An Economic Real-Time Microwave Plasma Impedance Measurement Method

A novel method for measuring microwave plasma impedance is presented. Plasma impedance is measured in real-time using three coupling probes and a microwave detector, rather than using a vector network analyzer or directional coupler, spectrometer. The measured impedance of a plasma filament at atmospheric pressure demonstrates that the impedance changes significantly with power variation, whereas the influence of airflow is minor. This implies that the impedance matching of atmospheric pressure microwave plasmas should take into account the effects of microwave power variations, and the use of a fixed matcher is not recommended for impedance matching of plasma jets unless they are operating at a fixed power. This measurement method avoids the intervention of other microwave power or expensive instruments, which facilitates the development of microwave plasma models and the tuning of efficiency.