The aim of the work was to establish a correlation between structural, electrical and thermoelectric properties of the disordered tin oxide films to study the possibility of their further applications as materials for thermoelectric converters. Disordered multiphase tin oxide films were synthesized by magnetron sputtering of tin onto glass substrates in argon plasma and subsequent two-stage annealing in air. The structural, electrical and thermoelectric properties of the films were varied by changing the temperature at the 2^nd stage of annealing in the range of 350–450 °C. It was found that the films synthesized at a temperature of 350 °C during the 2^nd stage of annealing procedure have an amorphous structure and are characterized by the highest value of specific electrical conductivity σ ≈ 28.5 S/m. Samples fabricated at temperatures 400 and 450 °C during the 2^nd stage of annealing are characterized by polycrystalline multiphase structure with both stoichiometric (SnO, SnO₂) and non-stoichiometric (Sn₂O₃ and Sn₃O₄) phases of tin oxides in their composition (with prevailing of SnO₂ phase for the samples annealed at 450 °C). It was found that these samples are characterized by a higher value of the Seebeck coefficient S (–156 μV/K and –163 μV/K, respectively) compared to the amorphous films, for which the value S = –90 μV/K. It was found that the electrical conductivity of both amorphous and polycrystalline tin oxide films in the temperature range of ≈ 80–300 K can be described within the frame of a model that assumes the activation of electrons from impurity levels in the band gap associated with oxygen vacancies in different charge states. It was demonstrated that for all types of the samples, the Pisarenko’s formula can be applied to evaluate the relationship between the Seebeck coefficient S and the position of the Fermi level E_F if the parameter r < –2.

The aim of this study was to develop and experimentally validate an algorithm for automatic selection of filter frequency characteristics and detection threshold in order to enhance the accuracy and reliability of gait phase detection. This challenge is crucial not only for objective rehabilitation and monitoring of motor activity, but also for sports analytics, ergonomics, gaming and engineering applications, as well as studies of human locomotion. An automated approach for optimizing the parameters of a gait phase detector based on data from a three-axis foot-mounted accelerometer is presented. This work implements an evolutionary artificial intelligence algorithm that mimics natural selection processes, providing automatic search for the optimal gait phase detector parameters by minimizing the error between the trajectory obtained from inertial measurement units and the reference (optical) trajectory acquired using an OptiTrack system. Details are provided regarding the formation and evolution of the parameter population, design of the objective function, and drift compensation methods utilized during acceleration integration. Experiments involving walking along a closed square path confirmed the high accuracy and robustness of the proposed method: the match between the optimized and reference trajectories demonstrates the practical applicability of the approach for precise gait reconstruction under different conditions. The proposed methodology is easily adaptable to individual movement characteristics and can be integrated into modern wearable sensor systems for a wide range of scientific and applied tasks

Increasing the efficiency of ultrasonic diagnostics and objects with curved surfaces, including cylindrical, spherical, etc., is an important scientific and technical task. The aim of the work was to develop a technique and experimentally investigate the excitation of surface rotating waves on cylindrical and spherical samples in contact with a metal substrate (support) using the proposed remote sounding method, where the substrate serves as an acoustic delay line for transmission-reception of signals between transducers and the object of investigation. The acoustic path of the suggested measuring scheme operating in shadow and echo modes has been analyzed and the dependences of the amplitude and velocity of the surface rotating waves excited in cylindrical steel and dural samples on their radius r, wave frequency ν and the number of revolutions n of the wave, while varying the angular wave number in the range p = 2πr/λ = 20–125 have been experimentally revealed. The quasi-linear growth of the wave attenuation coefficient from the sample diameter at frequencies ν = 1–5 MHz has been experimentally established. The growth of the distance travelled by the wave is accompanied by a drop in the amplitude of the wave according to a law close to the exponential law, reaching the greatest attenuation with a decrease in r. The change in the surface rotating waves velocity in the specified range of variation p did not exceed 1.5–2 %, increasing with decreasing sample radius and wave frequency. The obtained experimental data on the peculiarities of changes in the parameters of acoustic impulses during the passage of surface rotating waves through the crack and the model coatings of the specimens indicate the possibility of using the proposed method for the control of objects of the specified shape.

