Curvature-enhanced thermal radiation in micro-structure

Abstract

Thermal radiation management is important in various micro-systems, such as integrated photonic design, thermal logic computing and energy harvesting, but the curvature effect of micro-structures on thermal radiation almost remains elusive. In this work, the mechanism of curvature effects on radiation is studied from near-field to far-field based on concentric cylinders with fluctuation-dissipation theory (FDT). A general formula applied for anisotropic materials radiation is derived, with the SiO₂-VO₂ system analyzed as an example. The effects of curvature on radiation are investigated with SPPs, SPhPs and Hyperbolic surface modes. In near field-condition where the gap is smaller than the radius on the order of the tunneling depth, surface with curvature can transfer more heat radiation than plane, both for inner and outer surface. Some surface wave modes suppressed in planar geometries are activated in micro-cylindrical structures. Also, structure curvature enhances radiation in the far-field, enabling super-blackbody radiation in some cases. The results above are analyzed from the perspective that oscillators have more opportunity to radiate energy away from the curved structure. Lastly, the enhancement mechanism studied above is applied to thermal rectification with cylindrical configuration, the max rectification ratio can be up to 22 in GST-SiO₂ system, achieving an order-of-magnitude enhancement compared the ratio of 2 in planer structure. This work provides a further insight to thermal management in micro-systems.