High-performance Microwave Absorption Research Articles

Optimizing electromagnetic parameters to enhance the microwave absorbing properties of core–shell FeCo2O4@flaky FeSiAl composites

The high complex permittivity of flaky FeSiAl in microwave-absorbing materials leads to poor electromagnetic impedance matching and a narrow effective absorption bandwidth. To overcome this issue, we developed a novel approach by wrapping magnetic FeCo2O4 on the surface of flaky FeSiAl using a hydrothermal method, followed by calcination. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to confirm the formation of a FeCo2O4@flaky FeSiAl composite with a well-defined core–shell microstructure. The prepared FeCo2O4@flaky FeSiAl composite exhibited a significantly reduced complex permittivity, which improved its electromagnetic impedance matching performance. When filled in paraffin with a thickness of only 1.6 mm, the composite demonstrated excellent electromagnetic wave absorption performance, with an effective absorption bandwidth of 5.60 GHz (RL < − 10 dB), indicating its potential in the field of microwave-absorbing materials. These results were achieved owing to the unique properties of the FeCo2O4@flaky FeSiAl composite, demonstrating its potential as a high-performance microwave absorber. This study may be of significant interest to researchers and engineers in the fields of magnetism and magnetic materials, especially those in the microwave field.

Design and synthesis of graphene-like porous grapefruit peel/Ni0.5Co0.5Fe2O4 composite with high-performance microwave absorption

The rapid developments in communication technology and aerospace have prompted the renewal of electromagnetic wave (EMW) materials. Here, we have prepared graphene-like porous grapefruit peel/Ni0.5Co0.5Fe2O4 composite by in-situ generation. The graphene-like porous structure improves conductive loss and multi-polarization availably. Meanwhile, the addition of Ni0.5Co0.5Fe2O4 facilitates to introduce the magnetic loss. Moreover, the large number of pores promotes multiple reflections and scattering of EMW, thus improving EMW absorption performance. Through adjusting the carbonization temperature, the sample with extremely thin thicknesses (1.7 mm) achieves wide effective absorption bandwidth (5.14 GHz). It offers a path to the practical application of new absorbing materials with wider absorption bands and thin thickness.

A novel plasma-sprayed Ti4O7/carbon nanotubes/Al2O3 coating with bifunctional microwave application

High-performance microwave absorption coatings are critically required in the stealth defense system of military platforms. Regrettably, just optimizing the property but neglecting the application feasibility seriously inhibits its practical application in the field of microwave absorption. To face this challenge, the Ti4O7/carbon nanotubes (CNTs)/Al2O3 coatings were successfully fabricated by a plasma-sprayed method. For the different oxygen vacancy-induced Ti4O7 coatings, the enhanced ε' and ε'' values in the frequency of X-band is due to the synergistic manipulation of conductive path, defects and interfacial polarization. The optimal reflection loss of Ti4O7/CNTs/Al2O3 sample (0 wt% CNTs) is −55.7 dB (8.9 GHz of 2.41 mm), while the electromagnetic interference shielding effectiveness of Ti4O7/CNTs/Al2O3 sample (5 wt% CNTs) increases to 20.5 dB as the enhanced electrical conductivity. In special, the flexural strength of Ti4O7/CNTs/Al2O3 coatings first increases from 48.59 MPa (0 wt% CNTs) to 67.13 MPa (2.5 wt% CNTs) and then decreases to 38.31 MPa (5 wt% CNTs), demonstrating that an appropriate amount of CNTs evenly dispersed in the Ti4O7/Al2O3 ceramic matrix can effectively play the role of CNTs as the strengthening phase of the coatings. This research will provide a strategy by tailoring synergistic effect of dielectric loss and conduction loss for oxygen vacancy-mediated Ti4O7 material to broaden the application of absorbing or shielding ceramic coatings.

Hierarchical and Porous Structures of Carbon Nanotubes-Anchored MOF Derivatives Bridged by Carbon Nanocoils as Lightweight and Broadband Microwave Absorbers.

