Introduction. Determination of the physical and geometric properties of plasma is a relevant problem in the field of ion-plasma processes for micro- and nanoelectronics fabrication. The energy of ions and the nature of their interaction with materials define the effectiveness of ion-plasma technologies. The penetration depth and momentum transfer of ions affect the sputtering yield (Y) of the material, which is a key parameter in ion beam technologies. Changes in the ion beam shape have an effect on the ion density distribution. Previous studies have explored the possibility of modifying the design of the ion source to achieve annular or near-Gaussian beam profiles; however, this approach is associated with significant labor and monetary costs. An alternative approach consists in the use of external magnetic systems. Aim. Determination of the physical parameters of a system for ion beam treatment of micro- and nanoelectronic substrates and functional layers. Materials and methods. The research was conducted at the MT-11 Department of Bauman Moscow State Technical University (BMSTU) using the MVTU-11-1MC vacuum system. The material under investigation was silicon and argon ions. Cross-sectional analysis was performed using a CROSSBEAM 550 microscope. The magnetic field strength was determined using a TP2-2U milliteslameter. Results. Calculations and experimental investigations revealed the minimum sputtering yield (Y) to be 0.03 at oms/ion at an energy of 0.05 keV, with the maximum of 1.35 atoms/ion at 7 keV. Subsequently, the sputtering yield decreases to 1.05 atoms/ion at 250 keV due to ion implantation into the lattice structure. The external magnetic system of the source allows the beam cone angle to be modified, which increases the ion concentration at a specific point on the substrate, consequently enhancing the process efficiency. Conclusion. A methodology for calculating the energy of Ar+ ions generated by an annular ion source during Si substrate etching has been validated. Processing of the experimental results enabled the determination of the sputtering yield (Y). The derived expression for the magnetic field strength and magnetic field distribution will be used when simulating an additional external magnetic system designed to manipulate the ion beam shape.
Introduction. Recent years have seen an increased interest in research on small autonomous vehicles, in which naviga-tion are the fundamental problems that must be addressed. In outdoor environments, the use of global satellite naviga-tion systems remains the optimum solution due to their wide coverage, high level of automation, and ease of use. How-ever, operation in unknown and GPS denied environments, such as indoor spaces, is still a relevant research problem. The Valve Lighthouse (LH) system has been proposed for guiding mobile platforms in confined spaces due to its autonomous operation, low cost, ease of deployment, and miniature onboard sensors, which are particularly suitable for small scale vehicles. Nevertheless, similar to other indoor localization sensors, the LH system does not allow the reconstruction of an unknown environment (i.e., obstacle detection), which may lead to collisions and potential damage to the vehicle. Therefore, integration with a mapping system is necessary. Currently, an optimal choice for small scale platforms is ORB SLAM based on a monocular camera. The main drawback of monocular camera based systems lies in their inability to determine the scale factor of the map. In this regard, this paper proposes an algorithm to estimate the map scale factor of the ORB SLAM system through its integration with an infrared system.Aim. Determination of the map scale factor of the ORB SLAM system in an integrated infrared system.Materials and methods. The proposed algorithm is based on an extended adaptive Kalman filter with a Sage window combined with a maximum likelihood estimation method.Results. The proposed algorithm enables the determination of the map scale factor of the ORB SLAM system along each axis in real time. Conclusion. An algorithm is proposed to determine the map scale factor of the ORB SLAM system along each axis in real time within a system integrated with the Valve Lighthouse infrared system.
