Search for defects and assessment of the current condition of engineering structures with the help of georadars (review. Part II)

The relevance. The development of technical means for non-destructive testing and remote sensing is an important practical task. This is primarily due to the fact that modern means of non-destructive testing open up ample opportunities for the introduction of new technologies and increase the economic efficiency of measures for the maintenance of various technical and construction objects at a relatively low cost of such work. In this regard, the development of computational algorithms for processing primary data and software products for the subsequent interpretation of the results obtained using computer engineering systems is of great importance. The purpose of the work is to review technical means, signal processing methods and some computer-oriented engineering systems for solving problems of detecting various defects in engineering structures and building structures. Materials and methods. The paper provides a brief overview of methods for processing primary data sets obtained using pulsed GPR. At the next stage, processing is carried out using the GeoVizy program. Finally, the main focus of the work is on the analysis of the capabilities of modern computer engineering tools. Also used the numerical - analytical methods of the modern theory of diffraction and methods of signal analysis in the space-time domain. Results. The results are based not only on scientific articles, but also on the analysis of the capabilities of modern computer modeling systems, as well as some mathematical models obtained by the author. Conclusions. The results presented in the article allow one to talk about a new direction in scientific research. This direction can be defined as combined multi-parametric analysis - CoMPA. The purpose of this direction is to conduct research of various interrelated processes in technical structures by using the methods of mathematical physics, combining not only the analysis of their interaction with fields of different physical nature, but also involving the appropriate models from various areas of mathematical physics. The significance of the results obtained consists not only of new models of data processing and interpretation, but also of the prospects for further progress in the field of technical means of control and diagnostics.

Comparison of subsurface object recognition by artificial neural networks and correlation method

Background: The problem of searching for subsurface objects has a particular interest for construction, archeology and humanitarian demining. Detection of underground mines with the help of remote sensing devices replaces the traditional procedure of finding explosive objects, as it excludes the presence of a human in the area of possible damage during a charge explosion. Objectives: The aim of the work is to improve the recognition of three-dimensional objects and demonstrate the benefits of using a more informative data set obtained by a special antenna system with four receiving antennas. In addition, it is necessary to compare the effectiveness of artificial intelligence and the method of cross-correlation for recognition by subsurface radar, taking into account the additive noise of different levels present in practice. Materials and methods: The electrodynamic problem was solved by the finite difference time domain (FDTD) method. An artificial neural network (ANN) is trained on ideal signals to detect the features of the field that will be found in noisy data to determine to the position of the object. Cross-correlation also involves the use of an array of ideal signals, which will be correlated with noisy real signals. Results: The optimal and effective ANN structure for work with the received signals is created. It was tested for noise immunity. The recognition problem was also solved by the classical method of cross-correlation, and the influence of noise of different levels on its responses was studied. In addition, a comparison of the efficiency of their recognition using 1 and 4 sensors was made. Conclusions: For subsurface survey problems, a deep neural networks with at least three hidden layers of neurons should be used. This is due to the complexity and multidimensionality of the processes taking place in the surveyed space. It has been shown that artificial intelligence and cross-correlation techniques perform the object recognition well, and it is difficult to identify the best among them. Both approaches showed good noise immunity. The use of a larger data set of four receivers has a positive effect on the recognition results.

Statistical characteristics of geomagnetic storm activity during solar cycle 24, 2009–2020

Urgency. The atmosphere and geospace are widely used as a radio channel in solving problems of radar, radio navigation, direction finding, radio communication, radio astronomy, and the remote sensing of the Earth from space or the near-earth environment from the surface of the planet. The parameters of the atmospheric-space radio channel are determined by the state of tropospheric and space weather, which is formed mainly by non-stationary processes on the Sun (solar storms) and partly by high-energy processes on the Earth and in the atmosphere. Geospace storms give rise to the strongest disturbances of the atmospheric-space radio channel, and it is important to note that these storms are diverse, so that no two storms are alike. At the same time, storms have both similar and individual features. Currently, there is insufficient knowledge about both of these features, and their study remains an urgent task of space geophysics and space radio physics. In particular, the identification of general patterns is advisable by performing a statistical analysis of a large number of storms. The aim of this work is to statistically analyze the parameters of the solar wind and geomagnetic field during the Solar Cycle 24 activity (2009–2020). Methods and Methodology. The parameters of the disturbed solar wind (number density nsw, velocity Vsw, and temperature Tsw), the disturbed values of the By- and Bz-components of the interplanetary magnetic field, which is the cause of magnetic storms on Earth, as well as the indices of geomagnetic activity (AE, Dst and Kp) are selected as source input to the study. In this paper, geomagnetic storms with Kр ≥ 5 or G1, G2, G3, and G4 geomagnetic storms are considered. In total, there were 153 storms with Kp ≥ 5. The time series of the nsw, Vsw, Tsw maximum values, of the By- and Bz-components, and of the AE, Dst and Kp indices, as well as of the Bz-component and the Dst index minimum values have been analyzed. Results. The main statistical characteristics of the parameters of the solar wind, interplanetary magnetic field, and of the geomagnetic field have been determined for 153 events that took place during Solar Cycle 24. Conclusions. The geomagnetic situation during Solar Cycle 24 was calmer than during Solar Cycle 23.

