This study introduces a periodic structure composed of silicone foam reinforced with carbon fibers, designed as an electromagnetic absorber for microwave frequencies. This absorber, assimilated to an organic metamaterial, is fabricated using two simple methods. Firstly, the "particle-template" technique employs a sacrificial filler to create a composite with a low density of 0.33 g.cm⁻. Secondly, simple periodic structuring is achieved manually using scissors to form the metamaterial. The resulting absorber prototype, with a total thickness of 16 mm, demonstrates broadband absorption performance, maintaining a reflection coefficient (S11) below −10 dB from 4 to 18 GHz for both normal (0°) and oblique (30°) incidences of electromagnetic waves. These results validate the potential of this structured organic absorber.

This study reports a simple fabrication technique for creating a flexible, organic, and microwave -absorbing material using carbon fiber -loaded silicone foam. The "particle -template" elaboration method, using sugar crystals as sacrificial particles, is conducted. The material ' s density is adjusted by varying the sugar crystal concentration while ensuring effective dispersion of carbon fibers in the silicone foam matrix. The dielectric characterization of a composite with a density of 0.33 g.cm(-3) and loaded with 2 wt.% of 12 mm carbon fibers results in a permittivity ranging from 7 to 1.1 and a dielectric loss ranging from 1.9 to 0.7 across the frequency range of 2-18 GHz. These properties are used in a parametric study to optimize the overall dimensions of a structured absorber to achieve wideband absorption performance. The resulting prototype, with a total thickness of 16 mm, demonstrates promising performance by exhibiting broadband absorption (4-18 GHz), as predicted by simulation.

This paper presents a reconfigurable miniature monopole antenna partially loaded with a Tunable Magneto-Dielectric Material (T-MDM) in the VHF band. A parametric study optimised the amount of the T-MDM and its effect on miniaturization. The antenna achieves a 40% miniaturization rate with just 17% of its height loaded by a 2 mm thick MDM, and demonstrates 15% frequency agility in the VHF band.

This study presents the performance of a magneto-dielectric material (MDM) specially developed to enable the tunability of antenna devices operating in the VHF band. The magnetic susceptibility variation of the MDM material is controlled by a current flowing through the sample which creates a DC magnetic field inside the sample with the same symmetry as the magnetic domains. By changing the magnetization state of the MDM with a low DC magnetic field of 740 A/m, a tunability of 40% can be observed. The MDM tunability at VHF frequencies is also verified by microwave measurements for different magnetization states.

This work deals with the use of periodic structures, composed of silicone foam loaded with long carbon fibers (12 mm), for the elaboration of microwave absorber. This absorber, which can be considered as an organic metamaterial absorber, is made using two simple manufacturing concepts: a very simple elaboration method of the flexible silicone foam composite and a simple periodic structuring of the absorber. The proposed absorber presents low density (0.33 g.cm -3 ) and broadband absorption performance (reflectivity below −10 dB) between 4 and 18 GHz, for normal (0°) and oblique (30°) incidences of electromagnetic waves, with a thickness of only 16 mm.

In this paper, we propose a new and original absorbing material based on silicone foam loaded with long carbon fibers (12 mm). This flexible composite is structured in a periodic way, like "metamaterials". The originality of the proposed absorbing material resides, on the one hand, in the association of two simple fabrication concepts (a simple production of the silicone foam and a simple periodic structuring of this foam) and, on the other hand, in the use of dielectric lossy material to make periodic broadband absorbing structures. The idea here is to replace standard metamaterial absorbers, based on structured metallic film (often copper) deposited on a dielectric substrate, by organic metamaterial. Thus, a flexible absorber of 16 mm thickness, with the shape of a "chessboard" and having a broadband absorption bandwidth with the reflectivity below −10 dB in the frequency range of 4-18 GHz is proposed and implemented. Moreover, we also obtain a good absorption response by varying the incident angle up to 30°.

Magneto-Dielectric Material is used for the design of an electrically small monopole antenna at the VHF band. By loading partially with MDM along with metallic parasitic element and impedance matching of non-resonant (Small) Monopole, the proposed antenna achieves a miniaturization rate factor of the height greater than 70%, a satisfactory gain for this size and 10% of impedance bandwidth are obtained.

In this paper we address, both experimentally and theoretically, the very grazing scattering of He atoms off KCl(001) with incidence along the (100) channel. Our theoretical model combines a semiquantum description of the scattering dynamics and a high-precision interaction potential. By means of a thorough analysis of the quantum phase for in-plane scattering and rainbow trajectories, we are able to connect the presence of the physisorption well with the significant enhancements of the corrugation and rainbow angle, relative to the hard corrugated wall predictions. We trace this connection to dynamical effects on the incident and scattered beams due to their traversing of the physisorption well. Finally, we show that the inclusion of van der Waals interactions in the potential improves the theoretical accord with experiments for both the corrugation and the rainbow angle.

A simple methodology to fabricate ultra-porous and lightweight epoxy foam composites loaded with carbon fibers is presented. These materials are proposed for microwave absorbing application. The elaborated composite density can be controlled via proper proportioning of carbon fiber/solvent/surfactant/epoxy components constituting the absorber composites. The influence of the weight percentage of these different components, on the composite structure, is studied. The density of the composites can be reduced to 0.05g.cm(-3) while the density of the neat epoxy foam is about 0.12g.cm(-3). Dielectric characterization of composites elaborated with low weight percentages of carbon fibers (from 0.0125 wt.% to 0.075 wt.%) is conducted using free space method. The simulation of a multilayer absorber is conducted and predicts a promising absorption performance (reflection coefficient <-10 dB) for the wide studied frequency band; this result was confirmed by the measurement of a multilayer absorber prototype. Finally, these performances are compared to commercial absorber materials having same dimensions.