High-performance microwave absorption (MA) materials have attracted more and more attention because they can effectively prevent microwave radiation and interference from electronic devices. Herein, a new type of MA composite is constructed by introducing carbon nanotubes (CNTs)-anchored metal-organic framework derivatives (MOFDs) into a conductive carbonnanocoil (CNC) network, denoted as CNC/CNT-MOFD. The CNC/MOFD shows a wide effective absorption band of 6.7GHz under a filling ratio of only 9% in wax-matrix. This is attributed to the hierarchical and porous structures of MOFD bridged by the uniformly dispersed conductive CNC network and the cross-polarization induced by the 3D spiral CNCs. Besides, the as-grown 1D CNTs improve space utilization, porosity, and polarization loss of the composites, resulting in the increase of imaginary permittivity, which further realizes impedance matching and energy attenuation. The Ni nanoparticles in layers of MOFD and at the tips of CNTs generate magnetic loss, promoting the low-frequency absorption ability. Resultantly, RCS values of the optimized composite in all tested theta (θ) ranges are less than -25dB m2 at 9.5GHz, effectively reducing the probability of the target detected by the radar.

An MXene coating with electromagnetic wave absorbing performance

The increasing demand for electromagnetic wave absorbing (EMWA) coatings and the intensification of electromagnetic pollution has spurred research into high-performance flexible microwave absorbing (MA) materials. The magnetic-MXene-SiO2 (M-MXene-SiO2) was successfully synthesized to achieve improved MA performance. Based on the high dielectric loss capacity of transition metal carbides and carbonitrides (MXenes), by combining with Fe2O3, Fe3O4 and mesoporous silica nanoparticles (MSNs), the magnetic loss can be manipulated to improve impedance matching, reflection loss (RL), and effective absorption bandwidth (EAB, the bandwidth of RL < 10 dB). The minimum RL value of the designed composites can reach −38.14 dB. This work provides insight into the novel design of MA materials.

Construction of porous carbon for high-performance microwave absorbing: An efficient method to utilize direct liquefaction coal asphalt by-products

Construction of porous carbon for high-performance microwave absorbing: An efficient method to utilize direct liquefaction coal asphalt by-products

Heating induced self-assemble pomegranate-like Fe3C@Graphite magnetic microspheres on amorphous carbon for high-performance microwave absorption

Difficulty of multicomponent regulation and nanostructure design make it challenging to fabricate high-performance electromagnetic wave (EMW) absorption materials. Herein, pomegranate-like Fe3C@graphitic carbon embedded in amorphous carbon matrix (Fe3C@GC/AC) is successfully prepared through a viable heating induced self-assembly strategy. By adjusting carbonization temperature, controllable electromagnetic parameters and impedance matching characteristics of Fe3C@GC/AC nanocomposites could be acquired. Besides, dielectric loss and magnetic loss are offered by GC and Fe3C, while the amorphous carbon not only disperse Fe3C@GC nanoparticles well, but also strengthens interface polarization. The detailed analysis show that Fe3C@GC/AC nanocomposites exhibit excellent EMW absorption performance under the combined function of unique pomegranate-like nanostructure and various loss mechanisms of multi-components. Moreover, the strongest reflection loss value of optimal sample (RCF-700) is up to −96.3 dB (loss of EMW above 99.99999%) with a matching thickness of 2.08 mm, and the effective absorption bandwidth (EAB, RL < −10 dB) covers 6.38 GHz (11.62–18.0 GHz, covering Ku-band). In addition, the EAB can reach 14.08 GHz with the simulated thickness varies from 1.0 to 5.0 mm, covering 88% of the measured frequency range. The deep exploration of the bio-inspired structure of multi-component system provides a creative and effective way for high-performance EMW absorbers.

Enhancing broadband and intense microwave absorption properties of flaky FeSiCr powder by coating SiO2

Flaky FeSiCr@SiO2 composites with broadband and intense absorption were successfully synthesized by modified Stöber method. The phase, microstructure and morphology of flaky FeSiCr@SiO2 composites were investigated by XRD, FT-IR, SEM and TEM, confirming the successful preparation of SiO2 coating. The thermal behavior of flaky FeSiCr@SiO2 composites was analyzed by TGA/DSC. The results showed that the oxidation resistance of the coated FeSiCr powder was promoted. The electromagnetic wave absorption properties of samples with different contents of tetraethyl orthosilicate (TEOS) were systematically investigated. The sample synthetized with 10 ml TEOS possesses the optimal absorption performance, which is attributed to the synergistic effect of magnetic loss and dielectric loss. The minimum reflection loss is −65.3 dB at 4.4 GHz. And the maximum effective absorption bandwidth is 6.0 GHz with only a 1.5 mm thickness. In particular, by controlling the thickness of the absorber, the effective absorption bandwidth can reach 13.3 GHz (2.9–16.2 GHz), covering the entire C and X bands. Thus, the flaky FeSiCr@SiO2 composites can be used as high-performance microwave absorption materials.

