Annotation of the results obtained in 2023
1. DYNAMIC MAGNETIC PROPERTIES OF SINGLE LAYER THIN FILMS of Fe70Co30 A number of samples of thin Fe70Co30 films with a thickness from 100 to 1000 nm on a polymer substrate were studied. It has been shown that an increase in the thickness of the metal layer leads to degradation of the effective microwave magnetic characteristics of the samples. This transition is associated with a decrease in the quality factor of the natural ferromagnetic resonance peak in the samples. The samples demonstrate two magnetic absorption maxima in the range 1.0 – 20 GHz. The high-frequency absorption maximum corresponds to natural ferromagnetic resonance. The low-frequency absorption minimum is presumably associated with the motion of domain boundaries. It was also found that an increase in the thickness of the ferromagnetic layer leads to a change in the orientation of the magnetic anisotropy; the transition occurs at a film thickness of 500 nm. 2. DYNAMIC MAGNETIC PROPERTIES OF THIN FILMS OF PERMALLOY Ni80Fe20 OBTAINED BY REACTIVE MAGNETRON SPRAYING IN THE PRESENCE OF OXYGEN Single-layer thin films obtained using reactive magnetron sputtering of Ni80Fe20 permalloy were studied. It was found that an increase in the oxygen content in the gas mixture during sputtering leads to the formation of a mixed oxide of the conventional composition NiFeO. The obtained samples demonstrate a complex structure of the microwave magnetic spectrum with several absorption bands on the frequency dependence of the imaginary part of the magnetic permeability. As the oxygen impurity increases, the amplitude of magnetic losses decreases both in the absence of an external magnetic field and in its presence, which indicates a change in the magnetic structure and phase composition of the film. 3. STUDY OF MICROWAVE MAGNETIC AND DIELECTRIC PERMITTIVITY OF PARTICLES IN COMPOSITES WITH A MODEL MATRIX 3.1 STUDY OF COMPOSITE MATERIALS WITH ANISOTROPIC ARRANGEMENT OF PARTICLES A study was carried out of the microwave properties of composite materials magnetized to saturation with an anisotropic orientation of lamellar sendust inclusions. The dependences of dielectric and magnetic permeability on frequency and on the strength of the external constant magnetic field were measured. A coil was manufactured capable of creating a magnetic field with a strength of up to 4.63 kOe, which made it possible to magnetize anisotropic samples to saturation. It is shown that the dependences of the ferromagnetic resonance frequency on the external magnetic field differ for different volume fractions of inclusions in the sample. 3.2 STUDY OF THE INFLUENCE OF THE THICKNESS OF THE NON-MAGNETIC SIO2 SHELL ON THE SURFACE OF SPHERICAL IRON PARTICLES ON THE ELECTRODYNAMIC CHARACTERISTICS WHEN USED AS A FILLER OF COMPOSITE MATERIALS A method has been developed for depositing a SiO2 shell up to 450 nm thick on the surface of powdered iron particles. The method is based on the iterative process of hydrolysis of orthosilicic acid ester. A 500 nm thick SiO2 shell reduces the dielectric and magnetic permeability of KZh@SiO2-paraffin composites in the microwave frequency range. The decrease in dielectric and magnetic permeability is associated with a quantitative decrease in the magnetic fraction in the composite and is consistent with the Maxwell Garnett formula. SiO2 shells with a thickness of 450 nm increased the thermal stability of powdered iron particles, which is expressed in a shift in the onset of oxidation temperature from 166 to 331 °C. 4. FERROMAGNETIC MESOPOROUS IRON PARTICLES OBTAINED BY SPRAY PYROLYSIS FOR MICROWAVE APPLICATIONS It has been shown that the reduction of iron oxide particles obtained by spraying an iron nitrate solution with ultrasound at a frequency of 2.64 MHz at different temperatures affects the chemical composition, purity and morphology of nanostructured spherical iron particles. Ferromagnetic iron powders were synthesized from a Fe(NO3)3 solution using ultrasonic spray pyrolysis and then reduced at 350 – 500°C in hydrogen. Increasing the annealing temperature in hydrogen changes the chemical composition and increases the amplitude of the complex microwave permeability. It has been established that annealing at 400 °C is the most optimal, since it allows one to obtain iron powders that demonstrate intense microwave absorption and consist of ~90% α-Fe phase with a surface with low roughness and porosity. 