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 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 3D Seed-Germination-Like MXene with In Situ Growing CNTs/Ni Heterojunction for Enhanced Microwave Absorption via Polarization and Magnetization

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Xiao Li ◽  
Wenbin You ◽  
Chunyang Xu ◽  
Lei Wang ◽  
Liting Yang ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Seed Germination ◽  
Microwave Absorption ◽  
Magnetic Loss ◽  
Impedance Matching ◽  
Matching Condition ◽  
Ni Nanoparticles ◽  
Absorption Performance ◽  
Microwave Absorption Performance

Highlights Benefiting from the possible “seed-germination” effect, the “seeds” Ni2+ grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton. Compared with the traditional magnetic agglomeration, the MXene-CNTs/Ni hybrids exhibit the highly spatial dispersed magnetic architecture. 3D MXene-CNTs/Ni composites hold excellent microwave absorption performance (−56.4 dB at only 2.4 mm). Abstract Ti3C2Tx MXene is widely regarded as a potential microwave absorber due to its dielectric multi-layered structure. However, missing magnetic loss capability of pure MXene leads to the unmatched electromagnetic parameters and unsatisfied impedance matching condition. Herein, with the inspiration from dielectric-magnetic synergy, this obstruction is solved by fabricating magnetic CNTs/Ni hetero-structure decorated MXene substrate via a facile in situ induced growth method. Ni2+ ions are successfully attached on the surface and interlamination of each MXene unit by intensive electrostatic adsorption. Benefiting from the possible “seed-germination” effect, the “seeds” Ni2+ grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton. Due to the improved impedance matching condition, the MXene-CNTs/Ni hybrid holds a superior microwave absorption performance of − 56.4 dB at only 2.4 mm thickness. Such a distinctive 3D architecture endows the hybrids: (i) a large-scale 3D magnetic coupling network in each dielectric unit that leading to the enhanced magnetic loss capability, (ii) a massive multi-heterojunction interface structure that resulting in the reinforced polarization loss capability, confirmed by the off-axis electron holography. These outstanding results provide novel ideas for developing magnetic MXene-based absorbers.

scholarly journals Effect of Reaction Time on Microwave Absorption Properties of Fe3O4 Hollow Spheres Synthesized via Ostwald Ripening

Materials ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 2921 ◽  
Author(s):  
Wei Huang ◽  
Yujiang Wang ◽  
Shicheng Wei ◽  
Bo Wang ◽  
Yi Liang ◽  
...  
Keyword(s):  
Reaction Time ◽  
Microwave Absorption ◽  
Ostwald Ripening ◽  
Impedance Matching ◽  
Hollow Spheres ◽  
Absorption Properties ◽  
Microwave Absorption Properties ◽  
Magnetic Structures ◽  
Absorption Performance ◽  
Microwave Absorption Performance

Hollow magnetic structures have great potential to be used in the microwave absorbing field. Herein, Fe3O4 hollow spheres with different levels of hollowness were synthesized by the hydrothermal method under Ostwald ripening effect. In addition to their microstructures, the microwave absorption properties of such spheres were investigated. The results show that the grain size and hollowness of Fe3O4 hollow spheres both increase as the reaction time increases. With increasing hollowness, the attenuation ability of electromagnetic wave of Fe3O4 spheres increases first and then decreases, finally increases sharply after the spheres break down. Samples with strong attenuation ability can achieve good impedance matching, which it does preferentially as the absorber thickness increases. Fe3O4 hollow spheres show the best microwave absorption performance when the reaction time is 24 h. The minimum reflection loss (RL (min)) can reach −40 dB, while the thickness is only 3.2 mm.

scholarly journals Solvent-Free Synthesis of Ultrafine Tungsten Carbide Nanoparticles-Decorated Carbon Nanosheets for Microwave Absorption

2020 ◽  
Vol 12 (1) ◽  
Author(s):  
Yunlong Lian ◽  
Binhua Han ◽  
Dawei Liu ◽  
Yahui Wang ◽  
Honghong Zhao ◽  
...  
Keyword(s):  
Tungsten Carbide ◽  
Microwave Absorption ◽  
Impedance Matching ◽  
Weight Ratio ◽  
Solvent Free ◽  
Carbon Composites ◽  
Carbon Nanosheets ◽  
Solid Mixture ◽  
Absorption Performance ◽  
Microwave Absorption Performance