Combinational frequencies of HF doppler radar signals in the PC1 geomagnetic pulsation range

Urgency. The urgency of this work is determined by the necessity of studying MHD waves originating from various sources within the Earth–atmosphere–ionosphere– magnetosphere system and arriving at ionospheric heights. The object of research. A matter of this study is ionospheric disturbances that accompanied geomagnetic pulsations during the dawn terminator on 23–24 March 2010. Purpose of Work. The present work was aimed at revealing short-period ionospheric disturbances in the Pc1 micropulsation frequency range (1–5-Hz) and at investigating their spectral content. Techniques and Methotology. The dynamic spectra of the variations under study were obtained with the HF Doppler radar. Results. The ionospheric disturbances have been shown to arise mainly at combinational frequencies. The durations of such disturbances have been estimated to be of the order of one minute, and the disturbance frequencies 0.7 Hz, 1.5 Hz, and 2.5 Hz. The quasi-periodic interference in the 1–5-Hz frequency band has been detected to persist for over one-half hour to a few hours. Based on the model of the signal modulated by ULF waves in the ionosphere, the appearance of constructive interference at combinational frequencies has been validated. The intercomparisons of the variations obtained using the spectrograms and the known models for the phase-modulated signals have been made. A model for the amplitude- and phase-modulated signal reflected from the ionosphere has been developed, and the signal basic parameters have been determined. Conclusions. The HF Doppler sounding can be a means for studying ionospheric disturbances in the Pc1 geomagnetic pulsation range. During the study of time variations of the Doppler frequency shift during the spring equinox, the following results were found. The period of ionospheric perturbations reached 0.2–1 s, their duration varied from 1 min to more than 10 min. A noticeable increase in the amplitude of the beat is detected, which may be a sign of the appearance of lateral maxima in the Doppler spectra. The presence of oscillations in the frequency range of the first harmonic of the spectral resonance system of the ionospheric Alfvén resonator is established. Long-term ionospheric perturbations have a linearly increasing frequency of filling the wave packet. The rate of frequency change is close to 10–3 Hz/s.

Geomagnetic effect of the Albanian earthquake on November 26, 2019

Background. The main cause of geomagnetic disturbances is known to be space sources, processes acting in the solar wind and in the interplanetary medium, as well as falling large celestial bodies. Earthquakes also give rise to geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system comprises the single system where direct and reverse, positive and negative coupling take place. The mechanism of the earthquake effect on the magnetic field is poorly understood. A rock cracking, a fluctuating movement of fluids in pores, a corona discharge of the high-voltage static charge, etc., are thought to be the processes that give rise to the geomagnetic effect. In the course of earthquakes, seismic, acoustic, atmospheric gravity, and magnetohydrodynamic waves are generated, which provide for coupling between the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Purpose of Work. The paper describes the possible response in the level of the geomagnetic field to the earthquake of 26 November 2019 that took place in Albania. Techniques and Methodology. The measurements were taken with the fluxmeter magnetometer at the V. N. Karazin Kharkiv National University Magnetometer Observatory. It delivers 0.5 – 500 pT sensistivity in the 1–1000 s period range over a quite large frequency band of 0.001 to 1 Hz. To study the quasi-periodic processes in detail, the systems spectral analysis of the temporal dependences of the horizontal (H, D) geomagnetic field components has been employed. It includes the short-time Fourier transform, the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods, and wavelet transform, simultaneously. The wavelet transform employs the Morlet wavelet as a basis function. Results. The quasi-periodic variations in the level of the geomagnetic field observed to appear with a 6 min lag and to last for 70–80 min could be due to the earthquake. These disturbances could be transferred by the magnetohydrodynamic waves. The quasi-periodic variations that were observed to appear with a 97–106 min lag and to last for about 130–140 min were most likely due to the earthquake. They were transferred by the atmospheric gravity waves with a period of 7–14 min. A relative disturbance in the electron density in the atmospheric gravity wave field was observed to be approximately 5.3%. The results obtained from observations of Albanian and Turkish earthquakes show agreement. Conclusions: The magnetic variations in the 1–1000 s period range that were observed to occur before and during the earthquake have been studied.

