Split-ring resonator microplasma : microwave model, plasma impedance and power efficiency

The microstrip split-ring resonator (MSRR) microplasma source is analysed and characterized using a microwave model of the device. Throughout the discussion, experimental data for three MSRR designs are also presented. The model identifies the key parameters that control the performance of the device and results in the formulation of closed-form expressions useful for designing, analysing and comparing MSRR designs. Matching the microstrip characteristic impedance to the microplasma impedance is found to be a key factor in the performance of these devices and it can be even more critical than the quality factor of the ring resonator. Based on the model, average rf electric fields of up to 4MVm−1 at 1Wof input power are estimated to be generated in a 45μm gap device. Furthermore, the model is used to determine the plasma impedance and thereby obtain information on physical properties of the microdischarge. Electron densities of the order of 10(14) cm−3 are estimated in a 1W argon discharge at atmospheric pressure. Based on the values of the plasma impedance, it is also determined that up to 70% of the power input to the MSRR is coupled to the electrons in the microdischarge.