Absorption Bandwidth Research Articles

High-performance cobalt-embedded SiC nanofiber fabric for microwave dissipation

The incorporation of magnetic ingredients is critical for ceramic-based microwave absorbers with high efficiency. However, this task is becoming challenging due to the dispersion and oxidation issues. In this study, metal-organic framework (MOF) ZIF-67 was employed as the precursor of magnetic compounds and combined with a polymer solution to fabricate SiC textiles using the electrospinning technique. The microstructure analysis confirmed the successful introduction of MOF particles within the SiC nanofibers. Further examination of chemical compositions and magnetic properties revealed the encapsulation of magnetic compounds in hybrid SiC textiles. Since the applied fabrication approach ensures a superior dispersion and protection of metal compounds in a ceramic matrix, the microwave absorption of SiC fabric with both dielectric loss and magnetic loss exhibits a high reflection loss of -59.4 dB and a wide effective absorption band of 5.70 GHz. The current fabrication strategy for fabricating microwave absorbers with dual loss mechanisms advances the development of ceramic-based microwave absorption materials.

An ultrathin ultralight electromagnetic absorber based on shortcut glass-coated amorphous magnetic Fiber/Salisbury-like screen

A structural design methodology is proposed for an ultrathin, ultralight, and absorption-adjustable electromagnetic absorber. The proposed absorber (SFSL) consists of an absorbing layer with shortcut glass-coated amorphous magnetic fiber and a substrate layer with transmitting material. This absorber features a Salisbury-like screen structure and incorporates multiple loss mechanisms. By investigating the influence of fiber distribution, length, content, and substrate layer thickness on absorption performance, it has been determined that the weight per square meter and thickness of a single-layer SFSL can be lowered within 50 g/m2 and 1.5 mm respectively. Furthermore, the absorption intensity and bandwidth can be adjusted by manipulating these parameters. The SFSL exhibits resonant behavior similar to that of a metamaterial absorber; however, SFSL with randomly distributed fibers demonstrates broader and stronger absorption characteristics in the frequency range from 2 to18 GHz. Additionally, the thicknesses of the substrate layer and surface covering affect the electromagnetic response characteristics. This work provides a simple strategy for constructing an ultrathin and ultralight composite to achieve efficient absorption of electromagnetic waves.

Bayesian-neural-network accelerated design of multispectral-compatible camouflage layer with wide-band microwave absorption, customized infrared emission and visible transparency

Metasurfaces with customizable multi-spectrum compatibility have attracted a great deal of attention due to the increasing applications of stealth and camouflage. Compared with single-spectrum and fixed-scene camouflage metasurfaces, a camouflage metasurface with the designability and spectral-independence can adapt to more complex environments. However, this drastically increases the design complexity and time cost of metasurfaces. Here, we propose a method to design multispectral compatible function layer of camouflage which can achieve customizable wideband microwave absorption, visible transparency and selective infrared emission, simultaneously. The design of the camouflage layer is optimized and accelerated by Bayesian-neural network, which can be implemented based on a very limited amount of prior data and can greatly reduce the design complexity and time. To verify our method, an optical-transparent metasurface with digital infrared camouflage and low backward scattering was designed and fabricated. The simulation and experimental results well demonstrate the performance of multispectral compatible camouflage of the metasurface. We further explore the angular stability of the camouflage layer to the incident angle varying from 0 to 60° at microwaves. Our proposed design scheme provides a novel method to design spectrum-individual and devisable metasurfaces, which can be applied to camouflage in complex spectrum background

Hollow hydrangea-like Mo2C/MoO2/C composites with tunable phase compositions as highly efficient microwave absorbers

With the advancement of modern electronic communication technology, the development of efficient absorbing materials has attracted great interest. Here, hollow hydrangea-like Mo2C/MoO2/C composites are synthesized by soft template method. By adjusting the pyrolysis temperature, Mo2C/MoO2/C composites with different Mo2C and MoO2 contents and degrees of graphitization can be selectively synthesized. The Mo2C/MoO2/C-800 composite with the 30 wt% filler content exhibits a minimum reflection loss of −62.9 dB at 1.6 mm and achieves a maximum absorption bandwidth of 6.2 GHz at 1.9 mm. The interaction between the dielectric properties of each component and the unique 3D hydrangea-like structure promotes microwave absorption and dissipation. Besides, CST simulation further demonstrates the effectiveness of electromagnetic wave dissipation in practical applications. The excellent properties of the hydrangea-like Mo2C/MoO2/C composites indicate their promising applications in electromagnetic wave absorbers.

