Broad Absorption Bandwidth Research Articles

Synthesis of FeCoNi/C decorated graphene composites derived from trimetallic metal-organic framework as ultrathin and high-performance electromagnetic wave absorbers.

High-temperature pyrolysis of metal-organic framework (MOF) is an effective way to prepare lightweight and high-performance electromagnetic wave absorbers. In this work, iron cobalt nickel/carbon (FeCoNi/C) decorated graphene composites were fabricated by the two-step method of solvothermal reaction and pyrolysis treatment. Results of micromorphology analysis demonstrated that numerous octahedral FeCoNi/C carbon frameworks were almost uniformly distributed on the wrinkled surfaces of flaky graphene. Moreover, the electromagnetic parameters and wave absorbing properties of obtained composites were regulated through simply changing the addition amounts of graphene oxide. Significantly, the as-prepared FeCoNi/C decorated graphene composite with the addition amount of graphene oxide of 67.2mg exhibited the best electromagnetic absorption performance. The minimum reflection loss was as large as -66dB at 15.6GHz and broad absorption bandwidth reached up to 4.8GHz with an ultrathin thickness of 1.53mm and a filler loading ratio of 30wt%. Furthermore, the maximum absorption bandwidth was enlarged to 5.2GHz via slightly adjusting the matching thickness to 1.56mm. Additionally, the probable electromagnetic attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of MOF derived carbon-based magnetic composites as ultrathin and high-performance electromagnetic absorbers.

Flexible cobalt nanoparticles/carbon nanofibers with macroporous structures toward superior electromagnetic wave absorption

The increasing electromagnetic (EM) pollution that has seriously threatened human health and electronic devices urgently required high-performance absorbents toward attenuating EM wave (EMW). The combination of microstructure modulation and appropriate components regulation has proven to be a feasible strategy for improving the EMW absorption performance of absorbents. In this work, well-designed one-dimensional carbon nanofibers with macroporous structures and uniformly magnetic metal nanoparticles modification were prepared by the hard-template assisted electrospinning method followed by carbonization and template-elimination processes. The strong interfacial polarization loss and multireflection strengthened by the hollow structures and the magnetic loss induced by the introduced cobalt nanoparticles evidently enhanced the impedance matching level of the macroporous carbon nanofibers/cobalt nanoparticles (MCF/Co). As a result, MCF/Co composite offers broad absorption bandwidth (6.24 GHz) and strong electromagnetic wave absorption performance (−40.1 dB) at a thickness of 3.0 mm. This work inspires the rational one-dimensional macroporous carbon nanofibers design for new-generation EMW materials and provides an important research basis for the porous flexible EMW absorption materials.

Broadband Low-Profile Frequency Selective Rasorber Using Ultraminiaturized Metal-Graphene Structure

In this letter, a broadband and low-profile frequency selective rasorber with an ultraminiaturized metal-graphene structure is proposed. The rasorber is composed of two cascaded layers separated by an air spacer, a top lossy layer and a bottom bandpass layer. By supplying four branches of multiple vias connected stubs across a circular graphene film in the lossy layer, extra inductance and capacitance effects are introduced while guaranteeing the impedance match with the free space at the low frequency range. As a result, a broad absorption bandwidth is ensured from 1.96 to 10.2 GHz with the thickness of only 0.076 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_l</i> at the lowest absorption frequency, and the passband is at 12.83 GHz with the insertion loss of 0.23 dB. Besides, a miniaturized unit is achieved with the period of 0.039 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_l</i> , and the oblique angle incidence response is up to 45° for TE and TM modes. To validate the design, a prototype is fabricated and measured, and the screen-printing process of graphene resistive film as omnidirectional resistance is adopted to further reduce the profile. The measured results agree well with the simulation.

