Atmospheric-pressure plasma sources are used in plasma-assisted processing, biomedical treatment and sterilization, surface modification, environmental remediation, agricultural treatment, propulsion, photonics, and plasma-assisted acceleration. Many conventional sources rely on inductively coupled plasma, dielectric-barrier discharge, electrode-based discharge mechanisms, noble-gas feedstocks, sealed chambers, external matching networks, or bulky architectures. These limitations can restrict portability, scalability, operating efficiency, and deployment in resource- or size-constrained environments.
Air-breathing plasma platforms, including air-breathing electric propulsion and atmospheric cold plasma systems, benefit from generating stable plasma directly from ambient air. However, air breakdown at atmospheric pressure typically requires efficient power coupling, high localized electric fields, and careful gas-flow control. Existing microwave plasma structures may reduce power needs but often produce point-like or microscale discharges rather than elongated, controlled plasma jets.
Invention Description
Researchers at the University of Toledo have developed a compact cavity-resonant, air-breathing microwave plasma jet system that generates stable plasma directly from atmospheric air using a modified evanescent-mode cavity resonator. The assembly includes a metallic post disposed within a cavity to form the resonator, a capacitive micro-gap between the post and cavity ceiling, a radio-frequency port for coupling microwave energy, and an integrated gas-flow channel that directs atmospheric air into the high-field capacitive region A prototype operated near 2.25 GHz showed a reported Q-factor above 1,000, ignite plasma at 2.6 W, sustained discharge at approximately 1.5 W, and generated a well-defined ~7mm tubular plasma jet at about 10 W and 25 slpm atmospheric air.
The architecture can be scaled for different jet sizes, plume geometries, operating frequencies, and multi-jet arrays. The system is designed to reduce or eliminate reliance on noble gases, consumable gas supplies, complex external matching systems, and bulky plasma-source architectures.
Applications
• Biomedical sterilization, wound/skin treatment, and plasma-based treatment platforms
• Surface modification, materials processing, and plasma-assisted manufacturing
• Air purification, water purification, and portable environmental remediation
• Agricultural treatment and generation of plasma-activated air or water
• Air-breathing electric propulsion and very-low-Earth-orbit satellite systems
Advantages
• Generates plasma directly from atmospheric air, reducing or eliminating noble-gas feedstocks and consumable gas supplies.
• Compact, cavity-resonant microwave architecture supports portable and size-constrained implementations.
• Evanescent-mode resonator concentrates electromagnetic energy in a capacitive micro-gap for low-power ignition and sustainment with a very high energy conversion efficiency.
• Demonstrated stable tubular plasma jet formation rather than only point-like or microscale plasma discharges, enabling the technology for scaled plasma volume.
• Scalable design may support larger plumes, different operating frequencies, or arrays of air-breathing plasma jets.