Superior Electromagnetic Wave Absorption Research Articles

Graphene oxide/carbon nanotubes/CoxFe3-xO4 ternary nanocomposites: Controllable synthesis and their excellent microwave absorption capabilities

By regulating the addition of iron source, different magnetic contents and Co:Fe molar ratios of graphene oxide/carbon nanotubes/CoxFe3-xO4 (GO/CNTs/CoxFe3-xO4) (x = 0.6, 0.43 and 0.375) ternary nanocomposites (NCs) could be selectively synthesized by one-step hydrothermal method. The FE-SEM and TEM investigations indicated that the paper-like GO, CNTs and CoxFe3-xO4 nanoparticles were well bound together to form the good three dimensional hierarchical networks, which could effectively provide more interface contacts. Among these obtained samples, the as-prepared GO/CNTs/CoxFe3-xO4 (x = 0.375) ternary NCs displayed superior electromagnetic wave (EMW) absorption capabilities in terms of the optimal reflection loss value of −71.3 dB and the absorption bandwidth of 2.52 GHz. And the enhanced EMW absorption capabilities of GO/CNTs/CoxFe3-xO4 (x = 0.375) ternary NCs were analyzed in details. Therefore, a simple route was proposed to produce three dimensional hierarchical networks of GO/CNTs based NCs for simultaneous constructing more interfacial polarizations, dielectric and magnetic loss mechanisms, which was demonstrated to effectively optimize the EMW absorption performances and could be applied to design high performance EMW absorbers.

Novel 3D microsheets contain cobalt particles and numerous interlaced carbon nanotubes for high-performance electromagnetic wave absorption

The 3D microsheets contain cobalt particles and numerous interlaced carbon nanotubes (denoted as Co-NCNTs) with different pyrolysis temperature (700 °C, 800 °C and 900 °C) were successfully fabricated by a novel solution phase method. That is, polyolized the prepared g-C3N4 to form a g-C3N4@Co-glycolate hybrid precursor microsheets, which was then subjected to pyrolysis treatment under an inert gas. The effects of pyrolysis temperature in the range of 700°C–900 °C on the microwave absorption properties of the Co-NCNTs were investigated in detail. As an absorber, Co-NCNTs with the pyrolysis temperature of 800 °C exhibit superior electromagnetic wave absorption properties with the optimal reflection loss (RL) value of −46 dB in the thickness of 2.5 mm, wide effective bandwidth (RL ≤ −10 dB) of 7.2 GHz. This excellent performance attributed to the special microsheet structures, uniform Co particle distribution and the better impedance matching.

Urchin-like polyaniline/magnetic carbon sphere hybrid with excellent electromagnetic wave absorption performance

Uniform urchin-like polyaniline/magnetic carbon sphere (PANI/p-C/NiFe2O4) hybrid with superior electromagnetic wave absorption properties was successfully fabricated, and its morphologies and structures were investigated via SEM, XPS, XRD and FT-IR. Due to the fairly good matching of dielectric loss and magnetic loss, the PANI/p-C/NiFe2O4 hybrid sample with thickness of 2.5 mm showed a minimum reflection loss value up to −37 dB in the frequency range of 2–18 GHz, the effective absorption band width of 3.9 GHz, and the excellent electromagnetic wave absorption property both in absorption efficiency and effective absorption band.

Facile chemical synthesis of amorphous FeB alloy nanoparticles and their superior electromagnetic wave absorption performance

Currently, the magnetic metal based electromagnetic wave absorber have attracted extensively interest. However, how to control the high conductivity of magnetic metals and achieve good impedance matching of electromagnetic absorbing materials made by them have become a big problem at present. Herein, amorphous FeB nanoparticles were rationally synthesized by a wet method, which involves a simple three-step solution reaction. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM). Benefiting from their amorphous structure, the resulting FeB nanoparticles show good magnetic properties, dielectric losses and proper impedance matching, thus good microwave attenuation ability can be achieved in the low frequency range. The maximum reflection loss is −15 dB at 3.5 GHz with a thickness of 8 mm which can be mainly attributed to its excellent impedance matching in the frequency range of 2.5–4.5 GHz. These amorphous FeB alloy nanoparticles are expected to be promising candidates for efficient microwave absorbers in the S band.

