Broadening of infrared radiation band based on inorganic metamaterials for radiative cooling

Radiative cooling (RC) represents a crucial heat dissipation method for spacecraft and electronic devices. In these applications, broader infrared radiation contributes to more efficient cooling. Inorganic materials are extensively employed due to their exceptional resistance to photothermal degradation. However, the narrow infrared intrinsic absorption peaks of these materials present a significant challenge in broadening their radiation bands. This study introduces an innovative square-column metamaterial (SCMM) developed through the integration of a metasurface with an inorganic multilayer film, specifically Si₃N₄/Al₂O₃/SiO₂/Si₃N₄/Ag/(etched Si substrate), using optical etching technology. The incorporation of the metasurface structure extends and regulates the radiation band of the inorganic multilayer film from 8–13 μm to 8–20 μm. Through size adjustment of the square column, the emissivity in the 8–20 μm wavelength range increases from 80.3% to 92.1%. The achievement of broad and high infrared radiation is attributed to localized surface plasmon resonance and metal–insulator–metal cavities in the micrometer array. Moreover, the SCMM demonstrates excellent cooling characteristics in actual temperature measurements. This research offers an innovative approach for RC materials to address spectral requirements in specific applications.