Introduction. The rapid development of 5G and Beyond 5G mobile radio technologies does not diminish the importance of research into the accuracy of positioning in widely deployed 4G LTE networks. This paper presents the original results of an integrated study into the accuracy of device positioning in LTE networks under line-of-sight (LOS) conditions. Aim. To substantiate the possibility of achieving an accuracy of user equipment (UE) coordinates of less than one meter with the proper selection of PRS signal parameters and LTE radio access network configuration. Materials and methods. The accuracy limits of primary time-of-arrival (TOA) measurements in a separate radio link between a base station (eNB) and a UE using PRS positioning reference signals were assessed using mathematical modeling and simulation methods, including calculating the Cramer-Rao lower bound for primary TOA measurements. The maximum-likelihood and Fitz-likelihood TOA estimation algorithms were investigated. The accuracy limits of coordinate estimates are demonstrated during secondary processing of primary TOA measurements using the observed time difference of arrival (OTDOA) method. Results. An increase in the PRS signal bandwidth was established to lead to a decrease in the root mean square error (RMSE) of positioning. When using six resource blocks, positioning accuracy of less than 1 m in a coordinated network is achieved. In uncoordinated networks, the effect of intercell interference significantly degrades accuracy, in the vicinity of base stations in particular, where RMSE can reach 100 m. Conclusion. The study confirms the feasibility of achieving decimeter-level UE positioning accuracy in LTE networks under line-of-sight conditions with the eNB. The results obtained have practical implications for network optimization and can serve as a basis for further research.
Introduction. The safety of conducting activities on the snow and ice cover of a reservoir depends directly on the accuracy of its condition assessment. This is particularly important when landing a helicopter on unequipped and unexplored snow covered areas or frozen water bodies for transporting goods and people, evacuating victims, or conducting search and rescue operations. The ability to remotely assess the characteristics of snow and ice layers and reconstruct their structure makes it possible to conclude whether the selected site is suitable for helicopter landing or whether an alternative site, which meets the necessary requirements, should be selected. Ultimately, this determines the safety of aircraft landing.Aim. Development of a non invasive method for assessing planar layered media based on polarization relationships of backscattering signals with vertical and horizontal polarizations within a helicopter mounted subsurface sensing radar system.Materials and methods. The Engee platform and the Julia programming language were used to simulate the operation of a radar system for subsurface sensing.Results. An innovative method for remote assessment of the characteristics of planar layered media is proposed. The approach is based on analyzing the polarization properties of backscattered signals from the interfaces of layers within a planar layered medium, using both vertical and horizontal polarizations. Specific ranges of polarization backscattering ratios that correlate with varying densities of snow and ice layers at particular incidence angles are identified.Conclusion. The proposed non invasive method for analyzing planar layered media based on polarization characteristics of backscattered radio signals opens up new possibilities for the assessment of snow and ice cover. This approach makes it possible to evaluate unprepared and unexplored snow covered sites, as well as reservoirs covered with snow and ice, for helicopter landing. A distinctive feature of the proposed method lies in its ability to detect and characterize all layers within a multilayer environment, compared to existing methods that are limited to analyzing exclusively the near surface layer.
Introduction. The microfocus X ray tube is a key component in modern medical diagnostic, scientific research, and industrial applications. One of its main elements is the focusing system, with the magnetic lens at its core. The characteristics of this lens largely determine the spatial resolution of the device. Accurate consideration of thermal conditions is essential for ensuring the efficiency and reliability of the focusing system. The importance of thermal analysis has increased significantly due to the tightening requirements imposed on the quality of X ray images. Today, the electron-ic lenses of the X ray tube focusing system are cooled mainly by forced liquid cooling. However, this approach creates additional technological and economic difficulties during the manufacture and operation of the device.Aim. Construction of a numerical model of thermal processes in a magnetic lens, as well as determination of its optimal parameters for operation without forced liquid cooling and ensuring a micron diameter of the focal spot.Materials and methods. Numerical and analytical methods were used to construct a model of thermal processes in a magnetic lens. The results obtained were evaluated using numerical modeling of thermal processes implemented in the Comsol Multiphysics environment.Results. The temperature values of the magnetic lens coil obtained within the calculation model and as a result of simulation did not exceed the maximum permissible values. The temperature distribution graphs across the coil cross section obtained by the calculation and Comsol Multiphysics models showed good agreement, which confirms the validity of the calculations.Conclusion. The obtained optimal parameters of the magnetic lens ensure its stable operation under natural cooling.
