LAUSR

The microwave perturbation method (MPM) has been widely applied in measuring the electron density of low-pressure plasmas for its cheapness and convenience. However, it is difficult to measure the electron density of the atmospheric microwave plasma jet (AMPJ) due to the low measurement sensitivity of the MPM and the inhomogeneous spatial electron density of the AMPJ. In this article, we extend the MPM into measuring the AMPJ by proposing a microwave parallel resonant cavity (MPRC) and a Gaussian electron density distribution model. First, to obtain a high measurement sensitivity, the MPRC is compressed to enhance the electric field intensity. Then, to obtain the electron density, the resonant frequency shifts of the MPRC under plasma perturbations are calculated based on the Gaussian model and fit with the experiments. Finally, a 2.45-GHz AMPJ with inhomogeneous spatial electron density is measured by both the proposed method and optical measurements in various flow rates and microwave power. The results show that the electron density obtained by the proposed method agrees with that of optical measurements with a relative error below 3%, which shows great potential in engineering for the cheapness and convenience.