This work is devoted to a comprehensive study of the structural and electrophysical properties of citrogypsum, a high-tonnage byproduct of biochemical citric acid production. Compacted test samples were fabricated via cold isostatic pressing. The chemical and phase compositions of the investigated anthropogenic raw material were determined using X-ray fluorescence and X-ray powder diffraction analyses. The surface morphology and textural characteristics were investigated by scanning electron microscopy and gas adsorption methods. The temperature dependence of the electrical conductivity of the samples was studied by broadband impedance spectroscopy in the frequency range of 200 Hz to 5 MHz under high vacuum conditions (10-3 mmHg) at temperatures of 250 K and 300 K using a Janis vacuum cryostat. It was established that at 300 K in the high-frequency region (330 kHz – 5 MHz), the complex impedance plot (Nyquist plot) is completely governed by the contribution of grain boundaries. The presence of two relaxation regions on the plot is attributed to the bimodal nature of the differential particle size distribution (~80 and ~500 μm), which is strictly confirmed by laser diffractometry data. Decreasing the temperature to 250 K leads to a transformation of the impedance profile in the low-frequency region (600 Hz – 1.1 kHz), manifested by the appearance of a linear diffusion contribution transitioning into a bulk transport arc; this behavior is successfully described by an equivalent circuit with a parallel combination of the grain bulk resistance (Rg) and capacitance parameter (Cg). The revealed features of electrical transport substantiate the potential of using modified citrogypsum matrices as functional dielectric media for the components of solid-state electronics.
Quasi-optical system design of a space-based cryogenic multiband receiver for the ground-to-space very-long-baseline radio interferometer of the Millimetron space observatory operating in the 7 mm, 3 mm, 1,3 mm and 0.8 mm bands is presented in the paper. Quasi-optical system of the instrument includes a number of reflecting mirrors, frequency-selective mirrors and receiving horns. The synthesis of the mirrors was carried out using the Dragone criterion for compensating distortions on asymmetric mirrors. In addition to the classical quasi-optical approach, numerical electromagnetic simulation with the methods of integral equations and physical optics is used for analysis. The mode matching method is used to synthesize horn feeds. The final calculation of the quasi-optics with the telescope, including an estimation of the aperture efficiency, was performed using the physical optics.
The paper addresses the urgent task of improving the accuracy and safety of marine navigation by enhancing methods for monitoring local medium-wave (MF) radio navigation systems. A comparative analysis of the efficiency of electrically small antennas of electric and magnetic types under near-field radiation conditions is carried out. The antennas are intended for operation as part of a mobile autonomous measuring module mounted on an unmanned aerial vehicle. The study was performed at a frequency of two megahertz, corresponding to a wavelength of one hundred and fifty meters, with a receiving antenna height of one meter. The main parameters considered were radiation resistance, efficiency, effective length, and power delivered to the load under given signal propagation conditions. Efficiency in free space does not reflect the actual effectiveness of antennas in receiving mode near a transmitter. It is established that for electric antennas (dipole, loaded dipole, biconical), the radiation resistance is on the order of thousandths of an ohm, which, with comparable ohmic losses, provides an efficiency of tens of percent. For magnetic antennas (loop, spiral), the radiation resistance is several orders of magnitude smaller, as a result of which their efficiency approaches zero. However, when a purely active load is chosen, equal in magnitude to the total input impedance, magnetic antennas can provide load power comparable to that of electric antennas. The highest load power values with minimal size and weight are demonstrated by the loaded dipole, with an effective length of about one meter and an efficiency of about thirty-seven percent.