Synthesis of a one-dimensional carbon nanotube-decorated three-dimensional crucifix carbon architecture embedded with Co7Fe3/Co5.47N nanoparticles for high-performance microwave absorption

Low-dimensional cell-decorated three-dimensional (3D) hierarchical structures are considered excellent candidates for achieving remarkable microwave absorption. In the present work, a one-dimensional (1D) carbon nanotube (CNT)-decorated 3D crucifix carbon framework embedded with Co7Fe3/Co5.47N nanoparticles (NPs) was fabricated by the in-situ pyrolysis of a trimetallic metal–organic framework (MOF) precursor (ZIF-ZnFeCo). Co7Fe3/Co5.47N NPs were uniformly dispersed on the carbon matrix. The 1D CNT nanostructure was well regulated on the 3D crucifix surface by changing the pyrolysis temperature. The synergistic effect of 1D CNT and the 3D crucifix carbon framework increased the conductive loss, and Co7Fe3/Co5.47N NPs induced interfacial polarization and magnetic loss; thus, the composite manifested superior microwave absorption performance. The optimum absorption intensity was −54.0 dB, and the effective absorption frequency bandwidth reached 5.4 GHz at a thickness of 1.65 mm. The findings of this work could provide significant guidance for the fabrication of MOF-derived hybrids for high-performance microwave absorption applications.

Harnessing Pseudo-Jahn-Teller Disordering of Monoclinic Birnessite for Excited Interfacial Polarization and Local Magnetic Domains.

The symmetry in a polymorph is one of the most important elements for determining the inherent lattice nature. The MnO2 host tends to high-symmetry MnO6 octahedra as a result of the electronic structure t2g 3 eg 0 of Mn4+ ions, displaying an ordered structure accompanying with poor polarization loss and limiting its application toward high-performance microwave absorbers. Here, a pseudo-Jahn-Teller (PJT) distortion and PJT disordering design with abundant self-forming interfaces and local magnetic domains in the monoclinic birnessite-MnO2 host is first reported. The PJT distortion can give rise to asymmetric MnO6 octahedra, inducing the formation of interfaces and increased electron spin magnetic moment in the lattice. The resultant birnessite with PJT distortions and PJT disordering delivers an outstanding reflection loss value of -42.5dB at an ultralow thickness of 1.7mm, mainly derived from the excited interfacial polarization and magnetic loss. This work demonstrates an effective approach in regulating the lattice structure of birnessite for boosting microwave absorption performance.

Three-dimensional melamine sponge hollow carbon/Ni3ZnC0.7/carbon nanotubes with tunable high-performance microwave absorption performance

Constructing three-dimensional microstructure with special morphology is an important method to improve the flexibility, low density and high performance of absorbing materials. Herein, Ni3ZnC0.7/carbon nanotubes/melamine sponge hollow carbon (NZC/CNTs/SHC) composites were prepared by vacuum filtrating precursor containing NiZn ions and CNTs followed with calcining under N2 flow. The loading of NZC/CNTs can be tuned by controlling the filtrating time of 0.5, 1 and 2 h. The Ni3ZnC0.7 and CNTs were uniformly dispersed on the surface of melamine sponge carbon skeleton and the carbon shows hollow structure. The 2-NZC/CNTs/SHC composite (filtrating time of 2 h) exhibited a minimum reflection loss (RL) value of − 114.5 dB (1.3 mm) and an effective absorption bandwidth (EAB, RL<−10 dB) of 12.5 GHz at a matching thickness of 1.9 mm. The outstanding wave-absorbing properties of NZC/CNTs/SHC composites can be attributed to their unique hollow structure, which results in multiple reflections and scattering, interface/dipole polarization, improved dielectric and magnetic attenuation capability.