Metal organic framework (ZIF-67)-derived hollow CoS2/N-doped carbon nanotube composites for extraordinary electromagnetic wave absorption

The hierarchical hollow framework involving interconnected highly conductive N-doped carbon nanotube networks and CoS2 particles were successfully prepared by metal-organic framework (MOF) derived method. After the two pyrolysis process in the atmosphere of reducing gas and inert gases, numerous carbon nanotubes interlaced on the surface of framework and CoS2 nanoparticles also attached on the surface. The electromagnetic parameters of CoS2/NCNTs composites can be well controlled by regulating the loadings of sample in sample-paraffin mixture. The results demonstrate that CoS2/NCNTs with 50% loadings show superior electromagnetic wave absorption properties in the wide frequency range, almost covering the whole X bands (8–12 GHz) only with a relative thin thickness of 1.6 mm. Hierarchical hollow structure and better impedance matching performance between N-doped carbon nanocube and CoS2 nanoparticles contribute to the enhancement of microwave absorption ability. Our work confirms that hollow framework CoS2/NCNTs composites can provide a novel idea for designing high-absorbability microwave absorbers.

Facile synthesis of a novel flower-like BiFeO3 microspheres/graphene with superior electromagnetic wave absorption performances

In recent years, porous or layered magnetic materials have received increasing attention due to their low density and lightweight. In this work, porous BiFeO3 microspheres and three-dimensional porous BiFeO3 microsphere-reduced graphene oxide (RGO) composite (3D porous BiFeO3/RGO) were prepared by one-step etching processing using pure BiFeO3 particles as precursors. The precursor undergoes dissolution-recrystallization/reduction process, resulting in large amount of BiFeO3 fragments and graphene hybrid product, which forms 3D porous BiFeO3/RGO composite. Electromagnetic (EM) absorption performance measurements exhibit that at low thickness of 1.8 mm, porous BiFeO3/RGO composite can achieve reflection loss (RL) value up to −46.7 dB and absorption bandwidth (defined by RL <−10 dB) exceeding 4.7 GHz (from 12.0 to 16.7 GHz), testifying outstanding microwave absorbing performance. Compared with pure porous BiFeO3, improved EM wave absorption ability of as-prepared porous BiFeO3/RGO composite is attributed to interfacial polarization, multiple reflections, scattering, and appropriate impedance matching.

Nanofibrous membrane constructed magnetic materials for high-efficiency electromagnetic wave absorption

With the rapid advancement of modern technology, electromagnetic (EM) wave absorption materials become more and more indispensable to daily life and even national strategic areas. However, how to fabricate such materials in a manner of high-efficiency and broad frequency range remains a challenge and highly desired. Here, we proposed a new route to produce high performance EM wave membranes by combined techniques of electrospinning, stabilization and carbonization processes. NiFe2O4 nanoparticles and multiwall carbon nanotubes (MWCNTs) were respectively selected as the effective magnetic material and dielectric material to construct the highly flexible NiFe2O4/MWCNTs doped carbon nanofibers (CNFs). The fabricated composite membrane exhibits superior EM wave absorption behavior in a wide frequency range. For the EM wave absorption performance in C-band (4–8 GHz), X-band (8–12 GHz) and Ku-band (12–18 GHz), the reflection loss (RL) exceeding −20 dB are obtained in the frequency range of 5.36–18 GHz at a sample thickness of 2–5 mm. Similarly, the RL value of 45.60 dB can be realized for NiFe2O4/MWCNTs CNFs with a bandwidth of 12.96 GHz at a thickness of 2.5 mm. The as-synthesized NiFe2O4/MWCNTs CNFs nanofibrous membrane can be a promising candidate for light-weight and excellent EM wave absorbers. This research will afford an alternative solution for the fabrication of EM wave absorbing materials for wide practical applications.

