Broadband Electromagnetic Wave Absorption Research Articles

An ultra-broadband microwave absorber based on hybrid structure of stereo metamaterial and planar metasurface for the S, C, X and Ku bands

Broadband electromagnetic (EM) wave absorbers are persistently desired in the past decades due to their extensive applications in different fields. In this paper, we proposed and demonstrated a metamaterial absorber (MA) based on a hybrid structure of stereo and planar resistive metamaterial elements. In principle, this hybrid MA is a combination of the Dällenbach layer absorber and circuit analog (CA) absorber. By adjusting its dispersion feature, the stereo metamaterial based on standing resistive patch can work as a broadband artificial Dällenbach layer absorber for C, X and Ku bands. Such stereo metamaterial was also utilized as a dispersive dielectric spacer and a metasurface consisting of resistive circle rings was deployed on the top of it to implement an improved CA absorber for S and C bands. By combing them together, the proposed hybrid MA can achieve absorption over 90% in an ultra-broad bandwidth from S to Ku band (2.59–16.80 GHz). Since our design takes full advantage of the physical space, the hybrid MA achieves an actual thickness as only 1.075 times of the ultimate thickness corresponding to its absorption performance. Furthermore, the hybrid MA has comprehensive advantages in terms of stability against oblique incidence, easy processing and light-weight. The MA prototype was fabricated assisted by the silk screen printing process and its ultra-broadband absorption performance was experimentally validated by the measured results. The new concept of hybrid MA and specific design scheme proposed here provide a promising approach for broadband, low-profile and light weight EM absorber.

Construction of MOF-Derived Co/C shell on carbon fiber surface to enhance multi-polarization effect towards efficient broadband electromagnetic wave absorption

As a typical fascinating microstructure, the core-shell structure provides abundant possibility for material design in various fields including nano-engineering. In addition, the popular MOF derivatives have been widely explored and recognized as the most potential candidates for functional materials, especially in the field of microwave absorption (MA). Combined with the advantages of their structure and function, it is expected to maximize the synergistic effect and achieve amazing MA performance. In this paper, a series of core-shell CF@C/Co composites were assembled by using lightweight and conductive CF as the core and cubic ZIF-67-derived C/Co with controllable structure and adjustable graphitization as the shell. The intrinsic relationships between shell structure, component content, graphitization degree, electromagnetic parameters and various microwave loss behaviors are analyzed. After properly adjusting the degree of graphitization on the basis of derivation of various C/Co shells, A3-600 with obvious multi-polarization effect were obtained. A3-600 achieves an effective absorption bandwidth of 6.25 GHz at 1.71 mm and the best reflection loss of −71.95 dB at 1.78 mm. This dual strategy of shell evolution design and graphitization control has been proved to be an effective method to coordinate electromagnetic matching and construct multi-polarization effect to enhance the performance of MA.

Lightweight and high-efficiency microwave absorption of reduced graphene oxide loaded with irregular magnetic quantum dots

Due to the excessively high electrical conductivity and single dielectric properties of the graphene material, when used as a wave absorbing material, the imbalance of impedance matching causes strong reflection effects, resulting in poor wave absorbing performance. In this research, we partially reduced graphene oxide (GO) and loaded magnetic quantum dots (MQDs) through a one-step pyrolysis method, and a novel composite material of three MQDs (Fe, Fe3O4, Fe3C) embedded partially reduced graphene oxide (P-rGO) was prepared and the influence of pyrolysis temperature on its electromagnetic performance was systematically studied. The research found that ethylene glycol selectively reduced the CO functional group of the GO component and enhanced its dielectric properties; the loading of MQDs for a single carbon material increased the magnetic loss mechanism and improved the impedance matching and attenuation capabilities. In addition, the flaky structure of GO and the ultra-small nanostructure of MQDs suppress the eddy current effect and promote the occurrence of exchange resonance between magnetic particles. The prepared four sets of samples exhibit excellent absorbing properties in the 2–18 GHz frequency band. Among them, the samples prepared by pyrolysis at 800 °C can obtain 5.59 GHz broadband electromagnetic wave absorption at an ultra-thin thickness of 1.7 mm. The special quantum size effect and enhanced electromagnetic wave attenuation capabilities are the main reasons for the high-efficiency microwave absorption of MQDs/P-rGO composite materials.

