Technical Physics Letters最新文献

Dense plasma generators—plasma torches—have found wide application in various industries. The most common of them are electric arc gas heaters. Among electric arc plasma generators, plasma generators with gas discharge stabilization are the most widely used. The advantages of these plasma torches are high efficiency in various technological processes and a relatively simple design. This paper proposes a fairly versatile design calculation methodology for most possible gas-stabilized plasma torches, which is applicable to plasma torches with other methods of discharge stabilization. This methodology allows one to determine the main design dimensions of a plasma torch for a selected configuration and the main operating parameters of the process, or to perform a test calculation for a plasma torch with known dimensions.

Based on the general theory of transducers and Mason’s equations for the thermodynamic state of a piezoelectric medium, the transfer functions of a piezoelectric motor with an elastic multiplier for the developed force, velocity, and load displacement are obtained. Analytical expressions relating the parameters of the transfer functions to the design and piezoelectric characteristics of the multiplier and piezo actuator are determined. As a result, an approach to deriving the transfer functions of piezoelectric motors with external elastic elements is proposed.

The article examines ways to improve the technological flexibility of a robotic production line and enhance safety for human operators when interacting with it. This combined problem is a priority in the design and operation of robotic systems. Life-threatening emergencies may occur during the production process. They can cause equipment failure, necessitating urgent repairs or changing the speed of the production line, which will lead to changes in the production time of finished products. Therefore, this article focuses on the third stage of the robotic system’s life cycle, which involves human interaction with electrical devices, systems, and electrical machines. The problem of interaction between a process assembly module and a human specialist to increase technological flexibility was solved by implementing a voice assistant [1]. Comparing the resulting solution with recent research on this topic, we note the novelty of using a voice assistant, as opposed to ideas for standard, safe collaboration between humans and manipulators [2]. It is worth noting that the presented solution is one of the leaders in industrial robotics in terms of safety [3] and will allow enterprises to create jobs for people with disabilities.

The paper describes an electrical network with an electric-vehicle charging station and a proposed active harmonic filter control system for a hybrid distribution transformer (HDT). The results of modeling an electric grid with an electric-vehicle charging station, at which studies in steady state and in dynamics when an additional nonlinear load was connected and an HDT with the proposed control system has been used in comparison with a conventional power transformer were conducted, have been presented. On the basis of the simulation results, it can be noted that the use of an HDT with the proposed control system with an active harmonic filter provides a noticeable improvement in the quality of electricity for the end user. The results of the study have been discussed and relevant conclusions have been drawn.

Using the MWS CST software, a model of graphene metasurfaces under combined electric- and magnetic-field control, which includes the graphene complex permittivity tensor, has been developed and diffraction of a TEM wave normally incident onto a graphene nanoribbon metasurface in a dc magnetic field applied perpendicular to graphene has been simulated. The frequency dependences of the absolute value of the coefficient of transmission of the p-polarized TEM wave through the graphene nanoribbon metasurface have been calculated for different magnetic field inductions В₀ and Fermi levels E_f in the THz and far-infrared frequency ranges. It is shown that the frequency modulation index and maximum changes in the coefficient of transmission through the graphene metasurface increase with an increase in the magnetic field induction В₀ and a decrease in the graphene Fermi level E_f within the optimum range of 0.2‒0.35 eV at the THz frequencies.

In the article, the concept of external barycentric coordinates is introduced to generalize the applicability of the barycentric method for solving external value and initial boundary value problems of mathematical physics. The study is aimed at formulating a simple analytical relation that allows one to calculate barycentric coordinates that are external to a given arbitrary polygonal area with a given accuracy. The corresponding ratio is formed when drawing up an approximate analytical calculation rule, which is based on finding the solution of the external Dirichlet problem for the Laplace equation by the Fredholm method. This solution is based on the decomposition of the kernel of the Fredholm integral equation of the second kind by Legendre polynomials of the first and second orders with use of the Heine formula. As a result, the convergence rate of the external barycentric coordinates obtained by approximate analytical calculation is estimated when establishing exponential convergence in the Hilbert space and polynomial convergence in the space of continuous functions. The algorithmic features of the implementation of an approximate analytical solution with a structured representation of pseudo-codes of algorithms for calculating external barycentric coordinates formed mainly for the MathCad computer algebra system are clarified. The efficiency is demonstrated by specific examples. In conclusion, the author of the article hopes that the detailed results of the algorithmic implementation of calculation of external barycentric coordinates will arouse interest and make the publication material more accessible to a wide range of readers, which would lead to the development of the barycentric method for solving the boundary and initial boundary value problems of mathematical physics.