Introduction. In cochlear implant systems, automatic algorithms that include neural response telemetry are not always capable of determining the threshold stimulation current that generates an electrically evoked compound action potential with minimum amplitude on intracochlear electrodes. The target current can be determined by the linear regression method based on the data obtained during telemetry. However, this method does not consider the physiological characteristics of the human auditory system. Aim. Development of a methodology for determining the threshold stimulation current and its implementation in clinical practice, considering the actual physiological nonlinear dependence of the amplitudes of the electrically evoked potential of the auditory nerve on the stimulation current in cochlear implant users. Materials and methods. Three users of cochlear implant systems were involved. In each of them, it was impossible to conduct neural response telemetry using automated algorithms due to failure of the extracochlear electrode (while maintaining the clinical effect of the implant), lack of a technical сapability to support the automated algorithm (an early model implant), and meningitis with subsequent obliteration of the cochlea. An advanced (compared to the automated algorithm) telemetry was conducted for each user, performed post-operatively in two users and intraoperatively in one of them. Results. The proposed methodology involves the formation of the growth function of the amplitude of the electrically evoked action potential of the auditory nerve depending on the equivalent stimulation current, finding the first point of the telemetry of the nerve response with a coordinate (equivalent stimulation current, amplitude); finding the zero point corresponding to the maximum value of the current equivalent that does not generate a potential; determining the threshold equivalent current as the average value of the zero and first points. In total, threshold currents on 32 electrodes (for three users) were determined using the proposed methodology and the linear regression method. Conclusion. The methodology can be used in case of failure of the automated algorithm both intra- and postoperatively, thus enhancing the quality of medical care provided to the users of cochlear implant systems.
Introduction. Electret capacitive receiving transducers with moving plates are used in various devices, particularly as microphones in mobile phones. However, methods for calculating their sensitivity, including taking into account the electrical load parameters and other characteristics of such transducers, are insufficiently developed.Aim. To develop a mathematical model of membrane-type electret sensors for evaluating their sensitivity, taking into account the static deflection of the membrane, the characteristics of mechanical vibrations under the influence of an external periodic force of various origins, and the influence of the electrical load.Materials and methods. Computer simulation in the MATLAB environment.Results. The proposed calculation procedure is divided into three interconnected stages. The static stage accounts for membrane deflection under the influence of the electret-induced electric field. The dynamic stage describes membrane vibrations caused by an external periodic disturbance. The electrical stage determines the resulting electrical voltage at the transducer terminals. Analytical expressions for the static deflection of the membrane are derived, and the limits of its steady state are determined as functions of the parameters of the electret transducer capsule, including membrane tension, air gap thickness, electret film thickness, relative permittivity of the electret material, membrane and counter-electrode dimensions, etc. The technique for calculating membrane vibrations uses equivalent lumped parameters (membrane mass, acting forces, etc.) instead of distributed parameters, thereby eliminating the need to solve partial differential equations.Conclusion. The proposed calculation procedure provides a basis for the rational selection of electret transducer parameter values depending on the target performance requirements. The derived expressions enables the calculation of the amplitude–frequency characteristics of various electret transducer generators. The results obtained are useful for those designing new and optimizing existing electret transducer designs
Introduction. The Cramér–Rao lower bound for the root-mean-square error of height estimation in radio altimeters with continuous frequency-modulated periodic signals is determined. Analysis of the bound showed that a periodic stepwise change in the emitted signal frequency between two levels, the difference between which is equal to the selected deviation value, is a type of frequency modulation that enables the potential altitude estimation accuracy of lowaltitude radio altimeters. However, such signals cannot be used in existing radio altimeters that are based on beat frequency estimation. An alternative solution is to implement a phase-locked altitude measurement mode.Aim. To investigate the feasibility of implementing a phase altitude measurement mode in a low-altitude tracking radio altimeter using a phase-locked loop (PLL) for altitude estimation, and to verify its performance using mathematical simulation.Materials and methods. The stated problem was solved by constructing a mathematical model of a tracking radio altimeter with the PLL to implement the phase method for altitude estimation.Results. The conducted computer simulation demonstrated the operability of the PLL-based radio altimeter that utilizes the phase method of altitude estimation. When operating over a perfectly flat surface, the altimeter provides an unbiased and effective altitude estimate with signal-to-noise ratios greater than 5 dB. In the case of a rough surface, the quality of altitude estimation in the altimeter is approximately an order of magnitude higher than in tracking altimeters, which implement estimation of the beat signal frequency.Conclusion. The data obtained via computer simulation demonstrate the potential for achieving the height estimation accuracy in a PLL-based radio altimeter that combines frequency and phase measurement modes. Future research will examine the influence of various factors on the performance of the radio altimeter and its circuit design.
