Technical Physics Letters最新文献

Abstract—An experimental method was developed to determine losses in microstrip and coplanar transmission lines for devices operating in the frequency range of 77–81 GHz. The parameters of the scattering matrices are obtained using a vector network analyzer and frequency upconverters. The calculation of losses in waveguide-coplanar and coplanar-microstrip adapters is made.

Abstract—Since the stability of functional properties of a transparent conducting three-layer structure ZnO:Ga/Ag/ZnO:Ga is important for practical application, we studied its long-term durability and thermal stability in air environment. It has been demonstrated that after prolonged interaction with the air environment at room temperature (for ~1000 days) and further heat treatment in air at temperatures of up to 450°C (for up to 10 h), the three-layer structure retains its integrity and is characterized by a low sheet resistance R_s = 2.8 Ohm/sq at average transmittance in the visible range T_av = 82.1%.

Abstract—Based on regular porous polymeric membranes, the synthesis of metal and dielectric spearhead structures with given morphological characteristics was carried out. Copper structures with the ~1 μm height and dielectric spearhead microstructures made from iodic acid with the 12 μm height and 1 μm diameter were obtained. The possibility is discussed of using such optical elements to solve the problems of increasing the efficiency of IR radiation detection, signal amplification and conversion to visible and near-infrared ranges.

Abstract—Temporal characteristics of the localized damage development initiated by a short-time impact pointed loading of SiC ceramics which is widely applied as a protective material against the shock action upon engineering constructions and people were investigated. The statistics of crack nucleation and relaxation was studied with the methods of acoustic emission and electromagnetic emission, correspondingly. It was shown that the length of intervals between microcrack nucleations follows a power law specific to cooperative phenomena. The time distribution of decaying electric charges which appear on impact-induced crack edges and annihilate after the passage of impact wave was, in contrast, linear. The temporal pattern of the crack relaxation permitted identifying two sets of newly formed damages that are the tiny cracks localized in the grain bulk and those that interconnect grains.

Abstract—Wavelet analysis is one of the most efficient methods of the informative signals characteristics investigation. First shown the possibility of informative signals wavelet processing by means of the acousto-optic processor with time integration. The possibility of the realization of both power spectrum calculation and performance of wavelet transform of bioelectric signals in the real time mode has been proved. The analysis is listed which describes its operation in different modes.

The problem of synthesis of the three-link stepped Chebyshev’s microwave filter is reduced to two independent fourth-degree equations, including a single link wave impedance as unknown. The solution of Descartes—Euler is applied to these equations. It is proved that, in case wave impedances of extreme links are equal, the problem of the filter synthesis has two solutions. Identical phase-frequency responses correspond to these solutions. It is proved that for each link a product of the wave impedances relating to these solutions is equal to a square of the wave impedance of the transmission line including the filter.

A method to define the characteristic phases in the behavior of unidirectionally coupled systems located near the boundary of the generalized chaotic synchronization regime onset based on calculating the probability of the synchronous regime observation in an ensemble of coupled systems is proposed. Using the example of unidirectionally coupled Rössler systems in the band chaos regime, we have shown its efficiency in comparison with other known methods for detecting the characteristics of intermittent generalized synchronization.

The degree of influence of the electromagnetic field on oil dispersed systems depends on the dielectric properties of these systems, in particular oil. Dielectric properties of oil depend on the content of high molecular weight polar components: asphaltenes and resins. In this regard, a study was carried out of the dielectric properties of oil in the radio-frequency range, depending on the content of asphalt–resinous substances in it. The obtained results of experimental studies show the correlation of dielectric parameters with the ratio of the content of resins and asphaltenes in oil.

The flow regimes of water and crude oil in a Y-type microchannel were studied in a wide range of flow rates. Four different types of water-oil flow regimes have been identified: plug, droplet, parallel and chaotic. The ranges of existence of these flow regimes have been determined. Dependences of the length of water plugs and droplets in oil on various parameters have been established. Maps of the corresponding water-oil flow regimes have been constructed.

The results of numerical investigation of the hydrodynamic drag of a slit microchannel with a textured wall surface, as well as of the pressure drop in such a channel and the effective slip length on the wall for various Reynolds numbers, are presented. The channel height was 10 μm, and the length varied from 25 to 500 μm. It was found that the pressure drop in the textured microchannel was less than in a conventional one at any length. The dependences of the relative pressure drop, friction factor, and effective slip length on the Reynolds number were obtained for various channel lengths. A correlation that describes the dependence of the relative pressure drop on the Reynolds number for small channel lengths was proposed. The friction factor was described by a correlation expressed as 20/Re.