Analysis of Tuning Characteristics of Coaxial Microwave Plasma Torch with Bi-resonant Structure

In terms of CO2 decomposition and conversion, microwave plasma devices have become an effective technical means to achieve the goal of carbon neutrality because of their advantages of high efficiency and energy saving. However, when microwave devices are used, they usually need to adjust the resonant frequency to work efficiently and stably. In order to improve the energy utilization efficiency and working stability of CO2 microwave plasma devices, this study explores the influence of the structure parameters of the coaxial resonator on tuning is explored, and a bivariate tuning mode is proposed. Firstly, the physical model and equivalent circuit model of the coaxial microwave plasma torch are established, and the correlation between the discharge intensity of the plasma torch and the axial size of the coaxial resonator is analyzed. Then, the conductivity distribution models under different discharge states are established, and the tuning curve between the port reflection coefficient S11 and the axial dimension of the coaxial resonator under the corresponding distribution model is obtained by COMSOL simulation. Finally, the simulation results are compared with the equivalent circuit model, and the effects of univariate tuning and bivariate tuning, as well as the feasibility and characteristics of bivariate tuning mode, are analyzed. The results show that compared with the univariate tuning mode, the bivariable tuning mode can increase |S11| by an average of 5%-15%, and the minimum S11 value (i.e., the best resonant state) in different discharge states can be obtained within 3/4 wavelength, which can further improve the power coupling efficiency of the device, reduce the energy loss, and thus improve the CO2 decomposition and conversion efficiency. © 2024 Chinese Mechanical Engineering Society. All rights reserved.