5. STUDY OF MICROWAVE DIELECTRIC CONTINUITY OF MICROWIRES AT TEMPERATURES UP TO 800C A technology has been developed for the production of heat-resistant sheet samples up to 800C based on metal microwires. A study of the frequency dependence of the electrical characteristics of the obtained samples was carried out. The measurements were carried out using a quasi-optical measuring stand developed and created within the framework of this Project. It has been shown that a layer of material based on microwire does not change its properties as a result of annealing at a temperature of 800C. Analysis of the frequency dependence of the dielectric constant of the obtained samples using the Lorentz formula shows the existence of interaction between particles of the layer filler - sections of microwire of a given length. 6. EXPERIMENTAL DETERMINATION OF THE CURIE TEMPERATURE OF COMPOSITES WITH FINE GADOLINIUM POWDER Samples of model composites containing Gd powder from 5 to 50% vol. were obtsined. It is shown that a decrease in temperature, as well as an increase in the strength of the external static magnetic field, changes the appearance of the magnetic spectrum from relaxation to asymmetric resonance. Two previously undescribed physical effects were discovered: the dependence of the Curie temperature of the composite on the concentration of the ferromagnetic filler and a drop in the static magnetic permeability of the composite as the temperature decreases well below the Curie temperature, accompanied by a high-frequency shift of the magnetic absorption line. 7. OPTICAL PROPERTIES OF ULTRATHIN Pd AND Pt FILMS ON A QUARTZ SUBSTRATE AND ON TUNGSTEN TRIOXIDE FILMS Based on ellipsometric spectra and transmission spectra, the optical parameters of palladium and platinum films were determined. The Pd and Pt films had a thickness of 5 – 7 nm and were studied both on a pure SiO2 substrate and on films of tungsten trioxide WO3. Despite the extremely small thicknesses, the parameters of most films are described by the isotropic dielectric constant. It was found that films deposited directly on a SiO2 substrate had a positive (rather than the negative, characteristic of a metal) real part of the effective dielectric constant, while films deposited on WO3 exhibited metallic properties for unannealed films and properties characteristic of metal-dielectric composites. for films annealed at a temperature of 300C. 8. DEVELOPMENT OF ACTIVE METAMATERIALS BASED ON PERIODICALLY LOCATED INCLUSIONS 8.1. CREATION OF A NON-FOSTER ELEMENT FOR APPLICATION IN ACTIVE METAMATERIALS To overcome the fundamental limitation limiting from below the thickness of a passive radio-absorbing material, depending on the absorption band width, a single element of an active metamaterial has been developed. The developed metamaterial has an order of magnitude thinner than a passive material with similar properties. The designed non-Fostor element was fabricated by photolithography using a single-port impedance converter circuit based on a THS4303 operational amplifier. The agreement between experiment and simulation up to a frequency of 3 GHz is shown. 8.2 DEVELOPMENT OF A THz RANGE MODULATOR BASED ON THIN FILMS OF VANADIUM OXIDE The high-frequency reactive process of magnetron sputtering was optimized, which made it possible to obtain thin layers of VO2 with a metal-insulator transition, suitable for use as modulators in the THz range. The topology of the control element of the THz modulator, necessary for changing the phase state of the VO2 film by heating the film with an electric current, has been developed. In the frequency range 12 – 200 THz, the modulation depth of the transmission coefficient during PMD in VO2 is no less than 98.7%.

