Electromagnetic Wave Absorption Applications Research Articles

Bimetal–organic frameworks derived tuneable Co nanoparticles embedded in porous nitrogen-doped carbon nanorods as high-performance electromagnetic wave absorption materials

Bimetal-organic frameworks derived tuneable Co nanoparticles embedded in porous nitrogen-doped carbon nanorods for electromagnetic wave absorption applications.

Synthesis of MOF-derived Fe7S8/C rod-like composites by controlled proportion of carbon for highly efficient electromagnetic wave absorption

In this study, we firstly used the MOF-derived Fe7S8/C rod-like composites as absorbers and systematically investigated the synergistic effect of Fe7S8 and carbon in electromagnetic wave absorption applications. By controlling the introduced dosage of ferric salt, the proportion of carbon and Fe7S8 in composites could be adjusted, which made a significant effect on the electromagnetic parameters and absorption performance. When the carbon proportion was about 33.9 wt%, the synergistic effect between Fe7S8 and carbon guaranteed the optimized impedance matching and strong dissipation ability, presenting superb absorption performance. The optimal performance reflected in the minimum reflection loss of −68.86 dB at 12.08 GHz with a thickness of 1.67 mm, and the effective bandwidth was up to 4.56 GHz at 1.45 mm. Therefore, this study provides a facile method for preparing the Fe7S8/C absorbers and emphasizes the significance of the ratios between Fe7S8 and carbon on the electromagnetic parameters and absorption performance.

Tailing size and impedance matching characteristic of nitrogen-doped carbon nanotubes for electromagnetic wave absorption

Carbon nanotubes (CNTs) have important application in electromagnetic wave absorption due to their unique tubular structure, lightweight feature and high electrical conductivity. However, sole CNTs suffer from bad impedance matching characteristic, leading to unsatisfactory absorption performance. Herein we propose a universal SiO2-assisted strategy to fabricate Ni nanoparticle-encapsulated nitrogen-doped CNTs on the SiO2 spheres (Ni@NCNT@SiO2). Due to the spatial separating effect, the formation of large metal aggregates and large-sized NCNTs in the products are avoided effectively. In the meanwhile, the ideal impedance matching characteristic is also achieved due to the introduction of the non-conductive SiO2 spheres. As a result, even with a low matching thickness (1.3–2.0 mm), the reflection loss values of Ni@NCNT@SiO2 reaches −30 dB. Furthermore, the proposed method can be also used to fabricate Fe3C/Fe@NCNT@SiO2 and Co@NCNT@SiO2 with satisfactory absorption properties, demonstrating its universality for synthesis of high-performance absorbers based on CNTs.

Interfacial and defect polarization in MXene-like laminated spinel for electromagnetic wave absorption application

Manufacturing advanced absorbers is an effective way to deal with the greater electromagnetic pollution challenges associated with the application of 5G technology. While reasonable morphology design is an efficacious method to improve the absorption performance of the absorber. Herein, a series of Co-based spinel Co3O4/ACo2O4 (A = Ni, Cu, Zn) were successfully synthesized via a facile PVP-assisted hydrothermal method. It is worth mentioning that the Co3O4/ZnCo2O4 with MXene-like laminated structure was synthesized successfully for the first time (to our knowledge) by changing the type of elements in A position. The EAB of MXene-like laminated Co3O4/ZnCo2O4 absorber can reach 6.24 GHz (from 11.6 to 17.84 GHz) with a matching thickness of 2.62 mm. This excellent performance can be attributed to the multiple scattering, interfacial polarization, and polarization induced by lattice defects and oxygen vacancies (the dominant). This work offers a novel pattern for improving the EMW absorption ability of pure spinel by manufacturing MXene-like laminated Co-based spinel and adjusting annealing temperature reasonably.

