Vol 64, No 11 (2019)

A new method is proposed to represent electromagnetic field in inhomogeneous 2D periodic medium (PM) as a discrete set of amplitude vectors (AVs) each of which contains amplitudes of spatial harmonics of the field scattered by a particular particle. A scattering operator of a particle is introduced to establish a relationship of the amplitudes of harmonics of the scattered and excitation fields, and an external source is introduced to consider the scattering field that is not related to the excitation field of a particle. An exact nonlocal equation is derived for AVs to describe propagation of electromagnetic waves in PM, and an approximate localized difference equation (an analog of the wave equation in continuous medium) is obtained. Quadratic relationships are obtained for AVs: theorem on active power, Lorentz lemma, and reciprocity theorem. A problem of excitation of homogeneous PM by an external source is solved, and the Green function of PM is obtained. Boundary conditions for AV are introduced at the PM defects that disturb periodicity. A method to formulate and solve the boundary-value problem for AVs in PM with defects is proposed. Analytical solutions to canonical boundary-value problems of PM electrodynamics (eigenwaves of homogeneous PM, normal modes of a cavity, and eigenwaves of an infinite waveguide) are considered. Construction of efficient numerical algorithms for solution of boundary-value problems in electrodynamics of inhomogeneous PM is discussed.

It is experimentally shown that the microwave metainterferometer with a metastructure (metasurface or metaatom) as a tunable beam splitter possesses the unique possibility to specify selective magnetic and electric tuning of multiband filtration of electromagnetic waves. The investigation results are shown concerning the interferogram of a modified metainterferometer based upon the waveguide tee junctions in which the metastructure contains a ferrite plate or a structure made of conducting resonant elements compatible with the controlling elements or their combination with ferrite. The dependences of the shape, width, intensity, and frequency of the interference band on the value and sign of a magnetostatic field, on the relative position of ferromagnetic resonance and the band, and on the electric voltage on the varactors included in the discontinuities of elements. We have experimental results that open new methods and approaches in the design of switchable and tunable multiband microwave filters needed in multifunctional multichannel telecommunication systems.

2D problem of the diffraction of the TM plane electromagnetic wave by a cluster consisting of three self-similar silver nanocylinders with different sizes is considered. Rigorous numerical procedures are used to study quasi-static plasmon resonances in such a cluster. Frequency characteristics of the scattering cross section and spatial structure of the field in the vicinity of the cylinders are calculated for different angles of incidence of the plane wave, self-similarity coefficients, and diameters of cylinders. It is shown that an increase in the distance between the cylinders is accompanied by degeneration of the resonances of scattering cross section. When real loss of silver is taken into account, electric field at the exit of the cluster cannot be amplified by a factor of greater than 10.

The two-dimensional periodic dual-polarized antenna array in the form of a nonuniform multiconductor line of square cross-section conductors is proposed and studied. Using the approximate theory, matching characteristics of the two-conductor line with three different laws of impedance variation are studied and the optimum law is found. Electrodynamic modeling of an infinite two-dimensional periodic array of these elements is carried out using the finite element method at different scanning modes. Using a numerical experiment, the possibility of implementing the over wave region matching mode is demonstrated for arrays of 144 (12 × 12) and 576 (24 × 24) elements: for the array of 576 elements, the working bandwidth in the cophased mode was 1 : 34; when scanning in the sector of 90°, more than 1 : 15.

Automatic identity recognition in fast, reliable and non-intrusive way is one of the most challenging topics in digital world of today. A possible approach to identity recognition is the identification by voice. Characteristics of speech relevant for automatic speaker recognition can be affected by external factors such as noise and channel distortions, but also by speaker-specific conditions—emotional or health states. The improvement of a speaker recognition system by different model training strategies are addressed in this paper in order to obtain the best performance of the system with only a limited amount of neutral and emotional speech data. The models adopted are a Gaussian Mixture Model and i-vectors whose inputs are Mel Frequency Cepstral Coefficients, and the experiments have been conducted on the Russian Language Affective speech database. The results show that the appropriate use of emotional speech in speaker model training improves the robustness of a speaker recognition system – both when tested on neutral and emotional speech.

