关键词: 塔黄, 太阳辐射, 光学性质, 温度调节, 结构功能面

Abstract: Regarding the survival adaptation mechanisms of Rheum nobile in the high-altitude alpine environment of the Himalayas, this paper combines Finite Difference Time Domain (FDTD) optical simulation to investigate the thermoregulatory function of the densely packed spherical protrusion structures on its semi-transparent bracts. The greenhouse effect, as an effective strategy for maintaining suitable internal temperatures, typically requires high transmittance of shortwave solar radiation. Compared to ordinary rosette leaves, the bracts of Rheum nobile exhibit significantly enhanced solar radiation transmittance. Simulation analyses reveal that the surface protrusion structures enhance transmittance in the visible to near-infrared range, thereby more efficiently channeling solar radiation into the internal greenhouse space under strong sunlight and promoting the formation of the greenhouse effect. Further research shows that the hierarchical microstructure on the bract surface forms a graded refractive index layer, avoiding abrupt changes in refractive index and significantly suppressing light reflection, thereby improving transmittance efficiency. This enhanced transmittance enables Rheum nobile to effectively transfer environmental radiant heat into the greenhouse interior despite the limited volume of its bracts, providing new ideas for the design of bionic materials and systems related to radiation insulation.

Key words: Rheum nobile, Solar radiation, Optical properties, Thermoregulation, Structural-functional surface