Abstract In this work, the effect of Ge sample bombardment by energy Ei = 1.2 MeV mono‐energetic He+ ions within the fluence range of 1013–1.2 × 1015 cm−2 on the microwave reflection/transmission modification in the frequency range of 26–38 GHz is investigated. It is shown for the first time that such Ge treatment allows achieving a drastic increase in its interaction with microwaves. After the 1 µm thick undersurface area of Ge, accounting for less than 10−3 of its bulk, underwent the fluence of 1.2 × 1015 cm−2, the increase of the microwave absorption coefficient from 0.06 to 0.78 and decrease of the microwave reflection coefficient from 0.7 to 0.18 are observed. This is caused by the occurrence of dangling atomic bonds in nanoscale cavities inside the material. Most probable energy loss mechanisms of microwaves in modified Ge are suggested. Modified semiconductor structures can be used as microwave‐absorbing coverings, devices employing a periodic structure of materials or a gradient of its properties.

The study is devoted to the electrodynamic properties of composite materials based on AlN–5 wt

The epoxy composite materials (CMs) with a random distribution of nanosized Co3O4 and carbon nanoparticles (graphite nanoplatelets GNP and carbon nanotubes CNT) are fabricated. Complex permittivity, permeability, and shielding properties of composite materials with 30 wt% of Co3O4 and (2–5) wt% of nanocarbon are measured in the frequency range of 1–67 GHz using the transmission–reflection method. A significant increase of microwave permittivity and presence of several peaks on the dependencies of the imaginary part of permittivity on the frequency are found for three‐phase nanocarbon/Co3O4/epoxy CMs. The observed microwave shielding efficiency of three‐phase epoxy composites is enhanced compared to two‐phase nanocarbon–epoxy composites. Such enhancement of shielding efficiency correlates with the increase of DC conductivity of these three‐phase composites. The measured complex permittivity and permeability spectra for nanocarbon/Co3O4/epoxy CMs are used for modeling the reflection loss for studied composites. It is shown that the most preferable for microwave absorption is the composites containing 2 wt% of nanocarbon filler for a sample thickness of 0.5–0.7 mm. The highest reflection loss = 30 dB with an absorption bandwidth of 15 GHz is found for epoxy composite filled with 2 wt% of GNP and 30 wt% of Co3O4 for a sample thickness of 0.5 mm.

Graphite nanoplatelets (GNPs)—the segregated ultra-high molecular weight polyethylene (UHMWPE)-based composites with hybrid filler—decorated with Fe3O4 were developed. Using X-ray diffraction and scanning electron microscopy, it was shown that the decorated component has the shape of separate granules, or their clusters were distributed evenly over the GNPs surface. The individual Fe3O4 nanoparticles are predominantly rounded, with diameters of approximately 20–60 nm. The use of GNPs/Fe3O4 as a filler leads to significant decreases in the percolation limit φc, 0.97 vol% vs. 0.56 vol% for GNPs/UHMWPE- and (GNPs/Fe3O4)/UHMWPE segregated composite material (SCM), respectively. Modification of the GNP surface with Fe3O4 leads to an essential improvement in the electromagnetic interference shielding due to enhanced microwave absorption in the 26–37 GHz frequency range in its turn by abundant surface functional groups and lattice defects of GNPs/Fe3O4 nanoparticles.

Constructing a multilayered structure as an absorbing coating is an important tool for improving the characteristics of microwave absorbing (MA) and shielding materials. The influencing factors on microwave absorption performances of multi-layered structures are filler types and loading in composite layers, stacking sequences and thicknesses, etc. Multicomponent epoxy composites with various content (0–5 wt RL of multilayered composite structures using measured permittivity and permeability spectra showed good microwave absorptive properties. For example, the 4-layered composite structures based on GNP/Co3O4/epoxy layers showed a more pronounced reflection loss | RL_min| ≈ 36 dB (sample thickness is 2.5–2.7 mm) and effective bandwidth Δ f_10dB≈24 GHz compared with single layers. Much better microwave absorption properties of the multi-layered structures compared with the single composite layer can be ascribed to the improved impedance matching with free space and the addition of interior interfaces.

