Passive cooling effect of infrared metamaterial absorber

Over the past decade, infrared metamaterial absorbers have been extensively studied. Great efforts have been dedicated to design broadband, omi-directional, and high-efficient infrared absorbing structures with the potential sensing, detecting, and imaging applications. As a matter of fact, infrared absorber is also infrared emitter. Due to Kirchhoff's law, the frequency selective absorption equals to the frequency selective emitting which can be applied for passive cooling. In this work, infrared metamaterial absorbers at three crucial bands are realized by carefully designed sandwich structure of metallic pattern — dielectric spacer — metallic ground plane. The relationship between electromagnetic wave energy dissipation for absorption design and thermal radiation for heat transfer is discussed to explore the physical mechanism of passive cooling. Effective method associated with equivalent circuit approach reveals that the localized magnetic resonance determines the energy transfer. According to heat transfer theory, thermal cooling model of metamaterial covered heat object is proposed to analyze the effect of selective emitting. The integration form of Wien's law shows that the passive cooling effect is determined by both the emitting spectrum and heat source. After optimization, the proposed absorber can effectively improve the cooling rate of heat object experimentally. This technique can be used for the thermal control of electronic device.