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In recent years, absorbers related to metamaterials have been heavily investigated. In particular, VO2 materials have received focused attention, and a large number of researchers have aimed at multilayer structures. This paper presents a new concept of a three-layer simple structure with VO2 as the base, silicon dioxide as the dielectric layer, and graphene as the top layer. When VO2 is in the insulated state, the absorber is in the closed state, Δf = 1.18 THz (absorption greater than 0.9); when VO2 is in the metallic state, the absorber is open, Δf = 4.4 THz (absorption greater than 0.9), with ultra-broadband absorption. As a result of the absorption mode conversion, a phenomenon occurs with this absorber, with total transmission and total reflection occurring at 2.4 THz (A = 99.45% or 0.29%) and 6.5 THz (A = 90% or 0.24%) for different modes. Due to this absorption property, the absorber is able to achieve full-transmission and full-absorption transitions at specific frequencies. The device has great potential for applications in terahertz absorption, terahertz switching, and terahertz modulation. [ABSTRACT FROM AUTHOR]

The continuous development and application of laser technology, and the increasing energy and power of laser output have promoted the development of various types of laser optical systems. The optical components based on quartz materials are key components of high-power laser systems, and their quality directly affects the load capacity of the system. Due to the photothermal effect when the laser interacts with the quartz material and generates extremely high temperatures in a short period of time, it is impossible to experimentally solve the phenomena and physical mechanisms under extreme conditions. Therefore, it is very important to select a suitable method to investigate the thermal effect of intense laser interaction with quartz materials and explain the related physical mechanism. In this study, a three-dimensional quarter-symmetric laser heating quartz material geometry model by using nonlinear transient finite element method was established, and its transient temperature field distribution of the quartz material after being heated by a 1,064 nm continuous laser was investigated. In addition, the influence of different laser parameters (laser spot radius, heat flux and irradiation time), material parameters (material thickness, material absorption rate of laser) on the thermal effect of heating quartz material were also studied. When the laser heat flux is 20 W/cm2, the diameter of the laser spot is 10 cm, the irradiation time is 600 s and the thickness is 4 cm, the temperature after laser heating can reach 940.18°C, which is far lower than the melting point. In addition, the temperature maximum probes were set at the overall model, spot edge and rear surface respectively, and their temperature rise curves with time were obtained. It is also found that there is a significant hysteresis period for the rear surface temperature change of the quartz material compared with the overall temperature change due to heat conduction. Finally, the method proposed can also be applied to the laser heating of other non-transparent materials. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) still suffer from varying degrees of optical and electrical losses. To enhance the light decoupling and capture ability of Planar PSCs, an ultra-thin PSC structure with an Al2O3 pyramid anti-reflection layer (Al2O3 PARL) is proposed. The effect of the structure of the Al2O3 PARL on the photoelectric performance of PSCs was investigated by changing various parameters. Under the AM1.5 solar spectrum (300–800 nm), the average light absorption rates and quantum efficiency (QE) of PSCs containing pyramid-array textured rear layers (PARLs) were significantly higher than those of planar PSCs. The Al2O3 PARL-based PSCs achieved a light absorption rate of 96.05%. Additionally, electrical simulations were performed using the finite element method (FEM) to calculate the short-circuit current density (JSC), open-circuit voltage (VOC), and maximum power (Pmax). Based on the maximum value of the average light absorbance, the geometric structure of the Al2O3 pyramid PSCs was optimized, and the optimization results coincided with the JSC and QE results. The results of the electrical simulation indicated that the maximum JSC was 23.54 mA/cm2. Additionally, the JSC of the Al2O3 pyramid PSCs was 22.73% higher than that of planar PSCs, resulting in a photoelectric conversion efficiency (PCE) of 24.34%. As a result, the photoelectric conversion rate of the solar cells increased from 14.01% to 17.19%. These findings suggest that the presence of the Al2O3 PARL enhanced photon absorption, leading to an increase in electron–hole pairs and ultimately improving the photocurrent of the solar cells. [ABSTRACT FROM AUTHOR]

Utilizing the phase transition principle of VO2, this paper presents a tunable ultra-wideband terahertz perfect absorption device with simple structure and tunability. The proposed broadband terahertz perfect absorption device is a three-layer structure with a metal reflective layer, a silicon dioxide dielectric layer and a VO2 layer from bottom to top. It was found that the terahertz perfect absorption device's absorption could be dynamically adjusted from 1.2% to 99.9% when changing from an insulated to a metallic state. With the VO2 in the metallic state, the terahertz perfect absorption device has an absorption efficiency of more than 90% in 4.00 to 10.08 THz's ultra-broadband range and near-perfect absorption is achieved in the ranges of 4.71 THz to 5.16 THz and 7.74 THz to 8.06 THz. To explain the working principle of this terahertz perfect absorption device, this paper utilizes wave interference's principle, theory of impedance matching and electric field analysis. Compared to previously reported terahertz metamaterial devices, the vanadium dioxide device proposed in this paper is significantly optimized in terms of tunable range and absorption bandwidth. In addition, the terahertz perfect absorption device is polarization insensitive and maintains good absorptivity over a wide-angle incidence range. This tunable ultra-wideband terahertz perfect absorption device could have applications in the fields of modulation, stealth devices, and thermal emission devices. [ABSTRACT FROM AUTHOR]