The paper presents the results of investigation of multi-component epoxy composites containing silica gel globules coated with Fe oxide particles (SiO2-Fe oxide) and multi-wall carbon nanotubes (CNTs). The structure and phase composition of (SiO2-Fe oxide) globules were examined by XRD analysis, scanning electron microscopy, FTIR and Raman spectroscopy. It was found that the combination of SiO2 particles, (SiO2-Fe oxide) particles and conductive carbon nanotubes in epoxy composites leads to a sufficient increase in electrical conductivity compared to two-phase CNT/epoxy CM. For all samples of SiO2/CNT- and 22 wt.%(SiO2-Fe oxide)/2%CNT/epoxy CMs the negative temperature coefficient of electrical resistance (TCR) is observed. The coating of SiO2 globules with Fe oxides slightly influences the shielding properties. The addition of 2 wt.% CNT along with (SiO2-Fe oxide) filler into epoxy resin results in an increase of electromagnetic interference (EMI) shielding efficiency $$SE_{T}$$ up to 8–12 dB in the frequency range 26–54 GHz with a shield thickness of ~ 2 mm. The sufficient increase of $$SE_{T}$$ with the frequency indicates the prevailing part of EMI shielding due to absorption compared with reflection, $${{SE_{A} } \mathord{\left/ {\vphantom {{SE_{A} } {SE_{T} }}} \right. \kern-0pt} {SE_{T} }}$$ ratio reaches the values of 0.78–0.87 in the frequency range 36–54 GHz.

This work presents a new approach to enhance EMI shielding efficiency of nanocomposites of dielectric polymers, multiwalled carbon nanotubes (MWCNTs) and intrinsically conducting polymers for account of using core-shell morphology for conducting components. To realize this approach new ternary nanocomposites of poly(vinylidene fluoride) (PVDF), MWCNTs and poly(3-methylthiophene) doped by Cl- anions (P3MT) were prepared through synthesis of thermally stable core/shell nanocomposites PVDF/P3MT and MWCNT/P3MT. These binary nanocomposites were mixed with pure MWCNTs or PVDF followed by compression molding to prepare the ternary nanocomposites of different morphology to discriminate their EMI shielding properties in a wide frequency range (1-67 GHz). Values of the tangent of dielectric loss angle, the efficiency of transmission, reflection and absorption of microwave radiation, and shielding efficiency (SE) of the specified materials were found from analysis of spectral dependences of their complex dielectric constants. It was shown that while the melt mixing of the binary PVDF/P3MT nanocomposite with MWCNTs both in a pure state and in the binary nanocomposite (MWCNT/P3MT) expectedly strongly enhances SE of the former, this effect is non-linear and depends on presence/absence of the P3MT shell on the MWCNT core. The ternary nanocomposite PVDF/P3MT/MWCNT made of the binary polymer-polymer nanocomposite PVDF/P3MT and pure MWCNTs showed highest SE values at the frequencies above 4.5 GHz up to 68.4 dB at 67 GHz in the case of the 1 mm thickness sample. However, below 4.5 GHz the SE was higher in the case of the ternary nanocomposites containing core/shell MWCNT/P3MT nanocomposite instead of pure MWCNT.

Nowadays, people are constantly under the influence of electromagnetic radiation, which can cause health deterioration. The creation of ceramic materials that protect biological and technical objects from the negative effects of electromagnetic radiation is relevant for Ukraine and the world. The purpose of the study is to create composite ceramics with the addition of graphite and conduct experimental studies of the electrophysical properties of such material samples in the frequency range of 26–37.5 GHz. The results of experimental studies of the developed ceramics based on facing tiles with an electrically conductive additive of 10, 20, and 30 % wt. of graphite. To determine the parameters of the interaction of electromagnetic radiation with the samples, the modernized standard equipment – P2-65 microwave standing wave coefficient and attenuation meter, was used. The phase composition of the material was determined using the method of X-ray phase analysis using a DRON-3M diffractometer with CuKα radiation with a nickel filter. The developed composite ceramic materials meet the basic requirements for the operation of similar materials and can be used to weaken the high-frequency electromagnetic field inside premises located in the areas of radio radiation action, and for environmental purposes to reduce the intensity of the electromagnetic field outside the premises where sources of radio radiation are present. Thus, the developed composite ceramics have characteristics that allow them to be used in construction and in electronic devices for the purpose of effective shielding of harmful radio radiation, and the developed ceramics, according to the classification, can be classified as radio-absorbing.

