Impedance Measurement System for a Microwave-induced Plasma

An impedance measurement system for an atmospheric microwave-induced plasma is proposed using equivalent transmission line theory and a de-embedding process of an input impedance. An argon plasma was generated by using a microwave-induced discharge. The generator consists of a 2.45 GHz solid state power oscillator (SSPO), a circulator, a directional coupler, a three-stub tuner, a gas flow meter, and a plasma jet. The microwave source power was varied from 10 to 25 W, and the argon gas flux was varied from 1 to 5 L/min at atmospheric pressure. The experimental results for the microwave-induced plasma show the impedance behaviors of the resistance and the inductive reactance. The near unity voltage standing wave ratio (VSWR) from the experiment results ensures that the proposed measurement system is valid.