An Atmospheric Plasma Jet Array Based on the Evanescent-Mode Cavity Resonator Technology*

Atmospheric pressure plasma jets have attracted significant attention due to their diverse applications in fields such as health, material processing, and space propulsion. An evanescent-mode (EVA) cavity resonator plasma jet fabricated using CNC machining has demonstrated remarkable performance, achieving a power efficiency exceeding 80% with an electron density ranging around 10¹⁵ cm^-3 [1]. Such a high-Q resonator is known for its ability to concentrate microwave energy over a small region, making it well-suited to trigger gas breakdown with low input powers. Notably, a substrate-integrated waveguide (SIW)-based EVA plasma jet simplifies the fabrication and enhances the overall performance [2]. Moreover, it enabled a reduction in both the cost and physical footprint of the device. However, these plasma jet devices provided limited plasma volume, making them suboptimal for some applications such as material processing and electric propulsion.

This study introduces an array of plasma jets based on the SIW EVA cavity resonator technology, addressing the plasma jet volume limitation. The resonator, designed at a frequency of 910 MHz, extends the strong E-field region, resulting in a large volume of plasma. A uniform |E|-field on the order of 10⁵ V/m is observed at the resonance frequency with a 1-W input power. To ensure uniform gas flow, the channel is carefully designed, breaking a large inflow into smaller outflow channels directed through the central post of the EVA resonator. The flow splitter is fabricated using a stereolithography (SLA)-based 3D printing technique. Experimental investigations utilize helium flow rates ranging from 1 to 20 slpm and input power levels ranging from 1 to 20 Watts. These findings provide a comprehensive understanding of the performance and behavior of this resonant microwave plasma jet array, offering practical insights for the design and optimization of plasma jet technology.