Exciting broadband thermochromic transmission property opposite to vanadium dioxide in the atmospheric window

The traditional telecommunications band performs poorly in harsh weather conditions due to atmospheric absorption. In recent years, researchers have begun to study optical communication through atmospheric windows, and optical switches are an essential component of optical communication. A broadband atmospheric window optical switch was proposed based on Vanadium dioxide and magnetic polaritons(MP). It is formed by the stacking of two metal-dielectric-metal structures. The simulation results show that the modulation depth can reach 98.38%, and the extinction ratio is 17.93 dB. By calculating the magnetic field, we confirmed that the reason for the “off” mode is the coupling between the different MP modes, while the “on”mode is the excitation of MP. The optical switch we proposed may be applied to radiation cooling and optical satellite communication.

High-entropy rare earth stannate ceramics:Acid corrosion resistant radiative cooling materials with high atmospheric transparency window emissivity and high near-infrared solar reflectivity

In response to the development of the concepts of“carbon neutrality”and“carbon peak”,it is critical to developing materials with high near-infrared(NIR)solar reflectivity and high emissivity in the atmospheric transparency window(ATW;8–13μm)to advance zero energy consumption radiative cooling technology.To regulate emission and reflection properties,a series of high-entropy rare earth stannate ceramics(HE-RE_(2)Sn_(2)O_(7):(Y_(0.2)La_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Sn_(2)O_(7),(Y_(0.2)La_(0.2)Sm_(0.2)Eu_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7),and(Y_(0.2)La_(0.2)Gd_(0.2)Yb_(0.2)Lu_(0.2))_(2)Sn_(2)O_(7))with severe lattice distortion were prepared using a solid phase reaction followed by a pressureless sintering method for the first time.Lattice distortion is accomplished by introducing rare earth elements with different cation radii and mass.The as-synthesized HE-RE_(2)Sn_(2)O_(7)ceramics possess high ATW emissivity(91.38%–95.41%),high NIR solar reflectivity(92.74%–97.62%),low thermal conductivity(1.080–1.619 W·m^(−1)·K^(−1)),and excellent chemical stability.On the one hand,the lattice distortion intensifies the asymmetry of the structural unit to cause a notable alteration in the electric dipole moment,ultimately enlarging the ATW emissivity.On the other hand,by selecting difficult excitation elements,HE-RE_(2)Sn_(2)O_(7),which has a wide band gap(Eg),exhibits high NIR solar reflectivity.Hence,the multi-component design can effectively enhance radiative cooling ability of HE-RE_(2)Sn_(2)O_(7)and provide a novel strategy for developing radiative cooling materials.

Absence of the Impact of the Flux of Cosmic Rays and the Cloud Cover on the Energy Balance of the Earth

The energy of solar radiation absorbed by the Earth,as well as the thermal radiation of the Earth’s surface,which is released to the space through the atmospheric transparency window,depends on variations of the area of the cloud cover.Svensmark et al.suggest that the increase in the area of the cloud cover in the lower atmosphere,presumably caused by an increase in the flux of galactic cosmic rays during the quasi-bicentennial minimum of solar activity,results only in an increase in the fraction of the solar radiation reflected back to the space and weakens the flux of the solar radiation that reached the Earth surface.It is suggested,without any corresponding calculations of the variations of the average annual energy balance of the EarthЕ,that the consequences will include only a deficit of the solar energy absorbed by the Earth and a cooling of the climate up to the onset of the Little Ice Age.These suggestions ignore simultaneous impact of the opposite aspects of the increase in the area of the cloud cover on the climate warming.The latter will result from a decrease in the power of thermal radiation of the Earth’s surface released to the space,and also in the power of the solar radiation reflected from the Earth’s surface,due to the increase in their absorption and reflection back to the surface.A substantial strengthening in the greenhouse effect and the narrowing of the atmospheric transparency window will also occur.Here,we estimate the impact of all aspects of possible long-term 2%growth of the cloud cover area in the lower atmosphere byЕ.We found that an increase in the cloud cover area in the lower atmosphere will result simultaneously both in the decrease and in the increase in the temperature,which will virtually compensate each other,while the energy balance of the Earth E before and after the increase in the cloud cover area by 2%will stay essentially the same:E1-E0≈0.

Propagation Modeling and Characteristic Analysis of Terahertz Waves via High Altitude Platforms

Satellite-to-ground terahertz communication is limited by the power of signal source and antenna gain level,and has large path loss,which is difficult to implement.In this paper,a feasible scheme of satellite-to-ground terahertz communication using High Altitude Platforms(HAPs)as relay is presented,and the path loss on terahertz communication links is modeled and analyzed.Combined with the path loss model,the transmission loss along HAP-to-ground paths under different seasons and complex weather environment in Ali,Xizang,China is calculated.The results show that the transmission characteristics of terahertz waves in winter and summer are significantly different,mainly reflected in the number and bandwidth of usable atmospheric windows.Furthermore,the additional attenuation caused by the typical sand dust and ice cloud environment on terahertz band can reach 6.1 dB and 1.9 dB at the maximum respectively.With the aid of high gain antenna,the usable communication frequencies of the HAP-to-ground links in winter are significantly more than those in summer.When the transmitting and receiving antenna gain is 40 dBi respectively,the usable communication frequency can reach 1.35 THz in winter,while it is limited to less than 1 THz in summer,up to 0.493 THz.

Optical properties and cooling performance analyses of single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles

Radiative cooling can achieve cooling effect without consuming any energy by delivering energy into outer space(3K) through"atmospheric window"(8–13 μm). Conventional radiative cooling coating with multi-layer structure was severely restricted during application due to its complex preparation process and high cost. In this study, a single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles was proposed. The algorithm for calculating the radiative properties of the multi-particle system was developed. Monte Carlo ray-tracing method combined with that algorithm was used to solve the radiative transfer equation(RTE) of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles.The effects of particle diameter, volume fraction and coating thickness on radiative cooling performance were analyzed to obtain the best radiative cooling performance. The numerical results indicated that the average reflectivity of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles in the solar spectrum can reach 95.6%, while and the average emissivity in the "atmospheric window" spectrum can reach 94.9% without additional silver-reflectance layer. The average reflectivity in the solar spectrum and average emissivity in the "atmospheric window" spectrum of the single-layer radiative cooling coating with mixture of TiO_(2) particles and SiO_(2) particles can increase 4.6% and 4.8% compared to the double-layer radiative cooling coating. This numerical research results can provide a theoretical guidance for design and optimization of single-layer radiative cooling coatings containing mixed nanoparticles.