Introduction. X-ray analysis has been applied for visualizing the internal structure of various objects for over 100 years. However, this method began to be used for assessing the quality of plant seeds only in the early 1980s. The main impediment was a lack of specialized instruments, particularly X-ray sources, that could provide informative images. Advancements in the field of microfocus radiography allowed significant results to be achieved, including the preparation of the National Standard GOST R 596032021 "Agricultural Seeds. Methods of digital radiography".

Aim. An analytical review of Russian research studies in the field of X-ray diffraction analysis of plant seeds.

Materials and methods. Key stages in the development of microfocus X-ray diffraction analysis of seeds and individual parts of plants for agricultural and other purposes are considered. The design of instruments, including digital ones, created for the implementation of the method are described.

Results. In order to obtain informative X-ray diffraction images of plant seeds, which objects are generally characterized by small sizes and small density, the focal spot of the X-ray tube should not exceed several tens of microns under the voltage of not higher than several tens of kilovolts. As a system for visualizing a latent X-ray image, it is preferable to use image receivers based on a screen with a photostimulated phosphor or flat-panel solid-state X-ray detectors. These instruments have been successfully used to identify and describe the radiographic signs of a normal seed and nine main types of defects for 600 plant species.

Conclusion. In comparison with the conventional contact radiography, microfocus radiography produces X-ray images of seeds with a projection magnification of the image up to several tens of times. Such images permit highly detailed visualization of the structure of seeds that differ slightly in density.

Introduction. This paper investigates a transmission system based on FBMC/OQAM multiplexing. This system is characterized by a high spectral efficiency, thereby attracting interest as an alternative transmission method in future wireless mobile communication standards. However, a disadvantage of the system is the high complexity of signal processing. There are numerous publications that study the FBMC/OQAM system from a theoretical perspective. This paper presents an experimental study of a transmission system based on FBMC/OQAM.

Aim. Verification of a transmission system based on FBMC/OQAM multiplexing in a wireless channel.

Materials and methods. Computer simulation modeling in Matlab and experimental research using Keysight and Rohde & Schwarz certified measuring instruments.

Results. A model of synthesis and signal processing was developed, and a frame structure was proposed. The processing included synchronization, since the study was carried out in a wireless double-dispersive channel. Time synchronization was provided by the method of time-domain correlation. A preamble consisting of two symbols was used for CFO compensation. Channel estimation in FBMC/OQAM was conducted by pilot symbols spread over the time-frequency domain, a method with an auxiliary pilot to compensate for intrinsic interference, as well as Zero Forcing and a linear interpolator. As a result, dependences of the bit error rate on the Eb/N0 in various channels were obtained. An error rate of 10−4 was achieved under the Eb/N0 equal to 13.4 dB, 15.3 dB and 20.9 dB in the first, second and third channel, respectively.

Conclusion. A FBMC/OQAM-based transmission system with a linear equalizer can operate without a cyclic prefix in a multipath wireless channel, providing comparable noise immunity to OFDM-CP. Long frames should be used to obtain greater spectral efficiency, due to the presence of a transition zone at the beginning and end of the FBMC/OQAM frame.

Introduction. The ability to analytically determine some parameters of various radio devices, which are optimal according to the criterion of providing the set values of the modules and phases of transfer functions at the required number of frequencies, significantly reduces the time for numerical optimization of the rest of the parameters according to the criterion of forming the required frequency response and frequency response in the frequency band. Until now, such problems with respect to radio devices have been solved only for one stage of the "nonlinear part – matching device" or "matching device – nonlinear part" type. As a matching device, reactive, resistive, complex, or mixed quad-poles were used.

Aim. Development of algorithms for parametric synthesis of radio devices with an arbitrary number of identical cascades of the "nonlinear part – matching reactive quadrupole" type according to the criterion of ensuring the specified frequency characteristics. Non-linear parts are represented as a non-linear element and parallel or serial current or voltage feedback.

Materials and methods. Four-pole theory, matrix algebra, decomposition method, method of synthesis of microwave control devices, numerical optimization methods.

Results. Systems of algebraic equations are formed and solved. Models of optimal quadrupole conductors are obtained in the form of mathematical expressions for determining the relationships between the elements of their classical transmission matrix and for finding the frequency dependences of the resistances of two-pole conductors.

Conclusion. It is shown that the frequency characteristics of the studied radio devices from the same stages are identical or similar to the frequency characteristics of radio devices from the same stage, but with the signal source and load resistances changed in a certain way. Such schemes are called equivalent. A comparative analysis of the theoretical results (frequency response and frequency response of radio devices) obtained by mathematical modeling in the "MathCad" system, and the experimental results obtained by circuit modeling in the "OrCAD" and "MicroCap" systems, shows their satisfactory agreement.

Introduction. The digital representation of received radar signals has provided a wide range of opportunities for their processing. However, the used hardware and software impose some limits on the number of bits and sampling rate of the signal at all conversion and processing stages. These limitations lead to a decrease in the signal-to-interference ratio due to quantization noise introduced by powerful components comprising the received signal (interfering reflections; active noise interference), as well as the attenuation of a low-power reflected signal represented by a limited number of bits. In practice, the amplitude of interfering reflections can exceed that of the signal reflected from the target by a factor of thousands.