Currently, there is a wide variety of radar devices used both for free-space radar and for subsurface radar. The purpose of this work is to theoretically and experimentally substantiate the possibility of increasing the range of subsurface radar by increasing the power of the radiated ultrawideband signal and optimizing the characteristics of the antenna-feeder devices. The main research methods included calculations according to the recommendations of the International Telecommunication Union (ITU) for free space, as well as field measurements of the parameters of dipole and resistively loaded dipole antennas on a semi-cylindrical measuring stand. It is shown that shallow ground-penetrating radars with a dynamic range of 135 dB can provide radar at a distance of up to 1 km at frequencies below 40 MHz, and deep ground-penetrating radars with a dynamic range of 154 dB – up to 1 km at frequencies up to 420 MHz. It has been experimentally established that the efficiency of resistively loaded dipole antennas for the first pulses is 43-45 %, and the overall efficiency of the system using two antennas is about 22 %. It was found that reducing the vibrator resistance below 250 Ohms can lead to parasitic self-oscillations. The obtained results are confirmed by practical sounding data to depths of 150-200 m and more in permafrost regions. Thus, increasing the amplitude of the radiated signal by a factor of n increases the radar range proportionally to √n, which opens up prospects for creating ground-penetrating radars with a range of up to several hundred meters or more.
The paper proposes an approach to reconstructing the characteristics of commercially available sub-GHz and GHz frequency band antennas based on reverse engineering using electromagnetic modeling packages. The implemented process includes analyzing the manufacturer's source data, constructing and tuning an electromagnetic model, verifying it using available experimental data, and then performing a full simulation. The approach is demonstrated using a planar antenna with a declared operating range of 0.6–6.0 GHz. It is shown that the resulting frequency dependences of VSWR < 2.5–3.0 are in good agreement with experimental measurements, confirming the validity of the constructed model. Using reverse engineering, we obtained radiation patterns and their frequency evolution, which are not available in the manufacturer's documentation. It is established that in this case, there is a significant discrepancy between the calculated directivity characteristics and the manufacturer's data, indicating a difference in the manufacturer's interpretation of the directivity coefficient relative to the standard definition. A conclusion is made about the high efficiency of using reverse engineering in the selection and development of printed antennas with given electrodynamic parameters.
The paper presents the results of equipment development and experimental technique for improving the synchronization of the CCD spectrograph. The registration cycle of a spectrograph linear CCD matrix, with synchronization jitter in the microsecond range, is reported. The possibility of obtaining spectral data with time resolution using the developed measuring complex is shown.
This paper examines a method for calculating a two-dimensional spatial spectrum as a combination of two one-dimensional ones. Expressions are derived that allow us to estimate the reduction in the number of addition and multiplication operations required to calculate the two-dimensional spatial spectrum depending on the number of antenna array elements. The reduction in the number of mathematical operations required to calculate the two-dimensional spatial spectrum when it is calculated as a combination of two one-dimensional ones is estimated. It is shown that, with a single target in the resolution element, the two-dimensional spatial spectrum calculated as a combination of two one-dimensional ones is identically equal to the two-dimensional spatial spectrum estimated using the classical method. It is established that, with multiple objects in the resolution element, the shape of the two-dimensional spatial spectrum estimated as a combination of two one-dimensional ones is distorted–it differs from the spectrum estimated using the classical method. Distortions in the shape of the two-dimensional spatial spectrum calculated as a combination of two one-dimensional ones lead to the appearance of false targets and masking of the true ones.
