Smart regulation of thermal infrared radiation with meta-structured metal-insulator transition

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Nontechnical:Infrared (IR) images are produced by IR cameras capturing thermal IR radiation from hot objects. This process has a wide range of applications in night vision, thermography, remote sensing, medical imaging, and building monitoring. Despite extensive efforts, true innovations are sought to meet the needs of the rapidly advancing modern society. IR imaging is a two-step process. Power is radiated from a hot surface and then converted to an electrical signal by an IR camera. Current efforts to improve thermal imaging sensitivity focus on improving the camera, because the radiated power is believed to be limited by a physical law that dictates the amount of IR power radiated from the object at given temperature. Consequently, the temperature sensitivity for IR imaging is limited to ~ 0.04 degree C. However, this sensitivity is not fine enough, and prevents some critical applications of IR imaging. The PI will advance IR imaging by overcoming the physical law that limits radiated power. The PI will develop a coating material that drastically boosts the radiated IR power within a selected temperature range. This will effectively amplify the effective temperature variation of the object into large variation of IR imaged temperature. As a result, the temperature sensitivity of IR imaging with a conventional camera is improved by a factor of over 15, to below 0.003 degree C. Such an improvement enables sensitive detection of weak defects in integrated circuits, early diagnosis of sub-skin tumors, and inspection of sub-surface building cracks. The coating material can also be used to implement switchable radiative cooling to cool a surface when its temperature is higher than the preset temperature. The new devices to be developed and deployed will push the boundary of thermal imaging and radiative cooling much beyond the state-of-the-arts, promising great values for potential commercialization. Integrated with the research effort, the PI also proposes an educational program that will stimulate and prepare pre-college students for careers in engineering pertaining to infrared technologies.Technical:The goal of this project is to demonstrate smart, previously non-existing thermal IR regulation devices for ultra-sensitive sub-surface IR imaging and switchable radiative cooling. The PI plans to accomplish the goal by re-imagining the Stefan-Boltzmann law of thermal radiation by lifting its limitation, to achieve orders of magnitude enhancement in IR imaging sensitivity. Materials with metal-insulator transition integrated with plasmonic resonance enable a large switching in thermal radiation, a property not found in any conventional materials. The metal-insulator transition is engineered with doping and plasmonic resonance to achieve unprecedented physical properties of temperature-dependent emissivity, which are the key innovations in this proposal. Tungsten-doping substantially expands the working temperature range of vanadium dioxide, while micro-patterned metaphotonic design reverses and amplifies the contrast in IR radiation across the transition. The resultant switching in surface emissivity at tunable and preset temperatures lays the materials foundation to smart regulation of thermal IR radiation: drastic enhancement in IR imaging sensitivity, and switchability in radiative cooling.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.