Introduction. The determination of normative ranges for the biomechanical parameters of human motor activity is a relevant task for disorder diagnostics, orthopedic treatment planning, rehabilitation monitoring, and development of assistive devices. The creation of such a database requires a validated methodology for data collection and analysis.Aim. To develop and test a methodology for collecting and analyzing the biomechanical parameters of fundamental motor activities (walking, squats, lunges, torso bends) using modern motion capture systems with the purpose of compiling a normative database of spatiotemporal, angular, and electromyographic (EMG) characteristics.Materials and methods. The Qualisys motion capture system (kinematics), Kistler force plates (kinetics), and the Delsys Trigno EMG system (activity of key lower limb muscles) were used. Data was collected from eight healthy volunteers in a laboratory setting following a standard protocol. Preprocessing included marker trajectory interpolation, EMG signal smoothing, and outlier removal (based on IQR). Normative ranges (±1 SD) were calculated based on mean values and standard deviations.Results. A methodology for collecting biomechanical data for four types of motor activity (walking, squats, lunges, torso bends) was developed and tested. The average values and preliminary normative ranges for spatiotemporal, angular, and EMG parameters were obtained, reflecting characteristic movement patterns and muscle activation in healthy individuals. According to the results obtained, the proposed methodology is effective for comprehensive collection and analysis of biomechanical data. The use of Qualisys and Delsys Trigno systems ensured accurate recording of kinematic, kinetic, and EMG movement parameters. The developed preliminary normative ranges indicate the potential of the methodology for diagnosing movement disorders, rehabilitation, and engineering design (exoskeletons, prosthetics).Conclusion. The proposed methodology represents a reliable tool for an objective functional assessment of human motor activity. The obtained preliminary normative data serves as a foundation for further sample expansion and formation of a comprehensive database essential for clinical practice (diagnosis, treatment monitoring, rehabilitation) and engineering applications in movement correction.
Introduction. When measuring the distance with a laser rangefinder, interference along the path of the beam can significantly affect measurement accuracy. Classical filtering algorithms, which rely on the characteristics of the received signal, are unable to reliably distinguish the useful signals from natural interference and targets. In this work, we propose an algorithm for classifying objects based on processing echolocation path signals obtained by vertical laser rangefinder sensing. The main task is to distinguish useful signals against the background of natural interference, such as atmospheric aerosols, haze, and clouds. The problem is solved by a method based on isolating intensity peaks on an echolocation path, followed by their classification using machine learning methods. Owing to the preprocessing of the signal, the algorithm is compatible with systems having different parameters of the emitter and the receiving channel.Aim. To develop an algorithm for identifying and classifying objects on an echolocation path obtained by vertical sensing using a laser rangefinder.Materials and methods. Vertical sensing was carried out using an experimental stand, which includes a laser rangefinder with a radiation source of 100 mJ and a wavelength of 1064 nm. This made it possible to collect data in various meteorological conditions. The sample included echolocation traces obtained from different objects with different characteristics, such as monolithic structures, lattice structures, and natural interference encountered during vertical sensing. A comparative analysis of the following algorithms was conducted: logistic regression, random forest, gradient boosting, and a neural network algorithm. The metrics accuracy and F1-score were chosen to evaluate the prediction quality of the models. The models were trained on a dataset containing cloud structures, with a split into training and test sets.Results. The gradient boosting model demonstrated performance comparable with that of the neural network algorithm, achieving an F1-score of 0.89 on the test set. This makes it suitable for deployment in resource-limited systems without compromising predictive performance.Conclusion. The results confirm the effectiveness of the algorithm for useful signal discrimination under interference conditions, which is important for geodesy, navigation, and satellite sensing.