Facile Synthesis of Highly Defected Silicon Carbide Sheets for Efficient Absorption of Electromagnetic Waves

Stacking faults (SFs) within silicon carbide (SiC) are desired because these faults can enhance the electromagnetic (EM) absorption properties of the material. However, most reported SiC materials are prepared using expensive precursors possessing limited SFs. Herein, we report a facile and economical method to fabricate SiC sheets with a record-high SF density of over fourfold enhancement compared with previously reported SiC materials. The use of paper as a carbon source resulted in a 19-fold decrease in fabrication cost. The microstructure, defect structure, and EM wave absorption performance of the synthesized SiC sheets were investigated in detail. Enhancement of the SF content of the SiC sheets enabled significant interfacial dipole polarization, thereby imparting the sheets with superior EM wave absorption. SiC sheets with the maximum SF content obtained in this work revealed a minimum reflection loss of −22 dB and an effective EM wave absorption band (RL < −10 dB) covering the frequency range of 1...

Enhanced electromagnetic wave absorption properties of laminated SiCNW-Cf/lithium–aluminum–silicate (LAS) composites

The SiC nanowires have been in situ grown on the carbon fabric by thermal evaporation. Furthermore, to reduce the reflection of electromagnetic (EM) wave on the surface of EM wave absorbents and to improve the impedance matching, the laminated SiCNW-Cf/lithium-aluminum-silicate (LAS) composites were prepared through slurry impregnation and hot-pressing sintering methods using the fabrics as reinforced body. The as-prepared samples were characterized by X-ray diffraction (XRD), Raman spectra, field emission scanning electron microscope (FESEM) and high-resolution transmission electron microscope (HRTEM). The formation mechanism of SiC nanowires was specified. The SiCNW-Cf/LAS composites in this study exhibited superior EM wave absorption abilities and good impedance match in the frequency range of 2–18 GHz compared with SiCNW-Cf. A minimum reflection loss (RL) value of −37.8 dB was observed at 7.2 GHz with absorber thickness of only 3 mm. Moreover, the absorption bandwidth for RL less than −10 dB was 4.6 GHz (13.4 GHz - 18 GHz) when the absorber thickness decreased to 1.5 mm. A possible wave absorbing mechanism was discussed. This study proposed a facile method to fabricate a lightweight and broadband material with enhanced EM wave absorption performance.

Achieving tunability of effective electromagnetic wave absorption between the whole X-band and Ku-band via adjusting PPy loading in SiC nanowires/graphene hybrid foam

To synthesize lightweight and high-performance electromagnetic wave absorbing composite, SiC nanowire (SiCnw) and conductive polymer polypyrrole (PPy) were incorporated in graphene aerogel (GA) via chemical vapor infiltration combined with a simple chemical polymerization method. The SiCnw/GA with filler loading of 20 wt% has an effective absorption bandwidth of 5.1 GHz in the frequency range of 8.0–13.1 GHz covering the whole X band. After coating on PPy film, the SiCnw/GA-43 wt% PPy sample has an effective absorption bandwidth of 5.9 GHz in frequency range of 12.1–18.0 GHz covering the whole Ku-band at a very thin thickness of 1.83 mm. When adjusting the PPy loading to 66 wt%, the effective absorption bandwidth of SiCnw/GA-PPy could reach a high value of 6.4 GHz in frequency of 8.2–14.6 GHz covering the whole X-band at a thin thickness of 2.32 mm. Therefore, the SiCnw/GA-PPy foams could achieve tunability of effective absorption between the whole X-band and Ku-band by adjusting the loading of PPy or SiCnws. In SiCnw/GA-PPy absorbing materials, interfacial polarization, relaxation polarization loss, electronic dipole polarization and electrons hopping are major determining factors of superior electromagnetic wave absorption properties. The SiCnw/GA-PPy foams with excellent comprehensive performance are promising candidates as electromagnetic wave absorbing materials.