Manifestation of global seismic activity in the atmosphere and ionosphere

Background. In recent decades, the concept of earthquakes (EQ) has been formed as the final stage of a planetary continuous self-organizing process with periods of accumulation and relaxation of tectonic stresses. However, in the scientific literature, as before, studies of the response of atmospheric and ionospheric processes to individual strong EQs are presented. In this work, the coupling of processes in the lithosphere, troposphere and ionosphere is considered for the first time, taking into account new ideas about the seismic process against the background of processes caused by space weather, which is a new step in the study of the human environment. Objectives of the work is to find relationships in the Earth – atmosphere – ionosphere – magnetosphere system on a planetary scale with a change in global seismic activity (GSA). Materials and methods. The studies were carried out using four daily databases for 2007–2015 on space weather and the magnetosphere (solar and geomagnetic activity indices), the ionosphere (f0F2 is the critical frequency of the F2 region in the western and eastern hemispheres; TEC is the global ionospheric total electron content), the surface atmosphere (atmospheric pressure) and the lithosphere (maximum EQ amplitude per day). The method of superimposed epochs and other statistical methods of analysis were used. Results. Quasi-synchronous changes in magnetospheric, ionospheric, and tropospheric characteristics have been established during periods of a sharp increase in GSA. They often have a cyclical sawtooth character from one seismically active period to another, which indicates the possibility of continuous interaction of geospheres, and not only during periods of disturbances. In particular, an increase in f0F2 with a sharp increase in GSA by up to 0.5 MHz was found almost simultaneously in the eastern and western hemispheres. Conclusions. The results obtained indicate the possibility of long-term or continuous interaction of the lithosphere with the geospheres located above. Space weather changes can be one of the sources of synchronization. As a possible mechanism for the appearance of global effects in the atmosphere and ionosphere when the GSA changes, it is proposed to consider the role of the release of deep gases to the surface. This process is global and is associated simultaneously with both seismicity and the parameters of the Earth's rotation.

Quality control of substances by electromagnetic sensing in a waveguide

Relevance. The problems of remote non-destructive determination and control of quality indicators of a wide variety of material environments, in particular, household and food products, are relevant practically for all areas of the national economy, science and technology. The relevance of scientific research in the field of dielectrometry in the microwave range is also due to the needs for the development of high technologies in medicine and health care, the national economy in real time. The aim of this work is to develop the method of microwave waveguide dielectrometry based on the application of the theory of multilayer plane-layered dielectric structures to the determination of the complex dielectric constant of a substance from the values ​​of the standing wave ratio of the samples under study in a waveguide at two close frequencies. Materials and methods. The research is based on well-studied phenomena of interference of electromagnetic waves on multilayer plane-layered dielectric structures. By using a mathematical model of the phenomenon of interference of a plane electromagnetic wave on a three-layer dielectric structure, the ambiguity of determining the complex dielectric constant of a substance by the classical method of waveguide dielectrometry in the microwave range by measuring the standing wave ratio of a dielectric sample placed in the waveguide and the phase angle of the reflection coefficient is overcome. Results. A method is proposed for ensuring the unambiguity of determining the complex dielectric constant of a substance in waveguide dielectrometry on the basis of the theory of multilayer plane-layered dielectric structures. The method leads to an explicit expression for the complex reflection coefficient of an electromagnetic wave from the investigated dielectric sample placed in a rectangular waveguide. The complex dielectric constant of a substance is determined from the values ​​of the standing wave ratio at two close frequencies in the microwave range. By the found value of the dielectric constant and the tangent of the dielectric loss angle, the quality parameter of the substance is determined by comparing and optimizing two objective functions, including the arrays of reference values ​​of the complex dielectric constant obtained in the course of measurements and compiled in advance, and by comparing and optimizing the third objective function, previous functions. As an example of an indicator of the quality of a substance, the specific heat of combustion of coal was determined. Conclusions. The proposed method for determining the complex dielectric constant and quality indicators of dielectric materials in the microwave frequency range has been tested in the case of various types of coals, its efficiency has been proven and the reliability of the results has been proven. The method and the devices and software implemented on its basis are promising for non-destructive express control of dielectric materials and media.

