Electromagnetic wave absorbing properties of In–Sn/rGO composites supported by impurity defect

With the fast development of E-communication technology, effective electromagnetic wave absorbing materials are highly needed to address the growing electromagnetic pollution. Herein, Indium doped tin microsphere/reduced graphene oxide (In–Sn/rGO) composites with rich impurity defects were synthesized via the sol-gel and hydrothermal method. The excellent microwave absorption of In–Sn/rGO composites can be attributed to the modifications of electronics status and Fermi energy level after In doping. This can significantly increase the carrier mobility between In–Sn microspheres and rGO sheets to strike a superior interfacial polarization loss. As a result, the maximum absorptivity can reach ?51.16 dB at 8.73 GHz (thickness: 3.5 mm) with a lower filler loading of 10 wt%. Meanwhile, the synthesized In–Sn/rGO composites also exhibit an ultra-wide absorbing frequency range of 13.84 GHz (within the X band, Ku band, and most of the C band). This research provides a new idea for the synthesis of effective microwave absorbing material by introducing impurity defects.     

Apium-derived biochar loaded with MnFe2O4@C for excellent low frequency electromagnetic wave absorption

Given the rapid development of electrommunication and radar detection technologies, low frequency electromagnetic wave materials have received more and more attention. Herein, the Apium-derived biochar loaded with MnFe₂O₄@C has been successfully prepared by using co-solvothermal and calcination method. The cladding carbon layer on MnFe₂O₄ NPs is migrated from biochar via thermal diffusion, and the biochar is covered with the ferrite NPs as well. Thus, the combination of dielectric and magnetic loss endows the composite with excellent low frequency electromagnetic absorption ability i.e. the optimal microwave absorbing intensity is −48.92  dB at 0.78 GHz with an extended effective absorbing bandwidth of 0.38–1.78 GHz for only 2.5 mm thickness, being ascribed to nature resonance, multiple interfacial and surface polarization, strong electromagnetic attenuation ability and good impedance matching property in detail. This bio-based ferrite composites have great potential in preparation of MAMs due to the advantages of extraordinary performance, lightweight property, environmental protection and easy degradation.     

Ultra-broadband electromagnetic wave absorbent: In-situ generated silica modified conductive carbon fiber aerogels

The research and development of dielectric microwave absorbing materials with broad electromagnetic (EM) response is a significant project in EM wave absorption field. To achieve high-performance absorption and strong interfacial bonding at the same time, thermal-assisted in-situ bonding technology was applied to fabricating the dielectric composite absorbing materials. Thanks to the combination of vacuum filtration and in-situ hydrothermal reaction, the as-prepared binary composite aerogel shows both strong interface contacting and good mechanical stability. In addition, the carbon nanofibers/silica composite aerogel (CSA) exhibits ultra-broad effective bandwidth covering from S to Ku band, originated from the uniform dispersed silica aerogel in conductive carbon fiber network. In details, for CSA1 sample, the maximum reflection loss (RL) values and effective absorption bandwidth reach −46.2 dB (1.8 mm) and 5.2 GHz (1.5 mm). Meanwhile, the optimum RCS reduction values reaches 16.2 dB m² when the detection theta was set as 0°. For CSA2 sample, the effective absorption bandwidth reaches 8.64 GHz at 1.5 mm, and tends to possess lower frequency EM response covering the S-band. This work exhibits a kind of broad-bandwidth aerogel absorbers at low thickness, which shows huge potential in large-scale production of microwave absorbing devices.     