Using physical optics approximation, the analytical expression of the nonstationary field, bistatically scattered from the triangle on the surface of a metallic object, was obtained for an arbitrary time dependence of the incident wave field. The solution is a set of the scattered field expressions in the far zone 1) in direction of the beam specular reflection, in the shadow direction and in small angular neighborhoods of these directions (first-order maxima of scattering intensity), 2) in direction belonging to the cone of diffracted rays around one of the sides of the triangle, and in the small angular neighborhood of this direction (second-order maximum of scattering intensity), 3) in general case of scattering outside the above-mentioned directions of maxima of scattering intensity. On this basis the procedure of calculating the nonstationary scattered field, produced in the far zone by a metallic triangle, has been developed. Optimal condition of transition between calculations based on general and particular formulas has been determined and tested. Accuracy of calculations in time domain using the developed numerical procedure was demonstrated by comparing the scattered field for a monochromatic problem with the steady-state amplitude of scattered field oscillations under excitation by a radio impulse with rectangular envelope and high-frequency filling. In contrast to the monochromatic problem, for which the amplitude of the scattered field is characterized by a single complex number, in time domain the signal, scattered from the triangle, consists of five intervals of oscillations. The intervals correspond to the initial, intermediate and final parts of time dependence of the field at the observation point. They are related to expansion of the triangle’s part, which forms the scattered field, starting from infinitely small neighborhood of a vertex to the full coverage of the triangle’s surface, then to steady-state scattering, and finally to reduction of the triangle’s part, which contributes to the scattered field, to zero starting from deceasing by infinitely small neighborhood of the same vertex. Scattered field changes continuously in transitions between intervals, but the amplitude, phase, and constant components of oscillations undergo abrupt changes on transitions between intervals. The character of the time evolution of the field, scattered by a triangle, indicates the dominant role of the neighborhoods of its vertices in the formation of time response. The developed computer program can be considered as the basic component of combined numerical procedure to calculate scattering from a complex object in time domain, when scattering from one part of the object is determined in physical optics approximation, while scattering from the remaining part is calculated within a rigorous approach.
This paper presents a comparative analysis of terrain-referenced navigation of an aircraft using classical correlation-extremal algorithms and artificial intelligence methods under conditions of unpredictable terrain distortions. The terrain is modeled as a stationary random field with local nonstationary perturbations absent from the reference map. It is shown that such distortions violate the statistical assumptions underlying classical navigation algorithms and lead to rare but critical navigation failures. To provide an adequate assessment of navigation performance, an integral navigation reliability metric is introduced, defined as the probability that the positioning error remains below a specified threshold. Based on numerical simulations, the methods are compared in terms of root mean square error, probability of catastrophic failures, and computational complexity. The results demonstrate that artificial intelligence methods exhibit significantly higher navigation reliability under unpredictable terrain distortions, while classical algorithms retain advantages in accuracy and computational efficiency under idealized conditions. The potential of hybrid navigation algorithms combining analytical and learning-based approaches is substantiated.
The thermal characteristics of a commercially available high-temperature AD8229HDZ microcircuit, which is a high-precision instrument amplifier operating in the temperature range from −40°C to +210 °C. To measure the thermal characteristics, built-in protective diodes were used as heat source elements, connected in parallel to each pin of the microcircuit relative to the power supply pins of positive and negative polarity. Based on the results of measurements of the thermal impedance module, the values of four components of thermal resistance corresponding to the individual layers of the microcircuit design were identified and determined: the crystal, the solder layer, the ceramic landing pad and the housing. It is determined that the values of the thermal resistance of the crystal-solder layer, measured by symmetrically arranged protective diodes, vary within 3-4 %. Based on the results of measuring the temperature dependences of the thermal resistance of the crystal-solder layer junction in the temperature range from 25 °C to 150 °C, a difference in the steepness of the increase in thermal resistance with increasing temperature was revealed for symmetrically arranged protective diodes at the inverting and non-inverting inputs of the amplifier. It is shown that at a microcircuit body temperature of 200 °C, the difference in thermal resistances reaches 2 K/W, which may cause an imbalance of currents in the differential cascade and the appearance of additional signal distortions.
The relevance of research electromagnetic radiation from electronic computing devices is dictated by aspects of biological safety, information security, and electromagnetic compatibility. The use of artificial neural networks to study electromagnetic radiation represents a transition from classical deterministic models to data mining, which has certain advantages over analytical approaches and physical measurements. The practical technique for constructing a nonlinear approximating function of electromagnetic radiation from electronic computing devices using neural network simulation based on physical measurement data at discrete frequencies this article proposes. Personal computers are considered as electronic computing devices. To demonstrate the feasibility of using this tool, a test experimental setup for preparing training and test data was created. The mean absolute percentage error is used to evaluate the quality of the problem solution for the test set. Training was performed over 220 epochs, and the mean absolute percentage error for the test set was 22%. Examples of predicting electromagnetic radiation intensity using a trained neural network are provided. The obtained results demonstrate the capabilities of neural network simulation in solving electromagnetic compatibility problems.