Design and synthesis of ZnO nanoparticles decorated ultra-light nanoscale reduced graphene oxide for broadband electromagnetic wave absorption

Design and synthesis of ZnO nanoparticles decorated ultra-light nanoscale reduced graphene oxide for broadband electromagnetic wave absorption

Flower-like Ni/N-doped carbon composites with core–shell synergistic structure for broad-band electromagnetic wave absorption

The novel microstructure of magnetic-carbonaceous composites has become a prevalent route to improve electromagnetic wave absorption (EMWA) performance. Flower-like Ni/nitrogen-doped carbon (Ni/NC-X) composites with core–shell synergistic structure, N-doping and Ni-N bonds were rationally constructed and fabricated by hydrothermal methods and thermal decomposition with carbon reduction. The Ni cores were encapsulated within approximately 15 layers of the graphene shell, leading to the generation of a Ni/NC-X core–shell configuration. The EMWA performances of Ni/NC-X composites could be adjusted by modulating the acrylonitrile (AN) content. Benefiting from the synergistic effects of the core–shell configuration, a hierarchically flower-like architecture and the components (Ni and C), the flower-like Ni/NC-0.80 composite showed remarkable EMWA performance with a reflection loss (RL) of − 40.1 dB and a broad effective absorption bandwidth (EAB) of 10.05 GHz. The result of this study establishes a new strategy to prepare magnetic-carbonaceous composites by carefully designing the microstructure.

Plasma characteristics and broadband electromagnetic wave absorption in argon and helium capacitively coupled plasma* *Project supported by the Key Research and Development Plan of Anhui Province, China (Grant No. 201904a07020013).

A one-dimensional self-consistent calculation model of capacitively coupled plasma (CCP) discharge and electromagnetic wave propagation is developed to solve the plasma characteristics and electromagnetic wave transmission attenuation. Numerical simulation results show that the peak electron number density of argon is about 12 times higher than that of helium, and that the electron number density increases with the augment of pressure, radio frequency (RF) power, and RF frequency. However, the electron number density first increases and then decreases as the discharge gap increases. The transmission attenuation of electromagnetic wave in argon discharge plasma is 8.5-dB higher than that of helium. At the same time, the transmission attenuation increases with the augment of the RF power and RF frequency, but it does not increase or decrease monotonically with the increase of gas pressure and discharge gap. The electromagnetic wave absorption frequency band of the argon discharge plasma under the optimal parameters in this paper can reach the Ku band. It is concluded that the argon CCP discharge under the optimal discharge parameters has great potential applications in plasma stealth.

Retraction: A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption

Retraction of ‘A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption’ by Chaozhi Wang et al., RSC Adv., 2019, 9, 23843–23855, DOI: 10.1039/C9RA04405A.

Microwave metamaterial for broad-band perfect absorber applications

This article introduces lumped resistances loaded in triangular metamaterial structure, realize broad band electromagnetic wave absorber band through simple metamaterial design and just single layer structure. In addition, this design presents the resistances value effects, substrate thickness and power loss per material. The influence of resistances on absorbing band characteristics. The results show that: by changing the resistance value to adjust the absorption frequency band of the metamaterial. When the resistance is increased or decrease from the designed resistance, there is almost shift in the position of the absorption band. The change of the resistance value mainly affects the amplitude of the absorption band which is compared with traditional absorbing materials, Under the same absorbing performance conditions, it shows excellent single layer structure. The simulation confirms that absorption of this design-based metamaterial absorber exceeds 90% and it can be seen that the power is mainly consumed in the lumped resistances. The proposed idea offers a further design in developing new electromagnetic absorbers, which will impact a broad range of applications.

Research progress of new carbon based magnetic composite electromagnetic waveabsorbing materials

New carbon based magnetic composite absorbing materials have become the mainstream of electromagnetic wave absorbing materials because of their light weight and high performance. Carbon based wave absorbing materials have the advantages of low density, large specific surface, high conductivity, but also have the disadvantages of non-magnetic and low impedance matching level. They are often combined with magnetic loss materials to build light composite materials with various microstructures and multiple cooperative loss mechanisms to achieve efficient and broadband electromagnetic waveabsorption. On the basis of summarizing the research on the wave absorbing application of carbon matrix composites at home and abroad, this paper analyzes the research progress of new graphene, carbon nanotubes, biomass porous carbon and other carbon matrix magnetic composite wave absorbing materials with composition, composite method and microstructure as the main line, and finally points out the existing problems and future development trend of carbon based magnetic absorbing materials.

