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The results of studies of high-frequency electromagnetic properties of alkaline borosilicate glasses modified with lanthanum, titanium, and zirconium oxides concerning their structure are presented. The values of the spectral reflection and transmission coefficients are experimentally measured in the frequency range 12–18 GHz. The article presents typical spectra of the complex dielectric constant of the studied glass samples inthe range of 20 Hz–1 MHz, according to which both the real and imaginary parts decrease with increasing frequency, while the imaginary part decreases much faster. It is shown that the studied glasses can be used as a vacuum-tight dielectric base with low losses in the development of high-frequency devices operating in the microwave range. The influence of the chemical composition of the experimental glasses on the value of their dielectric permittivity in the frequency ranges of 20 Hz –1 MHz and 12–18 GHzis established. The structure of the studied glasses was studied by Raman spectroscopy. The influence of lanthanum, titanium, and zirconium oxides on the degree of polymerization of the structural framework was revealed. The presence of La2O3in sodium borosilicate glass causes a decrease in the polymeriza-tion of the borosilicon-oxygen framework of glass in the entire range of introduced concentrations since La2O3is in the octahedral position and acts as a modifier in the glass structure. The intro-ductionof zirconium oxide into the composition of sodium borosilicate glass has a more significant effect on the depolymerization of the glass structure than the addition of lanthanum oxide. The most serious structural changes are observed when TiO2is introduced into the compositions of such glasses, since it acts as a glass–forming agent, forming structural motifs [TiO4], which will combine with the silicon–oxygen component, forming Si–O–Ti type bridges.

The patterning of arrays of aligned multi-walled carbon nanotubes (MWCNTs) allows creating metastructures for terahertz (THz) applications. Here, the strips and columns from MWCNTs vertically grown on silicon substrates are prepared using CO2 laser treatment. The tops of the patterned arrays are flat when the laser power is between 15 and 22 W, and craters appear there with increasing power. Laser treatment does not destroy the alignment of MWCNTs while removing their poorly ordered external layers. The products of oxidative destruction of these layers deposit on the surfaces of newly produced arrays. The oxygen groups resulting from the CO2 laser treatment improve the wettability of nanotube arrays with an epoxy resin. We show that the patterned MWCNT arrays absorb the THz radiation more strongly than the as-synthesized arrays. Moreover, the pattern influences the frequency behavior of the absorbance.

The electromagnetic properties of structures with spatially periodic distributed graded refractive index were investigated in the terahertz frequency range. The band structure and electromagnetic response of material with harmonically distributed refractive index were calculated and analyzed. The analytical expressions for frequencies of the first and second bandgap are derived. 3D printed gyroid based architectures were proven to be harmonically graded refractive index structures with designed bandgaps in THz frequency ranges. The transmission coefficient of thermoplastic polyurethane-based samples were experimentally measured in the frequency range 100–500 GHz and compared with theoretical results. Due to losses in the real world produced samples, the predicted response is significantly dumped in the terahertz range and only traces of band gaps are experimentally observed. This funding paves the way toward a new generation of 3D printed THz components for gradient-index optics applications.

Here a simple and reproducible method for obtaining terahertz metasurfaces formed from multiwall carbon nanotubes (MWCNTs) is presented. The metasurfaces were obtained from a vertically aligned array of MWCNTs using a laser engraving technique followed by polymer covering. The structures under study demonstrate frequency-selective re ection in terahertz range following the Huygens{Fresnel formalism. For a normal incidence of the electromagnetic wave, the model for numerical calculation of backscattering from the metasurfaces was proposed. Lightweight and compact MWCNT-based metasurfaces are capable to replace conventional pyramidal absorbers and proved to serve as a versatile platform for scalable cost-ecient production of ultra-light electromagnetic components for THz applications.

Polymer composites containing nanocarbon fillers are under intensive investigation worldwide due to their remarkable electromagnetic properties distinguished not only by components as such, but the distribution and interaction of the fillers inside the polymer matrix. The theory herein reveals that a particular effect connected with the homogeneity of a composite manifests itself in the terahertz range. Transmission time-domain terahertz spectroscopy was applied to the investigation of nanocomposites obtained by co-extrusion of PLA polymer with additions of graphene nanoplatelets and multi-walled carbon nanotubes. The THz peak of permittivity&rsquo, s imaginary part predicted by the applied model was experimentally shown for GNP-containing composites both below and above the percolation threshold. The physical nature of the peak was explained by the impact on filler particles excluded from the percolation network due to the peculiarities of filler distribution. Terahertz spectroscopy as a versatile instrument of filler distribution diagnostics is discussed.