Control of dielectric properties of composite materials by editing low dielectric ceramics with anchored structure

Extensive research over the impact of the content of a particular constituent in composites on their electromagnetic wave-absorbing performance has been witnessed. However, an accurate summary regarding the impact of ceramics’ dielectric constant on electromagnetic absorption performance of ceramic/graphene composites is still ad referendum. In this paper, a series of low-dielectric ceramics were synthesized by precisely controlling the proportion of boric acid and subsequently integrated with reduced Graphene nanosheets (RGNSs) to fabricate ceramic/RGNSs composites for efficient electromagnetic wave absorption. The amorphous range of ceramics, which is affected by the boric acid content, controls the dielectric properties that subsequently affect the absorption performance. Increasing the amorphous range of ceramics was found to result in an increase in both maximum value and stability of the actual component of complex permittivity for SiBON/RGNSs composite material. Additionally, tangent values at X and Ku bands also exhibited an increase, leading to an augmented microwave absorption performance (maximum absorption bandwidth: 4.94 GHz; minimum reflection loss: −50.45 dB).

Fabrication of core-shell Fe4N@C with sea-island structure by one-step nitriding method as efficient electromagnetic wave composite absorber

Porous structure design and magnetic-dielectric composite are effective ways to develop electromagnetic wave (EMW) absorbing materials with light-weight, thin-thickness, large effective absorption bandwidth (EAB), and strong reflection loss (RL). This article presents a simple one-step nitridation method for synthesizing Fe4N@C compounds with sea-island like and core-shell structures. The optimal RL value of Fe4N@C is up to -60.01dB, and the EAB (frequency range for RL< -10 dB) is 5GHz (11.1-16.1GHz) with a thickness of 1.9mm. The EAB reaches 5.5GHz (12.5-18GHz) when the matching thickness is 1.7mm. The multi-component design achieved excellent impedance matching properties. The carbon frame connects the core-shell particles to form a three-dimensional porous structure, providing multiple reflection losses. Therefore, this work provides a convenient way to design efficient and lightweight EMW absorbers with special structures.

Study on microwave absorbing properties of reduced graphene oxide@Co/Fe81.5Si3B9P3C1Cu1Ti1.5 amorphous nanocrystalline composite

Electromagnetic pollution problems and military stealth technology need to be solved, the development of new wave absorbing materials has been imminent. In this study, reduced graphene oxide@Co (rGO@Co) powder is obtained by alcoholthermal method, afterwards the different contents of rGO@Co powders are also compounded with Fe81.5Si3B9P3C1Cu1Ti1.5 nanocrystalline powder by high-energy ball milling, obtaining rGO@Co/Fe81.5Si3B9P3C1Cu1Ti1.5 nanocrystalline composite powder, and powder morphology, the nuclear layer structure, soft magnetic properties and corresponding absorbing properties of the materials are studied. The research results are that rGO coats Co and Fe-based nanocrystalline of double magnetic cores in the composite powder, which realizes the synergy of the two magnetic cores to enhance the magnetic loss, is also compatible with the dielectric loss of rGO, and also improves the impedance matching. The minimum reflection loss (RLmin) is −44.18 dB, and the maximum effective absorption bandwidth (EAB) is 5.03 GHz in the amorphous nanocrystalline alloy matrix. When the addition of rGO@Co powder is 1 wt%, the RLmin of composite powder is −52.41 dB (3 mm), which is increased by 18.6 %. The EAB is 6.07 GHz (2 mm), which is increased by 20.7 %.

