths. Results indicate that increasing electron density, gas temperature, plasma length, and pencil length increases the radiated power by up to more than 60% of the entering power, and the radiation patterns can be highly non-uniform with strong backward lobe. The numerical finding were qualitatively confirmed experimentally. It was also found that it is possible to reduce radiation from the device by using appropriately designed cones, the presence of which does not impede its performance.