Papers by Keyword: Reflection

Abstract: Radiative cooling (RC) technology is becoming crucial with several prospective applications, either as a standalone or in conjunction with conventional cooling systems. The RC flux can be enhanced by tailoring selective spectral emissivity and suitable surface orientation (i.e., azimuth and tilting orientation). However, it has not been studied extensively from the perspective of emissivity modification in the composite layers. Polymer and ceramic particle composite’s emissivity (i.e. selective wavelength dependent spectrum) is based on the effective refractive index estimation. In this article we estimate the effective refractive index of the composite structures using Mie theory and the layer transmissivity approach. In the Mie theory, forward scattering from a composite sphere is monitored with respect to background refractive index. In the layer transmissivity approach, refractive index of composite is estimated from the transmission spectrum (i.e. Fresnel equations) of number of layers with different thickness. The refractive index from these two approaches is in the close agreement at large wavelengths (non-dimensional size parameter x=2πr/λ is below 1). However, the layer transmissivity approach yields a higher effective refractive index for the wavelength comparable to particle size (x =>1) inclusions with lots of fluctuations. The effective refractive index estimation aids in the designs of distributed Bragg stack and quasi-amorphous structure. The selective emissivity within the solar spectrum is also expected from quasi-amorphous structures of these existing polymer and ceramic particles composites. The potential applications of these findings are synthesis of coatings for radiative cooling of residential buildings and solar PV panel. Additionally, implementation of these coatings based radiative cooling phenomena would be very effective in terms of reduction of global warming and heat island effect.

Abstract: The paper shows that the introduction of up to 6 wt % of ferromanganese dust enhances the process of granule porization and improves the structural-mechanical properties. This is achieved due to the formation of low-base calcium hydrosilicates in the mineral matrix, reinforced by crystals of fayalite, orientite and pyroximite, which contribute to an increase in the dielectric component in the scattering of electromagnetic waves in the millimeter range. Granules with a developed pore structure in the frequency range from 110² to 3.1510³ Hz can absorb and scatter electromagnetic waves in the range of 54-58 dB. Granules in the temperature range from 20 to 300 °C are flame retardant and not prone to brittle fracture (F ≤ 4). The introduction of a 5% porous filler into the polymer matrix contributes to the growth of the effective part of the dielectric permittivity (μ to 1.5) and stabilization of the coefficient of attenuation of electromagnetic waves (from 2 to 4) in the range 110¹⁰ - 610¹⁰ Hz. The developed porous material is recommended to was used as a filler in the first layers of gradient-absorbing composites

Abstract: Radiation leaving the solid surface provides an important reference for detection in both military and civilian areas. In this paper, total radiation leaving a solid plate is calculated with different emissivities considering the environment radiation. The results prove that a lower emissivity of the surface material has a stronger reflection of irradiance from the Sun, and therefore may enhance the total radiation leaving the plate. This is different from most cases where a lower emissivity always leads to a smaller radiation effects. The emissivity of material coated to the solid surface should be properly chosen according to the detailed surrounding environment as well as the radiative properties of the solid parts in order to achieve a minimum radiation effects.

Abstract: Behavioral characterization of radar absorbent material consisting of Polyaniline (PaNi) and Barium M-Hexaferrite (BaM) has been successfully synthesized by solid state method. Polyaniline conductive material was synthesized using the polymerization method with DBSA dopant. A Radar Absorbing Materials (RAM) is characterized by X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Four Point Probe (FPP), Scanning Electron Microscope (SEM) and Vector Network Analyzer (VNA). The ion Zn ²⁺ is dopping into the BAM structure, where Zn ²⁺ ions replace Fe²⁺ ions in Hexaferrite barium so that the phase becomes soft magnetic materials . RAM and PANi particles are combined with ship paint to form radar wave absorbent coatings. The layer is coated with multilayer geometry on AH 36 type A steel, with thicknesses of 2.4 mm, 3.6 mm, 4.8 mm and 6 mm respectively. The X-band wave absorption was identified by VNA testing, where the maximum reflection loss value was found at 6mm thickness with a reflection loss value - 32.6 dB at 8.4 GHz frequency. Reflection loss values of multilayer variations with a thickness of 2.4 mm, 3.6mm and 4.8mm each have reflection loss values of -8.02 dB, -19.13 dB and -28.9 dB respectively in the x band frequency range.

