A Tunable Coaxial Microwave Atmospheric Pressure Room-Temperature Plasma Jet for Material Processing

A coaxial microwave atmospheric pressure room-temperature plasma jet generator based on a terminally compressed coaxial resonator is designed. A three-stub tuner is added on this generator to adjust the resonant frequency, lower the plasma excitation power, and get higher energy efficiency. Experiments show that this device can trigger argon and generate a plasma jet with only 8-W microwave input power. The gas temperature is as low as $39~^{\circ }$ C. By tuning the metal stubs, the energy efficiency of this device can increase up to 85%. The optical emission spectrum of the plasma jet shows dense reactive radicals such as OH and O. A preliminary surface treatment is tested for the device. The polyurethane (PU) and polyvinyl chloride (PVC) sheets show good hydrophilicity after 1-min plasma treatment and 5-min plasma treatment, respectively. The work in this article is helpful to the design of highly efficient microwave plasma jets and provides a new device for material processing.