Antennas play a fundamental role in modern communication systems by facilitating signal transmission and reception across various frequency bands. Each antenna is designed for specific applications based on its operating frequency range. Whether deployed for Car-to-Car Communication or military operations, antennas serve critical functions, with information security being paramount in military contexts. Vehicular antennas typically operate within the L Band, approximately 1 to 2 GHz, relying on satellites for signal communication. However, traditional transmission through the ionosphere faces limitations, notably the skip zone, where signal reception is hindered, leading to communication failures. To address this limitation, Near Vertical Incident Skywave (NVIS) communication has been developed. NVIS utilizes antennas with very high (> 75°) radiation angles and low HF frequencies to overcome skip zone challenges. Despite existing research efforts, achieving high radiation efficiency remains a challenge, often due to improper antenna angle settings. Additionally, previous studies have overlooked the importance of narrow beam focusing, crucial for long-range communication and direction finding. This paper aims to enhance antenna performance parameters such as efficiency and gain through the adoption of specific techniques. By optimizing antenna design and configuration, we aim to improve performance for ionospheric communication, particularly in military applications involving data and voice transmission.

Alternating current (AС) voltage measurement is one of the most common types of measurements in various fields of science and technology. To evaluate the AC voltage level, special voltmeters are used which allow recording of amplitude, average and/or root mean square (RMS) voltage values. Among these measuring instruments, voltmeters of mean square voltage are especially significant because RMS is a fundamental physical characteristic of an electrical signal and is a true measure of power. The wide distribution of non-sinusoidal signals necessitates the creation of voltmeters for direct measurement of RMS. The main component of such voltmeter is an AC voltage to direct current (DC) voltage measuring converter based on the root-mean-square value level (AC RMS-DC converter). An analysis of existing technical solutions shows that it is advisable to use a thermoelectric converter (TEC) for high-precision measurement of RMS voltage of an arbitrary shape with a spectrum in the frequency band from 20 Hz to 20–50 MHz. Such a AC RMS-DC converter must contain a differential semiconductor TEC and an input broadband voltage amplifier with low nonlinearity of the frequency response. The aim of the paper was to develop a measuring AC RMS-DC converter of arbitrary shape voltage in which special attention is paid to modernization of the TEC and reduction of the AC RMS-DC converter error using corection of the frequency response of the input amplifier and introduction automatic calibration of the output voltage. Features of semiconductor chips and design of TEC in the form of a microcircuit or microassembly, results of converter’s and TEC elements’ parameters measurements are presented. A significant influence of the frequency response of the input amplifier and the offset voltage of the TEC transistors on the AC RMS-DC converter error was noted. Modernization of the input amplifier and introduction of automatic calibration of the output voltage ensured an error in a sinusoidal signal converting of less than 1 % in the range from 20 Hz to 50 MHz.

The article presents an apparatus for generating an air plasma jet "ALOE". The device differs from known analogues in its compactness achieved due to absence of need to use inert gases (because they are replaced by ambient air) and the ability to determine the exposure dose. In terms of its characteristics this new product corresponds to world standards. There are no domestic analogues of it. Parameters and examples of using this device are presented. It will be in demand for healthcare, veterinary medicine, and cosmetology. The device can be used for disinfection of surfaces, including heat-sensitive ones, such as living tissues, and can serve as a prototype for development of various physiotherapeutic devices.

Currently, it is relevant to create moving objects orientation systems based on the integration of various types of primary information sensors. One way to solve the orientation problem is to use the TRIAD (Tri-Axial Orientation Determination) method which allows determining the matrix of direction cosines between two coordinates. The traditional TRIAD force method is based on the use of two reference vectors – of gravitational and geomagnetic fields, measured by accelerometers and magnetometers, respectively. The disadvantage of this method is – appearance of additional deviations during the accelerated movement of the object and influence of primary information sensors’ random errors. Modified TRIAD method which is based on measurements of three triads of sensors: magnetometers, accelerometers and gyroscopes was proposed in the article. Estimates of acceleration vectors of gravitational and geomagnetic fields were calculated taking into account gyroscope measurements. Then these estimates were combined with the accelerometers’ and magnetometers’ data. The complex gravitational and geomagnetic fields’ accelerations were used to form the direction cosine matrix by the TRIAD method. The suggested modified method can be used to implement free-form moving objects’ orientation systems, since it is 6–8 times more accurate compared to the classic TRIAD method. Attenuation of random sensor errors and disturbances due to object acceleration can be adjusted by use of weigh factors.

The reflection of a Gaussian laser beam from a flat Lambert disk is considered theoretically. It was found that the results of experimental measurements of the reflected beam power as a function of the disk radius at various distances from the photodetector to the target are in good agreement with the theoretical model. It was shown that when the radius of the laser beam is greater than the dimensions of the probed complex target this target can be replaced by an equivalent Lambert disk with the same laser radar cross section.