Introduction. In recent years, there has been a growing trend toward the miniaturization of printed radiators for phased arrays. At the same time, such radiators are frequently required to operate over an ultra wide bandwidth, support wide angle scanning, and enable dual polarization. To enhance the performance of printed radiators, matcing inserts with specific geometries and dimensions can be used.Aim. To increase the overlap ratio of a printed radiator while maintaining its ultra wideband performance and wide-angle scanning within an angular sector of ±60º, limited by the mismatch, and ensuring electrical compactness with a height not exceeding λ at the upper operating frequency through the use of various matching metal inserts.Materials and methods. Electrodynamic simulation of the radiator was performed as part of an infinite antenna array using the Ansys HFSS computer aided design software.Results. The use of metal rectangular inserts measuring 25.5 × 145.0 mm at the edges of the radiator allowed its operating frequency band to be extended, while the use of an additional insert in the aperture allowed its matching (radiator with combined inserts) to be improved. The operating frequency band of the original radiator, at a voltage standing wave ratio (VSWR) of ≤ 3, extends from 257.6 to 732.5 MHz, corresponding to an overlap ratio of 2.844. For the radiator with combined inserts, the operating band at the same VSWR level ranges from 164.9 to 677.5 MHz, yielding an overlap ratio of 4.109. The electrical dimensions of the proposed radiator are 0.339λ × 0.339λ × 0.678λ at the upper operating frequency of 677.5 MHz, and 0.083λ × 0.083λ × 0.165λ at the lower frequency of 164.9 MHz.Conclusion. The application of combined inserts in the radiator allows its overlap ratio to be increased at the same time as maintaining its ultra wideband performance, wide-angle scanning in the sector of angles up to ±60°, and compact dimensions. The proposed radiator can be used in phased arrays for radio communication, radar and radio navigation systems.
Introduction. Intensive research is currently focused on identifying materials suitable for the development of ad-vanced gas sensors and systems for water and air purification. Among the diversity of purification approaches, photocatalysis is viewed as a particularly promising method. Considering various potential materials, titanium dioxide stands out due to its physicochemical properties. Reactive magnetron sputtering is considered one of most effective techniques for titanium dioxide deposition. Aim. To investigate the influence of synthesis parameters on the efficiency of a TiO2-based photocatalyst for its further application in water purification and gas sensing.Materials and methods. Two series of five samples each were manufactured. In the first series, the sputtering duration was varied (3, 7, 10, 15, 30 min). In the second series, the argon-to-oxygen ratio in the reactive mixture was varied (90/10, 70/30, 50/50, 30/70, 10/90%). Subsequently, all samples in both series were irradiated for 2 h and then evaluated for hydrophilicity using an OSA 15 EC device.Results. Two dependencies, i.e., the contact angle as a function of sputtering duration and the contact angle as a function of oxygen content in the reactive mixture, were established. The employed method was found to be suitable for depositing photocatalytic titanium dioxide films. Upon an increase in film thickness, the contact angle index varies within 37 and 45º. A 10-fold increase in sputtering duration (from 3 to 30 min) caused no significant differences in the photocatalytic and hydrophilic properties of the samples. It was experimentally established that the most photoactive films are synthesized at Ar/O2 ratios of 90/10 and 10/90%.Conclusion. The developed photocatalytic titanium dioxide film can be recommended for a number of water purification tasks and for use in gas sensors.