The electrodynamic properties of new composite materials, produced by free sintering based on AlN with the addition of 1–5 wt

A new way to tune microwave radiation with phase transition hybrid organic–inorganic perovskites was developed.

In this study, the microwave absorbing properties of epoxy composites filled with micro-sized MoS2 and carbon nanotubes (CNT)/MoS2 were investigated in the frequency range of 1–67 GHz. Sample characterization was performed using electron microscopy and Raman spectroscopy methods. Direct current (DC) conductivity, complex permittivity, and shielding properties of composite materials with 50 wt. % of MoS2 and 1.5–2 wt. %CNT/50 wt.%MoS2 were measured. The permittivity of 50 wt. % MoS2/epoxy composite was found to be equal to 7.3, decreasing monotonically down to 4.5 at 67 GHz, while the imaginary part is equal to 1 and does not change. The addition of 2 wt. % of CNTs increases the real part of permittivity εr′ up to 30 at 1 GHz (13 at 67 GHz) and also leads to a large increase of the imaginary part of permittivity, with the most pronounced relaxation peak εr′′=10 at 10 GHz. Such an increase of dielectric loss correlates with the increase of DC conductivity up to 3.2 × 10−5 S/m as compared to the two-phase composite 50 wt. %MoS2/epoxy (σdc = 1.7 × 10−9 S/m). It was shown that 50 wt. %MoS2/epoxy composite exhibited an effective microwave absorption bandwidth of 9.9 GHz at the sample thickness of 2.0 mm with reflection loss minimum of -20.0 dB at 51.5 GHz. 2 wt. %CNT/50 wt. %MoS2/epoxy composite with a thickness of 0.9 mm showed a reflection loss minimum of −38 dB at 20.2 GHz with the absorption bandwidth of 3.68 GHz. The influence of sample thickness on position, width, and depth of EMR absorption maximums for the composites filled with MoS2 and mixed filler CNT/MoS2 was also determined.

Reconfigurable radio-frequency components are in high demand for modern communication systems as they can be involved in multiband and multistandard electronic devices. The key part of such components is an active switching element. This work offers a way to obtain an efficient microwave switch using vanadium dioxide-poly (methyl methacrylate) composite. Differential scanning calorimetry, SQUID magnetometery, and impedance spectroscopy measurements were used to characterize the phase transition in the proposed composite. Temperature induced metal-insulator transition occurs at technologically attractive 341 K. The transition leads to a change of microwave transmission trough VO2 -PMMA composite from -4.9 dB for low-temperature monoclinic form to -5.8 dB for high-temperature rutile form. This provides an ability to tune the material's transparency in the microwave range, while the shaping polymer matrix provides the proper mechanical processability of the switching element.

The results of experimental studies of the developed veneering ceramics with electrically conductive SiC admixtures of 10 and 20 wt.% are presented.The main electrodynamic characteristics of ceramics such as microwave permittivity, dielectric loss tangent, attenuation and reflection coefficients were measured by PNA N5227A Keysight Technologies vector network analyzer in the frequency range of 1-67 GHz.The instrument software automates measurements of complex permittivity and permeability of materials.The results can be presented in S-parameter format, ', ", tan, ' and ".The effective permittivity of the composite depends on the filling factor of the composite matrix with particles (the ratio of the total volume of particles to the entire volume of the medium).In the case of low concentrations of nanoparticles, the approach based on the Maxwell-Garnett effective medium theory provides fairly accurate results.The characteristics of the developed ceramics are shown, which allow its use in construction engineering and electronic devices in order to effectively shield harmful electromagnetic radiation.According to the classification, ceramics themselves can be attributed to radio-absorbing ceramics.