The results of studying the flow structure and the concentrations of toxic substances in the primary zone of a combustion chamber with a two-tier arrangement of injectors operating on kerosene are reported. The design features of injectors installed in the front device of the combustion chamber are given. The bench equipment and the combustion chamber section used in the study are described.

Background. Currently, methods for contactless control of the dielectric properties of semiconductor nanostructures and the matrix surrounding them evoke considerable interest. Optical modulation of the permittivity in combination with controlled tunneling processes enables targeted modification of the properties of low-dimensional structures and, consequently, optimization of the characteristics of semiconductor nanoelectronic devices. In this regard, semiconductor quantum dots (QDs) tunnel-coupled to the surrounding matrix are interesting, since in such structures the ({{A}^{ + }} + e) impurity complexes can form, the photoexcitation of which can significantly change the permittivity of a QD material, i.e., induce the photodielectric effect (PDE). The aim of this study is to theoretically investigate the effect of the tunnel transparency of the potential barrier on the PDE related to the excitation of the ({{A}^{ + }} + e) impurity complexes in quasi-zero-dimensional structures in an external magnetic field. Materials and methods. The relative permittivity change (RPC) has been calculated in the dipole approximation. The field dependence of the RPC has been plotted for InSb QDs. The numerical calculation and plotting have been performed using the Mathcad 14.0 and Wolfram Mathematica 10.2 numerical systems. Results. The dependences of the RPC in a quasi-zero-dimensional semiconductor nanostructure on external magnetic field and 1D dissipative tunneling parameters have been studied in the dipole approximation. The PDE dichroism related to the presence of an external magnetic field has been revealed. It is shown that an external magnetic field suppresses the PDE, which is associated with the increased localization of the electron wave function in a magnetic field and with a modification of the electron adiabatic potential. It is demonstrated that the RPC value depends on the parameters of dissipative 1D tunneling. Conclusions. In a magnetic field, the PDE can be effectively controlled by modifying the electron adiabatic potential and the electron wave function via changing the dissipative tunneling parameters.

Background. Conjugate boundary value problems for a system of Maxwell’s equations are fundamental in electrodynamics. Recently, there has been interest in the problems involving the presence of a thin graphene layer on the surface, which changes the conjugation conditions. The aim of this study is to obtain a system of integral equations for the vector boundary value problem on electromagnetic oscillations of a graphene-coated dielectric ball in a spherical coordinate system. Materials and methods. Using the Stratton‒Chu formula, the components of the field are expressed through surface currents and the conjugation conditions are used to obtain singular integral equations on the ball surface. Results. A system of singular integral equations with four unknown scalar functions on the sphere surface is derived. The properties of the system of integral equations are studied. Conclusions. The resulting system of singular integral equations can be solved numerically by known methods, for example, the Galerkin method or the collocation method.

Background. The inverse electromagnetic problems of inhomogeneity reconstruction in a dielectric body by the near-field measurements arise, for example, in the early diagnosis of breast cancer by microwave tomography. The solution of such inverse problems is the basis for the development of a technique for detecting inhomogeneities using microwave devices. The efficiency of the technique depends on the inverse problem solution accuracy. Therefore, the development of new, more accurate methods for solving the inverse problem of microwave tomography is highly relevant. Aim. This study is aimed at the development of a method for solving the electromagnetic inverse problem of microwave tomography using near-field measurements, i.e., restoring the structure of an inhomogeneous dielectric body from values of an electromagnetic field outside this body using a measuring setup. Methods. The inverse problem is solved by a two-step method for determining the inhomogeneity of a body, in which the current function inside the body is first found and then the permittivity function is calculated. The method is non-iterative and does not require a good initial approximation. Results. A two-step method has been used to solve the inverse problem of microwave tomography. The numerical results are presented. Inhomogeneous bodies in the shape of a hemisphere have been investigated. Experimental results are presented. Conclusions. The efficiency of the proposed technique for detecting inhomogeneities in a dielectric body by microwave tomography is demonstrated. The calculation and experimental data are reported.