Research of electromagnetic characteristics of planar chiral metastructures based on composite helices components taking into account the heterogeneous Bruggeman model

In this work a mathematical model of a chiral metamaterial is constructed which based on composite fine-wire helices components, which takes into account the properties of chirality, heterogeneity and dispersion. When constructing the model the chiral metamaterial was considered as a heterogeneous system and described by the Bruggeman model. Inthis work, analytical relationships were obtained for calculating the resonance frequencies of composite helices components. Thedispersion properties of the metamaterial were described using the well-known Condon model. As an example of using the constructed mathematical model, we solved the problem of the reflection (transmission) of a plane electromagnetic wave of linear polarization from a planar layer of the chiral structure under study based on composite helices microelements. A system of linear algebraic equations was obtained to determine the reflection and transmission coefficients of the main and cross-polarized field components. As a result of the numerical simulation, the frequency-selective properties of the metastructure were discovered and the frequencies at which the electromagnetic wave is captured by the planar layer of the metastructure were revealed. A similar effect can be used to creation of frequency selective concentrators (hubs) of microwave energy.

Estimation Method of Interpass Time for the Control of Temperature during a Directed Energy Deposition Process of a Ti–6Al–4V Planar Layer

Directed energy deposition (DED) provides a promising additive manufacturing method to fabricate and repair large metallic parts. However, it may suffer from excessive heat accumulation due to a high build rate, particularly during a wire feeding-type DED process. The implementation of interpass time in between two depositions of beads plays an important process role to passively control the interpass temperature. In this study, a method to estimate the proper interpass time using regression analysis from heat transfer finite element analysis is proposed for maintaining the interpass temperature during a wire feeding-type DED deposition of a planar layer. The overlapping beads of a planar layer are estimated using a polygonal-shaped bead profile in the finite element model. From the estimated proper interpass time, a selected proper interpass time scheme (PITS) is suggested for practical implementation. The selected PITS is applied in a thermo-mechanical finite element model to evaluate the temperature distribution and its effects on the depth of the melt pool, the depth of the heat-affected zone (HAZ), displacement, and residual stresses. By comparing the predicted results with those using a constant interpass time scheme (CITS), the selected PITS shows better control in reducing the depths of the melt pool and HAZ without severely inducing large displacement and residual stresses.

Waveguide amplification of dye fluorescece in NLC

The amplification of spontaneous fluorescence in a planar layer of a nematic liquid crystal doped with a DCM dye is experimentally studied in a waveguide mode of light propagation. The optical pumping threshold of the superfluorescence is 0.65 MW/cm2. The gain value reaches 0.0014 μm-1 at a pumping intensity of 1.38 MW/cm2. Full Text: PDF ReferencesLiquid Crystal Microlasers, Eds. L. M. Blinov, R. Bartolino (Kerala India, Transworld Research Network 2010). DirectLink H. Kogelnik, C. V. Shank, "Coupled‐Wave Theory of Distributed Feedback Lasers", J. Appl. Phys. 43, 2327 (1972). CrossRef I. P. Il'chishin, E. A. Tihonov, V. G. Tishchenko, M. T. Shpak, "Generation of a tunable radiation by impurity cholesteric liquid crystals", JETP Lett. 32, 25 (1980). DirectLink A. Yariv, M. Nakamura, "Periodic structures for integrated optics", IEEE Quant. Electr. 13, 233 (1977). CrossRef N. M. Shtykov, M. I. Barnik, L. M. Blinov B. A. Umanskii, S, P. Palto, "Amplification of the emission of a liquid-crystal microlaser by means of a uniform liquid-crystal layer", JETP Lett. 85, 602 (2007). CrossRef