Physics of Wave Processes and Radio Systems

Background. Modern research in the field of metamaterials opens up new horizons in the development of materials with unique electromagnetic properties that can be used in various applications, from telecommunications to medical diagnostics. Inhomogeneous non-reciprocal chiral metamaterials are of particular interest due to their ability to control the polarization of electromagnetic waves and alter their properties. However, such electrodynamic problems are often solved using numerical methods that require significant computational resources and time, which limits their practical application. Therefore, there is a need to develop approximate analytical methods for estimating reflection coefficients and understanding the physical mechanisms underlying these processes. Aim. Development of a method for approximate calculation of reflection coefficients of a flat homogeneous electromagnetic wave from a planar layer of an inhomogeneous non-reciprocal chiral metamaterial, taking into account the dispersion of material parameters. An analytical approach has been proposed that will allow obtaining solutions of different approximation orders and provide a deeper understanding of the physics of reflection processes. Methods. An analytical approach to calculating reflection coefficients based on field theory methods is used. Inhomogeneity and non-reciprocity of chiral metamaterial are taken into account. A number of approximate solutions have been developed to analyze the behavior of electromagnetic waves under various conditions of incidence and polarization. Results. The proposed analytical method makes it possible to efficiently calculate reflection coefficients for plane waves under various conditions of interaction with inhomogeneous non-reciprocal chiral metamaterials. Conclusion. New approach to calculation of reflection coefficients of plane electromagnetic wave from planar layer of inhomogeneous non-reciprocal chiral metamaterial is presented taking into account dispersion of material parameters. The developed analytical method provides faster and more efficient solutions compared to numerical methods and contributes to a better understanding of the physics of reflection processes in complex materials. The results obtained can be useful for further research in the field of metamaterials and their application in modern technologies.

Background. Curvilinear dipole antenna structures have been established as solution to the directivity problem associated with conventional dipole antennas, with length greater than half a wavelength. However, with the exception of the ‘concave Nu’ dipole, other curvilinear configurations of V-dipole antenna have yet to receive analytical attention in the open literature. This paper presents a comparative analysis of four of such configurations. Aim. Develop a detailed electric field integral equation formulation for internal electrodynamic problem of four curvilinear configurations of the V-dipole antenna structure, such that a method of moments solution becomes applicable. Methods. Unknown current distributions in the formulation are determined using the method of moments, with piece-wise linear basis and testing functions. Analytical results are then implemented in a FORTRAN computer program, for numerical results. Results. Analytical models for four curvilinear configurations of the V-dipole antenna as well as computational results for their input and radiation-zone characteristics. Conclusion. Computational results obtained reveal that in terms of maximum achievable directivity and return loss, the configuration with both arms curved, is the best performing; followed by the conventional-V, convex-Nu (one arm bent inwards), and concave-Nu (one arm bent outwards), in that order.

Background. The analysis of the results of the use of various machines and mechanisms in the national economy has shown that the roughness of the microrelief of their working surfaces largely determines the reliability and durability of their operation. In this regard, the study and development of modern new methods for measuring the roughness of a microrelief is an urgent task at present. Aim. The purpose of the work is to study and develop an optoelectronic method, algorithms and software for digital processing of images of microreliefs of the surfaces under study to measure their roughness directly during the technological process of their manufacture. Methods. The method is based on computer processing of images of the studied microreliefs, as a result of which the roughness parameters of these microreliefs are determined. For this purpose, two-dimensional correlation functions are calculated for halftone images of microreliefs of reference samples, with certain GOST methods and roughness parameters. For these functions, the average amplitudes U_cp of the variable components of the correlation coefficients are calculated and the analytical dependence of the GOST roughness parameter Ra on U_cp is constructed. To depict the studied microrelief with unknown roughness parameters, the variable component of the two-dimensional correlation function is also determined, and the arithmetic mean deviation of the profile from the middle line Ra is found based on the obtained dependence Ra = f(U_cp). Results. A new optoelectronic method for measuring the roughness parameters of microreliefs of machined surfaces is proposed, which is based on digital processing of their halftone images. As a result of such processing, a two-dimensional correlation function is calculated, the parameters of which serve to identify the studied microrelief and, thereby, to measure its roughness. The results of using this method to measure the surface roughness parameters of the compressor blade of a gas turbine engine are presented. Conclusion. The prospects of using the optoelectronic method and digital processing of images of microreliefs of mechanically processed surfaces in order to quickly measure their roughness parameters are shown. An algorithm for calculating a two-dimensional correlation function has been developed, which characterizes the microrelief under study and by the characteristics of which it is possible to identify it, that is, to measure its roughness. At the same time, the negative influence of side uninformative factors on the results of measuring the parameters of the microrelief, in particular, fluctuations in the power of the light flux and the angle of its incidence on the surface under study, is also eliminated. The results of the application of the developed optoelectronic method for measuring the roughness parameters of the surface areas of the compressor blade of a gas turbine engine, which are identical to the results of measuring their roughness by GOST profile methods, are presented.

Background. Frequency division multiplexing scheme is a promising technology for wideband digital communication. Systems like this have significantly increased the speed of wireless data transmission, including in complicated conditions of multipath propagation of a radio signal. The first step in designing radio equipment is to evaluate its effectiveness in terms of the use of allocated resources. Aim. The paper describes a mathematical model of multi-frequency digital radio systems and the architecture of a software and hardware platform designed to study the information and energy efficiency of these systems. Methods. The mathematical model is based on the Hilbert spaces and information theory. Its numerical implementation makes it possible to take into account the entropy of message sources, the spectral characteristics of the signal and interference, the signal-to-noise ratio, etc. Results. The paper presents the results of numerical experiments comparing the efficiency of radio communication systems based on frequency division multiplexing and quadrature amplitude modulation schemas, and shows the capabilities of the designed software and hardware platform. Conclusion. The constructed model for evaluating the effectiveness of multi-frequency digital radio communication systems and its implementation make it possible to automate the process of analyzing the characteristics of wireless communication systems.

Background. QS are the main mathematical tool for modeling data transmission systems, which are not without reason called queuing networks. The need to regulate such characteristics of mass service systems as waiting time in a queue or queue length is due to the improvement of the quality of operation of data transmission systems. The ability to regulate these characteristics allows minimizing the waiting time in the queue in the buffers of transmitting devices, as well as the volumes of buffer memory itself. To demonstrate this possibility, the paper examines queuing systems formed by both conventional distribution laws in the form of probability mixtures and time-shifted distribution laws. Aim. In this work, the hyperexponential and hyper-Erlangian distributions of the second order were chosen as components of the QS. Based on these distribution laws, numerical-analytical models were constructed for two queuing systems with normal and shifted distribution laws, with the derivation of a solution for the main characteristic of the queuing system – the average waiting time in the queue. As is known, the remaining characteristics of the QS are derivatives of the average waiting time. Methods. The paper uses a shift of the distribution laws to the right from the zero point. To derive a solution for the average waiting time in a queue, the classical method of spectral solution of the Lindley integral equation is used based on the Laplace transform of the distribution laws that form the considered QS. The obtained calculation formulas for the average waiting time in a queue allow us to calculate the characteristics of such systems for a wide range of changes in teletraffic parameters. Results. The obtained results can be used in modern teletraffic theory in the design and modeling of various promising data transmission systems, including the volumes of buffer memory of transmitting devices. Conclusion. The shift of the distribution laws in time leads to a decrease in their variation coefficients. Due to the quadratic dependence of the average waiting time on the variation coefficients of the arrival and service time intervals, a noticeable decrease in the average waiting time follows in systems with time shifts.