Facile synthesis of 2D MoS2/reduced graphene oxide hybrids with excellent microwave absorption

High-performance microwave absorption materials with tunable electromagnetic properties have long been the goal of researchers. It is still a challenge to achieve broad band absorption and lightweight performance by simply optimizing the chemical composition of absorbers. Molybdenum disulfide (MoS2) belongs to the two-dimensional transition metal disulfide with a layered structure similar to graphene. In this work, two-dimensional MoS2/reduced graphene oxide (MS/RGO) hybrids have been constructed through a convenient self-assembled hydrothermal method, in which MoS2 ultrathin nanosheets in-situ grow uniformly on the surface of RGO, constructing a unique hierarchical microstructure. Electromagnetic parameter measurements display that the dielectric behaviors of MS/RGO composites are optimized via changing the content of RGO, and meanwhile the superior microwave absorption properties are achieved with the filler-loading ratio of only 20 wt%. The widest effective absorption bandwidths (RL<−10 dB) of 5.68 GHz (12.32–18 GHz) and 6.32 GHz (11.20–17.52 GHz) are observed at a thickness of 2.0 mm for MS/RGO-10 and MS/RGO-15, respectively. When the thickness is raised to 5.0 mm, the reflection loss value of MS/RGO-10 composites reaches the minimum value of − 39.8 dB at 4.96 GHz. The improved performance can be explained by the strong interfacial polarization loss due to abundant heterogeneous interfaces, defect dipole polarization, conduction loss, and multiple reflections and scattering. The results indicate that the light-weight MS/RGO composite is considered as a promising candidate for high-performance microwave absorbers with an adequate absorption bandwidth.

Vertically stacked heterostructures of MXene/rGO films with enhanced gradient impedance for high-performance microwave absorption

Owing to high specific surface area and electrical conductivity, 2D materials are widely used for microwave absorption to address the problems of electromagnetic wave pollution, which induced by the advancement of wearable electronic devices and 5G wireless communication. However, the major challenges arise from the unsatisfied dielectric loss capacity that seriously limits the application of 2D-based microwave absorber. Herein, a vertical heterostructure architecture was exploited to synthesize MXene/rGO films, which deliver different impedance gradients. In particular, the MrG film with 80 wt% rGO content exhibit excellent microwave absorption with a minimum reflection loss value of −44.3 dB at 7.06 GHz (＞99.99% of the electromagnetic wave is absorbed) and an effective absorption bandwidth of 4.84 GHz at a thickness of 1.5 mm. The enhanced dielectric loss capacity is attributed to vertically stacked heterostructures, providing new electron transport and leap channels along the vertical direction of the films. Moreover, visualized power loss density simulations are first used to investigate the evolution of the loss densities, further confirming the synergistic interaction between MXene and rGO can substantially increase microwave absorption. This finding provides an alternative approach for the developing efficient, customizable, simple, and low-cost 2D material-based absorbers through controlling formation of vertical heterostructures.

One-step facile synthesis of MoS2 - reduced graphene oxide/ZnO nanostructure for high-performance microwave absorption

The tremendous development in electronic devices and their prolific implications have triggered a serious threat to our ambiance in form of electromagnetic interference (EMI) pollution. The present study manifests a feasible approach to design an alternative architecture of graphene-based material for improving the shielding performance through absorption in X-band frequency array. The MoS2-rGO/ZnO ternary nanostructure has been synthesized through a simplistic solvothermal approach. The studies suggest that the MoS2-rGO/ZnO ternary nanocomposite exhibits outstanding EM wave absorption and dissipation capabilities as compared to its constituent components. The average EMI SET (∼32 dB) of the studied MoS2-rGO/ZnO nanocomposite owes to the combined effects of various relaxations and polarizations of ZnO and MoS2-rGO. The synergic effect, as well as dielectric and magnetic losses, furnish the high shielding effectiveness. The incorporation of ZnO nanoparticles in MoS2-rGO nanocomposite results in a spectacular average value of EMI SET, making it appropriate for widespread applications.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation.

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96dB and 5.25GHz, respectively, while the absorbing thickness is only 2mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

Preparation of RGO/Fe3O4 Nanocomposites as a Microwave Absorbing Material

The hydrophobic nanocomposites of reduced graphene oxide (RGO) and Fe3O4 (RGO/Fe3O4) were prepared by a one-pot process through co-precipitation under alkaline conditions. The microwave absorption performance of the RGO/Fe3O4 nanocomposites was analyzed according to their electromagnetic parameters. The results showed that the RGO/Fe3O4 nanocomposites displayed better absorbing performance than the pristine Fe3O4 nanoparticles, owing to the synergistic effect of Fe3O4 and RGO. The maximum reflection loss (RL) of the RGO/Fe3O4 nanocomposites with a thickness of 2 mm reached −45.7 dB at 13.3 GHz, and the bandwidth (RL &lt; −10 dB) ranged from 11.5 to 16.5 GHz. However, the maximum RL of the Fe3O4 nanoparticles with a thickness of 5 mm only reached −5.3 dB at 5.7 GHz. The RGO/Fe3O4 nanocomposites have a great potential application in high-performance electromagnetic microwave absorbing.

