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

常压空气中的低温等离子体会产生极具活性的化学反应，可用于从医疗设备的水净化和消毒到伤口愈合和医疗治疗，甚至用于减轻发动机和类似设备的污染。虽然等离子体技术历来仅限于实验室，但现场便携式等离子设备可以在许多环境中发挥重要作用；传教士和救灾人员可以在资源匮乏的地区清理饮用水，医务人员可以在远离医院或诊所的地方治疗伤口，或者实地科学家可以使用它们进行快速土壤或水分析。除了手持应用之外，还很容易设想将微型等离子设备整合到车辆的尾气中，以帮助消除尾气污染物。制造便携式等离子设备的主要挑战之一是，它们本身就需要消耗电力，而对于大气压的空气，需要数千伏的电压才能运行。虽然电池供电的设备是可能的，但不需要车载电力来源并通过从周围收集机械或热能来操作的设备将非常有影响力。该项目将研究如何利用非中心对称晶体的偏振特性来开发大气压空气等离子体设备，这种设备可以通过直接从运动或废物/太阳热能转换能量来操作。这项基础研究的目标是建立低温等离子体工程，通过收集热能或机械能直接产生空气等离子体。该策略是利用非中心对称晶体的高极化率来产生极高的表面场，从而直接从晶体表面形成等离子体。压电晶体将用于机械到等离子体的能量转换，热释电晶体将用于热到等离子体的能量转换。通过电学测量和光学测量(包括汤姆逊散射、时间分辨成像和光学发射光谱)，将建立压电/热释电晶体特性与等离子体产生和等离子体特性之间的关系。将确定控制和增强等离子体形成的策略，包括操纵晶体构型(局部晶体极化)、晶体表面或几何形状(尖锐特征)以及能量输入到晶体的方式(开启与关闭谐波激发)的方法。最后，将探索设计仅依靠机械或热能工作的等离子体设备的方法，并将制定如何最有效地将振动或热量耦合到非中心对称晶体中以产生等离子体的设计规则。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.