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

TLDR

The study analyzes and characterizes a microstrip split‑ring resonator microplasma source using a microwave model. The authors develop a microwave model, validate it with experimental data from three MSRR designs, and use it to determine plasma impedance and infer microdischarge properties. The model shows that matching microstrip and microplasma impedance is critical, predicts electric fields up to 4 MV m⁻¹, electron densities around 10¹⁴ cm⁻³, and that up to 70 % of input power is coupled to electrons.

Abstract

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 4 MV m−1 at 1 W of input power are estimated to be generated in a 45 µm 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 1014 cm−3 are estimated in a 1 W 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.