Direct Growth of Edge‐Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High‐Performance Microwave Absorption

AbstractHigh‐performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave‐transmitting matrices is of paramount importance to bring it to real‐world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge‐rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si3N4 ceramics using only methyl alcohol (CH3OH) as precursor is reported. The large O/C atomic ratio of CH3OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si3N4 hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide‐based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.

Novel nanocapsules with Co-TiC twin cores and regulable graphitic shells for superior electromagnetic wave absorption.

The synthesis of nanometer materials with unique structures and compositions has proven successful towards the attenuation of electromagnetic (EM) waves. However, it is still a challenge to form special nanostructures by integrating magnetic/dielectric loss materials into one particle due to the difficulties in coupling the heterogeneous components. Herein, we present the synthesis of novel nanocapsules (NCs) with Co–TiC twin cores encapsulated inside graphitic shells using an arc-discharge plasma method. The thickness of the graphitic shell could be controlled by quantitatively tuning the carbon source concentration. The optimal reflection loss (RL) values of the prepared NCs was −66.59 dB at 8.76 GHz with a low thickness of 2.56 mm. The bandwidth of RL ≤ −10 dB was up to 14.4 GHz, which almost covered the entire frequency band, namely, the S to Ku band (3.6 GHz to 18 GHz). This superior EM wave absorption was ascribed to the specific double-core shell nanostructures and effective impedance matching between the magnetic loss and dielectric loss originating from the combination of the magnetic Co and dielectric TiC/C.

Synthesis of SiC nanofibers with superior electromagnetic wave absorption performance by electrospinning

A method combined electrospinning and preceramic polymer pyrolysis, annealing has been developed to fabricate SiC nanofibers. In this work, the effects of polycarbosilane (PCS) mass ratio (8.7 wt% ∼ 11.8 wt%) in precursor solution on microstructure and electromagnetic (EM) absorption properties of SiC nanofibers are systematically studied. The phase composition of SiC nanofibers are mainly inclusive of abundant SiC nanocrystallines, a small quantity of graphitic-like carbon coated on fibers surface and randomly distributed amorphous SiOxCy phase. When PCS mass ratio is 10 wt%, the SiC nanofibers present a minimum reflection loss (RL) value of −57.8 dB at 14.6 GHz with a absorber coating thickness of 1.9 mm and the effective absorption bandwidth (RL < −10 dB, 90% EM wave absorbed) covers from 6 to 18 GHz. As PCS mass ratio increasing, the EM absorption performance of SiC nanofibers gradually becomes poor. Multi-reflection among SiC nanofibers gradually weaken the incident EM wave. Moreover the interfacial polarization originated from heterogeneous interfaces which exist among SiC nanocrystallines, graphite carbon, amorphous SiOxCy dissipates EM wave energy contributed to high EM performance of SiC nanofibers. This work demonstrates a new kind of nano SiC EM absorption materials that has potential to be applicated in harsh environments.

Multiple Interfaces Structure Derived from Metal-Organic Frameworks for Excellent Electromagnetic Wave Absorption

Hierarchical yolk–shell nanostructure (NiO/Ni/GN@Air@NiO/Ni/GN) derived from Ni-based metal–organic frameworks (Ni-MOFs) is synthesized by solvothermal reactions. After successive carbonization and oxidation treatments, hierarchical NiO/Ni nanocrystals covered with a graphene shell are obtained with the yolk–shell nanostructure intact. The NiO/Ni/GN@Air@NiO/Ni/GN composites are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the NiO/Ni/GN@Air@NiO/Ni/GN composites exhibit superior electromagnetic wave absorption properties. A minimum reflection loss (RLmin) of −34.5 dB is obtained at 17.2 GHz with the thin thickness of 1.7 mm. In addition, the best microwave absorption properties are achieved with a 2.0 mm absorber layer (RLmin = −22.5 dB, bandwidth of 6.0 GHz). The outstanding absorption ability may arise from the unique yolk–shell structure and nanoporous carbon, which can tune the dielectric of the NiO/Ni/GN@Air@NiO/Ni/GN composites to acquire good impedance matching. Moreover, the interspaces can induce interfacial polarization and multiple reflections.

