scholarly journals Research on Percolation Threshold of Broadband Electromagnetic Wave Absorbing SiCN (MWCNTs) Composite Ceramics

2021 ◽  
Author(s):  
Shan Wang ◽  
Hongyu Gong ◽  
Desheng Qi ◽  
M. Zeeshan Ashfaq ◽  
Xigui Yue
Keyword(s):  
Electromagnetic Wave ◽  
Percolation Threshold ◽  
Reflection Loss ◽  
High Efficiency ◽  
Impedance Matching ◽  
Broad Band ◽  
Composite Ceramics ◽  
Absorption Mechanism ◽  
Absorption Performance ◽  
Addition Amount

Abstract A simple polymer derivation method was applied in this paper to prepare a series of SiCN (MWCNTs) composite ceramics by adjusting the mass ratio of multi-walled carbon nanotubes (MWCNTs). The percolation threshold of the corresponding MWCNTs addition amount when SiCN(MWCNTs) composite ceramics exhibit the optimal electromagnetic wave (EWM) absorption performance was studied, the effect of different addition amounts of MWCNTs on reflection loss (RL), effective absorption bandwidth (EAB), electromagnetic parameters, impedance matching parameters (Z) and attenuation coefficient (α) of composite ceramics was analyzed, and the EMW absorption mechanism of the corresponding composite ceramics when MWCNTs addition amount fix at percolation threshold was discussed. The results showed that composite ceramics exhibited the best EMW absorption performance when the addition amount of MWCNTs reached the percolation threshold (10wt%): the minimum reflection loss (RLmin) was -37.9 dB, and the EAB was 2.8 GHz at a thickness of 2.4 mm; its RLmin was -21.7 dB, and the EAB reached 4.7 GHz at a thickness of 1.7 mm. By changing the sample thickness from 1.0 mm to 5.0 mm, the EAB containing the C, X and Ku bands can be acquired. Therefore, it is expected to be a promising candidate for the new generation of EMW absorbers due to its light weight, high efficiency and broad band.

scholarly journals High-efficiency and ultra-thin electromagnetic wave absorption xAl2O3-(1-x)Sr0.85Gd0.15TiO3 ceramics in X-band

2020 ◽  
Author(s):  
Hui Xie ◽  
Chaoqun Yang ◽  
Yingying Zhou ◽  
Zhaowen Ren ◽  
Ping Liu
Keyword(s):  
Microwave Absorption ◽  
Reflection Loss ◽  
High Efficiency ◽  
Impedance Matching ◽  
Frequency Dispersion ◽  
Interfacial Polarization ◽  
Peak Frequency ◽  
Microwave Absorbing Materials ◽  
Absorption Performance ◽  
Microwave Absorption Performance

Abstract xAl2O3-(1-x)Sr0.85Gd0.15TiO3(x=0.2, 0.3, 0.4, 0.5) ceramics were fabricated by hot-press sintering. Their morphology, phase composition, conductivity, dielectric properties as well as microwave absorption performance were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), multifunction digital four-probe meter and vector network analysis, respectively. The microwave absorption of as-prepared xAl2O3-(1-x)Sr0.85Gd0.15TiO3 ceramics demonstrates excellent microwave absorbability. It is unexpectedly found that with a thickness of only 0.346 mm, xAl2O3-(1-x)Sr0.85Gd0.15TiO3 (x=0.2) ceramic exhibits an absorption bandwidth of 3.7 GHz (8.7-12.4 GHz), being consequential to reflection loss less than -10 dB (over 90% of microwave absorption). It is as well discovered that the minimum reflection loss and absorption peak frequency of xAl2O3-(1-x)Sr0.85Gd0.15TiO3 (x=0.3) with a thickness of 0.436 mm were -45.43 dB and 11.3 GHz, respectively. The prominent microwave absorption performance of the ceramic with such a thin thickness can be attributed to strong interfacial polarization, dielectric frequency dispersion, and good electromagnetic impedance matching. It indicates that the xAl2O3-(1-x)Sr0.85Gd0.15TiO3 ceramics with appropriate Al2O3 mass fraction and thickness showing good potential for effective microwave absorbing materials.

scholarly journals Tuning Dielectric Loss of SiO2@CNTs for Electromagnetic Wave Absorption

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2636
Author(s):  
Fenghui Cao ◽  
Jia Xu ◽  
Xinci Zhang ◽  
Bei Li ◽  
Xiao Zhang ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
High Performance ◽  
Low Cost ◽  
Impedance Matching ◽  
3D Structure ◽  
Carbon Matrix ◽  
Current Approach ◽  
Matrix Composites ◽  
Simple Method ◽  
Absorption Performance

