Adaptive thermal camouflage using sub-wavelength phase-change metasurfaces
Sub-wavelength metasurface designs can be used to artificially engineer the spectral thermal signature of an object. The real-time control of this emission can provide the opportunity to switch between radiative cooling (RC) and thermal camouflage functionalities. This performance could be achieved by using phase-change materials (PCMs). This paper presents a sub-wavelength dynamic metasurface design with the adaptive property. The proposed metasurface is made of vanadium dioxide (VO2) nanogratings on a silver (Ag) substrate. The design geometries are optimized in a way that both narrowband and broadband mid-infrared (MIR) emitters can be realized. At low temperatures, insulating VO2 nanogratings trigger the excitation of Fabry–Perot mode inside the grating and surface plasmon polaritons at the metal–dielectric interface with an emission peak located in the MIR region to maximize the RC performance of the design. As temperature rises, the PCM transforms into a metallic phase material and supports excitation of Wood's anomaly and localized surface plasmon resonance modes. Accordingly, the thermal signature is adaptively suppressed.