Energy Harvesting Approaches to Low-Temperature Plasma Generation for Field Applications

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Low-temperature plasmas in atmospheric-pressure air produce extremely reactive chemistry that can be used in applications ranging from water purification and sterilization of medical equipment to wound healing and medical therapeutics or even for mitigating pollution from engines and similar equipment. While plasma technology has historically been restricted to the laboratory, field-portable plasma devices could play an important role in a number of settings; missionaries and disaster responders could clean drinking water in low-resource areas, medical personnel could treat wounds far from a hospital or clinic, or field scientists could use them for rapid soil or water analysis. Beyond the hand-held applications, it is also easy to envision miniaturized plasma devices incorporated into the exhaust of vehicles to help destroy exhaust pollutants. One of the primary challenges for making portable plasma devices is that they inherently consume electrical power, and for atmospheric-pressure air, require thousands of volts to operate. While battery-powered devices are possible, devices that require no source of on-board electrical power and operate by harvesting the mechanical or thermal energy from their surroundings would be very impactful. This project will investigate how the polarization properties of non-centrosymmetric crystals can be utilized to develop atmospheric-pressure air plasma devices that can be operated by direct energy conversion from either motion or from waste/solar heat.The goal of this fundamental research is to establish the engineering of low-temperature plasmas that operate by harvesting thermal or mechanical energy to directly produce an air plasma. The strategy is to take advantage of the high polarizability of non-centrosymmetric crystals to produce extremely high surface fields leading to plasma formation directly from the crystal surface. Piezoelectric crystals will be used for mechanical-to-plasma energy conversion and pyroelectric crystals for thermal-to-plasma energy conversion. Relationships between piezoelectric/pyroelectric crystal properties and plasma generation and plasma properties will be established using electrical measurements and optical measurements (including Thomson scattering, time-resolved imaging, and optical emission spectroscopy). Strategies to control and enhance plasma formation will be determined including approaches that manipulate the crystal configuration (local crystal polarization), crystal surface or geometry (sharp features), and the way energy is input into the crystal (on versus off harmonic excitation). Finally, ways to engineer plasma devices that operate only off mechanical or thermal energy will be explored, and design rules will be developed for how to most effectively couple vibrations or heat into a non-centrosymmetric crystal for plasma generation.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.