Enhanced radiative energy tunneling with dielectric optical resonators and its usage in harvesting thermal energy inside a solid

远场热辐射是一种表面间的宽带能量传递。当表面之间的距离小于几十到几百纳米时，辐射光谱可以被限制在一个非常窄的频带内，其辐射强度可以比黑体极限高几个数量级。这种微观现象被称为近场热辐射。近场辐射中的高强度能量输运对于构建高效、高功率密度的热机（如热光伏）具有重要价值，从而降低运输和发电中的燃料消耗。然而，实现近场热辐射在实际应用中是具有挑战性的，因为在冷热表面之间需要几十到几百纳米的分离距离很难保持。本研究将通过放大非辐射热电场和由此产生的冷热表面之间的隧道距离，将近场热辐射的有用范围扩展到微米级。拟议的项目建立在研究者在近场能量传输和纳米光学谐振器的设计/制造方面的专业知识之上，纳米光学谐振器可以用超薄的超表面结构放大热电场。项目任务是首先将介电光学天线理论与维纳混沌展开相结合，利用合适的高质量介电光学谐振器（DORs）在不同温度下通过真空间隙了解两个有耗固体之间的共振、放大和辐射能量隧穿。这将允许确定隧道频率，效率和两个固体之间的距离作为DOR设计的函数。考虑寄生热传导和光伏器件量子效率的增强型长距离隧道辐射传热方案的能量收集系统的理论热效率将作为辐射强度和输出电压的函数进行研究。所获得的知识对于利用现有的工程技术建造高效率、高功率密度、轻型热机将是有价值的，这有可能减少温室气体排放和相关的环境影响，并增加国家的能源安全。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Far-field thermal radiation is a type of broadband energy transfer among surfaces. When the separation distances among surfaces are less than tens to hundreds of nanometers, the radiation spectrum can be confined to a very narrow band, where the radiation intensity can be orders of magnitude higher than the blackbody limit. This microscale phenomenon is called near-field thermal radiation. The high-intensity energy transport in near-field radiation can be valuable in constructing high efficiency, high power density thermal engines for thermal to electric energy conversion such as thermophotovoltaics, thereby reducing the fuel consumption in transportation and electricity generation. However, implementing near-field thermal radiation can be challenging in practical applications because the required tens to hundreds of nanometer separation distance between hot and cold surfaces are difficult to maintain. This study will extend the useful range of near-field thermal radiation to micron-levels by amplifying the non-radiative thermal electric field and the resulting tunneling distance between hot and cold surfaces. The proposed project is built upon the investigator's expertise in near-field energy transport and the design/fabrication of nano-optical resonators that can amplify the thermal electric field with ultra-thin metasurface structures. The project tasks are to first integrate dielectric optical antenna theory with Wiener Chaotic expansion to understand resonance, amplification, and radiative energy tunneling between two lossy solids across a vacuum gap with appropriate high-quality factors dielectric optical resonators (DORs) under different temperatures. This will allow for the determination of the tunneling frequencies, efficiencies, and distances between two solids as functions of DOR designs. Theoretical thermal efficiencies of energy harvest systems using the enhanced long-distance tunneled radiative heat transfer scheme with a consideration of parasitic heat conduction and quantum efficiencies of photovoltaic devices will then be studied as a function of radiation intensities and output voltages. The knowledge gained will be valuable in constructing high-efficiency, high-power density, lightweight thermal engines using currently available engineering techniques, which can have the potential to reduce greenhouse gas emissions and the associated environmental impacts and increase the nation's energy security.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.