Independent Control of Spectral and Directional Emissivity with Multilayer Structures

Abstract

Utilizing micro-nano structures to achieve directional and spectral control of thermal radiation holds significant scientific importance. It may significantly benefit a broad range of applications, including infrared light sources, radiation detection, and waste heat utilization of thermophotovoltaics. However, existing thermal emitters face challenges in realizing narrowband and directional emissivity and lack independent control of angular and spectral selectivity. This study develops a simple but novel approach to thermal emitter design that enables independent control of directionality and emissivity peak of thermal radiation. An angle-selective filter and a spectral selective emitter are selected as the structural components, and a series of different narrowband and directional thermal emitters are designed to show the advantage of independent tunability. After optimization with the NSGA-II algorithm, a narrowband and directional thermal emitter is achieved, offering high emissivity only at the given direction and wavelength. An emitter with only seven layers demonstrates a maximum emissivity of 0.97, an angular width under 20°, and a spectral width below 0.025 µm, as validated by angle-resolved emissivity measurements. This study provides a straightforward and effective route for designing narrowband and directional thermal emitters with promising applications in thermal radiation management.