Radiophysical methods in the study of physicochemical properties of liquids

Relevance: The creation of new express methods for the qualitative and quantitative analysis of solutions and suspensions and biological liquids, as well as the development of technical means for their implementation, are urgent tasks in various fields of science and technology, in particular, in biotechnology and biomedicine. Also, the relevance of the work is due to the need to optimize technological processes for the production and synthesis of nanomaterials. The purpose of the work is to verify theoretically and experimentally the possibility of using radiophysical methods to assess the physicochemical parameters of solutions and suspensions. Another purposes are optimization of the technological process of laser ablation and solution of the physicochemical problem of the synthesis of iron nanoparticles in magnetite shells. Materials and methods: The paper presents a comparative analysis of methods for calculating the effective parameters of the system dielectric – metal inclusions using the mixing formulas of Maxwell–Garnett, Bruggeman and the finite element method. It is shown that in the case of metallic inclusions, the Bruggeman formula gives a more adequate result, which is consistent with the experimental results. The analysis of aqueous suspensions of metal nanoparticles was carried out by the method of impedance spectroscopy. Results: A simple method has been developed for the synthesis of iron nanoparticles with a magnetite shell based on the reaction of controlled oxidation of iron nanoparticles by ozone. A microscopic analysis of the obtained particles was carried out and the rate of formation of the magnetic shell was determined. The method of impedance spectroscopy for measuring the concentration of metal nanoparticles in the process of laser ablation has been tested. It is shown that the state of sedimentation equilibrium of the suspension corresponds to a specific value of electrical conductivity. Conclusion: It is shown that the method of impedance spectroscopy can be used as an indirect method for assessing the qualitative and quantitative physicochemical parameters of solutions and suspensions. The simulation of the influence of the distribution of metal particles in a dielectric matrix on the electrophysical parameters of the suspension is carried out.

On anomalous absorption of electromagnetic radiationby a subwave metal wire

Background: The effect of anomalously strong absorption, scattering and attenuation of microwave electromagnetic radiation by thin conductive wires is considered. The investigated effect can be used in the development of radio-absorbing and radio-masking materials for various purposes. The aim of the work is to clarify the physical nature of the effect. Materials and methods:. On the basis of the generalized Lorentz-Mi theory the mathematical model of diffraction interaction of microwave radiation with a cylindrical object which material is characterized by a complex refractive index is constructed. The case of normal incidence of a plane electromagnetic wave of E- and H-polarizations on a cylinder is considered. Numerical calculations of the field distribution were performed in the MathCard environment. Results: It is shown that for thick cylinders with a diameter greater than the wavelength, characteristic resonant peaks of absorption and scattering of wave energy are observed. For very thin cylinders, the diameter of which is much smaller than the wavelength, there are maxima of absorption and scattering of energy of incident radiation, which cannot be explained by resonant phenomena. Simplified analytical expressions for the efficiency coefficients of attenuation, absorption and scattering of electromagnetic radiation by thin cylinders are obtained. The field distributions inside and outside the dielectric and metal cylinders at different ratios of their diameter and wavelength of incident radiation are calculated. The efficiency of radiation absorption by a thin wire at different ratios of its diameter and skin-layer thickness for wire material has been studied. Conclusion: It was found that the effect of abnormally strong absorption of microwave radiation by very thin metal wires is due to the existence of a skin effect for conductive materials that interact with microwave radiation. It is obtained that the maximum efficiency of radiation absorption is achieved when the diameter of the wire is twice less than the thickness of the skin layer. The observed effect of anomalous absorption is nonresonant.

Electromagnetic sensor for measuring the dielectric permeability of materials

Relevance: Problems of control and determination of electrophysical parameters of materials of different physical nature are relevant in terms of the development of express methods of analysis of substances in various fields of science and technology, in particular, in biotechnology and biomedicine. Also, the relevance of the work is grounded by the search and implementation of new non-invasive medical diagnostic methods. The purpose of the work is to experimentally test the method of calculating the dielectric constant of multilayer structures based on conformal transformation, to test the method of electromagnetic probing of objects with one-side access using a microstrip resonator. Materials and methods: The paper presents a method for calculating the effective dielectric constant of a three-layer structure using a microstrip resonator of a new shape. A number of solid and liquid materials were investigated experimentally. It is shown that the resonant frequency and quality factor of the resonator loaded with the investigated material allow to estimate the concentration of the components of binary solutions. The possibility of using a microstrip resonator as a plethysmographic sensor has been investigated. Results: An electromagnetic sensor for measuring the dielectric constant of objects with one-side access was developed. The description of the original design of the microstrip resonator is presented and its modeling and experimental research are carried out. The results of measurements of the dielectric constant of objects of different physical nature are obtained: solid dielectrics and biological liquids. The influence of relative glucose concentration on the resonant properties of the sensor was studied. The possibility of using the sensor as a plethysmographic sensor in biomedical systems is shown. Conclusion: Theoretical and experimental studies of a microstrip resonator of complex geometric shape, which are presented in the paper, confirmed the possibility of its use as a sensor of electrophysical parameters of materials with different dielectric constant and conductivity. A new method of blood flow registration is proposed, based on the fixation of changes in the effective dielectric constant of tissues containing blood vessels.