Reflection Coefficients Of Electromagnetic Waves Research Articles

Application of Innovative Electromagnetic Screens for Reconstruction and Restoration of Buildings

Protective properties of composite electromagnetic screens on the base of conventional commercial paints were studied. The shielding fillers included metal-containing products from industrial wastewater treatment. Such compositions with a thickness of 100 to 150μm, were found to allow reaching high-frequency electromagnetic radiation shielding coefficients up to 3.0-3.5. Reflection coefficients of electromagnetic waves reach up to 0.3, which meets contemporary technical requirements.

Effect of Reduced Graphene Oxide on Microwave Absorbing Properties of Al1.5Co4Fe2Cr High-Entropy Alloys.

The microwave absorption performance of high-entropy alloys (HEAs) can be improved by reducing the reflection coefficient of electromagnetic waves and broadening the absorption frequency band. The present work prepared flaky irregular-shaped Al1.5Co4Fe2Cr and Al1.5Co4Fe2Cr@rGO alloy powders by mechanical alloying (MA) at different rotational speeds. It was found that the addition of trace amounts of reduced graphene oxide (rGO) had a favorable effect on the impedance matching, reflection loss (RL), and effective absorbing bandwidth (EAB) of the Al1.5Co4Fe2Cr@rGO HEA composite powders. The EAB of the alloy powders prepared at 300 rpm increased from 2.58 GHz to 4.62 GHz with the additive, and the RL increased by 2.56 dB. The results showed that the presence of rGO modified the complex dielectric constant of HEA powders, thereby enhancing their dielectric loss capability. Additionally, the presence of lamellar rGO intensified the interfacial reflections within the absorber, facilitating the dissipation of electromagnetic waves. The effect of the ball milling speed on the defect concentration of the alloy powders also affected its wave absorption performance. The samples prepared at 350 rpm had the best wave absorption performance, with an RL of -16.23 and -17.28 dB for a thickness of 1.6 mm and EAB of 5.77 GHz and 5.43 GHz, respectively.

Principles of designing electromagnetic screens of the resonant type based on liquid protective compositions

The work explores the possibilities of creating resonance-type electromagnetic shields to protect workers and the population from man-made electromagnetic fields. It is shown that traditional resonant screens are not technological enough to cover large surfaces and are tuned to monochrome or narrow-band electromagnetic fields. Based on the analysis of the experience of using liquid shielding mixtures, the possibility of creating a multilayer structure without fixed layer thicknesses, which will allow protection against the influence of the frequency band, has been proven. At the same time, the wave resistance of the outer layer allows you to minimize the reflection coefficients of electromagnetic waves, which makes the material practically absorbent. A calculator for the preliminary calculation of the electrophysical properties of each layer is presented, which allows rationalizing the required coefficients. For calculations, the formulas of Odelevsky and Debye for the dielectric constant of mixtures are adapted. Experimentally obtained empirical coefficients are presented, which are a component of the ratio for obtaining acceptable screen parameters. To determine the exact concentration of the shielding filler in the matrix, a correction factor is provided. This is associated with errors when determining the volume content of the filler of low dispersion and differences in the morphology of the filler particles, which does not allow for an accurate calculation of the depolarization coefficient of the filler particles. Given the lack of reference data on the electrophysical parameters of the compositions due to their diversity, it is advisable to conduct thorough laboratory studies with different compositions of the compositions. This will make it possible to form a reference database that will speed up the execution of electromagnetic safety work and reduce their cost.

Designing finishing materials with a gradient of electrophysical properties

Тhe article discusses the basics of development and production of materials for shielding electromagnetic fields in a wide range of frequencies. The purpose of these materials is to cover large surface areas. The basic requirements for these types of materials have been established. The main ones are: the front surface must have electrophysical properties (dielectric and magnetic permeability) to ensure the lowest possible reflection coefficient of electromagnetic waves. At the same time, it is mandatory to simultaneously ensure the characteristics of strength, fire resistance, non-toxicity, etc. The content of radio-absorbing particles and effective dielectric (magnetic) permeability in the interlayer of the layered structure in the direction of growth of the substrate should ensure broadband and efficiency of the material. The dispersion dependence should ensure uniform absorption of electromagnetic energy and its passage from the input surface to the substrate in a given frequency range. Based on the maximum and minimum wavelengths of the shielding field, permeability and thickness of individual layers, calculations of the required thickness of the gradient material for a given reflection coefficient are given. Thanks to heat treatment of the surface of the material in the manufacturing process, the possibility of manufacturing monolithic metal-polymer screens with surface layers of low dielectric permeability is shown. The possibility of creating monolithic metal-polymer screens from ferromagnetic finely dispersed substances with an adjustable gradient in the direction from the front surface to the bottom is demonstrated, and a technical solution is given. This material can be used to control the ratio of shielding factors for high-frequency electromagnetic fields, ultra-low-frequency electric and magnetic fields, as well as concomitant shielding from natural magnetic fields.

