Electromagnetic Absorption Properties Research Articles

Fabricating lignin-based carbon nanofibers as versatile supercapacitors from food wastes

Recently, the high-value utilization of food wastes has attracted great interest in sustainable development. Focusing on the major application of electrochemical energy storage (ECES), light-weight lignin-based carbon nanofibers (LCNFs) were controllably fabricated as supercapacitors from melon seed shells (MSS) and peanut shells (PS) through electrospinning and carbonizing processes. As a result, the optimal specific capacitance of 533.7 F/g in three-electrode system, energy density of 69.7 Wh/kg and power density of 780 W/Kg in two-electrode system were achieved. Surprisingly, the LCNFs also presented a satisfied electromagnetic absorption property: The minimum reflection loss (RL) value reached −37.2 dB at an absorbing frequency of 7.98 GHz with an effective frequency (RL < 10 dB) of 2.24 GHz (6.88 to 9.12 GHz) at a thickness of 3.0 mm. These features make the multifunctional LCNFs highly attractive for light-weight supercapacitor electrodes and electromagnetic wave absorbers applications.

Preparation and characterization of an electromagnetic composite polypyrrole/polyethylene short filament geotextile

In this paper, firstly, polypyrrole was prepared by in situ polymerization using pyrrole as the monomer, hexahydrate ferric chloride as the oxidizer and dopant, and polyethylene geotextile as the substrate to prepare a polypyrrole/polyethylene short filament geotextile composite; secondly, the electromagnetic microwave absorption property and shielding property of the polypyrrole/polyethylene short filament geotextile composite were investigated; finally, the chemical structure of the polypyrrole/polyethylene short filament geotextile composite was characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Raman test methods. The results show that the reflection loss value is up to the minimum value of –17.53 dB in the frequency range of 0–3 GHz and the best absorbing performance is obtained at the frequency of 1.12 GHz. In the frequency range of 0.95–1.25 GHz, the reflection loss value is less than –10 dB, and the electromagnetic wave is effectively absorbed. The shielding effectiveness value is up to the maximum value of 16.07 dB at the frequency of 1.19 GHz, that is, the shielding ability becomes strongest at the frequency of 1.19 GHz; otherwise, the shielding effectiveness is higher than 14 dB in the frequency range of 0.17–3.0 GHz. The FTIR, Raman, XRD, and DSC tests result show that polypyrrole has been successfully loaded on the polyethylene geotextile, improving the crystallinity and thermal stability property of the composite.

Crystal structure, Curie temperature, and electromagnetic absorption properties in FexCo30Ni60−xSi5Al5 (x = 30, 35, 40, 45) high entropy alloys

In order to meet the requirements of future national defense for high temperature electromagnetic (EM) absorbing performance, a series of FexCo30Ni60−xSi5Al5 (x = 30, 35, 40, 45) high-entropy alloys (HEAs) powders was prepared and their Curie temperatures (TC) were measured by a self-made Wheatstone bridge. According to the results, varying the Fe/Ni ratio affected the crystal structure, Curie temperature, oxidation resistance, and electromagnetic absorbing properties of the above compounds. Since Fe has a BCC structure and is thus easier to form the solid solutions with Si and Al, the crystal structure of the alloy has changed from FCC toward BCC with increasing Fe dopant content. In turn, the Curie temperature (TC) decreased from 473.68 °C to 358.07 °C, being lower than their initial oxidation temperature (>800 °C). The reflection losses (RL) of powders at room temperature and high temperatures (≤500 °C) were calculated as well. It was found that the flake powders after ball milling gained a larger aspect ratio, resulting in the better absorption effect, which was due to high toughness and low strength characteristics of the initial FCC structure. Furthermore, the permittivity and permeability of alloys upon heating reached impedance matching at a certain temperature, thus achieving the greater RLmax value. Finally, the high-temperature EM absorption characteristics of HEAs were shown to merit a thorough study.