3D flower-like Co-based oxide composites with excellent wideband electromagnetic microwave absorption

Transition metal oxides because of their excellent dielectric properties have been population for electromagnetic wave absorption application. In this paper, through two-step synthesis, hollow CoSnO3 was in-situ growth between layers of self-assembled flower-like ZnCo2O4 in the solvothermal process. The multi-layer sheet structure of ZnCo2O4 nanoflowers provides growth space for CoSnO3, which can increase interface polarization and natural resonance. Hybrid structure expands the propagation path of electromagnetic waves and the times of reflections and scattering. By adjusting the content of the growing process of CoSnO3, the maximum reflection loss (RL) at 12.4 GHz was −56.0 dB, and the wide effective absorption bandwidth (EAB) of 6.24 GHz (RL < −10 dB) was obtained at a thin matching thickness of 2.6 mm ZnCo2O4@CoSnO3 composites showed satisfactory impedance matching in the frequency range of 2–18 GHz. Therefore, ZnCo2O4@CoSnO3 composites provides a new research idea for electromagnetic wave absorption in morphology designed.

Large-scale and low-cost synthesis of in situ generated SiC/C nano-composites from rice husks for advanced electromagnetic wave absorption applications

Electromagnetic interference and pollution are becoming more prevalent due to rapid development and wide adoption of information technology. As promising microwave absorbents, SiC nanomaterials have aroused extensive attention due to the good absorption and tunable electrical properties. However, practical implementation is hindered by limited and simple dipolar polarization and complicated fabrication process. Herein, in situ generated SiC/C nanocomposites are designed and prepared from natural rice husks via magnesiothermic reduction. The in situ generated SiC nanoparticles are anchored inherently within the connecting carbon matrix yielding an enriched SiC-C interface. The carbon concentration can be easily adjusted by adding different amount of RHs-derived nano SiO2 during the reaction in order that the optimal impedance matching and attenuation capability can be achieved. Consequently, the minimum reflection loss of −27.78 dB was obtained at 10.1 GHz with the thickness of 2.4 mm, while the effective absorption bandwidth is close to 3.9 GHz with the thickness of 1.6 mm. Considering the low-cost and large-scale advantages of the preparation protocol and excellent EM absorption properties, the fabrication strategy and in situ generated SiC/C materials have large potential for EM wave absorption applications.

Constructing 1T/2H MoS2 nanosheets/3D carbon foam for high-performance electromagnetic wave absorption

Three-dimensional (3D) carbon-based materials have attracted growing attention in the field of electromagnetic wave absorption applications. However, their high conductivity results in high dielectric constant, leading to impedance mismatching, and this characteristic finally weakens their electromagnetic wave absorption performance. In this work, 3D carbon foam (3DCF) was successfully prepared by calcining the melamine foam as the carbon framework precursor under N2 atmosphere. Subsequently, 1T-2H MoS2 nanosheets were uniformly assembled on the surface of the 3DCF skeleton through a solvothermal process. The diameter of the 3DCF skeleton was about 1 μm and the thickness of the 1T-2H MoS2 on the surface was about 150 nm. The 3D network brings in many advantages for microwave attenuation, including numerous conductive pathways, excellent impedance matching and multi-polarization processes. The composites exhibited a maximum reflection loss (RLmax) of −45.88 dB at 10.2 GHz with the thickness of 2.2 mm, and the effective absorbing bandwidth (EAB) was as wide as 5.68 GHz, implying their superb microwave absorption behavior. This work is believed to offer a strategy for the design of efficient 3D electromagnetic wave absorbers with low density in the future.

CuNi alloy/ carbon foam nanohybrids as high-performance electromagnetic wave absorbers

Three-dimensional (3D) carbon foams (CF) embedded with CuNi alloy nanoparticles have been constructed for electromagnetic wave absorption application. In the synthetic procedure, Ni2+ and Cu2+ were firstly adsorbed into the melamine foam (MF) to form Ni2+-Cu2+/MF composites, which were then subject to the pyrolysis treatment, resulting in the production of mesoporous CuNi alloy/CF. The texture characterizations indicate that CuNi alloy nanoparticles whose size distribution was 20–600 nm were embedded on the surface of the CF. Other than previous carbon structures, the CuNi/CF with CuNi alloy nanoparticles evenly distributed into the 3D carbon matrix inherits the characteristic of the 3D structured N-rich MF, which induces masses of dipole polarization, interfacial polarization and electromagnetic wave scattering. The CuNi11 exhibits excellent electromagnetic wave absorption performance with the reflection loss (RL) of −50.20 dB at a thin thickness of 1.6 mm. This work highlights the effect of metal compositions on the electromagnetic wave absorption performance and provides an environmentally friendly, low cost and easy-to-large-scale-preparation approach for the design of metal alloy/CF electromagnetic wave absorbers.

