Dynamic Measurement of Relative Complex Permittivity of Microwave Plasma at Atmospheric Pressure

Ge Wang,Huacheng Zhu,Yang Yang,Hui Pan,Shimiao Lai,Li Wu,Yongjie Zhou

doi:10.3390/pr9101812

Abstract

Complex permittivity is one of the most important parameters to characterize the interaction between microwave and medium, especially for microwave-excited plasma. It is convenient to study plasma’s dielectric properties and microwave propagation characteristics by measuring its complex permittivity. A dynamic measurement method of equivalent relative complex permittivity of microwave-excited plasma at atmospheric pressure is proposed in this paper. Firstly, a cavity based on WR-430 at a frequency of 2.45 GHz was specially designed in COMSOL. Then, the samples with different real parts of complex permittivity and loss tangent were simulated in the designed cavity to obtain their corresponding S parameters, and they were used to train the BP neural network until the error was lower than 0.001. A two-port network was built to excite the plasma. The input power, reflected power, and transmitted power could be measured by the transmission reflection method. Finally, the measured power values were converted into S parameters and used as inputs in the BP neural network. The plasma’s real parts of complex permittivity and loss tangent were obtained by inversion. The variation of plasma complex permittivity conforms to the interaction principles between microwave and plasma, which verifies the accuracy of the method.

Highlights

Plasma can be equivalent to a medium whose dielectric properties are characterized by equivalent complex permittivity
Complex permittivity is an important parameter representing the interaction of plasma excited by microwave
COMSOL Multiphysics was used to simulate the samples represented by a wide range of complex permittivity to obtain their corresponding |S11 | and |S21 | parameters

Summary

Introduction

Plasma can be equivalent to a medium whose dielectric properties are characterized by equivalent complex permittivity. By measuring the complex permittivity of the medium, the design of materials and cavity can be optimized in the simulation, which is of great significance to improve the utilization efficiency of microwave. Complex permittivity measurement has been applied in various fields such as aerospace and industry [1,2]. Some novel metamaterials and plasma with distinctive dielectric properties to those of conventional materials have emerged. The real part of their complex permittivity is negative [3] with a wide range, which fluctuates with the microwave frequency, power, temperature and pressure. It poses a new challenge to the measurement of complex permittivity

Methods

Results

Conclusion