Thermally expanded graphite belongs to a new class of graphite materials with unique physical, chemical and mechanical properties. Acoustic wave velocity is one of the most important characteristics for study of porous materials including thin porous sheets of thermally expanded graphite. In this paper peculiarities of symmetric mode S0 Lamb wave propagation and SH-wave with horizontal polarization in sheets of thermally expanded graphite are experimentally investigated. To determine their velocities a differential measurement scheme on the base of a low-frequency acoustic flaw detector DIO1000 LF and specialized piezoelectric transducers with dry point contact was used. Additionally the longitudinal wave velocity in direction of sheet thickness was determined using piezoelectric transducers based on polyvinylidene fluoride. Indicatrices of normal wave velocities in the rolling plane were plotted and it was shown that the maximum acoustic anisotropy is characteristic for the S0-mode. The velocity minimum corresponds to the longitudinal direction of the rolling plane in which the maximum elongation of gas pores was observed. Influence of thickness and density of thermally expanded graphite sheets on the velocities of normal waves was investigated and presence of the thickness range where the minimum velocity values were observed due to the maximum inhomogeneity of layers formed in the rolling process. Method for determination of dynamic elastic moduli of porous thermally expanded graphite sheets using experimentally measured velocities of normal waves was proposed. It was shown that in the longitudinal direction of the rolling plane the Poisson's ratio took negative values which allow to attribute the specified material to auxetics ones.

Kinetic indentation is widely used to measure physical and mechanical properties of materials as one of the most universal methods for non-destructive testing. This paper uses the latest advances in artificial intelligence and capabilities of the Python programming language libraries allowing to carry out accurate measurements of cast iron hardness based on the data of the material’s micro-impact loading diagram. It has been shown that use of machine learning allows eliminating gross errors and reducing the error of indirect hardness evaluation in several times – down to 10 units according to Brinell HB. It has also been established that formation of additional features for training models (based on traditionally used characteristics: penetration depths, indenter movement speed and contact forces at certain points in time) has a positive effect on the accuracy of measurements, but amount of measurements should also be optimized. Feasibility of effective use of machine learning to evaluate hardness has been demonstrated by comparing of calculated hardness values with data obtained with standard testing methods. Advantage of the developed testing method is the fact that the developed algorithms can be used for prompt diagnostics of cast iron hardness using existing equipment. It is appropriate to extend the proposed approach for determination of other mechanical properties of cast iron: yield strength, strain hardening index, creep, relaxation, determined by indentation methods.

Semiconductor materials based on ZnO and RE³⁺MnO₃ oxides are considered as potential candidates for spintronics. This article presents the methodology and results of studying the effect of magnetic circular dichroism for Zn_1-xCo_xO, Zn_1-x-yCo_xAl_yO and RE_1-x ³⁺A_x ²⁺MnO₃ film structures in the visible radiation range. It has been shown that the magnetic circular dichroism behavior of the manganite films reflects not only the magnetic, but also the charge component of the material. This indicates the possibility of studying the magnetic and transport characteristics of the films using the magnetic circular dichroism spectroscopy. Since the magnetic circular dichroism effect also directly probes the ground and excited electronic states of the film, it has been obtained data that update calculated parameters for describing the manganites band structure. In the case of the Zn_1-xCo_xO and Zn_1-x-yCo_xAl_yO films, the magnetic circular dichroism spectroscopy acts as a tool for detecting Co nanoparticles in the solid solution matrix of ZnO:Co and ZnO:(Co+Al).

Development of a high-power RF signal meter based on the method of calorimetric measurements, which in some cases is the only possible one is presented. The device is as a system of elements exchanging either energy or information, the operation and interconnection of which ensures the stability of its functioning. The main elements of the device are: a coordinated load and a two-circuit water-air cooling system that convert RF energy first into thermal electrical energy, and then into internal energy of the coolant (working fluid). The measurement and control system provides information display on the monitor and generation of internal control signals. The work focuses on the process of converting electromagnetic energy into internal energy of the coolant, since the matched RF load is integrated into the cooling system and requires special design and technological solutions to ensure efficient operation. A cooling and measurement system has been designed to test the developed RF absorber with a power of up to 5 kW. The parameters of the cooling system were determined based on minimizing the time to achieve thermal equilibrium (time to establish readings) and the set parameters (input temperature no more than 35 °С, temperature difference no more than 40 °С). Based on calculations of the electrodynamic model constructed by the partial domain method, the geometric dimensions were determined at which the voltage standing wave ratio of the load in the operating frequency range (from DC to 1300 MHz) will be the smallest. The article presents the results of designing a high-frequency wattmeter cooled by a liquid (water), examines the thermophysical processes occurring in it and the influence of the presence of a coolant in the cooling circuit.