Broadband directional control of thermal emission

Abstract

We experimentally realize a broadband directional thermal emitter by introducing a subwavelength photonic film consisting of multiple oxides that exhibit epsilon-near-zero (ENZ) regions at long-wave infrared wavelengths.

Passive daytime radiative cooling: Fundamentals, material designs, and applications

“…This broadband directional emitter enables meaningful heat transfer and energy applications, which can overcome the conventional limits on the angular response of selective emitter to improve performance in solar thermal conversion, thermophotovoltaics, radiative cooling, and waste heat recovery. 78…”

“…The effective heat transfer coefficient h = 0.5 W m −2 K −1 . (E)–(I) Directional emitter based on gradient epsilon‐near‐zero material structures (Reproduced with permission: Copyright 2021, AAAS) 78 . (E) and (F) SEM images of the experimentally fabricated multilayer photonic film structures.…”

“…The angle‐dependent emitters consisted of conventional oxides that exhibit high (> 0.7 and > 0.6) directional emittance (60–75° and 70–85°) in the broadband wavelength of 10.0–14.3 μm and 7.7–11.5 μm, respectively (Figure 10G,H). This broadband directional emitter enables meaningful heat transfer and energy applications, which can overcome the conventional limits on the angular response of selective emitter to improve performance in solar thermal conversion, thermophotovoltaics, radiative cooling, and waste heat recovery 78 …”

Observation of Non-Vanishing Optical Helicity in Thermal Radiation from Symmetry-Broken Metasurfaces

“…directivity. 16,17 However, the photon spin, as another crucial characteristic of electromagnetic radiation, is so far commonly ignored, due to the fact that conventional thermal emitters show weak to zero spin-angular momentum (SAM).…”

Spatially-Segmented Colored Radiative Cooler With Angle-Robustness

“…For example, in buildings, the cooler is traditionally installed on a rooftop, but the sidewall, which occupies most of the buildings, is also an option to maximize the cooling potential. Recently, directional control of heat emission that can be adjustable for the side-wall cooling has been highlighted [24], [25]. However, the high reflectivity in common radiative coolers seriously hinders using the sidewall because the reflected sunlight can damage adjacent buildings, walking pedestrians, and ecosystems [26]- [28].…”