Hollow double-shell structured Void@SiO2@Co-C composite for broadband electromagnetic wave absorption

Current electromagnetic wave (EMW) absorbing materials generally face the problem of narrow absorption bandwidth, which is the bottleneck in practical applications. Exploring new strategies and designing new architectures to overcome this problem is urgent but challenging. Here, a hollow double-shell structured magneto-electric composite, composed of an internal hollow cavity, a middle SiO2 matching shell and an outer Co-C porous shell ([email protected]2@Co-C), was prepared by assembling metal–organic-framework particles on hollow SiO2 cavity and pyrolysis. The multiple magnetic resonances, magneto-electric interface polarization, defect dipole polarization and conductivity of the composite can be well tuned by controlling the pyrolysis temperature. In particular, the hollow SiO2 cavity plays an essential role in improving impedance matching. Benefitting from the synergistic effect between hollow SiO2 cavity, porous carbon shell and Co particles, the [email protected]2@Co-C composite exhibits a broad effective absorption bandwidth above 7 GHz at a thin thickness of 2.2 mm, which is superior to other Co-C composites (less than 6 GHz). This work provides an effective solution for broadening the EMW absorption bandwidth.

Hollow SiC microtube with multiple attenuation mechanisms for broadband electromagnetic wave absorption

The hollow SiC microtubes were designed and prepared by the de-template of SiC/CF coaxial materials to enhance the electromagnetic wave absorption bandwidth of the SiC materials. The XRD, Raman, and TEM results indicated that the hollow SiC microtubes were composed of SiC, C, and amorphous SiO2 layers. The carbon particles uniformly embedded in the SiC particles and the amorphous SiO2 covered the outside of the SiC microtube. The dielectric properties of the hollow SiC microtube could be optimized by controlling its wall thickness. The hollow SiC microtube showed a broader electromagnetic wave absorption bandwidth compared to that of other SiC materials. The minimum reflection loss of hollow SiC microtube was −25.7 dB@14.9 GHz, and the effective absorption bandwidth was 5 GHz covering from 12.9 GHz to 17.9 GHz at a sample thickness of 2 mm. The uniform distribution of carbon contributed to improving the conduction loss of hollow SiC microtube. The interfacial relaxation loss causing by the outermost SiO2 layer enhanced the dielectric loss of the tubular SiC. Besides, the unique hollow structure of the SiC microtube significantly promoted the multi reflection and scattering of electromagnetic waves. The multiple attenuation mechanisms of tubular SiC highlighted the design of a novel structure for a high-performance electromagnetic wave absorber.

Fabrication of nitrogen-doped reduced graphene oxide/cobalt ferrite hybrid nanocomposites as broadband electromagnetic wave absorbers in both X and Ku bands

In this work, nitrogen-doped reduced graphene oxide decorated by magnetic cobalt ferrite (NRGO/CoFe2O4) hybrid nanocomposites were fabricated through solvothermal and hydrothermal two-step processes. Results of structure and micromorphology analysis manifested that numerous nanosized CoFe2O4 particles were uniformly anchored on the wrinkled surfaces of flake-like NRGO, and considerable nitrogen atoms had been doped into the crystal lattice of RGO. Moreover, the influences of additive amounts of CoFe2O4 and hybridization with NRGO on the electromagnetic parameters and absorption properties were carefully examined. Significantly, the as-synthesized nanocomposite with the content of NRGO of 13.76 wt% exhibited the optimal electromagnetic absorption capacity, i.e. the minimum reflection loss achieved −48.4 dB and broadest absorption bandwidth reached 6 GHz (12–18 GHz) under a small matching thickness of merely 1.9 mm and low filler content of 30 wt%. It should be mentioned that full absorption of both X and Ku bands was realized in the as-fabricated nanocomposites by facilely modulating the additive amounts of CoFe2O4 and matching thicknesses. Furthermore, the hybrid nanocomposites showed strong absorption intensity (≤ −20 dB, 99% absorption) in a wide thickness range of 1.9–5 mm. Besides, the potential electromagnetic absorption mechanisms were uncovered. Therefore, our results opened a novel idea for designing RGO-based dielectric/magnetic hybrid nanocomposites as high-performance electromagnetic absorbers.

Synthesis of reduced graphene oxides with magnetic Co nanocrystals coating for electromagnetic absorption properties

This paper reports a facile one-step reaction method to prepare rGo/Co hybrids with super-tiny Co nanocrystals coating on reduced graphene oxide, the rGo/Co hybrids have excellent electromagnetic wave absorption ability because of its good impedance matching and attenuation properties. The crystal structure, microtopography, and magnetic property of rGOs/Co hybrids were characterized by X-ray diffraction, transmission electron microscope, and vibrating sample magnetometer, respectively. Electromagnetic parameters were measured by vector network analyzer in the frequency range of 1–18 GHz using a coaxial line method. The rGOs can serve as perfect supports for dense coating of Co nanocrystals with an average size of 3.87 nm. Compared with pure rGOs and Co NPs, the rGO/Co hybrids exhibit excellent electromagnetic wave absorption properties with an optimal reflection loss (RL) value reaching up to − 52.73 dB at 14.34 GHz and a broad effective bandwidth (RL values lower than − 10 dB) of 6.2 GHz (11.8 to 18 GHz) at a thin thickness of 2.1 mm only. This work provides an efficient process to prepare a micro-nano composite absorber with strong and broadband electromagnetic wave absorption.