Multipath phenomenon reduces the performance of elevation angle estimation, intensively. In this study, a precise even symmetry relation and novel iterative array processing method have been presented based on the fixed beam method for estimating the elevation angle of low-altitude targets in specular and diffuse multipath environment. We propose an iterative beamforming process for retaining antenna aperture with precise even symmetry to eliminate multipath. The Kalman filter (KF) prediction have been used to reduce the computational load of the proposed method, and the frequency diversity and KF estimation to smooth sudden fluctuations in angle estimation. The proposed method estimates the elevation angle with very high precision as shown in simulation results in the multipath environment without the need for any advance knowledge.

This paper presents an essential technique for acquiring multi-GNSS signals using FFT. The fundamental approach of multi-GNSS satellite navigation is that the navigation information transmitted with the help of stand-alone GNSS system of numerous constellations is acquired by the receiver. The reason for the acquisition is to apprehend how many total numbers of satellites are currently visible to the user segment; also, the acquisition must determine the code phase and frequency of satellite signals. Although, there are three search domains, which are Doppler frequency, code phase, and code identification, in the acquisition processing, the emphasis of this paper will be on the search of the code phase. FFT based acquisition can decrease acquisition time of DSSS signals due to an increase in the power of DSP chips. The use of FFT based algorithms to perform acquisition of Direct Sequence Spread Spectrum (DSSS) is still the hot topic of research. The main purpose of this study is the analysis of the Multi-GNSS signal acquisition process using the Fast Fourier Transform (FFT) method. Based on MATLAB software platform; GPS, GLONASS, and BeiDou signals are acquired from the real IF signal records of GPS, GLONASS, and BeiDou. The output results of the FFT based acquisition are presented and discussed.

QWIP using group IV elements have created more interest among researchers for its potential application in optical communication as well as in optical interconnects. This paper presents modeling and theoretical analysis of Sn-based tensile strained type I direct band gap QWIP in which the active region has a multiple quantum well structure formed with Ge_0.92Sn_0.08 quantum wells separated by Si_0.11Ge_0.7Sn_0.19 barriers. The structure reported by V. Ryzhii et al. has been reproduced and the parameters like responsivity, power density and the dark current density have been analytically calculated. A comprehensive comparison of responsivity and power density of this proposed structure with the existing QWIP structure made of GaAs/InGaAs is reported here. An improvement in the field of responsivity is observed with the proposed model. The reduction of threshold power density corresponds to an effective operation of the QWIPs in incident infrared radiation. The intersubband electron transition and tunneling electron injection effects are considered here to predict a better performance of the proposed structure operated in infrared region.

In this paper, the main concern is the designing of microstrip structure for Hyperthermia and tissue heating. The purpose of this antenna designing is the capacity of doing an action in 2.24 GHz Frequency and the usage of Silicone tissue in spite of water bolus to decrease the burn percentage on skin to the least degree and solve the problems caused by the water bolus tissue. The function of the antenna by Moment Method and the frequency analysis method is simulated and developed through several stages and biologic tissue which includes three layers (skin, fat, muscle). The improvement in this antenna is the transformation of heating to the upper part of skin and fat layers. The results have been evaluated in four shapes, water bolus, water bolus—silicon, silicon—water bolus, and silicon alone. In first three shapes, the energy is not capable to permeate into the tissue in higher depths; and, it will stay in the fat tissue. Only when silicon has been used, the energy will permeate into the muscular tissue without any damages to the other body tissues. The size of the antenna (0.84 × 45 × 70 mm) and the coaxial 50 Ω has been used for feeding.

The features of phonon–magnon interconversion in acoustic resonator determine the efficiency of spin pumping from YIG into Pt that may be detected electrically through the inverse spin Hall effect (ISHE). Based on the methods developed in previous works for calculating resonator structures with a piezoelectric (ZnO) and a magnetoelastic layer in contact with the heavy metal (YIG/Pt), we present the results of numerical calculations of YIG film thickness influence on acoustically driven spin waves. We obtain some YIG film thickness regions with various behavior of dc ISHE voltage U_ISHE. At micron and submicron thicknesses, the higher spin wave resonance (SWR) modes (both even and odd) can be generated with efficiency comparable and even exceeding that of the main mode. The absolute maximum of U_ISHE is achieved at the thickness about s₁ ≈ 208 nm under the excitation of the first SWR.