Nonreciprocal thermal radiation metamaterial enhanced by asymmetric structure at extremely small incident angle

In recent research, magneto-optical dielectrics have been widely employed to achieve nonreciprocal thermal radiation. However, limited attention has been given to the influence of structural asymmetry on nonreciprocal behavior. At the same time, small-angle nonreciprocal thermal radiation has attracted growing interest in the field of energy harvesting. In this work, two asymmetric configuration are proposed to realize nonreciprocal thermal radiation within the spectral range of approximately 12∼12.7 µm, which is located in the atmospheric transmission window. The study begins with a grating structure and extends to two optimized configurations. The nonreciprocity reaches over 90% under 0.8° incidence at 12.64 µm or reaches 86% at multipoints. The design strategies, including slanted gratings, laterally offset gratings, and inclined cylindrical inserts, are central to this work and are shown to enhance the nonreciprocal effect. Also, the mechanisms of the three methods are analyzed. This tactics broadens the range of structural strategies for achieving nonreciprocity and offers new insights for applications in energy harvesting, thermophotovoltaics, and electroluminescent cooling.