This paper is concerned with investigation of the structure and microwave properties of epoxy resin composites with graphite nanoplatelets (GNPs) decorated by FeNi nanoparticles prepared by the salt impregnation. It was confirmed by SEM and XRD that the method gives nanopowder where the metal componentFe20Ni80 is in the form of nanoparticles (20-40 nm in diameter) which are distributed over the surface and edges of the GNPs. The graphite phase in the investigated nanopowder is predominant, and Fe20Ni80 component mainly contains fcc FeNi3. Measurements of magnetic properties confirmed that Fe20Ni80 are small, randomly oriented assembly of spherical (or close to spherical) particles on the GNPs surface. The saturation magnetization of GNP-Fe20Ni80 particles is 25 emu/g and it weakly depends on temperature. Electrical resistivity measurements have shown that decoration of GNPs leads to essential increase of conductivities well as improvements EMR absorption properties in high frequency range (26-60 GHz) in (GNP-Fe20Ni80)/with in compression GNP/epoxy under the same volume content of 1.45 vol. % (GNP-Fe20Ni80)/L285 composites demonstrated superior broadband absorption properties with microwave absorption efficiency higher than 97 % in the whole investigated frequency region.The effective absorption bandwidths are as high as 12.2 GHz were observed at the frequency range 41.9 and 53.2 GHz and 13.3 GHz at the frequency range 51.1 GHz-64.4 for this composite. It is assumed that decoration of GNPs surface by nanoscale Fe20Ni80 particles leads to a formation of the multiple dielectric and magnetic loss mechanisms, such as interfacial polarization, dipole polarization, space-charge polarization, eddy current loss, Debye dipolar relaxation, natural resonance and exchange resonance, which improve the microwave absorption properties of the investigated composites.

Conductive polymer composites are widely used for electromagnetic radiation protection. Several strategies can be employed for creating shield materials with enhanced efficiency: the use of a hybrid filler that contains nanoparticles of different types, specific structural design, and methods for decreasing the percolation threshold. We present the study of segregated polymer composites (SPCs) with ultrahigh molecular weight polyethylene (UHMWPE) matrix and hybrid fillers of NiFe-decorated graphite nanoparticles (GNPs). The microstructure, electrical percolation behavior, and electromagnetic shielding efficiency of the developed SPCs as a function of conductive filler content are determined. The combination of the advantages of the segregated structure with a synergistic effect of a hybrid filler in (GNP-NiFe)/UHMWPE allows decreasing the percolation threshold to 0.45 vol. %. The enhanced shielding efficiency of 37 dB in the frequency range of 26–37.5 GHz is achieved at the filler content of 3.4 vol. % in 1 mm thick composite samples. The dominant shielding characteristic of absorption renders hybrid composites with a segregated structure promising materials.

The electrical and microwave shielding properties of epoxy-based composites (CMs) filled with metal-nanocarbon Ni-C and Co-C core-shell particles have been studied for the broad frequency range (16-67) GHz. The decrease of electrical resistivity of CMs with the increase of Ni content in core-shell particles and temper-ature in the range of 77-293 K was found. The observed sufficient increase of microwave shielding efficiency (32-40 dB at sample thickness of 2.2 mm) in Ka- and V-band for CMs with high Ni content correlates with increased electrical conductivity. A high microwave absorption index (0.999 at f = 65 GHz) of (Me-C)/epoxy CMs can be attributed to the enhanced dielectric and magnetic losses. The modeling of microwave absorption capability of 60 wt% (Nix-C)/epoxy CMs showed that the microwave absorption peaks can be observed only for the narrow frequency range, (18-25) GHz at a sample thickness of 0.6-1.0 mm with the effective bandwidth (2.3-4.8) GHz.