Electrospinning fabrication and enhanced microwave absorption properties of nickel porous nanofibers

One-dimensional Ni porous nanofibers (Ni PNFs) were prepared through a facile electrospinning followed by hydrogen reduction process, and their electromagnetic characteristics and microwave absorbing properties were investigated. Benefiting from the unique microstructure, three-dimensional conductive network and multiple attenuation forms, Ni PNFs exhibit remarkably increased dielectric loss capacity and improved impedance matching level relative to Ni nanoparticles. Consequently, Ni PNFs offer a significantly enhanced microwave absorption property with a minimum reflection loss (RL) of −40.4 dB at a relatively low filling ratio of 30 wt% and an effective absorption bandwidth (RL<−10 dB) of 4.6 GHz (8−12.6 GHz). Our results demonstrate that the microstructure and morphology of materials have considerable influence on their electromagnetic performances and the as-obtained Ni PNFs can be a promising candidate for lightweight and high-efficiency microwave absorption or electromagnetic shielding.

Novel hierarchical structure of MoS2/TiO2/Ti3C2Tx composites for dramatically enhanced electromagnetic absorbing properties

In order to prevent the microwave leakage and mutual interference, more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation. In this work, we have successfully prepared MoS2/TiO2/Ti3C2Tx hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties. Supported by comprehensive characterizations, MoS2 nanosheets were proved to be anchored on the surface and interlayer of Ti3C2Tx through a hydrothermal process. Additionally, TiO2 nanoparticles were obtained in situ. Due to these hierarchical structures, the MoS2/TiO2/Ti3C2Tx composites showed greatly enhanced microwave absorbing performance. The MoS2/TiO2/Ti3C2Tx composites exhibit a maximum reflection loss value of −33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1 GHz (13.9–17 GHz) at the thickness of 1.0 mm, implying the features of wide frequency and light weight. This work in the hierarchical structure of MoS2/TiO2/Ti3C2Tx composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.

Preparation and excellent electromagnetic absorption properties of dendritic structured Fe3O4@PANI composites

Fe3O4, as a typical absorber, its electromagnetic wave (EMW) absorption properties are far from meeting the requirements of practical application due to its poor impedance matching. In this study, three kinds of novel heterogeneous structured composites, dendritic Fe3O4@(HCl doped PANI), Fe3O4@(p-TSA doped PANI) and Fe3O4@(dedoped PANI), were prepared via hydrothermal method combined with thermal reduction and in-situ polymerization, and their phase composition, microscopic morphologies, static magnetic properties, EMW absorption performance and absorption mechanisms were investigated. The results showed that the introduction of different medium doped and dedoped PANI greatly enhanced the EMW absorption performance of Fe3O4. The outstanding advantages of Fe3O4@(HCl doped PANI) were that the widest effective absorption bandwidth (EAB) up to 6.08 GHz in a relatively thin thickness of 2.1 mm. And the Fe3O4@(dedoped PANI) composite achieved strong absorption ability (− 53.08 dB@3.04 GHz) at low frequency in a relatively thin thickness (4.9 mm). The remarkable improvement of EMW absorption performance of dendritic Fe3O4@PANI composites could be attributed to the introduction of dissipation mechanisms, the optimization of impedance matching characteristics and the formation of appropriate conductive network microstructure. The dendritic Fe3O4@PANI composites are promising EMW absorption materials and have great practical application value.

Electromagnetic microwave absorption property of MoC synthesized via a facile solid-state reaction method

Electromagnetic microwave absorption property of MoC synthesized via a facile solid-state reaction method

3D-printed impedance gradient Al2O3 ceramic with in-situ growing needle-like SiC nanowires for electromagnetic wave absorption