Ultra-light 3D bamboo-like SiC nanowires felt for efficient microwave absorption in the low-frequency region

Nonmagnetic ceramics are ideal microwave absorbing materials used in high-temperature and oxidizing environments. However, low-frequency absorbing properties of this material are rarely reported because low-frequency absorbing requires nonmagnetic materials to have much higher permittivity. In this research, a series of three-dimensional architectures formed by SiC nanowires with different microstructures felt were fabricated to address this issue. The morphology of the SiC_nw (linear, bamboo-shaped, and worm-like) dominated by the VLS growth mechanism can be manipulated by the silicon vapor concentration, which is governed by the vaporization temperature of the mixed silicon source (Si and SiO₂) in different sintering processes. The spontaneously overlapped bamboo-shaped SiC nanowires in these felt enhance the permittivity and conductivity loss and produce multiple scattering effects on the incident EM waves, thus increasing the low-frequency wave absorption ability. The RL_min of the bamboo-shaped SiC_nw felt reaches ?44.3 dB at 3.85 GHz with the corresponding EAB of 0.64 GHz (3.6–4.24 GHz) at a thickness of 3.5 mm. The density of the SiC_nw felt is as low as 0.022 g/cm³ due to the high porosity (99.3%) of 3D networks, which fulfills lightweight requirements and highly efficient electromagnetic wave absorption.     

Polymer-derived Co2Si(Co)/SiCN composite ceramics with tunable microwave absorption properties

In this paper, Co₂Si(Co)/SiCN composite ceramics were synthesized by simple precursor-derived ceramics method. The phase composition, morphology, and microwave absorption properties of Co₂Si(Co)/SiCN composite ceramics at different pyrolysis temperatures (1000–1400°C) were studied. When pyrolysis temperature was 1300°C, carbon nanowires (CNWs), Co₂Si, Si₂N₂O, SiC and Si₃N₄ were in situ generated and the best electromagnetic wave (EMW) absorption performance was obtained. The minimum reflection loss reached−50.04 dB at 4.81 mm, and the effective absorption bandwidth broadened to 3.48 GHz (14.52–18 GHz) at 1.31 mm. The excellent EMW absorption performance mainly comes from the coexistence of multiple loss mechanisms, including the magnetic loss of Co₂Si, the conduction loss of CNWs, and the heterogeneous interfaces polarization between varieties of nanocrystals and amorphous ceramic matrix. By adjusting the sample thickness from 1 to 5 mm, the effective absorption of S1300 can cover the entire X and Ku bands, from 3.36 to 18 GHz. This study provides a simple way to synthesize high performance ceramic-based microwave absorbing materials.     

Designing of an rGO-based heterostructure for highly efficient microwave absorption performance and flame retardancy

To meet the increasingly serious challenges of electromagnetic pollution and fire hazards, highly efficient electromagnetic absorbing materials with good flame retardancy have been accurately developed. A complex high-performance electromagnetic absorber was designed by doping graphene oxide heterostructures (including zero-dimensional nanoparticles and two-dimensional graphene) containing cobalt, nickel and iron oxyhydroxide through the coordination effect. When 20 wt% CNFO@rGO was incorporated into paraffin, the minimum reflection loss (RL) reached -51.6 dB at a thickness of 3.5 mm, showing a high electromagnetic absorption efficiency. It was concluded that the excellent impedance matching, the best dielectric loss and the higher magnetic loss caused by the heterostructure combined with the electromagnetic parameters, Cole-Cole semicircle, impedance matching (Z) and attenuation coefficient resulted in excellent electromagnetic wave absorption performance. Moreover, the peak heat release (PHRR) and heat release rate (HRC) decreased by 55.5% and 55.1%, respectively, when 10 wt% CNFO@rGO was incorporated into the epoxy resin (EP), indicating enormous potential for the enhancement of flame-retarding electromagnetic absorbing materials.     