Modeling directivity of dipole antenna in borehole environment in oil reservoir

The authors have obtained the analytical relations for the plane electromagnetic wave reflection coefficient at the borehole-borehole environment interface. The numerical modeling of directivity diagrams is carried out on the scale of the gain factor of a dipole antenna arranged in the borehole environment in an oil reservoir. The modeling takes into account the influence exerted by the properties of the borehole fill material on the electromagnetic field of the antenna in the radio-frequency range.

Newton-ADE-FDTD Method for Oblique Incident Magnetized Time-varying Plasma

In this paper, the Newtonian equation of motion describing the movement of electrons when electromagnetic waves propagate in a magnetized plasma is combined with the traditional auxiliary differential equation finite difference time domain (ADE-FDTD) method. The FDTD iterative formulas of transverse magnetic (TM) wave and transverse electric (TE) wave of the electromagnetic wave obliquely incident on the magnetized time-varying plasma plate are derived. The biggest difference between this method and the ordinary ADE-FDTD algorithm is the addition of the logarithmic derivative of the time-varying plasma electron density to calculate the current density, which is called the Newton-ADE-FDTD method. Through Example 1, the reflection coefficient of electromagnetic wave incident on the magnetization time-varying plasma plate was calculated, and the correctness of the improved algorithm was verified. At the same time, the Newton-ADE-FDTD algorithm is used to calculate the reflection coefficient of electromagnetic waves incident on the magnetized plasma-dielectric photonic crystal. The results show that different incident angles have a greater impact on the reflection coefficients of left-handed circularly polarized wave (LCP) and right-handed circularly polarizedwave (RCP).

3D printing “wire-on-sphere” hierarchical SiC nanowires / SiC whiskers foam for efficient high-temperature electromagnetic wave absorption

• A materials-independent “wire-on-sphere” hierarchical structure was developed. • 3D printing hierarchical structure for structure design. • A catalyst-free PIP process was first developed to in situ grow SiC nw . • SiC nw /SiC w foam exhibits superior high-temperature EWA performance. • The EWA performance retention of SiC nw /SiC w foam at aeroengine simulation working environment was measured. Electromagnetic wave absorption (EWA) materials for use in extreme environments are of great interest. Herein, SiC nanowires / SiC whiskers (SiC nw /SiC w ) foam with unique “wire-on-sphere” hierarchical structure was developed for efficient high-temperature EWA. SiC w were assembled to porous SiC w spheres via spray drying and then SiC w spheres were 3D printed to SiC w foam. The catalyst-free precursor infiltration pyrolysis process was first developed to ensure that SiC nw can intentionally grow in situ on the surface of SiC w spheres, thereby achieving “wire-on-sphere” hierarchical structure foam. At room-temperature, the maximum electromagnetic wave effective absorption bandwidth (EAB max ) and minimum electromagnetic wave reflection coefficient (RC min ) of SiC nw /SiC w foam can reach 4 GHz and -57 dB, respectively. At 600 °C, the EAB max and RC min were 3 GHz and -15 dB, respectively. Furthermore, even oxidized at 1000–1500 °C, SiC nw /SiC w foam can still retain EAB max ranging from 2.7 to 3.9 GHz and RC min ranging from -16 dB to -64 dB, because the formation of SiO 2 layer with appropriate thickness can boost interfacial polarization and regulate impedance matching. The SiC nw /SiC w foam also shows the flexural strength as high as 17.05 MPa. All results demonstrate that the SiC nw /SiC w foam is a promising EWA material for applications of harsh environments. And the material-independent “wire-on-sphere” hierarchical structure and its novel preparation process should find the widespread use in the design and fabrication of high-efficiency EWA micro-nano materials.