 

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Annotation of the results obtained in 2021
1. Investigation of composite materials with inclusions with a "core-shell" structure, based on iron microparticles and a SiO2 shell. A method has been developed for obtaining "core-shell" structures with an iron core made of P-20 carbonyl iron and a dielectric shell (SiO2) up to 220 nm thick. The morphological, chemical and electromagnetic properties of the obtained structures have been investigated under various synthesis conditions. It was found that by varying the conditions of shell synthesis, it is possible to carry out a directed change in the properties of magnetic powders. A theoretical calculation of the values of the dielectric constant of powders was carried out according to the Maxwell Garnett formula, a comparison of the theoretical and experimental values ​​of the dielectric constant of composites was given. As a result of hydrolysis of TEOS, with the addition of ammonia, continuous dielectric SiO2 shells of various thicknesses were obtained on carbonyl iron particles. With an increase in the duration of hydrolysis from 0.5 to 4 hours, the thickness of the shell increases from 90 to 190 nm. In this case, the shell possessed a ratio of elements SiO3.3, which remains constant for all experiments in the series. With an increase in the concentration of ammonia, the thickness of the shell can be monotonically and directionally increased to 220 nm, and the composition of the shell is saturated with oxygen to SiO8.6. It was found that, even though changes in the chemical composition of SiOx can affect the dielectric properties of the shell, the main contribution to the change in the electrodynamic parameters of Fe @ SiO2 powders is made by differences in the thickness of the dielectric shells. This result was obtained by comparing the calculation results using the theoretical Maxwell Garnett model with experimental data. In the future, fine-tuning of the synthesis conditions can be used to create functional materials with the necessary electrodynamic parameters for applied and industrial problems. The results of this study are presented in the article Dolmatov, A.V .; Maklakov, S. S .; Zezyulina, P. A .; Osipov, A.V .; Petrov, D.A .; Naboko, A.S .; Polozov, V.I .; Maklakov, S.A .; Starostenko, S.N .; Lagarkov, A.N. Deposition of a SiO2 Shell of Variable Thickness and Chemical Composition to Carbonyl Iron: Synthesis and Microwave Measurements. Sensors 2021, 21, 4624. The article is available at https://doi.org/10.3390/s21144624 2. Experimental studies of the frequency dispersion of microwave permeability of composite materials with plate-shaped inclusions The dependences of the material parameters of composites based on a paraffin matrix filled with lamellar particles of sendust (Al0.054Si0.096Fe0.85) on frequency, external magnetic field, and volume fraction of inclusions in the material have been measured. It is shown that the effective permeability of the composites under study obeys the Wiener mixing formula. It is shown that the mixing formula, which correctly restores the intrinsic permeability of inclusions in the absence of an external field, becomes inapplicable when an external field is applied due to a change in the magnetic structure of the composite inclusions. An increase in the external field leads to the disappearance of the domain structure and an increase in the interaction between particles. To carry out these works, a modernization of the method for measuring the microwave characteristics of samples in a coaxial line was carried out, consisting in the use of an external electromagnet. The mechanisms that form the magnetic microwave spectrum of composites filled with sendust particles have been determined. It is shown that the main peak of the magnetic losses is associated with the splitting of the ferromagnetic resonance at the domain structure in particles - domain modes. The found frequencies of domain modes agree with the measured magnetic permeability. An increase in the external magnetic field leads to the disappearance of the domain structure, a decrease in the contribution of domain modes to the magnetic permeability, and an increase in the contribution of FMR on individual particles. The features of the magnetization of composite materials are investigated. It is shown that with a small fraction of inclusions in the sample, the external magnetic field is demagnetized on individual particles. Due to the different orientations of the particles in the isotropic composite, the peak of the magnetic loss splits when an external magnetic field is applied. An increase in the fraction of inclusions leads to the fact that the external field is demagnetized on the sample as on a single whole, and the splitting of the peak when the field is applied does not occur. Also, the peak is not split upon magnetization of samples with anisotropic particle orientation. The possibility of publishing the results obtained will be considered at subsequent stages. 3. Study of composite materials with inclusions based on hexaferrites An experimental study of samples of substituted barium hexaferrite BaFe (11.5-x) Ti0.5AlxO19 (0.1 <x <3.0) has been carried out. It was found that an increase in the content of Al3 + ions in this compound leads to a decrease in the lattice parameters and density of the samples. It was found that the value of the frequency of natural ferrimagnetic resonance exceeds 18 GHz. At the same time, a low-frequency resonance is observed, which is a resonance of domain walls. A correlation was found between the magnitude of the anisotropy field obtained by measurements using a vibrating magnetometer and the magnitude of the anisotropy field calculated from microwave measurements. For further investigation of materials with several maxima of magnetic losses, it is advisable, in addition to ferrites, to consider fillers based on ferromagnetic metals. 