A Coaxial Atmospheric Microwave Plasma Source With Low-Generating Power

Conventional atmospheric microwave plasma sources face challenges in achieving plasma generation at the milliwatt power level, often requiring a reduction in operating pressure to generate plasma at lower power levels. This article presents a novel atmospheric microwave plasma source based on the coaxial structure to generate plasma at the milliwatt power level at atmospheric pressure. First, numerical simulations based on the finite element method (FEM) and equivalent transmission line model (ETLM) have been done to design the structure. Simulation results show that at the optimal structure, the microwave reflection ratio $\vert {S}_{{11}}\vert $ at 2.45 GHz is equal to −19.58 dB before plasma excitation and the electric field strength reaches $6.03\times 10^{{5}}$ V/m when the input power is 1 W. Second, a practical experimental system is built according to the simulations. Experimental results show that the $\vert {S}_{{11}}\vert $ at its resonant frequency is −19.2 dB before plasma excitation, which agrees well with the simulations. Moreover, the minimum input microwave power values for generating argon, CO2, and air plasmas are 100 mW, 5 W, and 10 W, respectively. Finally, this novel atmospheric microwave plasma source has been used to decompose and convert CO2, the highest conversion rate and energy efficiency reach 24.1% and 49.2%, respectively, which are comparable to low-pressure microwave plasmas. Thus, the proposed microwave plasma source in this article has great potentials for industrial applications to reduce carbon emissions.