Orientation growth modulated magnetic-carbon microspheres toward broadband electromagnetic wave absorption

Surface magnetic configurations and electromagnetic responding behaviors can be efficiently modulated by controlling the growth of magnetic materials, which has always been a huge challenge. Here, an in situ orientation growth strategy is developed to build a micron scale Fe3O4–Fe3O4@C heterojunction via applying Kirkendall diffusion to the orientation growth process. Undergoing precipitation and phase transition process, the oriented Fe3O4 octahedron tightly rooted in anisotropy Fe3O4@C body, constructing various magnetic configurations and enhancing stray magnetic field intensity. As-synthesized magnetic-dielectric microspheres exhibited excellent energy conversion capacity toward electromagnetic wave, including strong reflection loss (RL: 40.8 dB, 2.0 mm) and ultra-wide absorption region (∼11.04 GHz, ∼69% of the tested frequency). Essentially, cross-space magnetic coupling enlarges the responding region beyond the material itself and strengthens electromagnetic wave disputation. Local charge density distribution around the grain boundary plays the key role in forming the enhanced interfacial polarization, which is characterized by the off-axis electronic holography. More importantly, the dynamic response mechanism was firstly observed under an applied magnetic field. Changing magnetic configurations induce the rearrangement of magnetic flux distribution, providing the internal magnetic feedback. Above-mentioned dielectric and magnetic properties of Fe3O4–Fe3O4@C composites make a breakthrough understanding toward the energy conversion mechanisms.

Malposed spoof surface plasmon structure with enhanced microwave absorption and compressive performances realized by carbon-based foams

In this paper, a malposed spoof surface plasmon (SSP) structure filling by carbon-based absorbent polymethacrylimide (PMI) foams is proposed, which realizes the bi-function of broadband electromagnetic (EM) wave absorption and mechanical enhancement properties. The malposed SSP structure is first designed to accomplish high-performance absorption at lower radar frequencies, whose 10-dB level absorptivity is obtained at the range of 4.8–10.2 GHz. After filling carbon-based PMI foams in the interior of hollow SSP structure, the effective absorption bandwidth can be extended largely to 18 GHz. Moreover, the measured results in the mechanical compressive experiment show that the compressive strength σpeak, energy absorption per unit volume Wv and energy absorption per unit mass Wm of the proposed foam-filled SSP structure can reach to 45.4 MPa, 13.57 × 103 KJ/m3 and 38.84 KJ/Kg, respectively, with the density only 0.35 g/cm3, which are more competitive comparing with many metallic sandwich core topologies. It is sure that the broadband microwave absorption performance and enhanced compressive property make our design more multifunctional, and have potential application in the practical stealth designs.

Three-Dimensional Carbon Networks Decorated with CoFe2O4 Nanoparticles Composites: Fabrication and Broadband Electromagnetic Wave Absorption Performance

A novel electromagnetic wave absorber of three-dimensional carbon networks decorated with CoFe2O4 nanoparticles (3DC/CoFe2O4) was prepared through a simple freeze-drying method followed by a high-temperature calcination process. The 3DC/CoFe2O4 composite prepared at 630 °C (S630) exhibits broadband electromagnetic wave absorption with only 20 wt% filler loading. The effective absorption bandwidth (reflection loss [RL] < −10 dB) of S630 reaches up 6.63 GHz, and the minimum RL of −19.5 dB is obtained at 15.45 GHz when the matching thickness is 2.5 mm. The excellent electromagnetic wave absorption performance of the 3DC/CoFe2O4 composite can be attributed to good impedance matching and strong attenuation capacity.