Introduction. Conventional implementations of adaptive MIMO-OFDM make suboptimal use of computational resources, as they require parallel execution of distinct algorithmic architectures: Space-Time Block Coding (STBC) for transmission reliability and spatial multiplexing for increased throughput. Consequently, the algorithmic development of a unified signal-processing architecture remains an open problem.Aim. This study develops and evaluates a unified adaptive MIMO-OFDM architecture that eliminates dedicated hardware STBC encoders from the transmit chain. This is achieved by compensating for the loss of orthogonality through an iterative receiver with soft interference cancellation while maintaining stable channel adaptation.Materials and methods. The proposed algorithm performs iterative soft-information exchange between a Soft V-BLAST detector and a Low-Density Parity-Check (LDPC) decoder. Its performance was evaluated through computer simulation against established reference schemes. To assess operability under non-stationary conditions, a link-adaptation algorithm for the Modulation and Coding Scheme (MCS) was implemented using the block-error-rate criterion.Results. The proposed iterative receiver achieves BER performance comparable to that of conventional STBC schemes within two iterations, without employing orthogonal transmit coding. Integrating the detector into the adaptation loop enables dynamic maintenance of a target error rate, effectively trading the diversity gain for increased channel throughput.Conclusion. The proposed unified architecture enables software-defined adjustment of the transmission strategy from maximum reliability to maximum spectral efficiency within a single algorithmic core, thereby minimizing computational and logic-resource overhead in transceiver implementation.
Introduction. In view of the growing demand for the quality and linearity of RF signal switches, microelectromechanical system (MEMS)-based switches (MEMS-SW) are attracting particular interest. Such devices offer several advantages over other technologies. This article examines the operational and manufacturing specifics of MEMS-SWs, including fabrication and sealing technologies, degradation mechanisms, and design improvements expected to enhance the device performance. Quantitative parameters of commercially available MEMS-SWs are presented. Aim. To review MEMS switch design, production, and factors influencing their mass adoption. Materials and methods. The literature review follows a chronological approach. For evaluating end-component parameters, sources published over the past 10 years were prioritized, while technologies and structural solutions were traced over longer periods to document the evolution of MEMS switches. The final dataset comprised peer-reviewed publications with factual data and official manufacturer specifications. Results. Key characteristics, production and packaging technologies, and required testing methods are described. Materials for MEMS-SW fabrication are analyzed, along with known degradation mechanisms and mitigation strategies. Design solutions for enhancing the performance and parameters of current MEMS-SW are discussed. Conclusion. Although MEMS switch structural components are relatively affordable due to the similarities of fabrication processes with CMOS technology, MEMS-SWs costs remain significantly higher than those of transistor and PIN diode switches, primarily due to packaging and testing expenses. MEMS-SWs outperform electromechanical relays in most applications and are preferable for solid-state switches when linearity and FOM are critical, rather than the size or the switching speed. Continued market growth and performance improvements are anticipated.
Introduction. In order to increase the accuracy of estimating the coordinates of a target, it is necessary to compensate for systematic errors in the nonlinear transformation of coordinates from a spherical system to a Cartesian one. In this paper, we consider the generalization of the well-known coordinate transformation algorithm with compensation for systematic errors when the radar is positioned and oriented arbitrarily in the global Cartesian coordinate system. By applying the proposed algorithm, the coordinate vector and error correlation matrix can be obtained in the global Cartesian coordinate system in the presence of range measurements and angular positions in the local spherical coordinate system associated with the radar position. The proposed algorithm is discussed with respect to trajectory filtering. As a result of the compensation of systematic errors and the calculation of the correlation matrix of the coordinate vector, the accuracy of trajectory tracking is enhanced. Aim. To improve the accuracy of trajectory tracking when using the Kalman filter with converted measurements by means of the mathematical expressions obtained to estimate the coordinates of a target and the error correlation matrix in the global Cartesian coordinate system. Materials and methods. The problem was solved using the methods of mathematical statistics, statistical estimation theory, and computer simulation. Results. Mathematical expressions for calculating coordinates and the corresponding correlation matrix within the global Cartesian coordinate system were derived. Furthermore, comparative graphs illustrating trajectory tracking errors, associated with the use of various methodologies for constructing a Kalman filter based on transformed measurements, were created. Conclusion. The use of explicit expressions for coordinate transformation, accompanied by compensation for systematic errors, illustrates the potential for a substantial enhancement in accuracy when the errors of primary measurements increase. This improvement can be achieved when applying both direct and straightforward coordinate recalculation methods and a Kalman filter for transformed measurements within the global Cartesian coordinate system.
