Investigation into the discharge characteristics and antimicrobial effects of different electrode configurations based on the needle–ring–ring structure

Cold atmospheric pressure plasma (CAP) has demonstrated broad potential in disinfection and sterilization. Among CAP generation methods, plasma jets based on needle–ring structures are widely adopted. To improve discharge performance, modified needle–ring–ring structures have been developed. However, variations in electrode configuration within this structure can markedly affect discharge dynamics and application outcomes. In this study, six configurations under the needle–ring–ring framework were systematically compared in terms of discharge characteristics and antimicrobial performance. Based on discharge imaging, optical emission spectroscopy, and the concentrations of long-lived reactive species (H₂O₂, NO^-₂, and NO^-₃), configurations with the bottom ring grounded produced stronger discharges than floating configurations. Among them, the configuration with the upper ring floating and bottom ring grounded produced the most intense plasma jet. Using Staphylococcus aureus as a model organism, the antibacterial efficacy of plasma-activated water was found to vary among configurations and increased significantly with treatment duration. Overall, when the hollow needle served as the high-voltage electrode, the configuration with the upper ring floating and bottom ring grounded yielded optimal plasma performance and the highest reactive species concentrations. This study provides experimental evidence to guide the design and optimization of high-efficiency plasma jets based on the needle–ring–ring structure.