Enhanced Infrared Emission by Thermally Switching the Excitation of Magnetic Polariton with Scalable Microstructured VO2 Metasurfaces

Abstract

Dynamic radiative cooling attracts fast-increasing interest due to its adaptability to changing environment and promises for more energy-savings than the static counterpart. Here we demonstrate enhanced infrared emission by thermally switching the excitation of magnetic polariton with microstructured vanadium dioxide (VO2) metasurfaces fabricated via scalable and etch-free processes. Temperature-dependent infrared spectroscopy clearly shows that the spectral emittance of fabricated tunable metasurfaces at wavelengths from 2 to 6 um is significantly enhanced when heated beyond its phase transition temperature, where the magnetic polariton is excited with metallic VO2. The tunable emittance spectra are also demonstrated to be insensitive to incidence and polarization angles such that the VO2 metasurface can be treated as a diffuse infrared emitter. Numerical optical simulation and analytical inductance-capacitance model elucidate the suppression or excitation of magnetic polariton with insulating or metallic VO2 upon phase transition. The effect of enhanced thermal emission with the tunable VO2 metasurface is experimentally demonstrated with a thermal vacuum test. For the same heating power of 0.2 W, the steady-state temperature of the tunable VO2 metasurface emitter after phase transition is found to be 20degC lower than that of a reference V2O5 emitter whose static spectral emittance is almost the same as that of the VO2 metasurface before phase transition. The radiative thermal conductance for the tunable metasurface emitter is found to be 3.96 W/m2K with metallic VO2 at higher temperatures and 0.68 W/m2K with insulating VO2 at lower temperatures, clearly demonstrating almost six-fold enhancement in radiative heat dissipation.