Passive Radiative “Thermostat” Enabled by Phase-Change Photonic Nanostructures

Abstract

A thermostat senses the temperature of a physical system and switches heating or cooling devices on or off, regulating the flow of heat to maintain the system's temperature near a desired setpoint. Taking advantage of recent advances in radiative heat transfer technologies, here we propose a passive radiative "thermostat" based on phase-change photonic nanostructures for thermal regulation at room temperature. By self-adjusting their visible to mid-IR absorptivity and emissivity responses depending on the ambient temperature, the proposed devices use the sky to passively cool or heat during day-time using the phase-change transition temperature as the setpoint, while at night-time temperature is maintained at or below ambient. We simulate the 1 arXiv:1902.01354v1 [physics.optics] 4 Feb 2019 performance of a passive nanophotonic thermostat design based on vanadium dioxide thin films, showing daytime passive cooling (heating) with respect to ambient in hot (cold) days, maintaining an equilibrium temperature approximately locked within the phase transition region. Passive radiative thermostats can potentially enable novel thermal management technologies, e.g. to moderate diurnal temperature in regions with extreme annual thermal swings.

Bioinspired Microstructured Materials for Optical and Thermal Regulation

“…Wilton et al had designed an adaptive radiative “thermostat” by VO 2 photonic nanostructures for thermal regulation at room temperature. [ 216 ] The solar spectrum weighted average absorptivity of the system at normal incidence is ≈15% for the dielectric phase and 6% for the metallic phase, which is sufficient to empower a radiative thermostat with the desired properties to perform passive temperature regulation. For VO 2 thin films in the purely metallic phase, a good quality mid‐IR Fabry–Perot cavity was constructed with the fundamental mode resonating at λ ≃ 10 µm, which leads to near unity emissivity at this wavelength.…”

Advances and challenges in commercializing radiative cooling

“…Thus, the VO 2 emitter can not only achieve RC in summer but also provide heating in winter and reduce the negative impact of RC through solar absorption at the same time (Fig. 4f) [90]. Similarly, lanthanum manganese perovskite La 0.7 Ca 0.3-x Sr x MnO 3 also undergoes phase transition with the change of ambient temperature, and the amount of doping can be controlled to adjust the phase transition temperature.…”

“…By introducing insulators such as SiO 2 , MgF 2 , or TiO 2 into VO 2 and aluminum layers, a destructive interference can be formed to increase the tunability of VO 2 ( Fig. 4d and e) [86,89,90]. In addition, it is also viable to increase the infrared absorptivity of VO 2 in high temperature metal state based on the plasma resonance [91].…”

Beyond the Visible: Bioinspired Infrared Adaptive Materials

“…Developing an IR radiative cooling system that can adapt to the surrounding environment is highly preferred. [ 74,75 ] Ono et al. proposed a self‐adaptive IR radiative cooling concept by developing a planar photonic multilayer system with phase‐changing VO 2 materials and spectrally selective filters, which was able to automatically switch IR radiative cooling according to the temperature changes of surrounding environment with no need of external energy input (Figure 9d,e).…”