Control of electromagnetic wave absorption properties in La-Co-Ti substituted M-type hexaferrite–epoxy composites

La-Co-Ti substituted Sr-hexaferrite, Sr0.906La0.094Fe11-2xCoxTixO19 (x = 0.8, 1.0, 1.2, 1.4) powder-epoxy (10 wt%) composites were fabricated for electromagnetic wave (EM) absorption application. Single M-type hexaferrite phase was confirmed by X-ray diffraction analysis for all the samples. Both saturation magnetization and coercivity of the composites decrease with increase of Co-Ti substitution x. Reflection loss (RL) of the hexaferrite powder–epoxy composites were calculated using their complex permittivity and permeability data. The EM absorbing frequency range is controlled by the substitution x because the ferromagnetic resonance (FMR) frequency of the samples is systematically varied following Snoek’s limit law. The hexaferrite sample with x = 1.2 is suitable for use as an X-band (8–12 GHz) radar absorber since RL < -10 dB is satisfied in the full X-band. Also, high EM absorbing performances in millimeter range, RL < -20 dB at 24 GHz (3 mm), and RL < -20 dB at 26.5 GHz (0.9 mm), could be achieved in the FMR-controlled La-Co-Ti substituted M-type hexaferrite-epoxy composite.

A rational route towards dual wave-transparent type of carbonyl iron@SiO2@heterogeneous state polypyrrole@paraffin composites for electromagnetic wave absorption application

The multi-shell composites with carbonyl iron (CIP) and heterogeneous state polypyrrole (PPy) uniformly dispersed in the double SiO2-paraffin permeable matrix (CIP@SiO2@doped PPy@paraffin and CIP@SiO2@eigenstate PPy@paraffin composites) were constructed by a facile method. The design of double permeable matrix and loose spiny space structure could effectively reduce the equivalent permittivity and enhance impedance matching. This hierarchical heterogeneous structure had adjustable electromagnetic parameters and conductivity, thus achieving high electromagnetic wave absorption performance. The best reflection loss (RL) value of the CIP@SiO2@doped PPy@paraffin composites could reach up to −71.8 dB at a thickness of 3.1 mm and the effective absorption bandwidth where RL < −10 dB was 6.8 GHz (11.2–18 GHz) at 2.1 mm. Moreover, the composites exhibited an excellent absorption property with absorption bandwidth below −10 dB of 14.3 GHz and −20 dB of 12.9 GHz at thickness ranging from 1.5 to 5 mm. After the alkaline desorption treatment, the CIP@SiO2@eigenstate PPy@paraffin composites showed good wave absorption performance at high frequency. Typically, a strong RL value of −66.9 dB at 17.9 GHz was achieved and the effective absorption bandwidth was 4.6 GHz. This work studied the electromagnetic characteristics of this new-type composites and explored its application potential as a wave absorbing material. It was found that the composites had good impedance matching in the dual permeable matrix, which was expected to provide a theoretical basis for the development of stealth field in the future.

Anisotropic Electromagnetic Absorption of Aligned Ti3C2Tx MXene/Gelatin Nanocomposite Aerogels.

Assembling Ti3C2Tx MXene nanosheets into three-dimensional (3D) architecture with controllable alignment is of great importance for electromagnetic wave absorption (EMA) application. However, it is a great challenge to realize it due to the weak van der Waals interconnection between MXene nanosheets. Herein, we propose to introduce gelatin molecules as a "chemical glue" to fabricate the 3D Mxene@gelatin (M@G) nanocomposite aerogel using a unidirectional freeze casting method. The Ti3C2Tx MXene nanosheets are well aligned in the M@G nanocomposite aerogel, yielding much enhanced yet anisotropic mechanical properties. Due to the unidirectional aligned microstructure, the M@G nanocomposite aerogel shows significantly anisotropic EMA properties. M@G-45 shows a -59.5 dB minimum reflection loss (RLmin) at 14.04 GHz together with a 6.24 GHz effective absorption bandwidth in the parallel direction (relative to the direction of unidirectional freeze casting). However, in the vertical direction of the same M@G aerogel, RLmin is shifted to a much lower frequency (4.08 GHz) and the effective absorption bandwidth decreases to 0.86 GHz. The anisotropic electromagnetic energy dissipation mechanism was deeply investigated, and the impendence match plays a critical role for electromagnetic wave penetration. Our lightweight M@G nanocomposite aerogel with controllable MXene alignment is very promising in EMA application.