We developed a simple method to fabricate SiO2-sphere-supported N-doped CNTs (NCNTs) for electromagnetic wave (EMW) absorption. EMW absorption was tuned by adsorption of the organic agent on the precursor of the catalysts. The experimental results show that the conductivity loss and polarization loss of the sample are improved. Meanwhile, the impedance matching characteristics can also be adjusted. When the matching thickness was only 1.5 mm, the optimal 3D structure shows excellent EMW absorption performance, which is better than most magnetic carbon matrix composites. Our current approach opens up an effective way to develop low-cost, high-performance EMW absorbers.

scholarly journals Enhanced Microwave Absorption and Electromagnetic Properties of Si-Modified rGO@Fe3O4/PVDF-co-HFP Composites

Materials ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 933 ◽  
Author(s):  
Yuexuan Li ◽  
Yugang Duan ◽  
Chengmeng Wang
Keyword(s):  
Microwave Absorption ◽  
Reflection Loss ◽  
High Efficiency ◽  
Vinylidene Fluoride ◽  
Synergistic Effects ◽  
Electromagnetic Properties ◽  
Absorption Mechanism ◽  
Simple Method ◽  
Absorption Frequency ◽  
Enhanced Absorption

Graphene has been regarded as one of the most promising two-dimensional nanomaterials. Even so, graphene was still faced with several key issues such as impedance mismatching and narrow bandwidth, which have hindered the practical applications of graphene-based nanocomposites in the field of microwave absorption materials. Herein, a series of Si-modified rGO@Fe3O4 composites were investigated and fabricated by a simple method. On one hand, the degree of defects in graphene carbon could be tuned by different silane coupling reagents, which were beneficial to enhancing the dielectric loss. On the other hand, the spherical Fe3O4 nanoparticles provided the magnetic loss resonance, which contributed to controlling the impedance matching. Subsequently, the electromagnetic absorption (EMA) properties of Si-modified rGO@Fe3O4 composites with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) were investigated in this work. As a result, the Si(2)-rGO@Fe3O4/PVDF-co-HFP composite exhibited the excellent EMA performance in the range of 2–18 GHz. The maximum reflection loss (RLmax) reached −32.1 dB at 3.68 GHz at the thickness of 7 mm and the effective absorption frequency bandwidth for reflection loss (RL) below −10 dB was 4.8 GHz at the thickness of 2 mm. Furthermore, the enhanced absorption mechanism revealed that the high-efficiency absorption performance of Si(2)-rGO@Fe3O4/PVDF-co-HFP composite was attributed to the interference absorption (quarter-wave matching model) and the synergistic effects between Si(2)-rGO@Fe3O4 and PVDF-co-HFP. This work provides a potential strategy for the fabrication of the high-performance EMA materials.

scholarly journals Spawns Structure of Rod-Like ZnO Wrapped in Cellulose Nanofibers for Electromagnetic Wave Absorption

2017 ◽  
Vol 2017 ◽  
pp. 1-6
Author(s):  
Bitao Fan ◽  
Qiufang Yao ◽  
Chao Wang ◽  
Ye Xiong ◽  
Qingfeng Sun ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
Reflection Loss ◽  
Cellulose Nanofibers ◽  
Absorption Properties ◽  
Composite Aerogel ◽  
Electromagnetic Wave Absorption ◽  
Wave Absorption ◽  
One Step ◽  
Absorption Performance ◽  
Minimum Reflection Loss

Spawns structure of rod-like ZnO wrapped in the cellulose nanofibers was successfully fabricated through a facile one-step hydrothermal method, and their electromagnetic wave absorption properties were investigated. The structure and properties of the composite aerogel were characterized. The enlarged morphology images showed that the as-prepared cellulose nanofiber/ZnO samples were spawns structure of rod-like ZnO wrapped in the cellulose nanofibers. The composite aerogel in a wax matrix exhibited excellent electromagnetic wave absorption performance over 2–18 GHz. The widest absorption bandwidth of 30 wt% contained with reflection loss values less than −10 dB was up to 12 GHz (6–18 GHz) at the thickness of 5.5 mm and the minimum reflection loss value reached −26.32 dB at 15.2 GHz when the thickness of the absorber was 3 mm.

scholarly journals High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite as attenuating agent

2020 ◽  
Author(s):  
Xia Fang ◽  
Lei Jiang ◽  
Limei Pan ◽  
Shuang Yin ◽  
Tai Qiu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Three Dimensional ◽  
High Thermal Conductivity ◽  
Composite Ceramics ◽  
Dielectric Constant And Loss ◽  
Spherical Graphite ◽  
Thermally Conductive ◽  
Absorption Performance ◽  
Hot Pressing Sintering ◽  
Addition Amount