4. Study of thin films of permalloy obtained by reactive magnetron sputtering in the presence of oxygen Using reactive DC magnetron sputtering of a permalloy target in the presence of oxygen, a number of samples of single-layer permalloy films with a thickness of 200 nm were obtained. A vacuum installation with a barrel-type substrate holder was used; A 12 µm thick lavsan film was used as a substrate. The dynamic magnetic characteristics were measured by the coaxial technique, for which a long narrow tape is cut out of the obtained film and twisted into a toroidal sample. With an increase in the oxygen content in a mixture with argon from 0 to 15 vol%, a decrease in the amplitude of the ferromagnetic resonance associated with pure permalloy and the appearance of new higher-frequency peaks in the spectrum are observed. We also found a threshold oxygen content at which the sample loses its ferromagnetic properties: it is 20 vol. %. The observed phenomena are presumably associated with the formation of the oxide phase in the composition of the film, which will be investigated at further stages. Permalloy films obtained by sputtering in argon were used to create a metamaterial consisting of periodic laminate structures. 5. Investigation of the applicability of mixing formulas for describing the microwave properties of periodic structures based on thin films A metamaterial in a dielectric matrix with inclusions in the form of conducting squares of small thickness compared to the longitudinal dimensions is investigated. This work aims to find a mixing formula for a correct description of the microwave properties of the system. The problem was solved using the numerical simulation of the transmission and reflection coefficients with periodic boundary conditions by the finite element method. The computational model was a semi-infinite layer of conductive inclusions of square cross-section and small thickness, placed in a dielectric matrix, with the possibility of changing the distance between the inclusions. Both a single layer and a multilayer structure with the number of layers up to 10. The distance between the layers was fixed or changed simultaneously with the distance between the elements in the plane. It is shown that the microwave properties of the investigated periodic structure are correctly described by the Maxwell-Garnett mixing formula. The calculation of the effective form factor of the inclusions has been carried out. It is shown that the applicability of the mixing formula does not depend on the number of layers in the system under study. Based on the results of the work done, it is planned to prepare a publication. 6. Investigation of the characteristics of metal-polymer composites in the optical range Films based on metal-polymer nanocomposites 2,3-dichloro-p-xylylene-silver have been created, and surface-enhanced Raman scattering (SERS) has been demonstrated on their basis. To obtain nanocomposites, the method of vapor deposition was used, which makes it possible to control the microstructure of the nanocomposite. In the process of self-assembly, nanocomposite films with inclusions of silver particles were formed on polynuclear substrates. The silver content varied from 2.5 to 16% vol. The possibility of using such substrates for the detection of low-molecular substances, for example, 2-nitrobenzoic acid, has been demonstrated, at which a gain of 10 ^ 4 has been demonstrated. The dependence of the enhancement of the SERS spectra on the microstructure of the nanocomposite and the silver content in it is determined. The optical and morphological properties of nanocomposites were also investigated and their dependence on the silver content was shown. It was shown that the nanocomposite is SERS-selective, because when working with complex solutions in the presence of high-molecular substances, the signal amplification was observed only for low-molecular substances. The results of the work are published in the article Boginskaya, I .; Gainutdinova, A .; Gusev, A .; Mailyan, K .; Mikhailitsyn, A .; Sedova, M .; Vdovichenko, A .; Glushchenkov, A .; Dorofeenko, A .; Ryzhikov, I. The Poly (chloro-pxylylene) -Ag Metal-Polymer Nanocomposites Obtained by Controlled Vapor-Phase Synthesis for SERS Effect Realization. Coatings 2021, 11, 1171. The text of the article is available at https://doi.org/10.3390/coatings11101171 7. Study of the dielectric constant of composite films of palladium and platinum Describing the optical properties of thin metal films has always been a challenge. The problems of averaging optical parameters, boundary conditions, and nonlocality have not yet been fully resolved. All of these problems lead to significant difficulties in predicting realistic responses of the desired nanostructures. Modern technology for the production of metal films allows the formation of highly homogeneous thin metal films. In this work, we investigated ultrathin films of palladium and platinum in various environments. The films are made by electron-beam sputtering. The ellipsometric and transmission spectra have been measured, and the dielectric constants of these films have been obtained. It is shown that ultrathin films of palladium and platinum are successfully described by the local and isotropic permittivity, which differs significantly from the known bulk values. However, this dielectric constant depends on neighboring materials, which indicates that ultrathin metal films can be considered as composites characterized by an effective dielectric constant and effective thickness. 