PEDOT coated Cu-BTC metal-organic frameworks decorated with Fe3O4 nanoparticles and their enhanced electromagnetic wave absorption

In this study, Cu3(1,3,5-benzenetricarboxylate) (Cu-BTC) metal-organic frameworks decorated with Fe3O4 nanoparticles were synthesized via the hydrothermal process. Subsequently, the obtained Fe3O4/Cu-BTC was coated by poly(3,4-ethylenedioxythiophene) (PEDOT) via in situ chemical polymerization methods. The chemical, structural, and magnetic hysteresis analysis of particles were carried oud via scanning electron microscope (SEM), X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), and fourier transform infrared spectroscopy (FTIR) machines. The characteristic peaks of C/F and P@C/F were obtained without any other impurities and extra peaks. The Fe3O4 decorated Cu-BTC displayed octahedral morphology with average particle size of 150–170 nm. As an electromagnetic wave absorber, the obtained Fe3O4 decorated Cu-BTC was mixed with 45% by weight of paraffin. For comparative studies, the PEDOT coated Fe3O4/Cu-BTC was also filled to the paraffin matrix. The higher real and imaginary part of permittivity values were obtained with introduction of conductive PEDOT shell. The electromagnetic wave absorption performance of composites was determined with permeability and permittivity values. The result exhibited that the strongest reflection loss was −18.3 dB at 17.5 GHz frequency with a thickness of 5 mm for PEDOT coated Fe3O4/Cu-BTC composite. It was proved that the conductive PEDOT coating on Fe3O4/Cu-BTC enhanced electromagnetic wave absorption capability of composite and the PEDOT coated Fe3O4/Cu-BTC can be considered as a good candidate for electromagnetic wave absorption applications.

A novel approach to prepare polyaniline/Polypyrrole@Cu-BTC/NH2-MIL-101(Fe) MOFs for electromagnetic wave absorption

In this study, the Cu-BTC and NH2-MIL 101 (Fe)@polypyrrole and polyaniline core–shell particles were prepared by in situ polymerization of pyrrole and aniline monomers on the surface of Cu-BTC and NH2-MIL 101 (Fe) for electromagnetic wave absorption applications. Firstly, the Cu-BTC (1,3,5 benzenetricarboxylic acid, BTC) and NH2-chromium (III) terephthalate (MIL-101) were synthesized by solvothermal method. Secondly, the surface of Cu-BTC and NH2-MIL 101 (Fe) mixtures were coated with polypyrrole (PPy) and polyaniline (PANI) by a polymerization of aniline (An) and pyrrole (Py) monomers and denoted as PP@Fe/Cu. For comparative studies, the aniline (An) and pyrrole (Py) monomers were polymerized in the same condition on the surface of NH2-MIL-101 (Fe) powder without the presence of Cu-BTC and the final powder was denoted as PP@Fe. The morphologies, phase structures and magnetic properties of products were characterized by scanning electron microscope (SEM), X-ray diffractometer (XRD), and vibrating sample magnetometer (VSM) machines. The complex permeability and permittivity values of PP@Fe and PP@Cu/Fe were determined in the range of Ku band (12.4–18 GHz). The electromagnetic wave absorption performances were evaluated using obtained permittivity and permeability values. It was observed that PP@Fe and PP@Cu/Fe composites displayed excellent microwave absorption performances. The existence of Cu-BTC into NH2-MIL 101 (Fe) further enhanced the minimum reflection loss from −60 dB to −80 dB.