Aim. In this connection, it is essential to take into account the effect of quantization noise on the signal-tointerference ratio.

Materials and methods. The article presents expressions for calculating the power and power spectral density (PSD) of quantization noise, which take into account the value of the least significant bit of an analog-to-digital converter (ADC) and the signal sampling rate. These expressions are verified by simulating 4-, 8- and 16-bit ADCs in the Mathcad environment.

Results. Expressions are derived for calculating the quantization noise PSD of interfering reflections, which allows the PSD to be taken into account in the signal-to-interference ratio at the output of the processing chain. In addition, a comparison of decimation options (by discarding and averaging samples) is performed drawing on the estimates of the noise PSD and the signal-to-noise ratio.

Conclusion. Recommendations regarding the ADC bit depth and sampling rate for the radar receiver are presented.

Introduction. Previous works considered the frequency characteristics and methods for fixing sensitive elements in the form of a wave ring resonator on surface acoustic waves in a housing made of various materials, as well as the influence of external factors on sensitive elements. It was found that the passband in such a case is sufficiently wide, which can affect adversely signal detection when measuring acceleration using the sensitive element under development. Therefore, it has become relevant to reduce the sensitive element’s bandwidth by changing the design of the interdigitated transducer (IDT).

Aim. To demonstrate an optimal topology for an IDT with a low bandwidth, leading to improved signal detection when acceleration affects the sensitive element.

Materials and methods. The finite element method and mathematical processing in AutoCAD and in COMSOL Multiphysics.

Results. Nine topologies of IDT are proposed. All these types were investigated using the COMSOL Multiphysics software on lithium niobate substrates, which material acts as a sensitive element. The frequency characteristics are presented. The data obtained allowed an optimal design of the ring resonator to be proposed: an IDT with rectangular pins without selective withdrawal.

Conclusion. Self-generation in a ring resonator can be performed by withdrawing no more than one pair of IDTs for 10 or more periods. In this case, the withdrawal of IDTs should be uniform. With an increase in the number of IDT withdrawals, the geometry of the ring resonator is violated, and the wave leaves the structure. The presence of a shared bus keeps the surface acoustic wave inside the IDT structure, and the narrowing of the periods towards the inner part of the structure makes it possible to improve the frequency characteristics of the ring resonator on surface acoustic waves.

Introduction. Technical diagnostics (TD) as a nascent discipline is rapidly developing in the field of both software and hardware. Modern TD methods, such as vibrometry, thermal control, JTAG testing and optical control, either exhibit high inertia, consume processor time, require suspension of the electronic device, or demand a galvanic contact with the study object, which is often unacceptable. These disadvantages can be eliminated by passive radio-sensor TD. To date, little information has been published on the parameters of electronic devices provided by this method.

Aim. Determination of the parameters of electronic devices, the assessment of which can be provided by passive radio-sensor TD.

Materials and methods. Signal radio profiles were obtained experimentally using metrological equipment and software-numerical methods for modeling radio wave processes. The parameters of the signal radio profile were calculated by a mathematical method for solving differential equations.

Results. The main principles and results of radio-sensor TD, as well as the simplest toolkit, are shown. An equation is obtained for the signal radio profile emitted by the electronic unit of the device, as well as an expression for its free components. An approach for assessing the TD correctness based on the number of free components of the received signal radio profile and the reference is described. The possibility of obtaining information about temperature, voltage drop, speed of emitting nodes, as well as the state of its components and modes of operation of p–njunctions is demonstrated. It is shown that this information is carried by the parameters of the basic equation for the signal radio profile.

Conclusion. The derived basic equation allows a non-contact, remote passive radio-sensor TD to be conducted by correlation analysis of the received signal, providing a detailed examination of malfunctions in each electronic unit. The described TD method based on the presented parameters is promising for assessing the technical state of electronic devices.

Introduction. The development of telemedicine systems intended to remotely monitor the health status of patients constitutes one of the most promising areas of contemporary science. Particularly relevant is the use of such systems to track the health of surgically treated patients. Since such patients are mobile, sensors measuring vital signs should not cause any discomfort in regular use. Thus, wearable smart trackers can be used for these purposes.

Aim. The paper aims to study the possibility of using smart trackers in a telemedicine system for monitoring patient health.

Materials and methods. In the study, a series of measurements was performed using GSMIN WR 41 smart bracelets in order to estimate their accuracy when measuring pulse, blood pressure, and oxygen saturation for different research subjects at rest and during intense physical exercises. In addition, the average measurement interval of the smart bracelet was determined; the operation of the smart bracelet in the telemedicine system for monitoring vital signs was considered.

Results. The studies show that an average error in the measurement of vital signs (except for systolic pressure) using the smart bracelet does not exceed 10 %. In order to avoid the high error in measuring systolic pressure, an algorithm for assessing the general health of patients was developed. In addition, it is shown that the smart bracelet can detect an abrupt change in the vital signs of patients, with the average time of their measurement and data transmission to the server of the telemedicine system coming to 45 seconds.

Conclusion. The study results indicate that smart bracelets can be used to remotely monitor the health of patients in real-time. These findings are confirmed by the telemedicine system designed on the basis of the smart bracelets considered in the paper.