8. Theoretical study of modified multipoles and interference effects between them A numerical, theoretical and experimental study of the terahertz metasurface supporting the pseudo-anapole mode is presented. The pseudo-anapole effect occurs when the electrical and toroidal dipole moments tend to a minimum, instead of destructive interference between the electrical and toroidal dipole moments in the normal anapole mode. This interaction makes it possible to suppress the resonance of the electric type radiation. Thus, it becomes possible to study multipoles of other families and higher-order excitations. The multipole contribution to the response of the metasurface is estimated using the multipole expansion method. This series has added such members of the multipole series as root-mean-square radii and their multipole interference. The geometric reconfiguration of metasurfaces has also been studied. Using scaling, we demonstrate that it is possible to independently control the toroidal and electrical responses of the metasurface. This, in turn, proves that these multipoles have different physical origins. In addition, we demonstrate that the proposed metasurface allows the excitation of coherent magnetic dipole and electric quadrupole modes, which is crucial for planar resonators and spaser generation in nanophotonics. The results of the work were published in the article Maria V. Cojocari, Anar K. Ospanova, Vladimir I. Chichkov, Miguel Navarro-Cía, Andrei Gorodetsky, and Alexey A. Basharin, Pseudo-anapole regime in terahertz metasurfaces, Phys. Rev. B 104, 075408 (2021). The calculated part of this article was supported by this project of the Russian Science Foundation No. 21-19-00138. The article is available at https://journals.aps.org/prb/abstract/10.1103/PhysRevB.104.075408 9. Experimental study of metamaterials based on PiN-diodes In this work, a tunable planar metamaterial with a high contribution of the toroidal dipole moment in the microwave range is studied theoretically and experimentally. The properties achieved in such a structure are controlled by turning on the PiN diode. It is shown that, depending on the resistance of the PiN diode, the metamaterial can be transparent or reflective. Such a metamaterial is relevant for a wide range of areas, for example, a method for reducing radar signature, suppressing scattering, and creating highly sensitive sensors and sensors of electromagnetic fields. 10. Investigation of the influence of higher modes and interference resonances on the measured values of the magnetic permeability in a coaxial line To take into account the influence of higher modes and interference resonances on the measured values of the permeability in the coaxial line, a technique has been developed for measuring the scattering matrix of a sample placed in a rectangular waveguide for further calculation of its material parameters. Methods have been developed for calibrating a rectangular waveguide using sliding short-circuited loads, using a set of fixed short-circuited loads, according to arbitrary specified standards. Preliminary numerical experiments have been carried out.

 

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Annotation of the results obtained in 2022
1. Dependences of the static and dynamic magnetic properties of single-layer ferromagnetic films ( Fe , Co , permalloy Ni 80 Fe 20, 79NM alloy, Fe (N)) on thickness have been studied. It was shown that with increase in thickness, a significant decrease in the amplitude of the microwave magnetic permeability and the cutoff frequency occurs. The observed phenomenon is based on an increase in the damping parameter due to the accumulation of defects in the bulk of the film and the departure of the magnetization vector from the plane of the film. The simulation shows that the cutoff frequency and the loss maximum frequency decrease linearly with the damping parameter. It is also shown that the contribution of the skin effect to the losses is negligible. The properties of multilayer structures in which the ferromagnetic layers are separated by SiO 2 dielectric layers are considered . It is shown that the degradation of microwave properties with increasing film thickness is reduced for multilayer structures relative to single layer structures. 2. Static and high-frequency magnetic properties depending on the phase-structural state and the magnetic structure of Fe 100-56.8 Ti 0-13.5 B 0-34.2 films obtained by magnetron deposition were studied by X-ray diffractometry , vibrational magnetometry and the stripe method for measuring magnetic permeability. An analysis of the magnetic hysteresis loops shows that the magnetic structure formed in the studied films consists of stochastic domains. The frequency dispersions of the magnetic permeability depend significantly on the composition of the films. Films containing 0, 5, 11, 14, 30% TiB 2 exhibit a resonant character of the spectrum. At 8% TiB2 , the spectrum acquires a relaxation character. Resonance on domain walls in the case of a stochastic magnetic structure manifests itself at frequencies reaching 1 GHz, which is much higher than in ferromagnets with a classical domain structure. Thus, the Asche law and resonance on the domain walls define the corridor in which the FMR frequencies of the studied films lie. 3. A technique has been developed for preparing samples based on a paraffin binder with an anisotropic arrangement of lamellar inclusions. Anisotropic composite materials with different concentrations of lamellar sendust inclusions were fabricated . In the absence of an external constant magnetic field, the properties of the composite are described by the Wiener mixing formula. When an external magnetic field is applied, the Wiener mixing formula turns out to be inapplicable, which is associated with different demagnetization processes on samples with different inclusion concentrations. In addition, a method has been developed for correctly estimating the particle size distribution and, at the same time, the particle form factor from electron microscopy images. 