Construction of porous carbon-based magnetic composites derived from iron zinc bimetallic metal-organic framework as broadband and high-efficiency electromagnetic wave absorbers

The fabrication of broadband and high-efficiency electromagnetic (EM) wave absorbers remains a huge challenge. Metal-organic framework (MOF) with large porosity and high specific surface area has been considered as a promising precursor for the preparation of novel EM wave absorbers. In this work, porous carbon-based magnetic composites derived from iron zinc bimetallic MOF were prepared by the two-step method of solvothermal reaction and high-temperature pyrolysis. Results of micromorphology analysis demonstrated that the morphology of carbon frameworks evolved from octahedron, polyhedron, sphere to porous sphere-like shape with the increase of pyrolysis temperature. Furthermore, the EM parameters and absorbing properties of obtained composites were regulated through simply changing the pyrolysis temperature. It was noteworthy that the as-prepared Fe3O4/C composite pyrolyzed at 700 °C exhibited the best EM absorption performance. The minimum reflection loss was as large as −60 dB and broad absorption bandwidth reached up to 4 GHz (8–12 GHz, covering the whole X band) at a matching thickness of 2.5 mm and a filler loading ratio of 40 wt%. Furthermore, the maximum absorption bandwidth could be enlarged to 5.4 GHz via reducing the matching thickness to 1.85 mm. Additionally, the probable EM attenuation mechanisms of attained composites were proposed. The results of this study would provide a reference for the preparation of porous carbon-based composites as broadband and high-efficiency EM wave absorbers.

Metal organic framework-derived hierarchical 0D/1D CoPC/CNTs architecture interlaminated in 2D MXene layers for superior absorption of electromagnetic waves

Nowadays, exploring effective electromagnetic wave (EMW) absorbing materials with ultrathin thickness, lightweight, broad absorption bandwidth, and robust absorption capability is crucial to solve EMW pollution issues. Ti3C2Tx is a potential candidate for effective EMW absorbing materials by virtue of its low density, excellent electrical conductivity, high specific surface area, and tunable terminal groups. However, the intrinsic attenuation mechanisms of single dielectric absorbers are limited for practical requirements. Herein, 0D/1D/2D architecture of CoPC/CNTs@MXene hybrids with 0D cobalt nanoparticles supported on porous carbon, 1D carbon nanotubes and 2D Ti3C2Tx nanosheets have been conceptualized and fabricated successfully. By pyrolyzing bimetallic ZnCo-MOF at 800 °C, a 0D/1D hierarchical CoPC/CNTs sample was initially produced, subsequently interlaminated between the Ti3C2Tx matrix via electrostatic self-assembly to fabricate CoPC/CNTs@MXene (CCM) absorbers. The impedance matching properties was optimized by modifying the CoPC/CNTs content. Remarkably, CCM-20 hybrids achieved strong EMW absorption capability (reflection loss of −54.2 dB) at 5.56 GHz, and CCM-30 hybrids achieved ultrathin (1.8 mm) and a broad effective bandwidth (EAB) below − 10 dB (5.6 GHz), which is superior to the magnetic-dielectric hybrids with comparable components reported previously. The exceptional absorption capability can be attributed to the synergistic effects of interface polarizations and magnetic loss. The intricate construction of the 0D/1D/2D architecture facilitates the multiple reflections and scattering of EMW. This work provides an idea for fabricating MXene-based composites with remarkable electromagnetic properties and a broad absorption bandwidth for potential applications.

Constructing magnetic iron-based core-shell structure and dielectric nitrogen-doped reduced graphene oxide nanocomposite for enhanced microwave absorption performance

A ferromagnetic nanocomposite Fe3O4@Fe/Fe4N/CFe15.1-NrGO, which is composed of elemental iron-based, iron nitride-based and iron carbide-coated ferroferric oxide core-shell structured nanospheres and nitrogen-doped partially-reduced graphene oxide (NrGO), has been successfully prepared by combining an initial hydrothermal processing, subsequent reducing agent impregnation and final solid-state thermal reduction. And then, we investigate the microwave absorption performance of Fe3O4@Fe/Fe4N/CFe15.1-NrGO nanocomposite in paraffin dispersion. When the loading mass of Fe3O4@Fe/Fe4N/CFe15.1-NrGO is 9.0 wt% in paraffin dispersion, the minimum reflection loss (RLmin) of microwave is as high as −30.5 dB at the thickness of 1.5 mm, and the corresponding effective absorption bandwidth (EAB < -10 dB) of 4.4 GHz (13.6 ∼ 18.0 GHz) is the 27.5% of the entirely measuring bandwidth from (2.0 ∼ 18.0 GHz). The excellent microwave absorbing performances of nanocomposite Fe3O4@Fe/Fe4N/CFe15.1-NrGO may be attributed to the following twoaspects: (i) the interfacial polarization of the core-shell structure of spheroidal iron-based constituents and the interface between an iron-based nanosphere and dielectric lamellar NrGO and (ii) a synergistic effect between dielectric properties of lamellar-structured NrGO and the magnetic properties of core-sell structured Fe3O4@Fe/Fe4N/CFe15.1. This electromagnetic absorber with core-shell structure and dielectric graphene properties can satisfy the requirements of ideal absorbers, such as strong absorption ability, broad absorption bandwidth, thin absorber thickness and low density. In addition, this work also provides a promising strategy to synthesize multivariate two-dimensional nanocomposite with light-weight and high absorption performance.