The potential of the pharmaceutical composition “Fluroscan”, based on the dipotassium salt of the Yb complex of 2,4-di(α-methoxyethyl)deuteroporphyrin IX, for IR luminescence diagnostics and theranostics of skin toxicity in the form of rosacea-like dermatitis is demonstrated. The prototype of a fiber-optic laser fluorimeter (developed in the V.A. Kotelnikov Institute of Radioelectronics RAS) operating in the spectral range of 900-1100 nm at an optical power of up to 10 mW was used for IR luminescence diagnostics and treatment monitoring. Patients were treated using a SOR Internacional S.A. irradiation lamp in the red spectral range (620-640 nm). It was found that a decrease in luminescence intensity after a therapy course indicated a decrease in metabolic activity and confirmed the effectiveness of the treatment.
The paper discusses a new resonant method of frozen biological tissues dielectric properties determination at temperatures ranging from –20 to –1°C in the frequency band of 100–200 MHz under phase transition of the frozen water containing in tissue. For carrying out resonant measurements, a special measuring cavity cell has been developed. This method has been tested using water ice, which is prepared from distilled water and has a well-known dielectric constant. The dielectric parameters of the frozen sea trout back were also measured in the 100–200 MHz frequency band and compared with previously published data.
A low-frequency loop antenna located in the ionosphere can be used as an effective tool for plasma diagnostics and radio communications. The problem of finding the far field of an antenna in a magnetoplasma such as the ionosphere was solved by several workers earlier. It was shown that the results may be reformulated in a simpler manner to express them in terms of the normalized characteristic plane waves of the medium. This has the advantage of showing clearly how the far field depends on the free space pattern of the antenna, on the shape of the dispersion surface, namely, on the curvature characteristics of this surface. This paper presents a relatively simple and intuitive computational procedure for determining the far-field strength of any small-sized (compared to the wavelength) source located in a cold, homogeneous, multicomponent magnetoactive plasma (the ionosphere), provided that the source's radiated power and its power radiation pattern are known. As an illustration, the results of calculating the field strength in the far zone of an elementary loop antenna located in the ionosphere are given for frequencies of 1 and 100 kHz. A qualitative analysis of the angular and frequency distribution of the field strength is performed for parallel and perpendicular orientations of the loop antenna. It is shown that plasma resonance and multipath propagation, arising from plasma anisotropy, lead to a significant angular redistribution of the loop field strength compared to radiation in free space.
The issue of interoperability in relation to the «Digital Sky» is considered. It is noted that the modern concept of the Digital Sky arose as a result of the intensive development and use of unmanned aircraft. Based on a summary of available domestic and international materials, a definition of the Digital Sky is formulated, emphasizing the paramount importance of ensuring interoperability. It is also noted that, judging by the draft Concept of the Digital Sky of Russia, it essentially addresses the need to ensure interoperability, albeit implicitly. An attempt is made to apply the domestic approach to ensuring interoperability of a wide range of information systems to the Digital Sky of Russia, through the construction of a digital twin. It is proposed to include a requirement for ensuring interoperability in the Concept.
The article proposes and provides a detailed analysis of a self-consistent equations method designed for studying the diffraction of electromagnetic waves on photonic crystal structures, which are a periodic two-dimensional lattice of dielectric spheres. The modeling was performed within the scalar approximation, which significantly simplified the mathematical formalism for systems characterized by weak dielectric constant contrast and subwavelength sizes of scattering particles (sphere radius smaller than the incident radiation wavelength). A key advantage of the developed approach is the explicit accounting of multiple scattering effects between all lattice elements. This ensures efficient determination of scattered wave amplitudes in the far-field zone and allows for the analysis of conditions for the formation of photonic band gaps (stopbands and passbands). To validate the theoretical model, a detailed comparison of calculated spectral characteristics, particularly transmission coefficients, with the results of rigorous numerical modeling performed by the finite element method was conducted. It is shown that the self-consistent equations method provides high accuracy in the long-wavelength part of the spectrum, when the radiation wavelength exceeds the structure period, as well as in the case of small values of the dielectric constant of the sphere material. Furthermore, this method imposes no restrictions on the ratios between the period of element arrangement in the lattice and the sphere radius and remains functional even with very dense structure packing. The work defines the limits of the method's applicability, associated with an increase in refractive index contrast and a decrease in the wavelength-to-lattice-period ratio, providing clear criteria for its use. The developed approach can be successfully applied for rapid preliminary analysis, parameter optimization, and design of flat photonic crystal structures and metasurfaces based on dielectric spheres, especially under conditions of weak scattering and moderate contrast of optical properties, which are of practical interest for modern optical devices.