As a novel type of additive manufacturing, three-dimensional (3D) printing can efficiently realize the manufacturing of ceramic devices with more sophisticated structures. In this study, the method combining digital light processing (DLP) 3D printing technology and modified ceramic precursor polysiloxane (PSO) was not only used to fabricate Al2O3 ceramic devices with a gradient impedance bilayer structure, which consist of a cross-twist/flat structure with a torsion angle of 60°, but also to prepare needle-like SiC nanowire absorbents grown in situ to further endow the ceramic functional characteristics. The microstructure was regulated by different times of impregnation, light-curing, and thermal treatment of ferrocene-modified PSO, and Al2O3/SiCnw/SiOC composites with different electromagnetic absorption properties were prepared. We found that the Al2O3/SiCnw/SiOC composite (sample 1400–2) exhibited the optimal microwave absorption performance when it was immersed and light-cured twice, which was ascribed to its comprehensive satisfaction of the impedance matching and attenuation characteristics. When the thickness of sample 1400–2 was as thin as 2.5 mm, the minimum reflection coefficient (RCmin) reached −44.35 dB, indicating that more than 99.9990% of the electromagnetic waves could be absorbed. As the thickness increased to 2.8 mm, the effective absorption bandwidth (EAB) in the X-band was 3.6 GHz, which indicated that the effective coverage rate was as high as 85.7%. The results indicate that the generation of the stacking fault, dipole and interfacial polarization of the Al2O3/SiCnw/SiOC composites, and increasing conductivity contribute to the promotion of dielectric loss. Thus, the Al2O3/SiCnw/SiOC composite with bilayer gradient impedance structures is a good candidate for stealth radar wave absorption.

Microstructural Design of Necklace-Like Fe3O4/Multiwall Carbon Nanotube (MWCNT) Composites with Enhanced Microwave Absorption Performance

In order to manufacture microwave absorbers with strong attenuation abilities and that are light weight, in this paper, ferromagnetic carbon matrix composites were prepared by the composite of carbon nanotubes with adjustable dielectric constant and Fe3O4. Fe3O4/MWCNT composites with well-designed necklace-like structure and controllable size in the range of 100–400 nm have been successfully achieved by a simple solvent thermal method. A series of samples were prepared by changing experimental parameters. The microwave absorption characteristics of these samples were studied from the dielectric constant and magnetic permeability in two aspects. The electromagnetic absorption properties of the composites show obvious differences with different microsphere sizes, different microsphere density and different proportion of additives. When the solvothermal time is 15 h and the microsphere size is 400 nm, the reflection loss reaches −38 dB. The interfacial polarization caused by the unique structural design and good impedance matching produce composites that possess excellent electromagnetic loss ability.

Edge selectively oxidized graphene on carbonyl iron composites for microwave absorption and radar cross-section performance at X- and Ku-band

This study examined the microwave absorption properties of graphene oxide-carbonyl iron particle (GOCIP) composites and edge selectively oxidized graphene-CIP (EOGCIP) composites with a variation of graphene contents. Due to the addition of selectively oxidized graphene (EOG) to CIP, the resultant EOGCIP composites revealed excellent electromagnetic (EM) absorption properties. Significantly, the minimum reflection loss (RLmin) of −45.37 dB at 10 GHz with a bandwidth (BW@−10 dB) of 4.08 GHz with a thickness of 1.52 mm observed for EOG (5.0 wt%)CIP (72 wt%) composite. Moreover, the highest value of RLmin reached −69.27 dB at 15 GHz with BW@−10 dB beyond 6.47 GHz with a thickness of only 1.33 mm for EOG (0.5 wt%)CIP (72 wt%) composite. In addition, the EOGCIP composites revealed the most robust reduction in the radar cross-section value of approximately 35 dBsm against that of Al flat plate with the same physical area. The EM absorption properties of EOGCIP composites were enhanced compared to those of GOCIP and CIP composites. The increasing content of EOG tunes the dielectric properties of EOGCIP composites to attain proper impedance matching. Moreover, the unique structure of EOG can induce dipolar and interfacial polarization, which increases the dielectric loss in synchronization with magnetic loss resulting in enhanced EM absorption properties. This study suggests a new approach for controlling the EM absorption properties, essentially in the X-band region, which is worthwhile for radar absorption materials (RAM) applications.

Lightweight, Fire-Retardant, and Anti-Compressed Honeycombed-Like Carbon Aerogels for Thermal Management and High-Efficiency Electromagnetic Absorbing Properties.