Currently, the problem of initial orbit determination for space objects based on angular coordinate measurements (right ascension and declination) under limited data conditions is of significant practical value. The aim of this work was to develop a non-iterative estimation method for the slant range vector of an unknown space object relative to an observation site under conditions of limited angular optical measurement data, enabling near-real-time determination of orbital parameters (semi-major axis, inclination, eccentricity, longitude of the ascending node, and argument of latitude). This is particularly relevant for operational orbit determination of unknown space objects to prevent hazardous close approaches and potential collisions, especially given the increasing number of satellite launches and the growing density of space debris in low Earth orbit. A method for initial orbit determination (in the absence of prior orbital data) of an unknown space object is presented, based on angular optical measurements over a short observation arc (< 0.5°) in two detection regions. The proposed method allows for the estimation of the slant range vector of an unknown space object relative to the observation site using angular measurement data and computed values of the velocity projection onto the frame plane of a reference satellite (with known orbital parameters). To estimate the velocity projection onto the frame plane, a method for detecting space objects in optical surveillance system video data is employed. Experimental optical observations of the detected SL-12/RB rocket stage were performed, including angular measurements and orbital parameter calculations. The absolute errors in determining the semi-major axis of the SL-12/RB rocket stage did not exceed 19.71 km. The absolute errors in orbital inclination i, longitude of the ascending node Ω, and argument of latitude u were 0.033°, 0.083°, and 0.046°, respectively.

In recent years, high-precision probe methods have been increasingly used to control the surface microstructure, mechanical and tribological properties of coatings instead of standard methods. The aim of the work was to study the tribological characteristics of the wear-resistant coatings (using the example of AlCrBN coatings deposited with changes in nitrogen pressure, substrate bias voltage and cathode current) at the microand nanolevel using the nanoscratch testing (nano-scratching) method. The nanoscratch testing method is a non-standard method of tribotesting the wear-resistant coatings and is based on the reciprocating movement of a spherical diamond indenter with a curvature radius of 226 nm on the surface (under a certain load). It was found that the friction coefficient decreases from 0.087 to 0.036 for coatings deposited with an increase in pressure from 2 to 5 Pa. When the bias voltage on the substrate changes from -50 to -150 V, the friction coefficient decreases from 0.077 to 0.041 and when the cathode current changes from 80 to 100 A, the friction coefficient remains virtually unchanged. The use of this method made it possible to perform multi-cycle tribotesting of the AlCrBN coatings, determine the average values of the friction coefficient, and completely eliminate the influence of microparticles (the characteristic defects for coatings deposited by the cathodic arc method) on the measurements. Thus, the effectiveness of the nanoscratch testing (nanoscratching) as a method for the control wear-resistant coatings is demonstrated.

Numerical modeling of semiconductor photodiodes’ electrical characteristics is an important task at the stage of their development and design. In this regard, it should be noted that one of the most promising methods that can be used for this purpose is the ensemble Monte Carlo method, which allows including, along with the dominant mechanisms of charge carriers’ scattering in the device structure, also the processes of impact ionization, which is very important for adequate modeling of a wide class of silicon photodiodes operating in the reverse bias mode. The aim of the work was to study the influence of the impact ionization process on the electrical characteristics of silicon photodiodes with a p-n-junction and a p-i-n-structure operating in the reverse bias mode under the influence of picosecond pulses of visible radiation. Using selfconsistent simulation by the ensemble Monte Carlo method, the electron ionization coefficient in bulk silicon at a crystal lattice temperature of 300 K was calculated and compared with known experimental data. Photoresponse in silicon submicron photodiodes with a p-n-junction and photodiodes with a p-i-n-structure was calculated for different thicknesses of the undoped i-region. It was shown that use of simple models similar to the Keldysh model with constant values of the threshold energy and other parameters for calculating the rate of the impact ionization process did not allow obtaining values of the ionization coefficient matched with experimental data in a wide range of electric field strengths. This result raises the question on the adequacy of the device structures’ electrical characteristics modeling with a non-uniform electric field when using such simple impact ionization models.