AbstractCarbides/carbon composites are emerging as a new kind of binary dielectric systems with good microwave absorption performance. Herein, we obtain a series of tungsten carbide/carbon composites through a simple solvent-free strategy, where the solid mixture of dicyandiamide (DCA) and ammonium metatungstate (AM) is employed as the precursor. Ultrafine cubic WC1−x nanoparticles (3–4 nm) are in situ generated and uniformly dispersed on carbon nanosheets. This configuration overcomes some disadvantages of conventional carbides/carbon composites and is greatly helpful for electromagnetic dissipation. It is found that the weight ratio of DCA to AM can regulate chemical composition of these composites, while less impact on the average size of WC1−x nanoparticles. With the increase in carbon nanosheets, the relative complex permittivity and dielectric loss ability are constantly enhanced through conductive loss and polarization relaxation. The different dielectric properties endow these composites with distinguishable attenuation ability and impedance matching. When DCA/AM weight ratio is 6.0, the optimized composite can produce good microwave absorption performance, whose strongest reflection loss intensity reaches up to − 55.6 dB at 17.5 GHz and qualified absorption bandwidth covers 3.6–18.0 GHz by manipulating the thickness from 1.0 to 5.0 mm. Such a performance is superior to many conventional carbides/carbon composites.

Urchin-Like Ni Microspherical Structure with Enhanced Magnetic Loss for Thin Microwave Absorber at Gigahertz

NANO ◽  
2017 ◽  
Vol 12 (03) ◽  
pp. 1750034 ◽  
Author(s):  
Yuping Sun ◽  
Zhengwu Pan ◽  
Hongming Long ◽  
Siu Wing Or ◽  
S. L. Ho ◽  
...  
Keyword(s):  
Microwave Absorption ◽  
Chemical Reduction ◽  
Magnetic Loss ◽  
Synthetic Strategy ◽  
High Anisotropy ◽  
Absorption Performance ◽  
Wet Chemical ◽  
5 Ghz ◽  
Microwave Absorption Performance ◽  
Absorption Measurements

We describe in this report a wet chemical reduction synthetic strategy for synthesizing urchin-like Ni microspherical structures, in which the nanowires self-assembled by Ni nanoparticles with the size of 5–20[Formula: see text]nm are assembled in a radial form from the center to the surface of the spherical oriented arrays. Urchin-like Ni microspherical structures exhibit the strong magnetic natural resonance peak at 7.0[Formula: see text]GHz and superior magnetic loss at 2–18[Formula: see text]GHz, originated from relatively high anisotropy energy of urchin-like shape. Electromagnetic absorption measurements show that the urchin-like Ni microspherical structures possess outstanding microwave absorption performance at 2–18[Formula: see text]GHz. An optimal reflection loss of [Formula: see text]21.98[Formula: see text]dB can be observed at 17.4[Formula: see text]GHz with a matching thickness of 1.4[Formula: see text]mm and the effective absorption (below −10 dB, 90% absorption) bandwidth is 5 GHz (12–17 GHz) with a thickness of 1.7[Formula: see text]mm. The excellent microwave absorption performance may be attributed to the good impedance, large attenuation constant and novel magnetic loss ability.

scholarly journals An Easy Method of Synthesis CoxOy@C Composite with Enhanced Microwave Absorption Performance

Nanomaterials ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 902
Author(s):  
Wenli Bao ◽  
Cong Chen ◽  
Zhenjun Si
Keyword(s):  
Microwave Absorption ◽  
Impedance Matching ◽  
Interfacial Polarization ◽  
Magnetic Composite ◽  
Easy Method ◽  
Electromagnetic Absorption ◽  
Absorption Performance ◽  
Matched Impedance ◽  
Microwave Absorption Performance ◽  
Minimum Reflection Loss

Design of interface-controllable magnetic composite towards the wideband microwave absorber is greatly significance, however, it still remains challenging. Herein, we designed a spherical-like hybrids, using the Co3O4 and amorphous carbon as the core and shell, respectively. Then, the existed Co3O4 core could be totally reduced by the carbon shell, thus in CoxOy core (composed by Co and Co3O4). Of particular note, the ratios of Co and Co3O4 can be linearly tuned, suggesting the controlled interfaces, which greatly influences the interface loss behavior and electromagnetic absorption performance. The results revealed that the minimum reflection loss value (RLmin) of −39.4 dB could be achieved for the optimal CoxOy@C sample under a thin thickness of 1.4 mm. More importantly, the frequency region with RL < −10 dB was estimated to be 4.3 GHz, ranging from 13.7 to 18.0 GHz. The superior wideband microwave absorption performance was primarily attributed to the multiple interfacial polarization and matched impedance matching ability.

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