In this paper, we propose a multi-resonance MM design which will be used for the realization of an ultra-wideband hybrid microwave absorber. The metamaterial absorber consists of a symmetrical structure, called V-shape, with different scales of coupled resonators and the hybrid absorber is carried out by the association of this metamaterial to a lossy dielectric layer, made of epoxy foam composite loaded with low weight percentage (0.075 wt.%) of 12 mm length carbon fibers. The simulation and measurement results of the hybrid material of 16.2 mm thickness show an absorption bandwidth between 2.6 GHz and 18 GHz for both normal and oblique incidences.

This article presents a strategy for designing optimal microwave planar multilayer absorbers based on epoxy foam composites loaded with carbon fibers of 12 mm length. Firstly, the impedance gradient principle (gradual loaded composites) was adopted to realize two multilayer absorbers, of 125 mm thickness, using slightly loaded composites (0.0125 wt% < CFs < 0.075 wt%) and relative highly loaded composites (0 wt% < CFs < 0.4 wt%), respectively. The simulation of these absorbers shows that composites with very low CF rates are sufficient to achieve a very close absorption performance and bandwidth to that of the commercial absorber, in the entire studied frequency range (0.75–18 GHz). Secondly, the genetic algorithm optimizer is used to achieve a multilayer absorber that presents the best compromise between absorption performance and thickness. Different CF-loaded composites and layer thicknesses are therefore tested; a multilayer absorber with a total thickness of 98 mm is then proposed. This absorber shows a better reflection coefficient and a better compromise (absorption/total thickness) than that of the commercial absorber, while presenting a reduction of 22% in thickness. The presented simulation and measurement results confirm that a judicious choice of the composition and the thickness of each layer is necessary to optimize the absorption performance of a planar multilayer absorber. This paper also shows the advantage of using an optimizer to improve the absorption performance while reducing the total thickness of the absorber. Graphical abstract

This work presents lightweight epoxy foams loaded with very low weight percentages (≤0.5 wt.%) of carbon fibers (CFs) with different lengths (3 mm, 6 mm, and 12 mm) as broadband microwave absorbing materials for anechoic chamber application. The effect of CF length on microwave absorption, especially on the absorption frequency band, is investigated for frequencies between 1 and 15 GHz. For the elaboration of composites, three different methods—spatula, shear mixing, and ultrasounds—are used for the dispersion of CFs. The observation of these CFs, after the dispersion step, shows a high fiber breakage rate when shear mixing is used, unlike when spatula or ultrasounds methods are used. On the other hand, the characterization of the elaborated composites highlights a correlation between the mixing methods, hence the fiber brakeage, and the measured reflection coefficient (reflection loss) of the composites. As a result, the minimum value of the reflection coefficient is shifted toward the high frequencies when the fiber breakage is observed, suggesting that short CFs absorb at high frequencies while long CFs absorb at low frequencies. Dielectric properties, extracted from the measurement in free space, of composites elaborated with different fiber lengths (3 mm, 6 mm, and 12 mm) confirm that short CFs (3 mm) show maximum losses at high frequencies (around 15 GHz) while long CFs (12 mm) show maximum dielectric losses at low frequencies (below 4 GHz). However, no significant variation is observed on the real part of the relative permittivity, as a function of fiber length, for these porous composites loaded with very low CF rates. A hybrid composite, with a mix of different CF lengths, is prepared and characterized. The simulation of the absorption performance of a pyramidal absorber, based on this hybrid composite, is compared to the one of pyramidal absorber based on composites loaded with a single length of carbon fibers. The pyramidal absorber-based hybrid composite predicts the best absorption performance, especially at the low frequency band. The simulated reflection coefficient of this absorber is less than −12 dB in all the studied frequency range, and less than −40 dB for frequencies higher than 3 GHz. This result confirms the interest of using a mix of carbon fiber lengths to achieve a broadband microwave absorber.

We present theoretical and experimental evidence of an anomalous surface corrugation behavior in He-KCl(001) for incidence along ⟨110⟩. When the He normal energy decreases below 100 meV, i.e., He-surface distances Z>2  Å, the corrugation unexpectedly increases up to an impressive ≳85%. This is not due to van der Waals interactions but to the combination of soft potential effects and the evolution of He-cation and He-anion interactions with Z. This feature, not previously analyzed on alkali-halide surfaces, may favor the alignment properties of weakly interacting overlayers.

In this paper, we propose a novel design of an ultra-wideband hybrid microwave absorber operating in the frequency range between 2 GHz and 18 GHz. This proposed hybrid absorber is composed of two different layers that integrate a multiband metamaterial absorber and a lossy dielectric layer. The metamaterial absorber consists of a periodic pattern that is composed of an arrangement of different scales of coupled resonators and a metallic ground plane, and the dielectric layer is made of epoxy foam composite loaded with low weight percentage (0.075 wt.%) of 12 mm length carbon fibers. The numerical results show a largely expanded absorption bandwidth that ranges from 2.6 GHz to 18 GHz with incident angles between 0° and 45° and for both transverse electric and transverse magnetic waves. The measurements confirm that absorption of this hybrid based metamaterial absorber exceeds 90% within the above-mentioned frequency range and it may reach an absorption rate of 99% for certain frequency ranges. The proposed idea offers a further step in developing new electromagnetic absorbers, which will impact a broad range of applications.