Correct measurement of the distorted objects length in images is an important task of probe microscopy. Existing measurement methods do not fully take into account the specifics of a given subject area. The purpose of this work was to develop an algorithm for locating the objects skeletons adapted to the images peculiarities in scanning probe microscopy and does not require significant computing resources. The limited speed of the probe microscope, contamination of the sample surface, and Non-ideality of the probe lead to typical disturbances in the form of stripes, 1/f noise, and brightness fluctuations and cause defragmentation of the skeletons of objects and a decrease in the accuracy of length measurements. The method proposed in this paper uses predictive relief estimates to eliminate the influence of these disturbances. The forecast is calculated based on extrapolation of information from the raster columns of the already scanned part of the image. The forecast interval is equal to the discretization interval of the image. The set of forecast estimates forms a predictive image, which is subsequently used to determine the length of objects. The peculiarity of predictive images is the sharpening of areas distorted by disturbances. This made it possible to defragment the skeletons and measure their length more accurately when locating objects using curvature detectors. Studies have shown that an increase in the integral prediction error is a indication of the need for additional image filtering from low-frequency or shock interference. At the same time, the use of predictive images reduces the relative deviation of the number of unrecognized skeletons and the average deviation of the maximum measured length. It has been established that control information in the form of forecast estimates can be used in image processing in probe microscopy to detect and partially eliminate disturbances. The formation of predictive images enhances the sharpness of objects and increases the probability of their correct selection using methods based on the analysis of changes in the brightness function.

Nowadays, there are many different methods of transformer diagnostics. The analysis of used methods and diagnostic systems indicates that a certain complexity of further development of existing methods and diagnostic systems has been achieved. This is due to the complexity of input signals, quite a large number of input factors, nonlinear multiple dynamic interrelationships with other parameters. One of the most promising types of diagnostics, to date, is frequency response analysis. The objective of this paper was to identify various transformer defects by analysing the frequency response. In this paper, frequency response analysis based on the three voltmeter method is used to detect core and winding defects. In a series of experiments, impedance and phase-frequency characteristics of transformers with core and winding defects are obtained. These characteristics show significant differences between the normal and emergency states of the transformers. The obtained characteristics in the form of pictures are the initial data for the convolutional neural network, which determines the type of defect. The use of frequency characteristics of single-phase and three-phase transformers in diagnostics of pre-failure states and failures will allow to create a universal hardware-software complex of diagnostics for transformers of different types and nominal data.

Electrical stimulation restorative treatment’s process of neuromuscular system’s diseases very important. Choice of the signal frequency-time parameters and its coordination with the biological tissues electrical parameters one of the main factors in the practice of electrical stimulation. The purpose of this article was to optimize the electrical action parameters in accordance with the muscles’s functional state. The studies were conducted on the biceps brachii of the upper limb of the subject and included: study of dependence of the effort developed by the muscle on the amplitude of the stimulating signal’s voltage and study of the interelectrode impedance phase-frequency characteristic of the upper limb biceps brachii of the subjects. As a result, relationship between the optimal value of the electrical stimulation frequency causing the maximum effort of the muscle and the magnitude of the phase shift of the phase-frequency characteristic of the tissues was determined. Dependence of the effort developed by the muscle during electrical stimulation on the amplitude of the stimulating signal magnitude at different values of electrical stimulation frequency was studied. It was established that with an increase of the stimulating signal amplitude, frequency of the phase-frequency characteristic’s extremum of the biotissue increases and accordingly the frequency of electrical stimulation that causes maximum muscle effort increases. Results of the work can be used in the design of electrical stimulation systems for musculoskeletal system with feedback.