Introduction. Improving the accuracy of estimating the location of a radio source directly depends on the accuracy of its angular coordinates. Therefore, the task of improving the operational accuracy of direction finding, taking into account the complexity of the signal and noise environment and the characteristics of wave propagation in the HF band, remains relevant. Modern radio direction finding systems typically use antennas sensitive to only one component of the electric field and do not account for changes in signal polarization when reflected in the ionosphere. This leads to direction finding errors of approximately 1°, which is insufficient for precise localization of the radio source.Aim. Modeling of the correlation interferometer and MUSIC methods taking into account the polarization structure of the received wave based on an antenna system consisting of triorthogonal antennas, and comparison of their accuracy characteristics with conventional direction-finding methods.Materials and methods. Mathematical modeling of polarization correlation interferometer and polarization MUSIC methods in the MATLAB software environment.Results. The mathematical model of a radio direction finder, incorporating an antenna system consisting of triorthogonal antennas and the proposed signal processing methods, was developed. The accuracy of estimating the angular coordinates of a radio source was compared depending on the signal-to-noise ratio and the amplitude ratio of the horizontal and vertical components of the electric field. It is shown that the use of a triorthogonal antenna system in combination with the proposed methods yields a several-fold increase in direction finding accuracy compared to conventional approaches. Dependencies on the signal-to-noise ratio for estimating the accuracy of polarization parameters (tilt angle and ellipticity of the polarization ellipse) were also obtained.Conclusion. Incorporating additional scanning of the polarization ellipse's tilt angle and ellipticity into the correlation interferometer and MUSIC methods provides a more accurate estimate of the angular coordinates of the radio source, taking into account the elliptical polarization of waves in the HF band. The proposed approach not only improves spatial resolution but also enables estimation of signal polarization parameters, which can be used to reconstruct the propagation trajectory of radio waves.
Introduction. Due to their high sensitivity to external influences, liquid crystal (LC) cells based on nematic materials, such as 5CB, are widely used in optoelectronic devices. However, the performance characteristics of such cells are significantly affected by operating conditions, including the presence of nanoparticles in their composition. Despite extensive research into the influence of electric fields on LC structures, a comprehensive analysis of switching dynamics under different driving signal shapes in the presence of magnetic nanoparticles such as CoFe2O4 remains limited. This study set out to investigate the effect of driving voltage waveform on the dynamic response of an LC composite with magnetic nanoparticles. Aim. To determine an optimal shape of the driving signal that minimizes switching time and ensures stable electro-optical properties of a LC cell with CoFe2O4. Materials and methods. The study was carried out on an LC cell containing nematic 5CB with uniformly distributed magnetic CoFe2O4 nanoparticles. The cell was driven by sinusoidal, rectangular, and triangular voltage signals generated by a function generator. Measurements were performed using an optical setup including a laser source, crossed polarizers, and a photodiode connected to an oscilloscope. Results. The shortest switching time (4 ms) was achieved with a sinusoidal signal. Rectangular signals produced a 6 ms response, while triangular signals resulted in 5 ms. An increase in the pulse duration led to a greater signal amplitude, having no effect on the switching speed. Conclusion. The study confirmed that the shape of the driving signal significantly affects the behavior of LC cells with CoFe2O4. The sinusoidal signal was found to be the most effective in terms of response time, which is important for the development of next-generation high-speed optical devices.
