Control of Far-Field Thermal Radiation Characteristics Based on Micro/Nano Structural Materials

This chapter investigates various strategies for actively and passively modulating far-field thermal radiation using micro/nano structured materials. The investigation begins with a thermoelectric tunable narrowband absorber. By exploiting the phase-change properties of vanadium dioxide and the tunable chemical potential of graphene, the absorber achieves a high modulation range (0.931) driven by temperature and voltage. The chapter then explores spectral control in one-dimensional periodic structures, such as pyramidal and smooth shapes designed via Hermite interpolation. It demonstrates that rotating the crystal axis of natural hyperbolic materials can shift the broadband absorption region and significantly expand the bandwidth. The physical mechanism is rooted in the "slow light" effect, where incident light is captured at different heights within the structure. Furthermore, the chapter analyzes two-dimensional periodic structures, showing that a gradient refractive index effect—derived from equivalent medium theory—enables near-perfect broadband absorption (up to 99.99%) through refractive index matching with air. Finally, the chapter addresses the adjustable Brewster effect in anisotropic crystals. By analyzing quartz with a tilted crystal axis, it derives new conditions for the Brewster angle in hyperbolic regions and shows how axis orientation can switch the effect on or off. This chapter highlights how geometric engineering and material anisotropy can achieve unprecedented control over far-field spectral and directional characteristics.