Recent advances in carbon nanotubes-based microwave absorbing composites

With the blossom of information industry, electromagnetic wave technology shows increasingly potential in many fields. Nevertheless, the trouble caused by electromagnetic waves has also drawn extensive attention. For instance, electromagnetic pollution can threaten information safety in vital fields and the normal function of delicate electronic devices. Consequently, electromagnetic pollution and interference become an urgent issue that needs to be addressed. Carbon nanotubes (CNTs) have become a potential candidate to deal with these problems due to many advantages, such as high dielectric loss, remarkable thermodynamic stability, and low density. With the appearance of climbing demands, however, the carbon nanotubes combining various composites have shown greater prospects than the single CNTs in microwave absorbing materials. In this short review, recent advances in CNTs-based microwave absorbing materials were comprehensively discussed. Typically, we introduced the electromagnetic wave absorption mechanism of CNTs-based microwave absorbing materials and generalized the development of CNTs-based microwave absorbers, including CNTs-based magnetic metal composites, CNTs-based ferrite composites, and CNTs-based polymer composites. Ultimately, the growing trend and bottleneck of CNTs-based composites for microwave absorption were analyzed to provide some available ideas to more scientific workers.     

Carbon–ceramic nanofiber embedded with LDHs-derived composites for enhanced electromagnetic wave absorption

Hydrotalcite-like layered double hydroxides (LDHs) exhibit distinct microstructures and atomic compositions, and thus, they are expected to be superior microwave absorbing materials. However, preparation of excellent absorbers from LDHs is still a challenging task. Herein, NiCo-LDHs@SiC/C heterostructure composites were designed and then heat-treated to obtain NiCo@SiC/C nanofibers. Finally, with a synergistic effect of dielectric and magnetic losses, the minimum reflection loss value of the sample could reach −56.3 dB with a thickness of 2.7 mm, and the maximum effective bandwidth absorption reached 6.8 GHz at 2.3 mm. Moreover, the simulated radar cross-section indicates that the NiCo@SiC/C nanofibers well suppress the electromagnetic scattering from metal trench structure. This result further indicates the outstanding microwave absorption properties of the nanofibers. This study contributes to the development of LDH materials in the field of wave-absorbing materials, and is an important guideline for exploring efficient microwave absorbers with fibrous structure.     

静电纺丝纳米纤维在吸波材料中的应用

随着电子设备的迅速普及，电磁干扰和电磁污染问题随之而来，因此，高性能电磁波吸收材料的设计迫在眉睫。静电纺丝纳米纤维复合材料具有质量轻、柔性大、易加工、兼容性强等优势，有望实现吸波材料“薄、轻、宽、强”的技术要求。该文首先介绍了电磁波吸收材料的吸波原理，之后综述了静电纺丝技术在吸波材料中的研究进展，包括静电纺丝纳米纤维与金属及其氧化物、碳纳米材料与导电聚合物、过渡金属碳化物的复合以及在多层吸波材料中的应用，总结了不同种类复合材料的优缺点。最后，展望了静电纺丝纳米纤维在吸波领域的发展趋势以及应该关注的问题。     

Microwave synthesis of worm-like SiC nanowires for thin electromagnetic wave absorbing materials

Thin thickness is always the pursuit of excellent electromagnetic wave absorbing materials. Herein, SiC nanowires with worm-like morphology were synthesized by microwave heating the mixture of expanded graphite and silica. The worm-like SiC nanowires exhibit an excellent microwave absorption ability at a thin thickness. With the filling ratio of SiC nanowires increases in the matrix, the dielectric loss and microwave absorbing ability are significantly enhanced; meanwhile the number of absorption peaks is gradually increased, and the absorption peaks also move toward a thinner thickness. When the nanowires filling ratio was 40?wt%, the minimum reflection loss reached down to ?35.2?dB and the effective absorption (RL?<??10?dB) bandwidth was 1.8?GHz?at a thickness of 1.3?mm. The possible growth mechanism of the worm-like SiC nanowires is that the intermediate reaction gas phases, SiO and CO, were confined in the relatively independent tiny pores of expanded graphite. This resulting in an excessive local gas phase pressure, which causes the nanowire growth direction changes randomly.     