The main development direction for current solar technology is to improve absorption efficiency and stability. To bridge this gap, we design in this paper a structure consisting of two multilayer disc stacks of different radii, one topped by a TiO2 disc and the other by a cascade disc stack composed of SiO2-Ti, for use in thermal emitters and solar absorbers. The innovation of our work is the exploitation of multiple Fabry–Perot resonances in SiO2-Ti cascade optical cavities to develop absorber bandwidths while investigating it in the field of thermal emission and many aspects affecting the efficiency of the absorber. The finite difference time domain method (FDTD) results show absorption averages as high as 96.68% with an absorption bandwidth of 2445 nm (A > 90%) at 280 nm–3000 nm solar incidence and even higher weighted averages as high as 98.48% at 1.5 solar air mass (AM) illumination. In order to investigate the physical mechanisms of our designed absorber in a high absorption state, we analyzed the electric field distributions of its four absorption peaks and concluded that its high absorption is mainly caused by the coupling of multiple Fabry–Perot resonance modes in the cascaded optical cavity. While considering this high efficiency, we also investigated the effect of complex environments such as extreme high temperatures and changes in the angle of incidence of the absorber, and the results show that the thermal radiation efficiency of the emitter is 96.79% at an operating temperature of 1700 K, which is higher than its thermal radiation efficiency of 96.38% at an operating temperature of 1500 K, which is a perfect result. On the other hand, we conclude that the designed structure is independent of polarization, while the absorber still has 88.22% absorption at incidence angles of up to 60°, both in transverse electric (TE) and transverse magnetic (TM) modes. The results of this study can help improve the performance of future solar absorbers and expand their application areas. [ABSTRACT FROM AUTHOR]

We designed a metamaterial far-infrared absorber based on an MDM (metal–dielectric–metal) structure. We made a hollow crossed Ti microstructure at the top of the absorber. It is known that the coupling effect of equipartitional exciton resonance and intrinsic absorption at the surface of the depleting material has a strong influence on the absorber. Based on this, we investigated the absorption characteristics of the absorber using the Finite Difference in Time Domain (FDTD) theory. The results show that the absorber absorbed more than 90% of the light within a bandwidth of 12.01 μm. The absorber has an average absorption of 94.08% in the longwave infrared (LWIR) to ultra-longwave infrared (UWIR) bands (10.90–22.91 μm). The polarization insensitivity of the designed absorber is demonstrated by analyzing the absorption spectra of the absorber at different polarization angles. By adjusting the relevant geometric parameters, the absorption spectrum can be independently adjusted. Furthermore, the absorber exhibits good incidence angle insensitivity in both transverse electric (TE) and transverse magnetic (TM) modes. The absorbers are simple and easy to configure for applications such as optical cloaking, infrared heat emitters, and photodetectors. These advantages will greatly benefit the application of absorbers in practice. [ABSTRACT FROM AUTHOR]

Coating structures with dynamically adjustable infrared emissivity are crucial in spacecraft components to cope with the transient thermal environments of space. For a long time, thermochromic phase change materials have been widely used in applications requiring emissivity adjustment, and optimizing the range of adjustable infrared emissivity has always been at the forefront of research. However, reducing the absorption of solar radiation has significant implications for the practical application and thermal stability of spacecraft components in space environments. In this paper, we propose a multilayer film structure based on the phase change material VO2 combined with the materials ZnSe and ITO to achieve low solar radiation absorption and adjustable infrared emissivity for intelligent thermal radiators in space. Through finite element simulation analysis of the structure, we achieve a solar radiation absorption rate of 0.3 and an adjustable infrared emissivity of 0.49. According to Stefan–Boltzmann's law, the structure exhibits strong radiative heat dissipation at high temperatures and weak energy dissipation at low temperatures to maintain the thermal stability of the device and ensure efficient operation. The intelligent thermal radiator operates based on the principles of Fabry–Perot resonance. Therefore, the multilayer structure based on the phase change material VO2 demonstrates excellent performance in both solar radiation absorption and adjustable infrared emissivity, showcasing its tremendous potential in the field of intelligent thermal control in aerospace. [ABSTRACT FROM AUTHOR]

As graphene-related technology advances, the benefits of graphene metamaterials become more apparent. In this study, a surface-isolated exciton-based absorber is built by running relevant simulations on graphene, which can achieve more than 98% perfect absorption at multiple frequencies in the MWIR (MediumWavelength Infra-Red (MWIR) band as compared to the typical absorber. The absorber consists of three layers: the bottom layer is gold, the middle layer is dielectric, and the top layer is patterned with graphene. Tunability was achieved by electrically altering graphene's Fermi energy, hence the position of the absorption peak. The influence of graphene's relaxation time on the sensor is discussed. Due to the symmetry of its structure, different angles of light source incidence have little effect on the absorption rate, leading to polarization insensitivity, especially for TE waves, and this absorber has polarization insensitivity at ultra-wide-angle degrees. The sensor is characterized by its tunability, polarisation insensitivity, and high sensitivity, with a sensitivity of up to 21.60 THz/refractive index unit (RIU). This paper demonstrates the feasibility of the multi-frequency sensor and provides a theoretical basis for the realization of the multi-frequency sensor. This makes it possible to apply it to high-sensitivity sensors. [ABSTRACT FROM AUTHOR]

Ti-bearing blast furnace slag is a kind of solid waste produced by Pangang Group Company through the blast furnace smelting method. A variety of valuable components can be extracted from the Ti-bearing blast furnace slag after acidolysis with concentrated sulphuric acid. In order to study the kinetics of acidolysis, this paper investigated the effects of the acidolysis temperature, acid- slag ratio and raw material particle size on the overall extraction rate of Ti4+, Mg2+ and Al3+ components at different reaction times, and simulated the acidolysis process by using the unreacted shrinking core model. The results showed that the acidolysis process was controlled by internal diffusion with an apparent activation energy of 19.05 kJ mol-1 and the semi-empirical kinetic equation of the acidolysis process was obtained. [ABSTRACT FROM AUTHOR]