Abstract High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite (SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount (3.8 MPa·m1/2 at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the three-dimensional morphology of SG, the composites exhibit a relatively higher thermal conductivity (76.82 W·m-1·k-1 at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss (8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of -14 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.

scholarly journals High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite as attenuating agent

2020 ◽  
Author(s):  
Xia Fang ◽  
Lei Jiang ◽  
Limei Pan ◽  
Shuang Yin ◽  
Tai Qiu ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Three Dimensional ◽  
High Thermal Conductivity ◽  
Composite Ceramics ◽  
Dielectric Constant And Loss ◽  
Spherical Graphite ◽  
Thermally Conductive ◽  
Absorption Performance ◽  
Hot Pressing Sintering ◽  
Addition Amount

Abstract High-thermally conductive AlN-based microwave attenuating composite ceramics with spherical graphite (SG) as the attenuating agent were fabricated through hot-pressing sintering. The SG maintains its three-dimensional morphology within the sintered bodies, which considerably impedes the sintering of the composites to some extent but slightly influences on the growth of AlN grains. The addition of SG reduces the strength of the composites, but provides a moderate toughening effect at the optimal addition amount (3.8 MPa·m 1/2 at 4 wt% SG). Benefiting from the low anisotropy, high thermal conductivity, and the three-dimensional morphology of SG, the composites exhibit a relatively higher thermal conductivity (76.82 W·m -1 ·k -1 at 10 wt% SG) compared with composites added with non-spherical attenuating agent. The dielectric constant and loss (8.2–12.4 GHz) increase remarkably as the amount of SG added increases up to 8 wt%, revealing that the incorporation of SG improves the dielectric property of the composite. The composite with 7 wt% SG exhibits the best absorption performance with a minimum reflection loss of -14 dB at 12.4 GHz and an effective absorbing bandwidth of 0.87 GHz. The excellent overall properties of the SG/AlN microwave attenuating composites render them as a promising material for various applications. Moreover, SG has a great potential as an attenuating agent for microwave attenuating composites due to its strong attenuation upon integration, high thermal conductivity, and low anisotropy.

scholarly journals High Efficiency Microwave Absorption Performance of Cobalt Ferrite Microspheres/multi-walled Carbon Nanotube Composites

2021 ◽  
Author(s):  
Hongmei Liu ◽  
Min Zhang ◽  
Kang Hu ◽  
Xiangkai Kong ◽  
Qiang Li ◽  
...  
Keyword(s):  
Microwave Absorption ◽  
High Efficiency ◽  
Magnetic Loss ◽  
Spinel Ferrite ◽  
Impedance Matching ◽  
Relaxation Processes ◽  
Nanotube Composites ◽  
Multi Walled Carbon Nanotubes ◽  
Absorption Performance ◽  
Microwave Absorption Performance

Abstract In this article, spinel ferrite CoFe2O4 and multi-walled carbon nanotubes (MWCNTs) composites are constructed by a facile one-step solvothermal method. The pure phase of CoFe2O4 particles is confirmed by X-ray diffraction patterns. Microstructure analysis demonstrates that monodisperse CoFe2O4 microspheres are wound by MWCNTs. By the introduction of CNTs, there is a significant enhancement in the imaginary part of permittivity (ε″) with the composites. The champion microwave absorption performance can be achieved in the composites by the balance of complex permittivity and permeability. When the mass fraction of CNTs is 3%, a minimum reflection loss (RLmin) of the composites is as high as -46.65 dB at 14.4 GHz at a thin thickness of 1.5 mm, and the corresponding effective absorption bandwidth below − 10 dB reaches 4.91 GHz ranging from 12.41 to 17.32 GHz which covers almost the whole Ku band (12.0–18.0 GHz). In other words, this as-synthesized composites show the most outstanding specific RLmin of -31.1 dB•mm− 1. Such superior microwave absorption behaviors of CoFe2O4/CNTs originate mainly from multiple dielectric relaxation processes, enhanced impedance matching and magnetic loss, as well as the considerable interface between mesoporous CoFe2O4 hollow microspheres and CNTs, and thereby promoting microwave reflection and scattering within the samples. Our results indicate that as-fabricated CoFe2O4/CNTs composites can be a promising microwave absorbent integrating with thin thickness, strong absorption ability, and broad bandwidth absorption.

scholarly journals Broadband Bi-Directional Polarization-Insensitive Metamaterial Absorber

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7339
Author(s):  
Feng Tian ◽  
Xia Ma ◽  
Han Hao ◽  
Xuewen Li ◽  
Jingdao Fan ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
Impedance Matching ◽  
Middle Layer ◽  
Metamaterial Absorber ◽  
Metal Plate ◽  
Equivalent Circuits ◽  
Practical Applications ◽  
Polarization Insensitive ◽  
Absorption Performance ◽  
Metamaterial Absorbers