The microwave absorbing and shielding properties of epoxy composites with multiphase filler were studied in a wide frequency range of electromagnetic radiation (EMR) (1–67) GHz. The multiphase filler consists of carbon nanotubes (CNTs) and dielectric (titanium dioxide TiO2) or ferromagnetic (carbonyl iron Fe) particles. The content of TiO2 or Fe was fixed and equal to 35 wt% and 30 wt%, respectively, while the CNT content was varied from 1 to 5 wt%. It was found that EMR shielding efficiency SET is sufficiently increased with carbon nanotubes content and thickness of the composite especially for epoxy CMs filled with carbon nanotubes and carbonyl iron. The measured complex permittivity data (and permeability for CNT/Fe/epoxy CMs) were used for simulation of the reflection loss RL for studied composites. The simulated data have shown that more pronounced reflection loss RLmin\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left| {\text{RL}_{\min } } \right|$$\end{document} = (30–44) dB is observed for 2–3 wt% CNT content in ternary epoxy CMs (sample thickness is 0.5–0.7 mm). For the higher CNT content (4–5 wt%), especially for CNT/Fe/epoxy CMs, the reflection loss RLmin\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left| {\text{RL}_{\min } } \right|$$\end{document} was decreased, i.e., the large contribution in EMR attenuation is provided due to EMR reflection on the first air-composite boundary. It was shown that effective bandwidth of RLmin\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left| {\text{RL}_{\min } } \right|$$\end{document} at level 10 dB can achieve (8–12) GHz and its position and RLmin\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left| {\text{RL}_{\min } } \right|$$\end{document} value can be manipulated by varying the composition and thickness of the composite sample. The absorbing performance of 4-layered composite structures was modeled using electromagnetic parameters of single-layer absorbers based on the three-phase composites and optimal layers composition and thickness were found.

Titanium oxide (TiO2) particles, used with conductive particles as fillers for composite materials (CMs) have recently been shown to produce high dielectric constant with low dielectric loss at frequencies up to 10 MHz. This work describes the microwave properties of L285 epoxy, filled with 1-5 wt. % of carbon nanotubes (CNTs) and 35 wt. % of TiO2 powder. A correlating dependence of the real and imaginary parts of permittivity versus CNT content has been observed, suggesting there are multiple factors taking part in formation of the permittivity with interfacial and dipole polarizations of filler clusters taking the main part. These factors can be exploited by varying the filler contents and particle size to obtain CMs with high permittivity and low dielectric loss as well as superior microwave absorbers.

The microwave properties of epoxy composites filled with 30 wt.% of BaFe12–xGaxO19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36–55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12–xGaxO19/epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga3+ concentration in the BaFe12–xGaxO19 filler and amplitude–frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was determined. Higher values of the resonance frequency fres (51.8–52.4 GHz) and weaker dependence of fres on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12–xGaxO19 (fres = 49.6–50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0–5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite.

Polyethylene (PE) based composites with segregated carbon nanotubes (CNTs) network was successfully prepared by hot compressing of a mechanical mixture of PE and CNT powders. Through comparison with a composite comprising randomly distributed carbon nanotubes of the same concentration, we prove that namely the segregated CNT network is responsible for the excellent electrical properties, i.e., 10−1 S/m at 0.5–1% and 10 S/m at 6–12% of CNT. The investigation of the complex impedance in the frequency range 1 kHz–2 MHz shows that the sign of real part of the dielectric permittivity ε r ′ changes from positive to negative in electrically percolated composites indicating metal-like behavior of CNT segregated network. The obtained negative permittivity and AC conductivity behavior versus frequency for high CNT content (3–12%) are described by the Drude model. At the same time, in contrast to reflective metals, high electromagnetic shielding efficiency of fabricated PE composites in the frequency range 40–60 GHz, i.e., close to 100% at 1 mm thick sample, was due to absorption coursed by multiple reflection on every PE-CNT segregated network interface followed by electromagnetic radiation absorbed in each isolated PE granule surrounded by conductive CNT shells.