Physiochemical properties and electromagnetic wave absorption performance of Ni0.5Cu0.5Fe2O4 nanoparticles at X-band frequency

Abstract Due to the unremitting emission of electromagnetic (EM) wave pollution from electronic and electrical devices, the fabrication of materials with EM waves absorption capacity is an active research domain. Ferrite nanoparticles are one of the widely studied materials in the area of EM wave absorption. Hence in this work, Ni0.5Cu0.5Fe2O4 nanoparticles were synthesized using four different coprecipitating agents (NaOH, KOH, NH4OH, and Na2CO3). The structure, composition, morphology, magnetic and thermal properties of all the samples were characterized and compared using XRD, FT-IR, XPS, FESEM, VSM and TGA analysis, respectively. The effect of coprecipitating agents on the EM properties of all the samples for optimum EM wave absorption was investigated and presented within the X-band frequency range. The Ni0.5Cu0.5Fe2O4 nanoparticles prepared with NH4OH was identified as the optimal material due to its superior physiochemical and EM properties. An enhanced EM wave absorption with optimum RL of −42.1 dB was achieved with the optimal material at 11.7 GHz, with 3.5 mm thickness. The material has an absorption bandwidth of 1.51 GHz. Thus, the use of NH4OH amongst other coprecipitants for Ni0.5Cu0.5Fe2O4 synthesis is more favorable for EM wave absorption application.

High-temperature electromagnetic wave absorption, mechanical and thermal insulation properties of in-situ grown SiC on porous SiC skeleton

Multi-functional integrated materials used in extreme environments are gaining increased interest. In this study, a binary porous SiC was fabricated by in-situ synthesis in a SiC skeleton. The binary porous SiC exhibited unique features of synergistic effects of high-temperature electromagnetic (EM) wave absorption, mechanical and thermal-insulation properties. The chemical-composition evolution was characterized by transmission electron microscopy and Raman spectroscopy. Electronic structures were investigated by X-ray absorption near-edge structure at the C K-edge. Based on a vapor–solid–liquid growth mechanism, a decrease in the vacancy defects and unoccupied C density of states (DOS) was manifested in the binary porous SiC. Introducing the second SiC phase resulted in sharply enhanced EM wave absorption performance. The minimum reflection loss was as low as −51 dB, and the effective absorption bandwidth at 600 °C was 3.2 GHz (from 9.2 GHz to 12.4 GHz) with a thickness of 2.4 mm. Meanwhile, the in-situ grown second SiC phase substantially increased the compressive strength to 34.25 MPa, which was nearly 15-fold that of the porous SiC. Moreover, the binary SiC showed a low thermal conductivity of 0.1572 W/m·K. All these results indicated that the binary porous SiC system was ideal for EM wave absorption applications at extremely high temperatures.

Facile preparation of CoS2 nanoparticles embedded into polyaniline with tunable electromagnetic wave absorption performance

Electromagnetic wave absorption has attracted wide attention due to electromagnetic wave pollution and radiation. The dielectric loss coating magnetic nanoparticles structure has a significant influence on electromagnetic wave absorption properties. In this manuscript, magnetic nanoparticles (CoS2) coated polyaniline (PANI) are synthesized via a facile and simple two-step strategy (a microwave assisted hydrothermal reaction followed an in-situ free radical chemical oxidative polymerization). The CoS2 nanoparticles are coated by PANI which is used as the matrix of electron conduction during converting electromagnetic energy into thermal energy. The electromagnetic wave absorption properties of PANI@CoS2 nanocomposites can be adjusted by changing the mass ratios of CoS2 and PANI. Compared with that of CoS2 nanoparticles or PANI, the electromagnetic wave absorption properties of PANI@CoS2 nanocomposites were significantly enhanced due to impedance matching and dielectric loss. When the mass ratio of PANI and CoS2 is 1:3, this nanocomposite exhibits excellent electromagnetic wave absorption. The maximum reflection loss can reach to −54.6 dB at electromagnetic wave frequency of 12.1 GHz and effective absorbing bandwidth is 4.76 GHz ranging from 9.63 to 14.39 GHz under corresponding nanocomposites thickness of 2.1 mm. Hence, PANI@CoS2 nanocomposites have potential application in electromagnetic wave absorption.