Abstract: Reflective heating polyester fiber is the fiber prepared by adding nanoparticle with reflecting infrared radiation into the polyester. The human body loses 60% of the total heat by heat radiation, but reflective heating fiber can reflect the body's infrared radiation back to the human body to minimize the loss of heat. In this paper, the purchased GTO powder is modified by silane coupling agent KH560, which is added into PET as a reflective heating powder, and PET fiber containing different content of GTO(0.3wt%,0.6wt%,0.9wt%) is prepared through adding masterbatch method. The particle size test shows that the average size of GTO powder modified by KH560 is about 180nm and the distribution is narrow, which meets the basic requirements of spinning. Through the SEM analysis of PET fibers cross-section, it is found that the GTO powder modified by KH560 were dispersed well in the PET substrate. The results of DSC and mechanical tests show that the fiber with 0.6wt% content of GTO powder have the improved elongation and the crystallinity degree. For the infrared thermal imaging and UV-VIS-NIR tests of the fabric, with the increase of the proportion of powder the infrared emissivity and reflectivity of the fabric increased, the warmth retention is also improved.

Abstract: Heat exchange through infrared radiation in air layers located inside building envelopes may be significantly modified in case of use of aluminium foil coatings therein. The intensity of conductive, convective and radiative heat exchange in these structures depends on the thickness of the air layer and the temperature difference on its surfaces. Generally speaking, application of aluminium foil in air layers of a building envelope improves its thermal insulation capacity. However, assessment of efficiency of such a solution and determination of the thermal resistance value of a given structure is often incorrectly determined and assumed for design calculations. The article analyzes the instructions and principles of determination of thermal insulation capacity of unventilated air layers. Provisions of two standards have been compared with results of tests of air layer parameters. The effect of different factors on heat exchange and insulation capacity of air layers with reflective coatings has been considered and assessed.

Abstract: We have investigated a possibility of photon propagation into the human tissue model (skin, fat, and skeletal muscle) by Monte Carlo method using Matlab program. There were some parameters of each tissue layer effecting on the light packet, for instance the absorption coefficient, scattering coefficient, anisotropy factor and thickness. It was found that the photon distribution on the surface of the human tissue and photon penetration into the human tissue under the propagation of 100,000 photons were - 0.8580 cm to + 0.7030 cm (served as two detection points) and 0.7220 cm respectively. Therefore, the simulation result gave the photon penetration depth of 0.2220 cm at the skeletal muscle. These numbers could be primarily used as a standard for design and construction of the tissue diagnostic instrument.

Abstract: The beautiful colors of the rainbow have always fascinated humans and especially children are inspired to various artworks such as drawing, canvas painting, poster, wall decals and so on. Since refraction and reflection of light cannot be seen taking place in raindrop during rainbow formation, children are unaware of all these details. Although throughout the year past, there are many literatures on theoretical and mathematical aspects of rainbow formation, however there are very few studies in education context to teach about this phenomenon to the children in particular by observing and measuring. Therefore, in this paper we are proposing a model that can be used for hands-on learning with high school students about the formation of spectrum in glass sphere. With the help of the model students can see the angle at which different color lights are deviated by the glass sphere and finally, students can also relate the concept learnt from this lesson to real life phenomenon about spectrum formation by rain drop.

Abstract: This article provides a comprehensive analysis on an explosion of welded insulted cylinder for liquid oxygen during unloading occurred in a company in 2014. The possible causes of the accidents are deduced through analysis on the operating principles of welded insulated cylinders, explosion energy estimation and related performance tests. On the basis of the accident analysis, this article presents that great importance should be attached to the safety in filling of welded insulated cylinders, replacement prior to filling and regular inspections, and also indicates the gap in currently existing rules on periodic examinations of welded insulated cylinders in China.

Abstract: In order to improve the stealth performance of antenna, a metamaterial absorber with high absorption, polarization-insensitive and wide angle based on the electromagnetic resonance is designed. Using of ultra-thin characteristic of absorber, they are attached to the microstrip antenna to reduce its radar cross section. The simulation results show that the new microstrip antenna’s radiation performance remains unchanged compared with conventional microstrip antenna and it has obvious RCS reduction in its working band. While the maximum reduction can reach 28dB at working frequency, and the in-band reduction of antenna is above 3dB. This indicates that the absorber can be used for antennas’ in-band stealth.