4. Using spray pyrolysis with reduction in a stream of hydrogen, iron powders with a hollow structure were obtained. A solution of iron nitrate III with various concentrations was used as a precursor . It is shown that the concentration of the precursor makes it possible to obtain spherical particles of various sizes, from 0.6 to 1 μm. The wall thickness of the hollow particles is estimated at 200 and 500 nm, respectively. The resulting powder materials exhibit high amplitude magnetic losses. At the same time , the imaginary part of the magnetic permeability of the composite filled with 0.6 μm particles has a broad peak with a complex structure. Composites filled with particles 1 µm in diameter show a good quality peak with a single maximum. The resulting composites have low magnetic losses at frequencies below 0.5 GHz, uncharacteristic of spherical iron . 5. A device was created that makes it possible to use the quasi-optical method for measuring sheet samples when heated to 1000°C. The device consists of a radio-transparent furnace and measuring horn antennas. The changes in the radiophysical properties of microwires based on Co with a diameter of 2 µm in a shell of borosilicate glass with a thickness of 7 µm have been studied . It is shown that the temperature dependence of the radiophysical properties of the studied microwire is absent at temperatures up to 700 °С , but when reaching 800 °С, an irreversible increase in the transmission coefficient occurs. These changes are caused by the destruction of the microwire due to a sharp increase in the difference between the thermal expansion coefficients of the core and the sheath. 6. Possibility of practical implementation of the measuring stand using rectangular waveguides with transverse dimensions of 7.2x3.4mm was studied. In this case, we used the method of calibrating the measured reflection coefficient using a sliding short-circuited standard. Numerical calculations and experimental measurement of a paraffin reference sample made it possible to reveal various types of errors. As a result, an improved measurement calibration technique for waveguide measurement ports has been developed. 7. Numerical simulation of a symmetric and asymmetric ( microstrip ) strip measuring cell and experimental measurement of the material parameters of samples in a microstrip cell were carried out. As a result of the study, the limits of applicability of the quasi - TEM approximation were determined when measuring the magnetic and dielectric permittivity. It is shown that this approximation is not applicable at a high degree of inhomogeneity of the section of the measuring cell with the sample under study. When using single-port short-circuited measuring cells, the measurement error of the dielectric permittivity is significantly reduced when the samples are placed far from the short-circuited wall, which indicates the advantage of using two-port feed-through cells. 8. Films of tungsten trioxide and palladium on a quartz substrate were annealed at 300 and 600 °С. The optical spectra of the annealed samples were measured, and the effective parameters of palladium films were found. The Garnett and Bruggeman mixing formulae were applied to the permittivity spectra of the palladium films. It was shown that the effective permittivity spectra of the films annealed at 600°C are well described by the Garnett formula, while the theoretical description of the remaining films requires further work. 9. The magnetic properties of the composite, which consists of 30% of the volume of gadolinium powder, distributed in paraffin, have been studied. It was found that the permittivity of the composite does not depend on either frequency or temperature. The Curie temperature of the composite is 15.5 °C , the phase transition occurs in the temperature range of ±10°C. The effect of temperature change on the S -parameters of the composite layer was studied. The effect of temperature on the magnetic permeability spectrum of the composite is described by the magnetization cluster model based on the Wiener mixing formula. A screen has been developed, the minimum reflection coefficient of about -20 dB is achieved at 0 ° C for a layer about 4.5 mm thick at a frequency of about 3.5 GHz; at 20°C, the reflectance of the layer is about -2dB. 9. Numerical modeling of the active metamaterial was carried out , as well as a separate non-Foster element with negative inductance. It is shown that the properties of an absorber made of an active metamaterial go beyond the fundamental limitation for passive materials, which relates the reflection coefficient, wavelength range, and coating thickness. An experimental verification of the results of modeling a non-Foster element was carried out, and the results obtained by calculation were confirmed. Metamaterial measurement boards based on a non-Foster element are made using photolithography . 10. A frequency-selective surface has been developed, which is a thin conductive layer with rectangular apertures formed over a thin VO 2 film with a pronounced metal-insulator transition. At a temperature of 30 °C , when the surface of a thin film of VO 2 is 4x10 5 ohm/square, the surface is a band pass filter. During the transition of VO 2 to the metallic state at a temperature of 80 °C , this surface predominantly reflects microwave radiation.

 

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