Construction of 2D/2D heterostructure with porous few layer g-C3N4 and NiCo2O4 nanosheets towards electromagnetic wave absorption

Developing high-performance materials with ultra-high reflection loss (RL ≤ -65 dB) for electromagnetic wave (EMW) absorption is pivotal to address electromagnetic pollution, but it is still challenging. Herein, a two-dimensional (2D)/2D PFL g-C3N4/NiCo2O4 heterostructure with porous few-layer g-C3N4 (PFL g-C3N4) and ultrathin NiCo2O4 nanosheets has been prepared by self-assembly, hydrothermal reaction, and calcination strategies. The 2D/2D heterostructure exhibits extraordinary EMW absorption property, achieving a reflection loss (RL) value of -68.59 dB and an effective absorption bandwidth (EAB) of 1.92 GHz at a matching thickness of 2.5 mm. As expected, the porous few layer g-C3N4 nanosheets provide rich interface which increases multiple reflection paths and enhances the conduction loss. The cooperative effects of magnetic loss, dielectric loss, and impedance matching contribute to the exceptional EMW absorption property of PFL g-C3N4/NiCo2O4 (2D/2D) heterostructure. The potential of PFL g-C3N4/NiCo2O4 in actual radar stealth is verified through radar scattering cross-section (RCS) simulation. This work paves the way for utilizing 2D/2D heterostructure as an ultra-efficient EMW absorbers.

Significantly Enhanced Electromagnetic Wave Absorption Performances and Corresponding Mechanism of LaMn1-xFexO3 Perovskites

Improving the performance of LaMnO3 perovskite is essential to make it an efficient and ultra-light electromagnetic wave (EMW) absorbing material. In this work, LaMn1-xFexO3 powders (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by controlling the doping of Fe3+ ions at the B-site using the citric acid-assisted sol-gel method. The effects of Fe3+ ions doping content on crystal structures, magnetic properties and EMW absorption performances were investigated. The obtained LMFO-4 sample exhibited a minimal reflection loss of -54.99 dB at 13.68 GHz, with an adequate absorption bandwidth (RL < -10 dB) spanning 4.56 GHz (11.6∼16.16 GHz) at a matching layer thickness of 2.0 mm. The exceptional EMW absorption performances could be attributed to the Jahn-Teller effect, the double-exchange interactions and the magnetic interactions of Mn and Fe ions. Furthermore, the Computer Simulation Technology (CST) simulations demonstrated that the Radar Cross Section (RCS) value of LMFO-4 was lower than -25.10 dBm2 across angles ranging from -90° to 90° with a thickness of 2.0 mm, indicating the remarkable radar wave attenuation ability. These insights provided valuable guidance for advancing perovskite-based materials tailored for efficient and ultra-light electromagnetic wave absorption applications.

Preparation of broad-bandwidth porous carbon electromagnetic wave absorption materials from agricultural waste corncob

Developing advanced electromagnetic wave-absorbing materials tend to focus on the characteristics of low cost, renewability, environmental friendliness, strong absorption, wide bandwidth, and lightweight. This paper described the preparation of porous carbon electromagnetic wave-absorbing materials with strong absorption, broad bandwidth and thin thickness by one-step charring of corncob, an agricultural waste. The corncob porous carbon (CPC) materials were prepared when the charring temperature was 600 °C, the charring time was 3 h and the activator ratio was 0.25:1. The obtained CPC exhibited porous microstructure with average pore size of approximately 1 μm. Its specific surface area was 713.971 m2·g−1, with pore volume of 0.289 mL·g−1 and high degree graphitization. CPC showed excellent electromagnetic wave absorption performance with minimum reflection loss (RL min) of −38.21 dB and effective absorption bandwidth (EAB) of 5.6 GHz at a relatively thin thickness of 2.0 mm. CPC was capable of absorbing 99.9 % of electromagnetic wave (EMW).