For the purpose of evaluation of the effectiveness of nanosecond electromagnetic pulses application for the treatment of malignant neoplasms, experimental studies are conducted on Lewis lung carcinoma (LLC) cells. An equivalent electrical circuit is compiled for the pulse exposure target, which is a microplate with biological material (tumor cells) located between the electrodes of the experimental setup. The pulse transformation on the load is analyzed and a numerical evaluation of the characteristic physical quantities is performed. The results of biological experiments in vitro on the effect of nanosecond pulses on LLC tumor cells are presented, where the significant inhibition of tumor cell proliferation and an increase of efficiency with combined use with the antitumor drug Cisplatin-Teva are observed. The dependence of the cytotoxic effect on the repetition rate of the applied electrical pulses is also studied.
The nonlinear response of a one-dimensional superconducting metamaterial based on 54 non-hysteretic radiofrequency superconducting quantum interference devices (RF-SQUIDs) was experimentally studied. The dependences of the system's resonant frequency on the pump tone power were measured in a two-tone excitation mode both in the absence and with the application of an external constant magnetic field. The metamaterial exhibits bistable behavior over a wide range of pump powers, indicating its potential for use in quantum electronic devices and superconducting parametric amplifiers.
Remarkable progress has been reached in the development of intense radiation sources and new optical elements for the vacuum ultraviolet spectrum. This progress has served as the basis for the development of many promising practical applications: X-ray lithography, X-ray holography, microscopy, and so on. For development of this trend, in particular, to optimize the parameters of sources and select optical elements, high-quality quantitative (absolute) measurements of radiation characteristics are necessary. However, conducting such measurements in the vacuum ultraviolet range of the spectrum is a rather complex task. This is because in this spectral range, all substances exhibit high absorption, which varies greatly depending on wavelength. That’s why all emission detectors needs independent calibration against a reference source over the entire wavelength range, since their sensitivity depends on the properties and purity of the absorbing surface. The presented work shows the method of photometry of monochromatic radiation in the ultraviolet spectrum, using two instruments: a calibrated thermal column and a photoelectric multiplier, the window of which is covered with a thin layer of salicylic acid sodium.
This study examines the auto emission properties of nanostructured cathodes based on carbon foils, including thermally expanded graphite, pyrolytic graphite, and graphene. Owing to their unique physical and chemical characteristics–high electrical conductivity, mechanical strength, thermal stability, and low work function–carbon nanostructures demonstrate significant potential as cold electron sources for modern vacuum electronic devices. The paper discusses the structural features of various carbon materials, emphasizing how nanoscale morphology, surface roughness, and the presence of sharp edges or layered microstructures influence field emission performance. Special attention is given to fabrication techniques, including CVD-grown carbon foils, laser-induced surface structuring, and methods for forming graphene and pyrolytic graphite films. Experimental results show that nanostructured carbon foils provide stable emission at relatively low electric fields, and modifications such as creating micro and nano protrusions can substantially enhance electron emission. Modeling of electron trajectories confirms the suitability of carbon-foil-based emitters for planar and lateral configurations used in display pixels and other compact electron sources. The study highlights key challenges related to stability, reproducibility, and long-term degradation, and outlines directions for future research aimed at scalable manufacturing and improved durability of carbon-based field emitters.