Electromagnetic and microwave absorption properties of FeSiAl and flaky graphite filled Al2O3 composites with different FeSiAl particle size

The increasing electromagnetic interference problems have drawn much attention to microwave absorbing materials. To satisfy the needs of practical application, FeSiAl and flaky graphite filled Al₂O₃ composites were sintered by hot-pressing for microwave absorption application. The effect of FeSiAl particle size on the electromagnetic and microwave absorption properties was investigated in the X-band (8.2–12.4 GHz). The results show that the dielectric properties enhance significantly with increasing FeSiAl particle size, which is attributed to the increased interfacial polarization and conductance loss. As a result of the favorable impedance matching and appropriate electromagnetic attenuation, the reflection loss (RL) of the composites filled with 25–48 μm flaky FeSiAl achieves -15.2 dB at 10.6 GHz and the effective absorption bandwidth (RL < -10 dB) is 1.2 GHz in 10.0–11.2 GHz with a matching thickness of 1.0 mm. It indicates that FeSiAl and flaky graphite filled Al₂O₃ composites are potential candidates for thin-thickness microwave absorbing materials, and the microwave absorption properties can be enhanced by adjusting absorbent particle size.     

Decoration of worm-like Cu2S particles on CuCo2S4 micro-spheres: An effective strategy to improve the electromagnetic dissipation feature

Civilization can be shielded from the dangerous electromagnetic spectrum by using microwave absorption materials, however, absorbing electromagnetic radiation with thin thickness and high bandwidth remains a challenge, especially at scales that are significant. Herein, we propose a novel architecture where worm-like Cu₂S particles are decorating CuCo₂S₄ micro-spheres were decorated, and this method is thought to be a successful one for enhancing the created nanocomposite's ability to dissipate electromagnetic radiation. Changing the filler loading percentage allows the nanohybrids' electromagnetic characteristics and microwave dissipation effectiveness to be efficiently changed. This leads to the creation of ultra-bandwidth absorbers with thin thickness, which are then tested using waveguide and free-space techniques. The sample with a thickness of 1.4 mm has a maximum reflection loss of ?18 dB and a maximum bandwidth of 3.6 GHz. The hetero-structures, multi-interfaces, and multiple relaxations phenomena, as well as the combined effects of the two components, are credited with the superior microwave absorption performance compared with the state-of-the-art. This finding demonstrates that CuCo₂S₄/Cu₂S nanohybrids pave the way for the development of future high-performance microwave absorption materials.     

Fabrication and microwave absorbing property of WO3@WC with a core-shell porous structure

Special microstructure can significantly improve the microwave absorption property of rare materials. In this paper, porous WC powders were successfully synthesized by spray granulation method. Then, WO₃@WC materials with core-shell porous structure can be prepared after 410 °C heating treatment at different time to form the outer WO₃ oxidation layer. In addition, the microstructure, morphology, phase analysis and electromagnetic property were fully studied by investigating the WC-based materials in different structures. For WO₃@WC core-shell porous materials, when the coating thickness was 2.1 mm, the maximum reflection loss can reach ?19.4 dB at 12.6 GHz, which shows quite good microwave absorbing effects. The core-shell porous structure enhances the original microwave absorption performance due to the multiple reflection reflections and polarizations.     

Enhanced electromagnetic wave absorption of Fe-doped silicon oxycarbide nanocomposites

Polymer-derived ceramics (PDCs), such as SiOC, SiCN, SiBCN, and SiC are considered the best candidates for designing high-performance microwave absorber due to their controllable structure, homogeneous element composition at atom level, tunable electromagnetic and electrochemical properties. Herein, Fe ions doped silicon oxycarbide (Fe ions-SiOC) ceramics have been successfully fabricated via solvothermal method. The electromagnetic absorption performances of the nanocomposites prove to be controllable via tailoring Fe ion contents. The Fe ions effectively enhance both the interfacial polarization of amorphous SiOC, and the dielectric properties of the nanocomposites but barely effect magnetic properties of the nanocomposite. As for 0.16 mol/L-SiOC ceramics annealed at 1450°C, the effective absorption bandwidth as high as 2.00 GHz and reflection loss of −59.60 dB at 5.40 GHz with the thickness of 4.55 mm are obtained. Such work opens up a novel and simple route to scale up the PDC-based materials with broadband and excellent microwave absorbing performances.     