Synthesis of Co3O4@C/Ti3C2Tx MXene composites for enhanced electromagnetic wave absorption

Due to the harmful effects of electromagnetic pollution on human bodies and electronic devices, efficient microwave absorbing materials have garnered significant attention. In this paper, highly efficient microwave-absorbing Co3O4@C/Ti3C2Tx composites were synthesized by a combination of hydrothermal and electrostatic self-assembly methods. Benefiting from the synergistic effects of the multiple reflections in the Co3O4@C core-shell structure and the high conductivity coupled with the large surface area of Ti3C2Tx, the composite material, with a mass ratio of 1: 2, exhibits remarkable wave absorption capabilities, achieving a minimum reflection loss (RL) of −35.2 dB at a thickness of 4.5 mm and an effective absorption bandwidth (EAB) of 7.4 GHz within the 2–18 GHz frequency range. It is noteworthy that the smaller the RL value, the higher the material's absorption performance, and the wider the frequency range covered by the EAB, the better the overall absorption effect. Specifically, an RL value below −10 dB corresponds to an absorption rate of 90 %, which further enhances to 99 % for RL values below −20 dB. The outstanding electromagnetic wave absorption performance of the Co3O4@C/Ti3C2Tx composites can be primarily attributed to the synergy between the multiple reflective absorptions offered by the core-shell structure and the exceptional conductivity and high specific surface area inherent in the MXene material. These findings underscore the promising potential of Co3O4@C/Ti3C2Tx composites for electromagnetic absorption applications and offer a novel perspective for the design of MXene-based magnetic absorption materials.

Microwave absorption properties of one-step formed CNTs/Fe3O4-carbonyl iron superflexible buckypaper by directional pressure filtration

In order to realize the integration of structure and function of microwave-absorbing materials, carbon nanotubes/magnetic nanoparticle buckypaper (CNT/MNP BP) self-supporting, ultra-flexible, ultra-thin and ultra-light composites were prepared by composing CNTs with MNPs through directional pressure filtration technology. The BP composite, with a bulk density of 0.62 g/cm3 and a thickness of 0.21 mm, can be uninterruptedly tightly wound around a 4 mm diameter glass rod many times without structural damage. The microwave-absorbing properties and magnetic properties of the CNT/MNP composites with different compositions and contents were systematically analyzed. The CNT-Fe3O4 Buckypaper with 33.3 wt% Fe3O4 content (CF33.3 %) has the best electromagnetic wave absorption capability, with a minimum reflection loss value of −52.01 dB and an effective absorption bandwidth of 4.08 GHz. The VSM test shows that the saturation magnetization strength of CF33.3 % is 38.4 emu/g. The excellent electromagnetic wave absorption performance is attributed to the polarization and conduction losses of CNTs, natural resonance, exchange resonance and eddy current losses of MNPs, and multiple scattering and reflection within the porous network structure of the composites. The CNTs and MNPs has good dispersion in the buckypaper, where CNTs construct a superflexible skeleton besides an excellent conductive network. The self-supporting superflexible CNT/MNP BP composites have a good application prospect in the field of wearable electronic devices in the future.

Electromagnetic wave absorption performance of rapid emergency magnesium phosphate cement (MPC) canvas

This study leverages the rapid emergency protection advantages of magnesium phosphate cement (MPC) canvas to develop a novel electromagnetic wave-absorbing material based on MPC canvas. The composite is composed of an MPC matrix with magnetite and iron powder as absorbers, arranged in a gradient structure. The research investigates the effects of absorbers and gradient contents on the electromagnetic wave absorption performance (EWAP) of MPC canvas. Experimental results show a maximum RL of −37.2 dB in the 2–18 GHz range, with a 6.3 GHz absorption bandwidth below −10 dB. Simulations further confirm that the gradient MPC canvas exhibits excellent EWAP across different frequency bands. The gradient design effectively adjusts the electromagnetic parameters through multiple reflection, scattering, and interference attenuation effects within the multilayer structure, enabling broadband absorption of electromagnetic waves.

Fe2O3-decorated multiwall carbon nanotube composites for boosted microwave absorption

Developing microwave absorption (MA) materials with a strong absorption ability over a wide bandwidth through a simple and environmentally friendly approach remains a tremendous challenge. Herein, we propose to use an Fe3+–tannic acid framework to assist the dispersion of multi-walled carbon nanotubes (MWCNTs) and successfully prepare MWCNTs/porous carbon/α-Fe2O3 composites through freeze-drying and subsequent heat treatment. The dielectric properties and MA performance can be regulated by the heat treatment temperature, which leads to tunable crystalline structure, composition, and graphitization degree of MWCNTs. Consequently, the MWCNTs/porous carbon/α-Fe2O3 composite heat-treated at 300 °C exhibits a high reflection loss (RL) of −58.9 dB and an effective absorption bandwidth (5.28 GHz) with a matched thickness of 2.26 mm at a filler proportion of only 5 wt%, and the related frequency bandwidth with RL below -10 dB reaches 14.3 GHz at a thickness of 2–5 mm. In conclusion,the balance between conduction and polarization loss endows the composite with excellent impedance matching and boosting MA performance. This study offers a guideline for fabricating excellent MA materials through a simple, environmentally friendly method.