Introduction. Quantum well infrared photodetectors (QWIPs) are among the key components of modern infrared imaging systems and are widely used for various applications, including space research, medical diagnostics, etc. One of the most important characteristics of a QWIP is the background-limited performance (BLIP) temperature, which is determined based on the equality condition between the background current and the dark current flowing through the photodetector. This parameter represents the operating temperature of the photodetector. Increasing the operating temperature can significantly reduce the requirements imposed on the cooling system. Since the background current depends on environmental conditions and the cryostat aperture, it is primarily requir ed to reduce the dark current values. The dark current is strongly dependent on the doping level of the quantum wells. However, the doping concentration also affects the photodetector sensitivity, creating a trade-off between sensitivity and dark current level.Aim. To investigate the effect of the doping level of quantum wells based on the GaAs/AlGaAs material system on the BLIP temperature.Materials and methods. Experimental photodetectors were fabricated by molecular beam epitaxy. The parameters of the samples were selected to ensure a peak spectral response wavelength in the range of 8…9 μm. The variable parameter was the doping level of the quantum wells with silicon. After completing the planar processing technological route, the current–voltage characteristics of all test photodetectors were measured in the temperature range of 65…77 K, and the corresponding curves of static current sensitivity were plotted.Results. A reduction in the doping level from 9.0·1017 to 4.5·1017 cm–3 was found to lead to a significant decrease in the dark current within the operating voltage range. This made it possible to increase the BLIP temperature from 69 to 71 K. This was associated with the expected decrease in photosensitivity; however, its value remained above the threshold level of 0.15 A/W.Conclusion. The obtained data demonstrate that optimization of the quantum well doping level in QWIPs provides for a reduction in the photodetector dark current. As a result, the device can be operated at higher temperatures.
Introduction. For transportation systems and, in particular, autonomous devices, accurate position determination is an essential requirement. In outdoor environments, the Global Positioning System (GPS) remains the optimal solution due to its broad coverage, high level of automation, and ease of use. However, in indoor environments, the significantly weakened GPS signal creates serious difficulties for accurate localization. For navigation of transportation devices in confined spaces, the Valve Lighthouse system has been proposed. Although this system exhibits rather low random noise, capable of achieving millimeter-level precision, its accuracy is sensitive to installation-related distortions in the received signal. This leads to errors in position estimation. The current literature lacks methods for identifying these distortions and performing system calibration. To address this gap, this paper proposes an algorithm for estimating the coefficients of a signal error model based exclusively on the coordinates of the transportation device. Aim. Calibration of the signal of an infrared system using exclusively the coordinates of the transportation device in the coordinate system associated with the base station. Materials and methods. An HTC Vive error model of an infrared system was used. The proposed approach is based on Newton’s method and uses a dataset of the true coordinates of the transportation device in the coordinate system associated with the base station, as well as the coordinates determined by the system. Results. The proposed method makes it possible to determine the coefficients of the signal error model of an infrared system using a single base station. Conclusion. A method for calibrating the signal of an infrared system using a single base station is presented. This method is based on Newton’s method and a dataset of transportation device coordinates in the system coordinate frame.
Introduction. In the field of radar monitoring of airspace, multicopter discrimination is a highly relevant task, which includes determination of their class, i.e., small-, medium, or heavy multicopters. The discrimination task is directly related to the analysis of radar signatures and determining the rotor number in a multicopter. Regarding the construction of radar rotors for aircrafts, radar systems obtained using the method of inverse synthetic aperture radar (ISAR) are particularly interesting. In order to create such signatures, information on the rotational frequency of the rotors is required, which can be determined using the method proposed in this paper. Aim. Development of a methodology for estimating the number of rotors in a multicopter based on the analysis of the radar signal of secondary modulation caused by blade rotation. Materials and methods. The task of estimating the number of rotors is related to the task of estimating the frequency of their rotation, which, in turn, is considered as the task of accumulating secondary modulation responses created by rotation in the signal structure with simultaneous compensation of phase incursions. For simulation purposes, a monochromatic signal with a frequency of 10 GHz was considered. Correlation processing and statistical analysis were used to implement and evaluate the algorithms used in the methodology. Results. A methodology for estimating the number of rotors in a multicopter based on the analysis of secondary modulation signals was developed. Its operability was tested by simulating different scenarios of target movement. Conclusion. The developed methodology for estimating the number of rotors in a multicopter based on the analysis of secondary modulation signals forms a basis for developing an algorithm for imaging quadcopter rotors using the ISAR method. Information on the number and rotation frequencies of rotors can be used to construct radar signatures of multicopter rotors based on the ISAR method followed by subsequent evaluation of design features and distinction between single and integrated targets.