In situ preparation of carbon/Fe3C composite nanofibers with excellent electromagnetic wave absorption properties

Poly(vinyl pyrrolidone) (PVP)-based carbon/Fe3C composite nanofibers (C/Fe3C CNFs) have been successfully prepared by carbonization of as-electrospun PVP/ferric nitrate nanofibers. Unlike the pristine PVP nanofibers, the PVP/ferric nitrate nanofibers can retain fibers structure after carbonization, in which Fe3C nanoparticles are well-dispersed. More importantly, the as-prepared wax composites exhibit high electromagnetic wave absorption abilities, which can be attributed to the formation of the C/Fe3C CNFs “conductive network”, and leads to a more effective dielectric loss in terms of dissipating the induced current in the wax composites. Specifically, the CNFs/wax composites with a low filler ratio of 10wt% shows the minimum reflection loss of −62.6dB at 11.25GHz in a thin matching thickness of 3.6mm, and the effective bandwidth below −10dB can reach up to 6.5GHz. Thus, this work demonstrates a facile, cost-effective synthesized strategy to prepare carbon-based lightweight composite nanofibers with superior electromagnetic wave absorption properties.

Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses.

Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 μm were fabricated by a solvothermal method combined with carbon reduction. The pore size of the synthesized Ni/C composite microspheres ranged from several nanometers to 50 nm. The porous Ni/C composite microspheres exhibited a saturation magnetization (MS) of 53.5 emu g(-1) and a coercivity (HC) of 51.4 Oe. When tested as an electromagnetic (EM) wave absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM wave absorption at thicknesses of 3.0-11.0 and 1.6-7.0 mm in the corresponding frequency ranges of 2.0-12 and 2.0-18 GHz, respectively. The superior EM wave absorption performances of porous Ni/C composite microspheres were derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, and the porous structure.

Multiple-phase carbon-coated FeSn2/Sn nanocomposites for high-frequency microwave absorption

Rapid expansion in microelectronic devices has prompted increasing research efforts in development of high-frequency electromagnetic wave absorption materials. Multiple-phase FeSn2/Sn/Graphite core–shell nanoparticles synthesized by an arc-discharge method, with controllable components and structures, present a typical cloaking feature aroused from the superior electromagnetic wave absorption. Based on transmission line theory, we prove quantitatively that more than 90% of the electromagnetic power can be attenuated at 9–18 GHz. Experimental results coupled with theory calculations by the Cole–Cole equation and the eddy-current model, further reveal that such high performances are originated from the onion-type interfacial architecture at nanoscale and the desirable impedance match resulting from multiple phase components.

In situ synthesis of novel urchin-like ZnS/Ni3S2@Ni composite with a core–shell structure for efficient electromagnetic absorption

A core–shell ternary ZnS/Ni3S2@Ni composite exhibiting superior electromagnetic wave absorption properties was synthesized.

Synthesis and electromagnetic properties of FeNi alloy nanofibers using an electrospinning method

FeNi alloy nanofibers have been prepared by an electrospinning process followed by air-calcination and H2 reduction to develop electromagnetic (EM) wave absorbers in the giga-hertz (GHz) frequency range. The thermal behavior and phase and morphology evolution in the synthetic processes were systematically investigated. Through the heat treatments of calcination and H2 reduction, as-spun PVP/FeNi precursor nanofiber has been stepwise transformed into nickel iron oxide and FeNi phases but the fibrous shape was maintained perfectly. The FeNi alloy nanofiber had the high aspect ratio and the average diameter of approximately 190 nm and primarily composed of FeNi nanocrystals with an average diameter of ~60 nm. The FeNi alloy nanofibers could be used for excellent EM wave absorbing materials in the GHz frequency range because the power loss of the FeNi nanofibers increased up to 20 GHz without a degradation and exhibited the superior EM wave absorption properties compared to commercial FeNi nanoparticles.