Papers by Keyword: Mie Theory

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: In this research, we detailed how the following factors affect the scattering of light by nanofluids: (1) nanoparticle sizes, (2) volume fraction of nanoparticles, and (3) nanoparticle materials. Mie theory was used to calculate the radiative properties of the nanofluids. The radiative properties were then applied into the Radiative Transfer Equation (RTE) to solve for the transmittance and reflectance of light through the nanofluids. The RTE was solved using the Monte Carlo method. Results showed that when the size of nanoparticles and the volume fraction increase, absorption and scattering coefficients increase as well. For silver nanofluids, absorption and scattering coefficients decrease beyond nanoparticle size of about 50 nm. Transmittance of light decreased when nanoparticle sizes increased. When comparing between TiO₂, Ag, and SiO₂ nanofluids, Ag nanofluids exhibit the highest light absorption followed by TiO₂ and SiO₂.

Abstract: Light scattering caused by pores detrimentally affects the optical transparency of transparent ceramics. Herein, Mie theory has been used to calculate the cross-section of pore scattering in transparent ceramics, and the influence of wavelength, pore size distribution and refractive index has been discussed in detail. For wavelength between 200 nm and 2000 nm, the scattering cross-section decreases with increasing wavelength, which means that pore scattering is more detrimental to short-wavelength transparency. With ZOLD function simulating the pore size distribution inside the ceramic, it has been found that the scattering is strongest when the most-probable diameter d_m equals the incident light wavelength λ. And FWHM (full width at half maximum) parameter a also affects the scattering cross-section. a between 0.003 and 0.7 is necessary for obtaining high optical transparency in visible wavelength range. The method presented in this work is available for the estimation of scattering effect in different kinds of materials, which may be useful for future design of high-transparency ceramics.

Abstract: The Au/SiO₂ nanocomposite was produced using surface active agent P123, and its optical absorption spectra was measured by spectrophotometer. It was found that the intensity of absorption peak was strengthened and underwent a red-shift as the neutralization reaction time extended. The variation of optical extinction property of one gold particle (GP) with different size had been investigated by Mie theory. It was found that the extinction property of the single spherical GP possessed an obvious size effect. The extinction property of Au/SiO₂ nanocomposite had been analyzed by Maxwell-Garnett (MG) theory. It showed that the extinction peak underwent a red-shift and the extinction intensity was strengthened when the size of gold nanoparticles (GNs) increased. The theoretical and the experimental results show that the extinction property of Au/SiO₂ nanocomposite changes because the scattering effect of GNs are strengthened when their sizes increased by controlling the neutralization reaction time.

Abstract: The second derivative of the remission function of several magnetic materials is calculated for the parameterization of the position and intensity of the absorption bands of diffuse reflectance spectroscopy. The reflectance spectra are obtained by ultraviolet-visible spectroscopy (UV-VIS) from 400 to 1100 nm at increments of 1nm. The noise of the remission function results on errors after calculating the second derivative. Therefore, filtering of the remission function is needed before taking any action on this signal. Several methods are tested in order to calculate the second derivative. The best polynomial resulted on a second order wavelet function which is applied to the filtered remission function. Light scattering Mie theory is used to prove the behaviour of the reflected light. This research provides a method to identify and quantify magnetic particles, as well as the crystal size.

Abstract: Fabrication, optical property of nano coreshells and their potential applications in chemical and biological sensors have attracted much research interest. In this paper, we simulated the effect of size, structure, and dielectric properties as well embedding medium on the optical properties of gold or silver coated coreshell nanoparticle and the corresponding effects both of phase-retardation and of electron interface scattering as well as the nansize effect were discussed. Intriguing transition of the optical properties was simulated when a two-phase core-shell nanoparticle changes gradually into the single phase nanoparticle. We also obtained a good correlation of the simulation to the experimental results. Thus, the simulation has many implications and can guide further core-shell nanostructure fabrication with optimization of its optical properties.

Abstract: The determination of the spherical particle-sizes in colloidal suspension by Angular Light Scattering presents a lot of advantages, i.e.: the relative simplicity of the experimental installations, and its non-destructive character. The intensity of the scattered light is related with the radius of a particle by Mie Theory. However, the dynamic characteristic of the measurements establish a variations of the scattered intensity with the time which it has not considered. In the case of the particle suspended in water, the intensity of the scattered light measured in each angle θ is the superposition of the scattered intensity for each particle. In consequence, the intensity of the light scattered will be related with a particle-size distribution function, that in this work is assumed as a δ function. Then, the dependence of the scattered intensity with time is studied evaluating the variation of the center point of δ function with time taking account to the standard deviation of angular scattered intensity. The accuracy of the method is evaluated throw the deviation of the particle-size distribution taking in to account the standard deviation of the angular intensity scattered by calibrated particles of latex. A correct evaluation of the dynamic method is realized in terms of the static approach.