ЗАСАДИ РОЗРОБЛЕННЯ РІДКИХ СУМІШЕЙ ДЛЯ ЕКРАНУВАННЯ ЕЛЕКТРОМАГНІТНИХ ПОЛІВ ШИРОКОГО ЧАСТОТНОГО ДІАПАЗОНУ

Purpose: A liquid material based on commercially available paints and fine iron ore concentrate has been created. With a filler content of 60-70 %, the coefficients of shielding of the electric field of industrial frequency is 2,6-9,1; magnetic field of industrial frequency is 4,5-6,2; electromagnetic field of ultrahigh frequency is 4,4-8,5. At the same time, the reflection coefficients of electromagnetic waves are at least twice lower than those of metal screens. Method: A calculation tool is provided for converting the weight content into the volume content of the shielding filler. This makes it possible to apply the Lorentz and Maxwell-Garnett ratios to predict the electrical and magnetic properties of metal dielectrics. To determine the reliability of adhesion of the obtained mixtures with the application surfaces, the study of the chemical and colloidal properties of the mixtures for application on gypsum board has been performed. Scientific novelty: It is established that the reduction of surface tension, surface wetting angle, work of adhesion, cohesion and wetting forces, spreading coefficient are within the limits that ensure the reliability and durability of adhesion of the material to surfaces. Results: It is shown that the reduction of the protective properties on the water-dispersion carrier is due to the oxidation of the filler. Liquid compositions are made on the basis of a number of paints and varnishes and iron ore concentrates, which can cover large surfaces in various shapes and configurations. Practical significance: In order to use the obtained mixtures in the fields of ensuring the electromagnetic compatibility of electrical and electronic equipment, it is necessary to increase the protective properties. This is possible by increasing the concentration of the shielding filler or increasing the specific conductivity of materials in the solid state by adding to the liquid mixture of fine material with high conductivity.

Антиклассическое приближение в задаче об отражении электромагнитной волны от неоднородной среды

Expressions are derived for the reflection coefficients of electromagnetic waves with "p" and "s" type polarizations from a semi-infinite dielectric medium having an inhomogeneous layer. The influence of the layer was taken into account by the method of perturbation theory in a quadratic approximation of the layer thickness. A method is proposed for converting expressions derived using perturbation theory into other expressions that give more accurate values of the reflection coefficient. The angular dependences of the reflection coefficient obtained by the developed method are compared with those obtained by the numerical solution of electrodynamic equations. Requirements for the layer characteristics are formulated to minimize the error of the analytical solution.

Anticlassical approximation in the problem of electromagnetiv wave reflection from an inhomogeneous medium

Expressions are derived for the reflection coefficients ofelectromagnetic waves with p and s type polarizations from asemi-infinite dielectric medium having an inhomogeneous layer. Theinfluence of the layer was taken into account by the method of perturbationtheory in a quadratic approximation of the layer thickness. A method isproposed for converting expressions derived using perturbation theory intoother expressions that give more accurate values of the reflectioncoefficient. The angular dependences of the reflection coefficient obtainedby the developed method are compared with those obtained by the numericalsolution of electrodynamic equations. Requirements for the layercharacteristics are formulated to minimize the error of the analyticalsolution. Keywords: dielectric medium, inhomogeneous layer, electromagnetic wavereflection coefficient, analytical calculation, perturbation theory.\

Hierarchically structured elastomer for absorption-dominated electromagnetic interference shielding in an ultra-wide band

Flexible electromagnetic interference (EMI) shielding materials with low secondary electromagnetic radiation are urgently required for next-generation precise electronic devices and wearable electronics. However, realizing ultra-low microwave reflectivity and sustaining strong absorption feature in a wide frequency range remains a great challenge. Here, natural rubber-based flexible hierarchical composites were fabricated by combination of honeycomb-like 3D networks with selectively distributed ferro/ferric oxide modified graphene (F@rLG) magnetic particles and densely interconnected conductive networks (RL) with fulfilled multiwall carbon nanotubes (MWCNTs) via latex compounding together with co-vulcanization method. The resulting hierarchical bilayer elastomer has the EMI shielding coefficient of 34.4 dB at RL thickness of 0.18 mm, and achieves minimum electromagnetic wave reflection coefficient of 0.1. Moreover, in almost entire Ku band, over 80% incident electromagnetic waves can be absorbed, indicating its excellent capability in minimizing the secondary electromagnetic pollution. And this double-layered flexible material exhibits excellent stability in EMI shielding performance after the deformation cycles of 500 times. In addition, both the influence of precisely manipulated distribution of nanoparticles on the EMI property and the absorption-dominated approach via coupled layers were investigated in depth. This work paves a way for designing flexible EMI shielding materials with low secondary electromagnetic contamination.