Ordered porous carbon materials (PCMs) have potential applications in various fields due to their low mass densities and porous features. However, it yet remains extremely challenging to construct PCMs with multifunctionalization for electromagnetic wave absorption. Herein, the honeycombed-like carbon aerogels with embedded Co@C nanoparticles are fabricated by a directionally freeze-casting and carbonization method. The optimized aerogel possesses low density (0.017g cm-3 ), fire-retardant, robust mechanical performance (compression moduli reach 1411 and 420kPa in the longitudinal and transverse directions at 80% strain, respectively), and high thermal management (high thermal insulation capability and high-efficiency electrothermal conversion ability). Notably, the optimized aerogel exhibits the excellent electromagnetic wave absorption properties with broad effective absorption bandwidth (13.12-17.14GHz) and strong absorption (-45.02dB) at a thickness of only 1.5mm. Density functional theory calculations and the experimental results demonstrate that the excellent electromagnetic wave absorption properties stem from the synergetic effects among high electrical conductivity, numerous interfaces and dipoles and unique ordered porous structure. Meanwhile, the computer simulation technology (CST) simulation confirms that the multifunctional aerogel can attenuate more electromagnetic energy in a practical environment. This work paves the way for rational design and fabrication of the next-generation electromagnetic wave absorbing materials.

Ultralight, compressible, and anisotropic MXene@Wood nanocomposite aerogel with excellent electromagnetic wave shielding and absorbing properties at different directions

The advanced electromagnetic interference (EMI) shielding and electromagnetic (EM) wave absorbing materials are greatly desired for the elimination of increasingly serious electromagnetic radiation pollution. Herein, the natural wood was delignified to fabricate the wood aerogel as a porous framework, then f-Ti3C2Tx nanosheets were assembled into the wood aerogel to give a novel ultralight, highly compressible and anisotropic MXene@Wood (M@W) nanocomposite aerogel (0.108 g/cm3), which possesses both EMI shielding and EM absorbing properties at the different directions. Because of the anisotropic wood aerogel skeleton, the M@W aerogels present channel-like microstructure and ideal structural load carrying capacity at the parallel growth direction, and the layered microstructure and highly compressibility at the vertical growth direction are obtained at the same time. By regulating the f-Ti3C2Tx MXene loading, the as-prepared M@W aerogel can achieve a striking high EMI shielding effectiveness of 72 dB at the parallel growth direction and a broadened effective absorption bandwidth covering 8.2–12.4 GHz at the vertical growth direction simultaneously. This work provides a facile alternative strategy for developing wood-derived anisotropic MXene@Wood nanocomposite aerogel, which possesses both EMI shielding and EM absorbing properties at different directions.

Electromagnetic wave absorbing properties of SrFe12-2xCoxTixO19 hexaferrite–CNT–epoxy composites

A wideband electromagnetic (EM) wave absorber for the X-band (8–12 GHz) is designed using M-type hexaferrite, SrFe12-2xCoxTixO19 (x = 1.1, 1.2, 1.25, and 1.3)–CNT (0–3 wt%)–epoxy (10 wt%) composites. As x increases from 1.1 to 1.3, the ferromagnetic resonance (FMR) of the hexaferrite powder gradually decreases from 15.0 GHz to 6.4 GHz due to the decrease of magnetocrytalline anisotropy. The EM absorption frequency range changes in accordance with changes in the FMR frequency. Among the series of samples, the x = 1.25 sample demonstrates EM absorption properties optimized for the X-band with the lowest reflection loss (RL) of −40 dB and satisfying RL <−10 dB in the 7–13 GHz range. When 1 wt% carbon nanotubes (CNTs) are added to the composite (x = 1.25), permittivities ε′ and ε″ increased significantly owing to the CNT particle’s high conductivity, and the intensive EM absorbing region expanded to a wide frequency–thickness range. A further increase in the CNT content (2–3 wt%) weakened the overall EM absorption due to an increase in reflection. Adding 1–2 wt% of CNT to hexaferrite is very effective because it not only increases the shielding effectiveness, but also yields better EM absorption at lower thicknesses of 1.5 mm or less.