Conventional metamaterial absorbers eliminate the transmitted electromagnetic wave by attaching the metal plate with the unidirectional absorption performance; these absorbers limit the practical applications to a large extent. In this paper, we present a broadband bi-directional metamaterial absorber by etching chip resistors on the resonators for expanding the bandwidth, and two orthogonal I-shaped structures are pasted on the both sides of the ultra-thin substrate (FR-4) instead of the metal plate for enhancing absorptance of the absorber. Simulated results show that absorptance of the designed absorber is larger than 0.9 in 1.43–2.51 GHz along the forward and backward directions under both TE and TM polarizations. Microwave experiments in the chamber are performed to verify the simulations, and the experimental results exhibit the excellent agreement with the simulations. Additionally, two I-shaped structures are orthogonally pasted on an ultrathin substrate, leading to the impedance-matching of both forward and backward directions, and the absorptance can be tailed dynamically via the middle layer of the substrate. The physics of the absorption are visualized by using a transmission line based on equivalent circuits. We claim that the designed bi-directional metamaterial absorber can be a good candidate for electromagnetic stealth and energy harvesting.

scholarly journals Gamma Irradiation-Induced Preparation of Graphene–Ni Nanocomposites with Efficient Electromagnetic Wave Absorption

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2145 ◽  
Author(s):  
Youwei Zhang ◽  
Hui-Ling Ma ◽  
Ke Cao ◽  
Liancai Wang ◽  
Xinmiao Zeng ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Electromagnetic Wave ◽  
Impedance Matching ◽  
Ni Nanoparticles ◽  
X Ray Diffraction ◽  
Electromagnetic Wave Absorption ◽  
Wave Absorption ◽  
Reduced Graphene ◽  
Gamma Radiolysis ◽  
Absorption Performance

A facile and environmentally friendly method is proposed to prepare reduced graphene oxide–nickel (RGO–Ni) nanocomposites using γ-ray irradiation. Graphene oxide (GO) and Ni2+ are reduced by the electrons which originated from the gamma radiolysis of H2O. The structure and morphology of the obtained RGO–Ni nanocomposites were analyzed using X-ray diffraction (XRD) and Raman spectroscopy. The results show that Ni nanoparticles were dispersed uniformly on the surface of the RGO nanosheets. As expected, the combination of RGO nanosheets and Ni nanoparticles improved the electromagnetic wave absorption because of the better impedance matching. RGO–Ni nanocomposites exhibited efficient electromagnetic wave absorption performance. The minimum reflection loss (RL) of RGO–Ni reached −24.8 dB, and the highest effective absorption bandwidth was up to 6.9 GHz (RL < −10 dB) with a layer thickness of 9 mm.

scholarly journals NiS2@rGO Nanosheet Wrapped with PPy Aerogel: A Sandwich-Like Structured Composite for Excellent Microwave Absorption

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 833 ◽  
Author(s):  
Zhi Zhang ◽  
Qi Lv ◽  
Yiwang Chen ◽  
Haitao Yu ◽  
Hui Liu ◽  
...  
Keyword(s):  
Electromagnetic Wave ◽  
In Situ Polymerization ◽  
Impedance Matching ◽  
Interfacial Polarization ◽  
The Novel ◽  
Step Method ◽  
Absorption Bands ◽  
Absorption Performance ◽  
Electromagnetic Pollution

To reduce electromagnetic pollution as well as increase the accuracy of high-precision electronic equipment, more attention has been paid to new electromagnetic wave (EMW) absorbing materials, which have the advantages of strong absorption, wide absorption bands, and a narrow thickness. In this study, a novel ternary type of the NiS2@rGO/polypyrrole (PPy) sandwich-like structured composites was synthesized via a facile two-step method, in which the hydrothermal method was used to prepare NiS2@rGO binary composites and then the in situ polymerization method was used to synthesize the PPy, which acted as the outer layer of the sandwich-like structure. The morphologies and electromagnetic absorption performance of the NiS2@rGO/PPy were measured and investigated. A sample with 6 wt% NiS2@rGO/PPy loading paraffin-composite obtained an outstanding reflection loss (RL) of −58.7 dB at 16.44 GHz under a thickness of 2.03 mm. Simultaneously, the effective electromagnetic wave absorption bandwidth for RL < −10 dB, which covered 7.04 to 18.00 GHz (10.96 GHz), was achieved by changing the thickness of the absorber from 2.0 to 3.5 mm. The results not only suggest that the NiS2@rGO/PPy composite has excellent performance in the field of EMW absorption but also prove that the novel sandwich-like structure can contribute to appropriate impedance matching through multiple relaxation and interfacial polarization processes.

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