Fabrication of hierarchical PANI@W-type barium hexaferrite composites for highly efficient microwave absorption

Hexagonal barium ferries is a promising and efficient microwave (MW) absorbing material, but the low dielectric loss and poor conductivity have limited their extensive applications. In this work, a simple tactic of coating conductive polymer PANI on hexaferrite BaCo₂Fe₁₆O₂₇ is presented, wherein the dielectric properties are customized, and more significantly, the electromagnetic loss is greatly enhanced. As displayed from structural characterizations, PANI were coated equably on the surface of hexaferrite grains by an in-situ polymerization process. The outcomes exhibit the as-prepared PANI@hexaferrite composite has remarkable electromagnetic wave absorption capacity. When the thickness is 6.0 mm, the minimal RL of ?40.4 dB was achieved at 2.9 GHz. The effective absorption bandwidth (RL < ?20 dB) of 0.65 GHz, 0.53 GHz, 0.65 GHz, 0.52 GHz, 0.46 GHz and 0.39 GHz was achieved separately when the thickness ranges from 4 to 9 mm. The highly efficient MW absorbing performance of PANI@hexaferrite composite were the consequence of multiple loss mechanisms and perfect impedance matching. It is demonstrated that the PANI@hexaferrite composite with excellent MW absorption performance is expected to be potential MW absorbers for extensive applications.     

Temperature dependent microwave attenuation behavior for carbon-nanotube/silica composites

SiO₂-matrix composites filled with 2, 5 and 10 wt.% multiwalled carbon nanotubes (MWCNTs) were prepared to evaluate the dielectric properties and microwave attenuation performances over the full X-Band (8.2–12.4 GHz) at a wide temperature ranging from 100 to 500 °C. On the basis of the conductivity induced by the structure of the MWCNT, the transport of migrating and hopping electrons in the MWCNT micro-current network has been discussed, and the effects of MWCNT content and temperature on the electronic transport and conductivity have been investigated. These effects also have great influences on the dielectric properties, electromagnetic wave propagating and microwave attenuation performances of the composites. The behavior of electromagnetic interference (EMI) shielding and microwave absorption provide the technical direction for the design of microwave attenuation materials and also indicate that CNT-based composites could be promising candidates for microwave attenuation application.     

Dual gradient direct ink writing of functional geopolymer-based carbonyl-iron/graphene composites for adjustable broadband microwave absorption

As a novel type of moulding technology, additive manufacturing (AM) can realise the rapid manufacturing of complex structures. This research applied dual gradient direct ink writing (DGDIW) with in-situ dispersion to fabricate multi-materials in an extensive gradient range. Functionally graded materials (FGM) have emerged as intelligent composites with peculiar advantages in wave absorption applications. An FGM geopolymer containing carbonyl-iron and graphene (CIG) powders with graded structure was successfully fabricated to enhance the wave-absorbing property via DGDIW three-dimensional (3D) printing. Compared with the non-structured homogeneous geopolymer composites, FGM composites performed more consecutive and effective absorbing from 2 to 18 GHz, resulting in a significantly increased electromagnetic (EM) wave absorption property. Combining with the gradient content of CIG fillers, the impedance matching and electromagnetic attenuation of 3D printed gradient lattice structure geopolymer composites has been significantly improved, the minimum reflection loss can reach ?46.47 dB at 17.58 GHz with a broadband absorption of 14.62 GHz (3.38–18.00 GHz). The results provided a promising strategy for fabricating functional graded ceramic composites with great potential as an absorption device in wave absorption applications, especially in protective structures, radiation-proof equipment/architecture, and defence constructions.     