Enhancement of the microwave absorption properties of PyC-SiCf/SiC composites by electrophoretic deposition of SiC nanowires on SiC fibers

The employment of coating technique on the silicon carbide fibers plays a pivotal role in preparing SiC fiber-reinforced SiC composites (SiCf/SiC) toward electromagnetic wave absorption applications. In this work, SiC nanowires (SiCNWs) are successfully deposited onto the pyrolytic carbon (PyC) coated SiC fibers by an electrophoretic deposition method, and subsequently densified by chemical vapor infiltration to obtain SiCNWs/PyC-SiCf/SiC composites. The results reveal that the introduction of SiCNWs could markedly enhance the microwave absorption properties of PyC-SiCf/SiC composites. Owing to the increasing of SiCNWs loading, the minimum reflection loss of composites raises up to −58.5 dB in the SiCNWs/PyC-SiCf/SiC composites with an effective absorption bandwidth (reflection loss ≤ −10 dB) of 6.13 GHz. The remarkable enhancement of electromagnetic wave absorption performances is mainly attributed to the improved dielectric loss ability, impedance matching and multiple reflections. This work provides a novel strategy in preparing SiCf/SiC composites with excellent electromagnetic wave absorption properties.

Microwave-based synthesis of (NiCo)x/(MnO)y/C composites and their tunable wave absorption properties in the K band

The combination of metallic and carbon components offers tremendous advantages in the development of advanced composites for electromagnetic wave absorption (EMWA) applications. Herein, hollow (NiCo)x/(MnO)y/C microspheres (MSs) possessing hierarchically porous structures were successfully synthesized via a facile microwave-assisted method followed by a carbonization step. The EMWA performance of the (NiCo)x/(MnO)y/C MSs in the K-band region could be tuned and optimized by adjusting the NiCo/Mn molar ratio, with a NiCo/Mn ratio of 1:1 affording the best EMWA performance. The NiCo/MnO/C MSs exhibited a minimum reflection loss value of -32.3 dB (at 21.4 GHz) and an effective absorption bandwidth (EAB, RL ≤ −10 dB) of 8.33 GHz (from 18.17-26.5 GHz) at a thickness of only 1.0 mm in the K band. The excellent EMWA performance of the (NiCo)x/(MnO)y/C MSs composites can be attributed to a strong EMW attenuation capacity and good impedance matching, which arise through the synergistic action of the components (NiCo alloy, MnO and C) and hierarchical pores.

Design and analysis of negative permittivity behaviors in barium titanate/nickel metacomposites

As an important supplement to the metamaterials, negative permittivity in 'natural' materials has attracted increasing attention, while some fundamental regulation mechanisms and common theoretical principles have not yet been systematically explored. In this paper, the permittivity transition is investigated along with insulator-conductor conversion in BaTiO3/Ni composite. When the Ni content in BaTiO3/Ni composites is lower than and higher than the percolation threshold, Lorentz-like and Drude-type negative permittivity behaviors is obtained, respectively. In addition, the fundamental principles of negative permittivity are discussed, especially the validity of the Kramers–Kronig relations and the relationship between the negative permittivity and the reactance characters. Further, a universal regulatory mechanism of the Drude-type negative permittivity profile is qualitatively analyzed. Negative permittivity and negative permeability are achieved simultaneously in BaTiO3/Ni composites with 35.56 vol% of Ni loading, which show potential application in electromagnetic wave absorption and shielding.

A biomass derived porous carbon for broadband and lightweight microwave absorption

With the continuous progress of science and technology, the traditional magnetic material is no longer able to meet the new complex electromagnetic (EM) environment due to its high bulk density. Therefore, the novel excellent EM absorber with the feature of thin thickness, low density, broad absorption bandwidth and strong absorption intensity is highly desired. Herein, we fabricated a porous carbon with ultrahigh porosity through a facile KOH activation from biomass waste pumpkin seed shell for lightweight EM wave absorption application. By optimizing the porous structures, the strong absorption intensity of −50.55 dB is achieved at thin thickness of 1.85 mm under low filler content of only 10 wt %. More interestingly, a broad frequency bandwidth of 7.4 GHz could cover the whole Ku band. These outstanding microwave absorption performances, couple with low cost ingredients and ease of fabrication process enable the porous carbon framework as the next generation promising candidate for lightweight and remarkable EM absorber.