A complex analysis of the dependence of the absorption coefficient of polymer composites with nonmagnetic carbon inclusions on the real and imaginary parts of the complex permittivity, as well as on the material thickness is performed in frequency range 26–37 GHz. The composites containing 0.2 wt % of carbon fibers have been obtained. It has been experimentally found that the corrugation of the composite surface substantially increases the absorbability (from 63 to 92% at a frequency of 30 GHz and a thickness of 4.50 mm) upon a decrease in the sample mass (by 28%). A method has been proposed for calculating the absorptance of corrugated composites in the microwave range.

Чтобы быть полностью применимым, композитный материал должен быть недорогим и подходить для традиционных методов изготовления, например 3D-печати. В данной статье электромагнитные свойства композитов на основе PLA с графеновыми наночастицами и многостенными углеродными нанотрубками были исследованы в микроволновом диапазоне частот.

This work was supported in part by FP7-PEOPLE-2013-IRSES-610875 NAmiceMC, FP7 Twinning Grant Inconet EaP 004. P. Kuzhir is thankful for support by Tomsk State University Competitiveness Improvement Program. Lab-STICC is UMR CNRS 6285.

Elastomer-based porous structures realized by selective laser sintering (SLS) are emerging as a new class of attractive multifunctional materials. Herein, a thermoplastic polyurethane (TPU) powder for SLS was modified by 1 wt.% multi-walled carbon nanotube (MWCNTs) or a mixture of MWCNTs and graphene (GE) nanoparticles (70/30 wt/wt) in order to investigate on both the synergistic effect provided by the two conductive nanostructured carbonaceous fillers and the correlation between formulation, morphology, and final properties of SLS printed porous structures. In detail, porous structures with a porosity ranging from 20% to 60% were designed using Diamond (D) and Gyroid (G) unit cells. Results showed that the carbonaceous fillers improve the thermal stability of the elastomeric matrix. Furthermore, the TPU/1 wt.% MWCNTs-GE-based porous structures exhibit excellent electrical conductivity and mechanical strength. In particular, all porous structures exhibit a robust negative piezoresistive behavior, as demonstrated from the gauge factor (GF) values that reach values of about &minus, 13 at 8% strain. Furthermore, the G20 porous structures (20% of porosity) exhibit microwave absorption coefficients ranging from 0.70 to 0.91 in the 12&ndash, 18 GHz region and close to 1 at THz frequencies (300 GHz&ndash, 1 THz). Results show that the simultaneous presence of MWCNTs and GE brings a significant enhancement of specific functional properties of the porous structures, which are proposed as potential actuators with relevant electro-magnetic interference (EMI) shielding properties.

Phenol formaldehyde resin (PFR) based composites with multiwalled carbon nanotube (MWCNT) additives (2 and 5 wt.%) were prepared and their electromagnetic (EM) properties were investigated in Ka-band frequency range (26–37 GHz). It was demonstrated that the combination of such materials in a double-layered structure allows achievement of the significant attenuation of EM radiation. The electromagnetic response of considered double-layered system was modeled by solving the electric field integral equation, utilizing the Green's function technique. Absorption up to 96% in the 26–37 GHz frequency band was both predicted and experimentally observed.

International audience; The electromagnetic response of a heterostructure based on a monolayer of hollow glassy carbon spheres packed in 2D was experimentally surveyed with respect to its response to microwaves, namely, the Ka-band (26-37GHz) frequency range. Such an ordered monolayer of spheres mimics the well-known ``moth-eye''-like coating structures, which are widely used for designing anti-reflective surfaces, and was modelled with the long-wave approximation. Based on the experimental and modelling results, we demonstrate that carbon hollow spheres may be used for building an extremely lightweight, almost perfectly absorbing, coating for Ka-band applications.

3D carbon periodic architectures based on Gibson-Ashby cells are reported and investigated in the microwave (Ka-band: 26–37 GHz) range. Compared to more classical reticulated or cellular carbon foams, these periodic 3D structures are much more absorptive, and display resonant behaviour in microwave ranges depending on their cell size.

The microwave-absorbing properties of a heterostructure consisting of an ordered monolayer of porous glassy carbon spheres were experimentally and theoretically investigated in the Ka-band (26–37 GHz) frequency range. The electromagnetic response of such a “moth-eye”-like all-carbon metasurface at a normal incidence angle was modelled on the basis of long-wave approximation. Modelling parameters in the Ka-band were used to estimate and predict the absorption properties of monolayers in free space in the range 1–40 GHz. Experimental and theoretical results demonstrate that a metasurface based on porous glassy carbon spheres is an inert, lightweight, compact, and perfectly absorbing material for designing new effective microwave absorbers in various practically used frequency ranges.