Thermal Radiation Modulation Structures Based on Vanadium Dioxide
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Thermal Radiation Modulation Structures Based on Vanadium Dioxide

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Abstract

Thermal Radiation is intrinsic emission of electromagnetic waves from all matter that has a temperature greater than zero Kelvin. In the past decades, many applications related to thermal radiation have been studied and developed. However, most of these applications are based on materials with static emissivity, which is limited to the range from 0 to 1. Due to the fast development of material science and fabrication techniques, the emissivity of latest thermal infrared (IR) materials is already very close to unity. Thus, thermal performance with constant emissivity is saturated. In recent years, thermal radiation modulation materials have opened a new page in thermal radiation research and applications by breaking the performance limit and overcoming the intrinsic disadvantages of conventional, constant-emissivity materials. In this dissertation, multiple innovative thermal radiation modulation materials and structures based on the phase transition material, vanadium dioxide, are presented. For thermography applications, infrared (IR) camera reads the surface temperature by assuming a constant high emissivity (~0.9) of the target objects. Thus, if the emissivity of the target is different from 0.9, IR camera will be deceived, and the temperature readout (T_IR) will differ from the real surface temperature (Ts). In chapter 2-3, we demonstrate that by modulating the emissivity, we can achieve novel T_IR- Ts relations which enable applications that are impossible with conventional materials. By modulating the emissivity to nearly 1/T^4 dependence with graded W-doping in VO2 thin films, we achieve a temperature-insensitive T_IR at different values over a wide temperature range. The T-insensitive T_IR can be utilized for IR camouflage and IR decoy applications. We also develop a thermal imaging sensitizer (TIS) that has sharp emissivity increase during the phase transition of W-doped vanadium oxide (WxV1-xO2). The resultant high dT_IR/dTs can bring more than 15 times of enhancement to the sensitivity of conventional IR cameras. The TIS may find its applications in electronics, building construction and medical diagnostics. In chapter 4-5, we discuss our research effort on energy-saving in building temperature regulations. As the emissivity of conventional cool roof materials has reached the physical limit in recent years, we further improved the energy saving potential by developing a temperature-adaptive radiative coating (TARC) with switchable emissivity. TARC acts as a high-emittance radiative cooler coating at (and only at) high temperatures, while retaining heat under the surface at low temperatures. Simulations and experiments showed that the TARC may outperform all conventional roof materials in terms of cutting energy consumption for households. To tackle the critical problems of the building application of TARC, such as scalability, durability and color tunability, we explore a scalable temperature-adaptive radiative coating (STARC) produced with a roll-to-roll method. With the new polymer-based structure, STARC have lower cost and longer lifetime. Moreover, the color of STARC can be tuned with IR-transparent pigments for the needs of aesthetic and solar absorption optimization. A field with carefully designed mock-up houses directly proved the temperature regulation ability of STARC. The application of STARC and TARC can also be expanded to a wider scope, such as tents, vehicles, clothes, space objects and mobile electronics.

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This item is under embargo until September 27, 2026.