Multi-shell bowl-like carbon microspheres for lightweight and broadband microwave absorption

Carbon materials have made significant progress in the field of microwave absorption (MA), but achieving wide effective absorption bandwidth (EAB) at low filler content still remains a great challenge. In this work, we design multi-shell bowl-like mesoporous carbon microspheres (MBMCs) by a facile hard template method for efficient MA. It is demonstrated that the spacing between inner and outer shell and second shell thickness play a vital role on the configuration of carbon microspheres. By controlling the second addition of silica template, the microstructure of carbon microsphere evolves from spherical to bowl shape geometry. Expanded shell spacing is beneficial for forming bowl-like microsphere. The dielectric loss and MA properties are highly associated with the configuration of MBMCs. Well-proportioned MBMCs with appropriate shell spacing present wide EAB of 7.3 GHz under a low filling ratio of 12 wt.%. This work paves a new way to broaden EAB and lower filling content of carbon materials via asymmetric multilayer microstructure design.

Fabrication of core–shell nickel ferrite@polypyrrole composite for broadband and efficient electromagnetic wave absorption

Herein, nickel ferrite@polypyrrole (NiFe2O4@PPy) composite was prepared by a simple two-step route of solvothermal synthesis and in-situ oxidation polymerization reaction. The results of micromorphology analysis showed that the obtained NiFe2O4@PPy composite had a unique core–shell structure, good magnetic performance and electrical conductivity. Furthermore, the as-prepared magnetic/conductive NiFe2O4@PPy composite exhibited notably enhanced electromagnetic wave (EMW) absorption performance than pure NiFe2O4 and PPy. When the filling ratio was 17.5 wt% and the matching thickness was 2.24 mm, the optimal minimum reflection loss (RLmin) of −56.25 dB and a broad effective absorption bandwidth (EAB) of 5.2 GHz were achieved for NiFe2O4@PPy composite. With slightly increasing the matching thickness to 2.6 mm, the maximum EAB of 7.12 GHz could be reached. Additionally, the probable EMW absorption mechanism was elucidated. Therefore, this work could provide a valuable reference for the preparation of magnetic ferrite/conductive polymer composites as broadband and high-efficiency EMW absorbers.

MOFs-derived copper selenides nanoparticles implanted in carbon matrix for broadband electromagnetic wave absorption

Selenide-based functional composites materials demonstrated tunable dielectric properties and heterogeneous interface design, which has been widely studied in electromagnetic (EM) wave absorption field. Herein, Metal-organic frameworks (MOFs) derived carbon coating copper selenide (Cu2-XSe@C) composites were successfully fabricated by using the Cu-MOFs as precursor. After reacting with the gaseous Se in the selenization annealing process, the metal host was converted into the Cu2-XSe nanoparticles, where embodied in the carbon matrix transformed from the organic linker. Based on the tunning dielectric property and building heterogeneous interface, MOFs-derived Cu2-XSe@C composites displayed outstanding EM wave absorption performance. Though the conduction loss, interfacial and dipole polarization behaviors, the minimum reflection loss (RLmin) value of Cu2-XSe@C-600 composites reached to −74.3 dB at 11.7 GHz when the thickness is 2.0 mm. The efficient absorption bandwidth (EAB) can be regulated via controlling the applied thickness. When the thickness is 2.3 mm, above-mentioned Cu2-XSe@C-600 got the broadest absorption performance with the EAB of 5.5 GHz from the 7.7–13.2 GHz, covering the whole X-band. Therefore, MOFs-derived selenide-based composites shed a new design strategy for constructing broadband EM wave absorption, especially in radar stealth applications.

