Ultra-High Efficiency Microwave Plasma for Extreme Low-Power Applications

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Cold plasma is a critical technology in many application fields such as plasma medicine, food preservation, water treatment, reconfigurable electronics, high-quality lighting, electric propulsion systems, sterilization, and microfabrication. However, generating stable plasma is not a trivial task as bulky, expensive, and energy-hungry units are often required. To facilitate widespread use, particularly in low resource settings, there is a need for high efficiency, low power, and low-cost plasmas. Preliminary results indicate that it is indeed possible to achieve plasma of required density with very low input power, even in the milliwatts range, by properly employing microwave resonant structures. Hence, the overarching objective of this effort is to fundamentally investigate extremely low-power and highly efficient resonant microwave plasmas using theoretical, computational, and experimental approaches. This research will advance the knowledge on the fundamental understanding of low-temperature resonant microwave plasmas and is expected to elucidate the interactions between electromagnetic waves and plasmas including self-sustained resonant microwave plasmas. The outcomes of this research will pave the road for the next generation of low-cost and readily available plasma generators. This project is expected to change the understanding of not only the plasma community but also the engineering community that rely on conventional bulky and cumbersome plasma sources that inherently limit their applications. The research results will also be utilized for educational purposes, both at the undergraduate and graduate levels, as well as for scientific demonstrations to children to increase their knowledge about plasma and potentially attract them to the STEM field.Although DC, pulse, and RF plasmas have been extensively explored, there is no comprehensive understanding of microwave plasmas, especially in resonant mode. Resonant microwave plasma occurs in the alpha–discharge regime with an extremely low sheath voltage drop, ensuring that the ignited plasma is stable with no electrode erosion as an important lifetime issue. The proposed research is aimed at developing a theoretical framework for extreme high efficiency and low power plasmas, simulating their behavior computationally, and experimentally validating the theory and computational models. Such plasma can potentially be powered by low-power and readily available supplies including cell phones, solar cells, or even batteries, which makes it safe, low cost, portable, and readily available to many end users. To turn this vision into reality, four major objectives are being pursued: (1) development of a fundamental understanding of resonant microwave discharge physics, (2) assessment and utilization of proper high quality-factor microwave resonant structures, (3) design and implementation of innovative engineered electrodes, and (4) investigation of pre-ionization (e.g., DC and RF) and pulsed microwave techniques. In addition, arrays of scalable resonators will be employed for larger plasma regions. The results of this research are expected to facilitate the realization of ultra-low power plasma sources that can become directly available to many end users.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.