Papers by Keyword: Effective Medium Theory

Abstract: Polymer composite materials based on polypropylene matrix and carbon nanoparticles of various shapes: spherical particles - carbon black and anisotropic nanoparticles - carbon nanofibers, were obtained by the melt technology. A character of the dependences of the electrical conductivities on the concentration of carbon nanofillers has been revealed. A simulation of the electrical conductivity of the polymer composite in the region of the concentration of the filler at the threshold of the flow of electric current and below it was carried out.

Abstract: Based on effective medium theory, the temperature dependence of effective dielectric permittivity, ε_e(T), on core radius (a) and thickness (t) of non-ferroelectric dead layer (DL) on the surface of inhomogeneous grains of ferroelectric film made up of cylindrical ferroelectric grains was theoretically investigated. It was found that ε_e(T) increases with increasing core radius but decreases with increasing DL thickness. In this work, an equation expressing the relationship among ε_e, a and t was derived. This equation is very useful for the preparation of a ferroelectric film to desired properties.

Abstract: In the paper is presented calculation of hygric properties of hollow brick block. Namely it is adsorption isotherm, water vapour diffusion resistance factor and moisture diffusivity. The brick block cavities was filled only by air. In first step the properties of brick body were measured. Then the properties of the whole brick block were calculated by using homogenisation techniques.

Abstract: We present the study based on extended Maxwell-Garnett effective medium theory for the effective dielectric function of the diamond like carbon film with embedded silver nanoparticles (DLC-Ag) and rigorous coupled-wave analysis to evaluate resonance characteristics in a visible range of periodic 1-D grating structure on their base. The relief sub-wavelength grating structures on base DLC-Ag nanocomposite have been investigated for sensing applications.

Abstract: As part of the weak electrolyte, Multiphase Composite System’s structure is more complex. So the conductive electrolyte ion transport has some difficulty to understanding the mechanism. And the present study has not yet reached a consensus, but through the ion conduction mechanism in-depth research on polymer electrolytes Preparation of important guiding significance. Current theories include ionic conductivity effective medium theory (EMT), MN law, WFL equation, NE equation, dynamic bonding penetration model.

Abstract: Dependences of distribution, penetration, reflection and absorption of microwaves in the layers of conductive micro-particles on the frequency of the incident radiation and size of particles are obtained and investigated. Layers of conductive spherical particles as the shell, and without it are accepted in our work as the most common model of powder metals. So, this study allows to describe and classify features of electromagnetic wave heating of various metal powders and to predict the performance, in which it will be effective heating of metal powders by electromagnetic radiation.

Abstract: In this work, effect of the number of stainless steel-aluminum nitride (SS-AlN) cermet layers and stainless steel (SS) volume fraction in each of cermets on the optical properties of SS-AlN solar selective coatings was theoretically investigated based on the effective medium theory and optical properties of SS and ceramic AlN. Results shows that increasing the number of cermets does not improve the optical performance of solar selective coatings in terms of solar absorptance and thermal emittance at 80 oC, and the two-cermet-layer structure, one having a high metal volume fraction (HMVF) and other having a low metal volume fraction (LMVF), is the most suitable due to better optical performance and easier preparation. Theoretical results also shows that, for double SS-AlN cermets structure selective coatings, optimized LMVF and HMVF are 0.35 and 0.6, respectively, optimized thickness of cermets with LMVF and HMVF are 50 and 60 nm, respectively, and optimized thickness of AlN anti-reflection film is about 60 nm. Comparisons of reflectance of a sample deposited by a pulse magnetron sputtering coater between measured and calculated showed that theoretically predicted reflectance were highly agreed with those experimentally measured, indicating that the theoretical method used in this work can pretty predict the optical properties of SS-AlN cermet solar selective coatings.

Abstract: This paper presents a parametric study of the radiative properties of patterned wafers with a polysilicon gate array on the Si substrate, considering the effect of wavelength and polarization. While the gate sizes are very small compared to wavelength, the results show rather unusual phenomena. The absorptance calculated by effective medium theory (EMT) is in agreement with finite-difference time-domain (FDTD) in the cases with small gate and period sizes. With the increase of period and decrease of the ratio of the gate width to the pattern pitch, both EMT and FDTD results for TM mode approach to pure silicon since the grating effect diminishes. Besides, the TE absorptance curve separates from that of plain Si at the wavelength equals to the grating period, this is because the gate can interact with its neighboring region by diffraction and the diffraction effects are weak, when the wavelength is small. It also shows a slight increase in the gate height can drastically increase the absorptance and the increased gate height shifts the peak absorptance to longer wavelength. This work is of great importance for optimization of advanced annealing techniques in semiconductor manufacturing.

Abstract: Using self-consistent effective-medium theory, we studied the complex elastic compliances of conducting disordered heterogeneous piezoelectric-polymer systems. The considered system is a random mixture of piezoelectric spheroids and polymer ones with the same orientation. The proximate cause of the effective elastic constants frequency dependencies was considered. The nature of the obtained spectra was analyzed.

Abstract: The effective complex piezoelectric and dielectric constants of disordered heterogeneous systems of the type of statistical mixtures with the components in the form of spheroid-shaped particles equally oriented but randomly arranged in space were studied. It has been found for the first time that in such systems there appears a giant piezoelectric enhancement accompanied by a giant relaxation of piezoelectric coefficients and the dielectric permittivity. Piezoelectric and dielectric spectra differ significantly from the Debye ones and are of Davidson-Cole type. The influence of the aspect ratio of spheroids on the effects under consideration was studied. The physical mechanisms responsible for the anomalies in the behavior of piezoelectric coefficients and the dielectric permittivity were considered.