Wideband mid-infrared thermal emitter based on stacked nanocavity metasurfaces

Efficient thermal radiation in the mid-infrared (M-IR) region is of supreme importance for many applications including thermal imaging and sensing, thermal infrared light sources, infrared spectroscopy, emissivity coatings, and camouflage. The capability of controlling light makes metasurface an attractive platform for infrared applications. Recently, different metamaterials have been proposed to achieve high thermal radiation. To date, broadening of the radiation bandwidth of metasurface emitter (meta-emitter) has become a key goal to enable extensive applications. We experimentally demonstrate a broadband M-IR thermal emitter using stacked nanocavity metasurface consisting of two pairs of circular-shaped dielectric (Si3N4) – metal (Au) stacks. A high thermal radiation can be obtained by engineering the geometry of nanocavity metasurface. Such a meta-emitter provides wideband and broad angular absorptance of both p- and s-polarized light, offering a wideband thermal radiation with an average emissivity of more than 80% in the M-IR atmospheric window of 8–14 μm. The experimental illustration together with theoretical framework places a basis for designing broadband thermal emitters, which, as anticipated, will initiate a promising avenue to M-IR source.

Ultra-narrowband and highly-directional THz thermal emitters based on the bound state in the continuum

The development of novel and cost-effective THz emitters, with properties superior to current THz sources, is an active and important field of research. In this work, we propose and numerically demonstrate a simple yet effective approach of realizing terahertz sources working in continuous-wave form, by incorporating the new physics of bound state in the continuum (BIC) into thermal emitters. By deliberately designing the structure of slotted disk array made of high-resistivity silicon on top of a low index dielectric buffer layer supported by a conducting substrate, a quasi-BIC mode with ultra-high quality factor (∼104) can be supported. Our results reveal that the structure can operate as an efficient terahertz thermal emitter with near-unity emissivity and ultranarrow bandwidth. For example, an emitter working at 1.3914 THz with an ultranarrow linewidth less than 130 MHz, which is roughly 4 orders of magnitude smaller than that obtained from a metallic metamaterial-based thermal emitter, is shown. In addition to its high monochromaticity, this novel emitter has additional important advantages including high directionality and linear polarization, which makes it a promising candidate as the new generation of THz sources. It holds a great potential for practical applications where high spectral resolving capability is required.

Radiative Flux of a Spectral Distribution at the Surface of a TPV Thermal Emitter Resulting from the Combustion of Biomass: Case of Palms Nut Shells

Thermo PhotoVoltaic (TPV) system convert into electrical energy the radiation emitted from an artificial heat source (i.e., solar or combustion) by the use of photovoltaic cells. In the last decade, TPV system has gained an increasing attention as cogeneration system for the distributed generation sector. Nevertheless, these systems are not fully developed and studied: several aspects need to be further investigated and completely understood. In this study, we modeled and investigated by performing numerical simulation on the feasibility of the TPV system exploiting waste heat energy during biomass combustion. To achieve this goal, we considered a TPV system in which we evaluated and analyzed the waste heat flux resulting from the combustion of the palm nuts shells as well as the corresponding temperature received at the surface of the TPV Thermal-emitter. Furthermore, we evaluated the heat intensity. Results obtained shows that the average temperature at the TPV absorber-emitter is around 1600k. Different variation of the net heat flux at the TPV absorber-emitter are observed for different position. The maximum heat intensity is around 15*1010 W.m-2.µm-1 for a wave length of 2000 nm. These results indicate that the model presented herein is therefore suitable for the design of the TPV system.

Tunable Narrowband Silicon-Based Thermal Emitter with Excellent High-Temperature Stability Fabricated by Lithography-Free Methods

Thermal emitters with properties of wavelength-selective and narrowband have been highly sought after for a variety of potential applications due to their high energy efficiency in the mid-infrared spectral range. In this study, we theoretically and experimentally demonstrate the tunable narrowband thermal emitter based on fully planar Si-W-SiN/SiNO multilayer, which is realized by the excitation of Tamm plasmon polaritons between a W layer and a SiN/SiNO-distributed Bragg reflector. In conjunction with electromagnetic simulations by the FDTD method, the optimum structure design of the emitter is implemented by 2.5 periods of DBR structure, and the corresponding emitter exhibits the nearly perfect narrowband absorption performance at the resonance wavelength and suppressed absorption performance in long wave range. Additionally, the narrowband absorption peak is insensitive to polarization mode and has a considerable angular tolerance of incident light. Furthermore, the actual high-quality Si-W-SiN/SiNO emitters are fabricated through lithography-free methods including magnetron sputtering and PECVD technology. The experimental absorption spectra of optimized emitters are found to be in good agreement with the simulated absorption spectra, showing the tunable narrowband absorption with all peak values of over 95%. Remarkably, the fabricated Si-W-SiN/SiNO emitter presents excellent high-temperature stability for several heating/cooling cycles confirmed up to 1200 K in Ar ambient. This easy-to-fabricate and tunable narrowband refractory emitter paves the way for practical designs in various photonic and thermal applications, such as thermophotovoltaic and IR radiative heaters.