Sequential Architecture Induced Strange Dielectric‐Magnetic Behaviors in Ferromagnetic Microwave Absorber

AbstractThe high filler loading (FL) is a bottleneck in developing lightweight ferromagnetic microwave absorbers (MAs) for the actual applications. Sequential architecture design of MAs can induce strange physical behaviors due to the unique coupling‐enhancement effect between functional units, providing a vast potential for achieving high microwave absorption performance. However, the FLs of current sequential MAs fail to be designed on demand because the strange dielectric‐magnetic behaviors cannot be fulfilled. The influence of sequential architecture engineering on the macroscopic properties or microscopic loss mechanism still needs more exploration. Herein, based on four mesoscopic models (particles, chains, bundles, and fibers) of ferromagnetic functional units, a series of ferromagnetic MAs with different sequential architectures are prepared via a bottom‐up self‐assembly method. The fibrous samples exhibit the best microwave absorption performance (−51.3 dB, 4.12 GHz) at a breakthrough FL of 2 wt%, which is one order of magnitude less than other ferromagnetic MAs. Strange dielectric‐magnetic behaviors, including negative permittivity and heterodromous chiral vortex, occur due to functional units with lateral and fibrous configurations. Further, four special models are established to reveal the microwave attenuation evolutionary mechanism. This study clarifies the relationship between sequential architecture and strange dielectric‐magnetic behaviors, which provides new sight to understand microscopic electromagnetic loss mechanism.

An Ion-Engineering Strategy to Design Hollow FeCo/CoFe2 O4 Microspheres for High-Performance Microwave Absorption.

Although assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self-aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi-ion synergistic regulation strategy to design assembled hollow-shaped cobalt spinel oxide microspheres. Dominated by the coordination-etching effects of F- and the hydrolysis-complex contributions of NH4 + , the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe2 O4 bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe2 O4 composites exhibit excellent microwave absorption performances with minimal reflection losses (RLmin ) as high as -51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi-ion and even multi-ion synergistic engineering mechanisms.

Co3O4 Nanoparticle-Modified Porous Carbons with High Microwave Absorption Performances

Carbon materials derived from natural biomaterials have received increasing attention because of their low cost, accessibility, and renewability. In this work, porous carbon (DPC) material prepared from D-fructose was used to make a DPC/Co3O4 composite microwave absorbing material. Their electromagnetic wave absorption properties were thoroughly investigated. The results show that the composition of Co3O4 nanoparticles with DPC had enhanced microwave absorption (-60 dB to -63.7 dB), reduced the frequency of the maximum reflection loss (RL) (16.9 GHz to 9.2 GHz), and had high reflection loss over a wide range of coating thicknesses (2.78-4.84 mm, highest reflection loss <-30 dB). This work provided a way for further research on the development of biomass-derived carbon as a sustainable, lightweight, high-performance microwave absorber for practical applications.

Morphology engineering of defective graphene for microwave absorption

Graphene with abundant defects has been considered as the most lightweight electromagnetic functional materials. Although important, the dominant electromagnetic response of defective graphene with diverse morphologies is rarely the focus of existing research. Herein, the defective graphene with two-dimensional planar structure (2D-ps) and three-dimensional continuous network (3D-cn) morphologies were dexterously designed with 2D mixing and 3D filled systems of polymeric matrix. A comparison between the topologies of defective graphene-based nanofillers and the microwave attenuation behaviors was examined. Defective graphene with 3D-cn morphology can achieve ultralow filling content and broadband absorption, which is attributed to the presence of numerous pore structures that promote impedance matching, induce continuous conduction loss and provide multiple reflection and scattering sites for electromagnetic wave attenuation. Comparatively, by virtue of the increased filling content of 2D-ps, the dielectric losses primarily originate from the dielectric genes, including aggregation-induced-charge transport, abundant defect and dipole polarization, resulting in good microwave absorption at low thickness and low frequency. Therefore, this work provides a pioneering insight into morphology engineering of defective graphene microwave absorbers, and it will guide future exploration of customizing high-performance microwave absorption materials based on graphene-based low-dimensional building blocks.