Thermochromic emission regulation for switchable omnidirectional radiative cooling and directional infrared stealth

Low emissivity required for infrared stealth in the atmospheric window may hinder a surface's radiative cooling, potentially suppressing temperature decreasing and increasing its detectability. Consequently, concurrent optimization of radiative cooling capability and infrared stealth performance remains a critical challenge in advanced surface design. One possible solution lies in regulating the directionality of surface emissivity effectively. In this work, a VO₂-based metasurface with switchable directional infrared stealth (DIS) and omnidirectional radiative cooling (ORC) is proposed. In DIS mode, the metasurface enables radiative cooling through directional emission at large angles while maintaining infrared stealth at low detection angles. Owing to the phase transition of VO₂, the metasurface can switch to ORC mode, where omnidirectional high emissivity is achieved to enhance radiative cooling when infrared stealth is not required. The geometric parameters of the metasurface are determined through a target-oriented design strategy by combining an equivalent circuit model with a transmission line model. During the phase transition of VO₂ between metallic and insulating states, omnidirectional and directional high emissivity can be achieved through the excitation of Magnetic Polaritons and the Plasmonic Brewster Angle effect, respectively. For a spacecraft with internal temperature 700 K, the proposed metasurface can effectively reduce the surface temperature by 342.85 K compared with the perfect stealth surface in ORC mode. Due to perfect emissivity at 85° while normal emissivity is suppressed to 0.18, radiation intensity can be reduced by 48.54% compared to the diffuse emission surfaces with the same hemispherically averaged emissivity in DIS mode. The proposed switchable directional emissivity design method for phase transition material based metasurface in this research provides a promising approach to solving the challenge of balance radiative cooling and infrared stealth for surface regulation of spacecraft.