Radioelectronics and Communications Systems

Recent designs of metamaterial embedded microstrip patch antennas for wireless applications (review)

Mahesh Gatram — 2024-08-26

Metamaterials are artificial structures arranged homogeneously. It exhibits the properties of electromagnetic waves not discovered in naturally available materials. These materials play a significant role in developing and applying recent trending technologies. The eminent characteristics of metamaterials (MTM) enhance antenna performance regarding gain, bandwidth, efficiency, and multiband generation. These materials will also help improve the isolation of MIMO antennas. So, metamaterial behavior is embedded in the patch antenna to enhance its performance. This paper reviews recent progress in metamaterials and metasurfaces (MTS) to design curtail antennas, gain-bandwidth enhancement, isolation improvement techniques, miniaturization, and beam splitters. The MTSs are part of MTM in uniform/non-uniform structure arrangement. The MTS structures reduce the surface current distribution and enhance the antenna’s performance based on the arrangement of structures. Nowadays, the demand is for wideband, multi-band, high data rates, and beam-splitting to cover the entire region supported by 5G communication to provide good user services. So, the MTM and MTS structures play a significant role in designing such antennas to meet the challenges of present and future generations in the telecommunication systems.

Localization of disturbance region of formal parameters of steganographic cover to ensure steganosystem stability

Ivan Bobok — 2024-08-26

The effectiveness of information security in any industry critically depends on the theoretical basis, which is based on the methods and algorithms used. Existing mathematical approaches do not fully eliminate theoretical problems in information security, leaving the task of their improvement and further development urgent. Today, one of the most effective and powerful means of information security is steganography. Given this, the study aims to increase the efficiency of steganographic systems. The efficiency of a steganographic system is understood as an assessment of its resistance to attacks against an embedded message, with a digital image considered as a cover. The goal of the work is achieved by substantiating the localization of the perturbation region of formal parameters of the complete set, defining the cover as a result of the steganographic transformation, which is the maximum number of blocks of the cover matrix. The most important result of the work is obtaining a sufficient condition for ensuring the resistance of the steganography algorithm to disturbances, which has been practically implemented during the development of the steganographic transformation of the singular decomposition region of the cover matrix and made it possible to increase the steganosystem efficiency by 57% as compared to the prototype. The obtained sufficient condition can be effectively used to select parameters of the steganomethod, which will ensure its relatively significant resistance to disturbing actions and a priori qualitative assessment of the insensitivity degree and reduction of the sensitivity of a steganomessage, as has been demonstrated in this study work using examples of specific steganomethods.

Passive positioning and movement direction method based on Doppler shift change

Spartak Mankovskyy — 2024-08-26

The paper proposes a method for determining the location and direction of an object (hereinafter referred to as the OwlEars-1 method) based on changes in the Doppler shift of the signal emitted by this object. To determine the location, three short measurements are taken over one signal period to determine the relative change in the Doppler shift between these three measurements. There are several prerequisites for obtaining correct results. It is assumed that the object’s speed is known with a specific error, and the trajectory of movement is linear over the interval of three consecutive measurements. The absence or incomplete fulfillment of these prerequisites affects the method’s accuracy. The key advantages of the method are the use of the Doppler shift change as an input signal and the absence of the need for high-precision synchronization of receivers. The input data for the method is in the form of a change in the Doppler shift, instead of a signal without a Doppler shift, which allows the method to be applied to ambiguous signals. Low requirements for receiver synchronization simplify the implementation of the method, since only the change in the Doppler shift is used, unlike the phase method, where the TDoA (time difference of arrival) phase shift is the main parameter. The proposed mathematical model of the method has been validated by a series of simulations, particularly for a moving object emitting an acoustic signal. Further research steps are defined to investigate the method’s accuracy for various deviations from the assumptions made in the method.

Cardiointervalogram determination from video sequence of human face

O. V. Guseva — 2024-08-26

The process of obtaining human pulse signals in the remote photoplethysmography system has been developed. The procedure is based on the use of a video camera that remotely and contactlessly records video of a human body area, in particular, its face, analysis of the dynamics of signals reflecting red, green, and blue light from the skin, and subsequent synthesis of these signals to obtain photoplethysmographic pulse signals. The main attention is paid to determining cardiointervals of the photoplethysmogram to implement variational pulsometry systems. The stages of implementing the remote photoplethysmography method are considered. An algorithm for processing color traces from a face video has been developed, based on forming a “mask” of a pulse and constructing a cross-correlation function. The results of calculations and experiments on restoring photoplethysmographic signals are presented. The methods were tested on our videos, where three areas of the human body were selected as regions of interest: forehead, cheek, and neck. The results indicate the possibility of determining cardiointervalograms using the correlation method of analyzing processed color traces.

Properties of low-temperature GaAs obtained by LPE method for terahertz devices

Semen Krukovskyi — 2024-08-26

The paper presents the results of studying the peculiarities of the high-resistivity low-temperature gallium arsenide formed by the liquid-phase epitaxy (LPE) method under the influence of complex doping of gallium melts with the rare earth element dysprosium and aluminum. The electrophysical properties of the epitaxial layers were studied using the Van der Pauw method. The measurements were carried out in the frequency range of 80–145 GHz using a quasi-optical setup based on a VNA vector analyzer with a pair of frequency expanders operating in the VDI WR-3.4 range. This made it possible to measure the full complex scattering parameters of the two-pole. It is shown that at concentrations of dysprosium (3.7–5.0)×10^–2 at.% and aluminum (2.1–3.8)×10^–4 at.%, high-resistivity layers of GaAs, Al_0.05Ga_0.95As, Al_0.1Ga_0.9As with resistivity values of (3–7)×10⁵ W·cm are formed. The comparison of the studied transmission-reflection spectra of terahertz signals in the specified frequency range through the epitaxial structure of GaAs–SiGaAs (substrate) and the semi-insulating gallium arsenide substrate showed that they were identical. Low-temperature LPE, which is based on the simultaneous doping of gallium melts with aluminum and dysprosium, can be used to form high-resistance layers of gallium arsenide and its solid solutions suitable for use in devices of the terahertz range.