Co/C broad band electromagnetic wave absorption composite derived from preferred precursor ZIF-67: preparation and performance

A simple sacrificial template method was used to prepare Co/C composite with cobalt nanoparticles embedded in nitrogen-doped polyporous graphite carbon as an efficient electromagnetic wave (EMW) absorbent. Effects of solvent polarity, ratio of Co2+ to 2-methylimidazole and pH value of reaction system on precursor metal–organic skeleton ZIF-67 were systematically studied by a single variable method, and then the optimal preparation process was obtained. Thermal decomposition time and temperature of precursor ZIF-67 are the keys to the formations of ferromagnetic metal cobalt particles and carbon matrix. Therefore, effects of calcined temperature in inert atmosphere on the carbon content, graphitization degree, magnetic properties and microwave-absorbing performances of Co/C composite prepared were studied, and then nitrogen-doped porous composite Co/C composed of a highly dispersed core–shell Co@graphite nanoparticles coated by amorphous carbon skeleton was successfully prepared by optimizing pyrolysis technology. Composite Co/C-900 obtained by ZIF-67 calcinated at 900 °C exhibits excellent EMW absorption performances at low filling amount; its maximum reflective loss (RLmax) reaches − 34.41 dB at 17.49 GHz with the test thickness of 2.0 mm only, and most importantly, when the test thickness is 2.5 mm, its effective absorption bandwidth (RL < − 10 dB) reaches 7.37 GHz (10.18–17.5 GHz), spanning the X and Ku bands. The synergistic effects of the self-loss (dielectric loss and magnetic dissipation) and structural attenuation (multiple scattering and interface polarization) of Co/C-900 obtained greatly improve its impedance matching with free space and attenuation coefficients to EMW, significantly widening its effective bandwidth. As a new high-performance EMW absorbent with thin thickness, light weight, strong absorption capacity and wide bandwidth, the Co/C composite optimized by precursor preparation and calcination process should have a broad application prospect.

Hierarchical CoxAlylayered double hydroxide@carbon composites derived from metal–organic frameworks with efficient broadband electromagnetic wave absorption

Porous carbon-based composites have attracted extensive attention because of their good performance.

Porous core-shell zeolitic imidazolate framework-derived Co/NPC@ZnO-decorated reduced graphene oxide for lightweight and broadband electromagnetic wave absorber

High-efficiency microwave absorbers, characteristic of thin thickness, lightweight, broad bandwidth and strong absorptivity, have presented the immense potential in daily communication and radar stealth. Herein, a novel 3D heterostructured material with high specific surface area and high porosity, namely Co/NPC@ZnO/rGO, was constructed via a facile four-step method, in which porous core-shell Co/NPC@ZnO NPs with the diameter of around 700 nm prepared by the direct pyrolysis of ZIF-67@ZnO NPs were uniformly implanted onto and tightly wrapped in pleated rGO nanosheets. Benefiting from the well-designed components and configurations that can lead to the desirable impedance matching, occupying a crucial position in the entire absorption process; and the enhanced attenuation capacity derived from unique porous and core-shell architectures; the as-prepared composites evenly mixing the paraffin matrix with 30 wt% display the dramatically exceptional microwave absorbency, achieving the optimal reflection loss(RL) of −45.4 dB at thickness of only 2 mm, and especially, the valid response bandwidth of 5.4 GHz, when the mass percentage of Co/NPC@ZnO to GO is 3:1. Additionally, coupling with the merit of lightweight originating from the porous appearance of Co/NPC@ZnO and the inherent nature of rGO, this research exhibits the tremendous reference value for the assembly of ideal lightweight and wideband microwave absorbents in the future.

Broadband and strong electromagnetic wave absorption of epoxy composites filled with ultralow content of non-covalently modified reduced graphene oxides

High-efficiency microwave absorption epoxy nanocomposites filled with ultralow content of non-covalently modified reduced graphene oxides (rGO) are prepared via an in-situ polymerization method. Here, the porous and folded rGO nanosheets are successfully functionalized by strong π-π interaction between conjugated imidazole and graphene sheets. The combination of electron microscope and synchronous radiation X-ray small angle scattering (SAXS) techniques unambiguously illustrates that the non-covalently modified graphene nanosheets in the epoxy composites are well-dispersed and extensively winkle. Hence, compared with pristine rGO/epoxy composites, the composites containing the highly dispersed rGO demonstrate more ideal impedance matching and stronger microwave dissipation based on the experimental and simulated results. The composites remarkably achieve excellent microwave absorptions (minimum reflection loss of −65 dB, with a matching thickness of 1.8 mm), an extremely broad absorbing bandwidth of 7.48 GHz (RL < −10 dB) and ultralow filler loading (1–2 wt%). Moreover, the composites possess high hydrophobicity, endowing them attractive functions of self-cleaning. This work provides a promising, facile and scalable approach for designing and fabricating graphene-based nanocomposites with hydrophobicity and excellent microwave absorption capacities.