SUBSTANTIATION OF APPLICATION FEATURES OF LIQUID MIXTURES FOR SCREENING OF ELECTROMAGNETIC FIELDS

The protective and rheological properties of composite materials based on water-dispersed paint and iron ore concentrate were studied. Features of liquid mixtures application for shielding of magnetic field of industrial frequency and electromagnetic field of ultrahigh frequency were substantiated. The study of the protective characteristics and rheological properties of composite materials based on water-dispersed paint and iron ore concentrate indicates the possibility of their use for shielding electromagnetic fields of a wide frequency range. It was found that the efficiency of the composite material (total shielding coefficient and reflection coefficient of electromagnetic waves) depends on the dispersion of the shielding filler, so the particle size analysis of iron ore concentrate was performed. The analysis shows that the predominant size of iron-containing particles is 23‒24 μm, which is quite acceptable for their uniform distribution in the body of the matrix. Shielding protective material was made of water-dispersion paint with the addition of iron ore concentrate in weight quantities of 15, 30, 45, 60%. The shielding coefficients of the electromagnetic field of industrial frequency and ultrahigh frequency with different filler content were measured. It was found that if the concentration of filler exceeds 30%, both the rheological characteristics of the mixture and the shielding coefficients of electromagnetic fields are unsatisfactory. A dramatic increase in shielding coefficients occurs at a filler concentration of 40%. This mixture has acceptable adhesive properties. It was established that the shielding coefficients could be enhanced if the dispersion of the filler is increased, which will contribute to the stability of the colloidal mixture and improve the rheological properties.

Design of liquid composite materials for shielding electromagnetic fields

This paper reports the principles of design and the examined protective properties of liquid materials for shielding the electric, magnetic, and electromagnetic fields over a wide frequency range. The materials were made on the basis of iron ore concentrate and a pigment additive, with water-dispersed and geopolymer paints used as a matrix. The tests of protective properties for the electrical and magnetic components of the electromagnetic field of industrial frequency showed that the electric field shielding coefficients at a concentration of the screening substance of 15−60 % (by weight) equaled 1.1−8.6; magnetic field – 1.2−5.3. The shielding coefficients of the material based on a water-dispersed paint are lower than those of a geopolymer one, which can be explained by the oxidation of an iron-containing component and a decrease in electrical conductivity. The shielding coefficients of the electromagnetic field with a frequency of 2.45 GHz are 1.2−7.9. The highest coefficients are inherent in the material with filler made of iron ore concentrate and titanium-containing pigment powder in a ratio of 1:1. To design materials with the required (predictable) protective properties, the relative magnetic, dielectric permeability of materials was calculated. It is shown that the obtained data are acceptably the same as the results from direct measurements of magnetic and dielectric permeability and could be used to calculate the wave resistance of the material and the predicted reflection coefficient of electromagnetic waves. Thus, there is reason to assert the need to build a database on the frequency dependence of effective magnetic and dielectric permeability in order to automate the design processes of composite materials with predefined protective properties.

The use of lighting techniques for rapid remote determination of moisture content of sunflower seeds growing in the fields

The method is proposed and the ability to perform rapid remote determination of the moisture content of sunflower seeds using millimeter – range microwave radiation is experimentally investigated. A laboratory experimental setup for measuring the reflection coefficient of electromagnetic waves from sunflower inflorescences in the frequency range of 25.86 – 37.5 GHz has been created. Experimental studies of the value of the reflected signal from sunflower inflorescences on both sides of the plant were carried out in order to create a mathematical model that takes into account the difference between the reflected signal from the inflorescence side with sunflower seeds and the reverse side. Experiments were conducted for inflorescences of maturity different degrees.

RADIO-WAVES REFLECTION AT REMOTE SENSING OF UNDERLYING COVERS

Monitoring technologies are rapidly developing at present and allow to extract and use non-coordinate information about objects. Noncoordinate information is the information about the type and properties of an object under study. Remote sensing is the main method of solving monitoring problems where special positioning belongs to the radar methods, based on space-time processing of signals and, in particular, on methods of radio polarimetry. It is necessary to have information about the surface in order to solve the monitoring task. The slightest changes in the electrical and physical properties of such areas as salinity, humidity, soil composition, etc. will lead to a change in the basic electrodynamics of the surface, notably its complex dielectric permittivity. The article demonstrates the precise solutions to the problems of radio-waves reflection from a layered surface with various laws of changes of the complex permittivity  in depth. Media with exponential and quadratic laws of variation  for arbitrary angles of incidence of the radio wave on the surface are considered. Precise decision is obtained for layered media with the law of change in the complex permittivity the polynomial and linear characteristics. A similar problem for the parabolic layer is considered separately. The detailed analysis of radio waves reflection from the medium with a matching layer is carried out. The nature of the electromagnetic field inside the transition layer is studied in detail. The article is illustrated by the graphs showing the dependences of an electromagnetic wave reflection coefficient on the layered medium with linear and exponential laws of variation of the complex dielectric constant over depth.

