Controlling the directionality of thermal radiation has long been a subject of intense scientific inquiry. Addressing this challenge head-on, a research team led by Professor Sun Kyung Kim at Kyung Hee University has achieved a remarkable milestone by uncovering an extraordinary phenomenon. For the first time, they observed the enhancement of thermal radiation in the horizontal direction while simultaneously suppressing it in the vertical direction from a silicon substrate containing a precisely engineered microstructure.

When a structure emits thermal radiation energy primarily sideways instead of forwards, an intriguing optical phenomenon unfolds when viewed through a thermal imaging camera. Depending on the viewing angle, the structure seemingly appear or disappear. In the experiment, when the thermal imaging camera was rotated from a vertical angle, no discernible image showed up. Yet, at rotation angles exceeding 60 degrees, the structure's image suddenly emerged with striking clarity.

Integrating such structures into electronic devices, such as smartphones, could notably enhance the thermal comfort experienced by users operating these devices at close distances. Professor Kim envisaged a broad range of applications for this technology, remarking, "The implementation of structures that emit radiation sideways can greatly contribute to maintaining thermal comfort for users employing electronic devices in close proximity."

SEM images of a fabricated microstructure (left) and the results of thermal camouflage experiments (right) 

[Reference] Jin-Woo Cho, Yun-Jo Lee, Jae-Hyun Kim, Run Hu, Eungkyu Lee, and Sun-Kyung Kim, Directional radiative cooling via exceptional epsilon-based microcavities, ACS Nano, 10.1021/acsnano.3c01184

[Main Author] Sun Kyung Kim (Kyung Hee Univ.), Jin Woo Cho (Kyung Hee Univ.)

* Contact : sunkim@khu.ac.kr