This article presents a strategy for designing optimal microwave planar multilayer absorbers base... more 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.
2021 XXXIVth General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2021
In this paper, we propose a multi-resonance MM design which will be used for the realization of a... more 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.
In this work we address, both experimentally and theoretically, the very grazing scattering of He... more In this work 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 vdW interactions in the potential improves the theoretical accord with experiments for both the corrugation and the rainbow angle.
We present theoretical and experimental evidence of an anomalous surface corrugation behavior in ... more 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 > 2Å, 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 alignement properties of weakly-interacting overlayers.
This article presents a strategy for designing optimal microwave planar multilayer absorbers base... more 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.
This study presents the performance of a magneto-dielectric material (MDM) specially developed to... more 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. A current flowing through the sample, which creates a DC magnetic field inside the sample with the same symmetry as the magnetic domains, controls the magnetic susceptibility variation of the MDM. By changing the magnetization state of the MDM with a low DC magnetic field of 740 A.m-1 , a tunability of 40% can be observed. The MDM tunability at VHF frequencies is also highlighted by microwave measurements for different magnetization states.
Abstract A simple methodology to fabricate ultra-porous and lightweight epoxy foam composites loa... more Abstract 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
This work presents lightweight epoxy foams loaded with very low weight percentages (≤0.5 wt.%) of... more 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...
In this paper, we propose a novel design of an ultra-wideband hybrid microwave absorber operating... more 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 frequen...
In this paper, we propose a novel design of an ultra-wideband hybrid microwave absorber operating... more 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 frequen...
This article presents a strategy for designing optimal microwave planar multilayer absorbers base... more 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.
2021 XXXIVth General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2021
In this paper, we propose a multi-resonance MM design which will be used for the realization of a... more 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.
In this work we address, both experimentally and theoretically, the very grazing scattering of He... more In this work 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 vdW interactions in the potential improves the theoretical accord with experiments for both the corrugation and the rainbow angle.
We present theoretical and experimental evidence of an anomalous surface corrugation behavior in ... more 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 > 2Å, 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 alignement properties of weakly-interacting overlayers.
This article presents a strategy for designing optimal microwave planar multilayer absorbers base... more 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.
This study presents the performance of a magneto-dielectric material (MDM) specially developed to... more 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. A current flowing through the sample, which creates a DC magnetic field inside the sample with the same symmetry as the magnetic domains, controls the magnetic susceptibility variation of the MDM. By changing the magnetization state of the MDM with a low DC magnetic field of 740 A.m-1 , a tunability of 40% can be observed. The MDM tunability at VHF frequencies is also highlighted by microwave measurements for different magnetization states.
Abstract A simple methodology to fabricate ultra-porous and lightweight epoxy foam composites loa... more Abstract 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
This work presents lightweight epoxy foams loaded with very low weight percentages (≤0.5 wt.%) of... more 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...
In this paper, we propose a novel design of an ultra-wideband hybrid microwave absorber operating... more 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 frequen...
In this paper, we propose a novel design of an ultra-wideband hybrid microwave absorber operating... more 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 frequen...
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