Synthesis, Structure and Electromagnetic Properties of Nanocomposites with Three-component FeCoNi Nanoparticles

Infrared heating was used to synthesize FeCoNi/С nanocomposites, where nanoparticles of FeCoNi ternary alloy are stabilized and uniformly distributed in the carbon matrix volume. The authors studied the impact of synthesis temperature and percentage ratio of metals upon the structure, composition and electromagnetic properties. X-ray phase analysis and Mossbauer spectroscopy showed that ternary alloy nanoparticles with different compositions and crystalline lattice types can be formed with the rise in synthesis temperature and iron concentration. Resonator method was used to examine frequency dependencies of relative complex dielectric and magnetic permeabilities of nanocomposites in the range of 3–12 GHz. Calculation of reflection coefficient based on experimental permeability data showed that by varying synthesis temperature and percentage ratio of metals one can control the frequency range of effective absorption of electromagnetic waves. It was established that increase in relative iron content from 33 to 50 rel.% leads to the shift of minimal electromagnetic wave reflection coefficient band from f ~ 12+ GHz to frequency f ~ 6 GHz at identical absorber thickness.

Исследование коэффициента отражения плотной двухкомпонентной плазмы

In the work, the angular dependences of electromagnetic wave reflection coefficients from two-component dense plasmas have been investigated. The results for the dielectric function obtained in the framework of the moments method [1] and of the Mermin model’s [2] are presented in comparison with the experimental data [3-6]. In Mermin’s model both collision static and collision dynamic frequencies have been taken into account. The static characteristics of this system are designed to use the theory of linear dielectric response, where the Deutsch potential is considered as an interparticle interaction potential [7]. It is shown that, in contrast to the moment method, the Mermin model can be used only for shorter incident radiation waves of both s- and p- polarizations. On the other hand, the results obtained by the method of moments are applicable in a wider range of investigations, which concern the reflection of electromagnetic radiation from dense plasmas. In the framework of the method of moments in connection with super-intertwining chains the possible further development ways of the theory of electromagnetic waves reflection from plasmas, which use the calculation of static structural factors, have been marked.

The Influence of Conductivity on the Reflected Ground Penetrating Radar SIgnal Amplitude

Within the ground-penetrating radar (GPR) bandwidth a subsurface materials is considered to be an ideal dielectric, which is not always the case. We have developed the dependence of the reflection coefficient of electromagnetic waves with regard to conductivity, which showed a significant effect of the difference in conductivity on the reflectivity and signal amplitude. This was confirmed by physical modeling. The electrical conductivities of a geological media should be taken into account when solving direct and inverse problems, survey design planning, etc. Ground-penetrating radar can be used to solve the problem of mapping of the halocline or to determine water contamination.

Radio-physical properties of radiotransparent thermal protection materials in ablation mode

Experimental method for assessing the impact of the effects of high-temperature ablation processes on the radio physical characteristics of radiotransparent thermal protection materials (RTPM) is developed. Researches for the following RTPM with various structures of glass fillers are completed: press material (radiotransparent thermal protection press material or RTP-200); glass-fiber laminate (glass-fiber radiotransparent organic ceramic matrix or GFR-CM); reinforced composite material of class SiO2–SiO2 (high-temperature radiotransparent ceramic organic matrix or HTRC-OM). The influence of physicochemical transformations in the surface layer of RTPM on transmission and reflection coefficients of electromagnetic waves of RTPM samples and on the value of their complex permittivity is determined.

Nernst heat theorem for the thermal Casimir interaction between two graphene sheets

We find analytic asymptotic expressions at low temperature for the Casimir free energy, entropy and pressure of two parallel graphene sheets in the framework of the Lifshitz theory. The reflection coefficients of electromagnetic waves on graphene are described on the basis of first principles of quantum electrodynamics at nonzero temperature using the polarization tensor in (2+1)-dimensional space-time. The leading contributions to the Casimir entropy and to the thermal corrections to the Casimir energy and pressure are given by the thermal correction to the polarization tensor at nonzero Matsubara frequencies. It is shown that the Casimir entropy for two graphene sheets goes to zero when the temperature vanishes, i.e., the third law of thermodynamics (the Nernst heat theorem) is satisfied. At low temperature, the magnitude of the thermal correction to the Casimir pressure between two graphene sheets is shown to vary inversely proportional to the separation. The Nernst heat theorem for graphene is discussed in the context of problems occurring in Casimir physics for both metallic and dielectric plates.