One-step pyrolysis derived Fe and heteroatom co-doped biochar composites for efficient microwave absorption

Electromagnetic (EM) pollution frequently disrupts the regular operation of sophisticated electrical devices, necessitating the urgent development of lightweight EM wave absorbers that possess powerful absorption capability. Herein, we report a simple method for the preparation of Fe and heteroatom co-doped biochar composites (FeX-BC, where X = N, S) by directly carbonizing the precursors of anhydrous FeCl3, cherry kernel powder, and heteroatom dopants (melamine or Na2S2O3·5H2O). By adding different amounts of dopants during the synthesis of the precursors, it is possible to adjust the heteroatom content of the FeX-BC samples with precision. It is worth mentioning that the FeN0.1-BC composite delivers the best EM wave absorption performance with an effective absorption bandwidth of 4.8 GHz and a minimal reflection loss of −63.2 dB. Furthermore, the significant attenuation of EM wave can be attributed to the synergistic interplay of magnetic loss, dielectric loss and the enhanced impedance matching. This study introduces a simple methodology for the fabrication of EM wave absorbers, a significant contribution to the synthesis, advancement, and functional applications of biomass-derived materials.

One-step fabrication of a novel fiber-based absorber for flexible, tunable and boosted microwave absorption

The increasingly intricate electromagnetic environment necessitates higher anti-electromagnetic interference capabilities for electronic devices, thereby demanding a flexible absorbing material that can adapt to multiple forms, is lightweight, and exhibits excellent electromagnetic wave (EMW) absorption properties. In this study, we have developed a novel flexible absorbing material (FAM) based on glass-coated amorphous magnetic fibers (SFs) and Dallenbach-like absorbing structures through wet forming technology. By combining high-performance absorbing fiber with textile structures, the FAM demonstrates EMW absorption performance along with lightweight flexibility and shape adaptability. This paper explores the influence of process parameters in wet forming technology on FAM formation; as well as examines the construction of broadband absorbers through structural optimization. A single-layer FAM with a thickness of 1.7 mm (SFs length 8 mm, content 3 g/m2) achieves an impressive reflection loss (RL) value of −60.1 dB at 11.6 GHz. Furthermore, optimized multi-layer FAM attains effective absorption bandwidth (EAB: RL ≤ −5 dB) across a wide range from 3–14 GHz. This work presents a new approach for developing ’lightweight, thin, wide, and strong’ absorbing materials based on fiber and textile structures which holds significant implications for civilian electromagnetic interference protection as well as military electromagnetic stealth technology.

Structural modification of mesoporous lanthanum oxide into 3D coral-like and nano needle-like structure for effective broadband microwave absorbing materials☆

Structural modification of three dimensional (3D) materials for the application of dielectric loss-based microwave absorbing materials (MAMs) usually relies on intricate synthesis process and can pose challenges in terms of scalability and mass production for practical application. In this work, we reported a successful attempt in modifying the 3D structure of mesoporous lanthanum oxide (La2O3) for effective broadband MAMs candidate via simple co-precipitation process. The inclusion of cetyl-trimethylammonium bromide (CTAB) and hydrothermal aging treatment result in a significant transformation of La2O3 particles from their original polygonal form to a 3D coral-like and nano needle-like structure. The utilization of CTAB and hydrothermal aging results in the increase of surface area and a two-fold increase in pore volume of the resulting La2O3. Due to its unique 3D structure, the 3D coral-like and nano needle-like La2O3 materials possess a broadband electromagnetic (EM) wave absorption characteristic with the effective absorption bandwidth (EAB) covering the C-band frequency range. Specifically, in the La2O3 C-H sample (with CTAB – with hydrothermal), it exhibits strong EM wave absorption with a reflection loss (RL) value of –33.07 dB which equals to 99.95% EM wave absorption at a thickness of only 1.50 mm. The detailed analysis of EM wave absorption properties reveals that the improvement of La2O3 materials to attenuate EM wave energy arises from the dielectric loss phenomenon, the enhanced interfacial polarization, multiple reflections mechanism, and conduction loss mechanism induced by the 3D structural formation of the La2O3 structure. This work proposes a novel and efficient approach in synthesizing and modifying 3D materials for effective broadband EM wave absorption.