Electromagnetic Wave Absorption Properties of Barium Ferrite/Reduced Graphene Oxide Nanocomposites

Reduced graphene oxide (rGO) and M-type hexagonal ferrites such as BaFe12O19 have attracted great attention as electromagnetic (EM) wave absorbing materials in recent years. In this research, different weight percents of BaFe12O19/rGO nanocomposites were incorporated into the microwave absorbing layers and their EM wave absorption was investigated. Barium ferrite was synthesized through the co-precipitation method. Graphene oxide (GO) was synthesized through the modified Hummers’ method. The synthesized GO was reduced to rGO nanosheets using a reducing agent. The synthesized barium ferrite and rGO were then mechanically milled to form BaFe12O19/rGO nanocomposite. The chemical bondings, phase analysis, magnetic properties, particle morphology, and EM wave absorbing properties were investigated using FTIR, XRD, Vibration Sample Magnetometer (VSM), FESEM, and Vector Network Analyzer (VNA), respectively. The saturation magnetization (Ms) and the coercivity (Hc) of the synthesized BaFe12O19/rGO nanocomposite were 31 emu/g and 1.5 kOe, respectively. The EM absorption properties in the X-band (8.2-12.4 GHz) showed that the maximum reflection loss (RL) of -7.39 dB could be obtained for the nanocomposite containing only 10 wt. % of BaFe12O19/rGO nanocomposite in a resin matrix with a thickness of 2 mm.

The electromagnetic absorbing properties of plasma-sprayed TiC/Al2O3 coatings under oblique incident microwave irradiation

High performance absorbing coatings attract great interest because of the urgent demand for radar stealth technology. However, most reported absorbing coatings focused on the incident microwave were perpendicular to the surface of the coatings. Here, a kind of absorber of TiC/Al2O3 was prepared by plasma spraying method and the influence of TiC content and oblique incident microwave irradiation on the absorbing properties of TiC/Al2O3 were reported. The absorbing performance firstly increased and then decreased with increasing the TiC content due to the impedance matching and attenuation constant cannot match well at the same time. Meanwhile, compared with TE polarization, TM polarization of the plasma-sprayed TiC/Al2O3 coatings was more sensitive to the incident angle. This study demonstrates the feasibility of plasma-sprayed TiC/Al2O3 absorbing coatings for electromagnetic applications.

Electromagnetic and microwave absorption properties of MWCNTs based polymer nanocomposites

Purpose The purpose of the present work is to fabricate composite with strong absorbing nature and with more strength. The usage of wireless communication is increasing day by day, electromagnetic absorbing material is required to reduce this pollution. In the present experimental investigation, composites were fabricated for zero and 45° fiber orientation and as a filler material of Multiwall Carbon Nanotubes (MWCNTs) for the proposed percentage in the composites. Microwave absorbing properties were investigated for both perfect electric conductor (PEC)-backed composites and without PEC-backed composites. Design/methodology/approach The electromagnetic absorbing performance was analyzed based on complex permeability, complex permittivity, dielectric tangent and magnetic tangent losses. The experimentation was done by Vector Network Analyzer in the frequency range of 8.2 to 12.4 GHz by X-band. The surface morphological study was done. The mechanical and thermal properties are also investigated for these composites. Findings By investigating the experimental values, the induced percentage of MWCNTs and PEC of composites affects the electromagnetic and microwave absorption properties of the composites. The microwave absorption properties improved when the composites were able to absorb wide bandwidth and low reflection loss. The best results are obtained for PEC-backed composites for 5%, which is about −43.56 dB at 11.1 GHz compared to without PEC-backed composites. The reflection loss is developed by the dielectric loss initiated from MWCNTs and by PEC. Originality/value To the best of the authors’ knowledge, no work was reported on hand lay-up method and PEC-backed composites in electromagnetic absorption properties with regression analysis.