Electromagnetic wave absorbing properties of glucose-derived carbon-rich SiOC ceramics annealed at different temperatures

A kind of glucose-derived carbon-rich silicon oxycarbide (glucose-SiOC) nanocomposite with excellent electromagnetic wave absorbing performance is obtained via solvothermal method, and then pyrolyzed at high temperature (1300°C and 1400°C) under argon atmosphere. The structural evolutions and the electromagnetic wave absorbing capabilities of the nanocomposites have been systematically investigated. The resultant 3 mol/L glucose-SiOC ceramic exhibits a heterostructure, in which nanosized glucose-derived carbon and SiC particles decorate on amorphous SiOC network. Benefitting from the nanosized carbon, SiC particles and the heterostructure attributes, the 3 mol/L glucose-SiOC ceramic displays a strong electromagnetic wave-absorbing property. The minimum reflection coefficient of the 3 mol/L glucose-SiOC ceramic pyrolyzed at 1400°C reaches −27.6 dB at 13.8 GHz. The widest effective absorption bandwidth attains 3.5 GHz in Kμ-band. This work opens up a novel and simple route to fabricate polymer-derived ceramics with excellent electromagnetic wave-absorbing performance.     

SiC network reinforced SiO2 aerogel with improved compressive strength and preeminent microwave absorption at elevated temperatures

Improved compressive strength and preeminent microwave absorbing properties are of great importance to meet the harsh requirements of the thermal environment. Herein, the SiC network reinforced SiO₂ aerogel composites were synthesized via the carbonation, chemical vapor deposition, and sol-gel process using melamine sponge as the precursor and carbon foam as the structural template, followed by a heat treatment in the elevated temperature range of 300–1200 °C. The results showed that the compressive performance was significantly enhanced as a superior compressive response of 3.46 MPa at 9.49 % strain was obtained owning to the strengthened SiC skeleton wrapped by the SiO₂ aerogel with the rising temperature. Besides, the composite after being warmed at 900 °C was provided with an efficient electromagnetic absorption capacity with a minimum reflection loss value of −55.38 dB at 16.56 GHz and a maximum effective frequency bandwidth of 8.16 GHz at 4.10 mm, resulting from the optimal attenuation constant as well as superior impedance matching ratio. Given the outstanding compressive strength and microwave absorbing characteristics, the aerogel composite has a good prospect in the complex electromagnetic fields.     

Formation of Sn filled CNTs nanocomposite: Study of their magnetic,dielectric properties and enhanced microwave absorption performance at gigahertz frequencies

The Simplistic formation, advantageous configuration, non-colossal magnetoresistance and broadband absorption are important parameters for microwave absorbent materials. In this study, a core-shell nanocomposite comprising of Sn-filled carbon nanotubes (Sn/CNTs) was prepared by arc discharge method. The microstructure, morphology and surface composition of Sn/CNTs-based core-shell nanocomposites were characterized in detail. Sn/CNTs nanocomposite showed a magnetic signal due to the broken bonds and defects at interfaces in Sn/CNTs. The weak ferromagnetism was found to be helpful in improving magnetic permeability in the Sn/CNTs which confirms its role as a magnetic loss material under incident electromagnetic wave. Sn-filled CNTs revealed an appropriate value of dielectric constant, which plays an important role in impedance matching upon incident electromagnetic wave. The composite of Sn-CNTs and paraffin with a 50 wt % loading showed the lowest reflection loss (RL) of ?43.87 dB at 10 GHz, with a wide effective absorption band (RL ≤ ?10 dB) of 3 GHz in thickness of 2.3 mm. This enhanced performance is attributed to the combined effect of the conduction loss in one-dimensional core-shell architecture, the interfacial loss Sn-CNT interface, the magnetic loss due to defects-induced ferromagnetism in Sn shell, and in the carbon-containing atomic layers of CNTs.