Hydrothermal Synthesis and Microwave Absorption Properties of Nickel Ferrite/Multiwalled Carbon Nanotubes Composites

It is well accepted that the microwave absorption performance of ferrite can be enhanced via the hybridization. However, it is still very challenging to design the hierarchical nanostructure of ferrite hybrids to fabricate wave absorbing composites with both the high efficiency and lightweight. Herein, we successfully realize the in-situ synthesis of nickel ferrite/multiwalled carbon nanotubes (NiFe2O4/MWCNTs) hybrids with a large-scale production by the hydrothermal method. The structural characteristics, morphology, electromagnetic and microwave absorption properties were analyzed by X-ray diffraction, scanning electron microscope and vector network analyzer. The morphological study shows that NiFe2O4 nanoparticles with a small size (tens of nanometers) are coated on the MWCNTs, leading to a three-dimensional hierarchical nanostructure. The NiFe2O4/MWCNTs hybrids show satisfied microwave absorption properties. Typically, the optimized sample shows the minimum reflection loss of −19 dB at 11.3 GHz, and the bandwidth of the reflectivity below −10 dB is 2.5 GHz with a thin thickness of 1.5 mm. This result shall be due to the improved dielectric losses or interface polarization etc. Our results demonstrate a facile approach for the design of ferrite-based microwave absorber to meet the requirements of lightweight, thin-thickness and high efficiency.

Magnetic Fe3S4 LTMCs micro-flowers@ wax gourd aerogel-derived carbon hybrids as efficient and sustainable electromagnetic absorber

As a dielectric loss-type absorber, lamellar transitional metal chalcogenides (LTMCs) become more and more popular in the electromagnetic (EM) absorbing field due to their unique two-dimensional sheet structure. However, it remains challenging for metallic sulfides to obtain magnetic loss, further promoting loss mechanism. Herein, magnetic Fe3S4 LTMCs micro-flowers@ wax gourd aerogel-derived carbon composites are fabricated through a facile pyrolysis process and subsequent hydrothermal method. Compared to a pure biomass carbon or Fe3S4, Fe3S4@C composites exhibited an optimized and adjustable EM characteristic, which can be put down to the synergistic effects between the dielectric/magnetic loss and the impedance match. The sample shows superior EM absorption properties with a minimum reflection loss (RL) of −58.85 dB at 3.1 mm and a broad effective bandwidth (EBW) of 5.40 GHz at the matching thickness of 2.0 mm with a filling ratio of 20 wt%. In addition, the radar cross section (RCS) simulation confirms that the material can effectively suppress EMW (−8.51 dB m2 at zero degree) in practical applications. Therefore, it is believed that the as-prepared Fe3S4@C hybrids can be one of the prospective candidates as high-efficiency EMW absorbers.

MoS2-Decorated/Integrated Carbon Fiber: Phase Engineering Well-Regulated Microwave Absorber

HighlightsA facile one‐step hydrothermal method for producing gram‐scale 1T@2H-MoS2 by imbedding the guest molecules and ions was developed.The influence of different MoS2 phase for electromagnetic absorbing properties was explored by analyzing electromagnetic parameters of 1T/2H MoS2 and 2H MoS2 with 50%, 40%, 30%, 20%, 15%, and 10% filler loading.Taking the advantage of 1T/2H MoS2, the flexible CF@1T/2H MoS2 was also synthesized to mind the request of flexible portable microwave absorption electronic devices.

Lightweight PVDF/γ-Fe2O3/PANI foam for efficient broadband microwave absorption in the K and Ka bands

Lightweight magnetic polyvinylidene fluoride/ferric oxide/polyaniline nanofiber (PVDF/γ-Fe2O3/PANI) foams with excellent microwave absorption performance in the K (18–26.5 GHz) and Ka (26.5–40 GHz) bands were successfully fabricated using heat shaping and a sacrificial templating method. By varying the diameter of the PANI nanofibers (50, 100 or 500 nm), the electromagnetic microwave absorption (EMWA) properties of the composite foams could be precisely tuned. PVDF/γ-Fe2O3/PANI-50 foams with a PANI nanofiber diameter ~50 nm delivered the best all-round EMWA performance, demonstrated by minimum reflection loss (RLmin) values of −38.7 dB at 26.33 GHz and −38.4 dB at 28.9 GHz at an absorber thickness of 2.5 mm. Further, the effective absorption bandwidth (EAB) of the composite could be adjusted to cover the entire 18–40 GHz frequency region simply by changing the absorber thickness (from 1.5 to 3.5 mm). This work introduces a simple low cost strategy for designing high performance microwave absorbers.