Flower-like NiO to flower-like NiO/Ni@C microspheres: An effective strategy to comprehensively improve the loss capabilities

It was well recognized that the penetrated electromagnetic (EM) wave could be dissipated by means of magnetic loss, polarization loss and conduction loss. In order to improve their loss capacities and take full advantage of flower-like geometrical morphology, in this study, we proposed a simple route for the production of flower-like core@shell structure NiO/Ni@C microspheres through the carbon thermal reaction using NiO microflowers as precursor. The obtained results revealed that our proposed strategy successfully synthesized the core@shell structure magnetic carbon-based multicomponent nanocomposites without destroying the geometrical morphology of precursor. By regulating the annealing temperature, the as-prepared NiO/Ni@C microspheres with different contents of Ni and degrees of graphitization could be selectively synthesized, which effectively boosted their magnetic loss, polarization loss and conduction loss capabilities. Therefore, the elaborately designed NiO/Ni@C microspheres displayed the superior microwave absorption performances including strong absorption capability, broad absorption bandwidth and thin matching thicknesses compared to the NiO precursor. In summary, our findings not only provided a simple route to design and synthesize flower-like core@shell structure magnetic carbon-based nanocomposites as novel microwave absorbers, but also presented an effective strategy to comprehensively improve their loss capacities.

Ultra-broadband and completely modulated absorption enhancement of monolayer graphene in a near-infrared region.

Achieving ultra-broadband and completely modulated absorption enhancement of monolayer graphene in near-infrared region is practically important to design graphene-based optoelectronic devices, however, which remains a challenge. In this work, by spectrally designing multiple magnetic plasmon resonance modes in metamaterials to be adjacent to each other, near-infrared light absorption in monolayer graphene is greatly improved to have an averaged absorption efficiency exceeding 50% in a very broad absorption bandwidth of about 800 nm. Moreover, by exerting an external bias voltage on graphene to change Fermi energy of graphene, the ultra-broadband absorption enhancement of monolayer graphene exhibits an excellent tunability, which has a nearly 100% modulation depth and an electrical switching property. This work is promising for applications in near-infrared photodetectors, amplitude modulators of electromagnetic waves, etc.

Hollow Co9S8 nanoparticles with carbon shells for wide-band and efficient microwave absorption

Aiming to obtain advanced microwave absorbing materials with high absorption efficiency, broad absorption bandwidth and low density, herein, a novel nanocomposite with irregular hollow nanostructure of Co9S8@C was successfully prepared via a soft template and annealing method. Due to the shrinkage process of the Co9S8 nanospheres by annealing, Co9S8 cores and carbon shells were easily obtained. Because of the unique microstructure with irregular outer shells and heterogeneous interfaces, improved polarization loss, multiple reflection loss as well as the impedance matching capability was achieved. As a result, greatly enhanced microwave absorption performance with a reflection loss (RL) of − 51.3 dB at 4.12 GHz, and effective absorption bandwidth (RL<−10 dB) of 5.44 GHz at a thickness of only 1.35 mm was obtained, suggesting the unique Co9S8@C nanocomposite in this work to be an intriguing and promising microwave absorber.

Experimental and theoretical study on broadband electromagnetic wave absorption of algae-like NiO/carbon nanotubes absorbers

Rational construction of nanocomposites with special structure is still a considerable challenge in developing high-performance electromagnetic (EM) wave materials. In this work, NiO and multiwall carbon nanotubes(MWCNTs) intertwined as a new algae-like material is designed and fabricated by a facile and simple strategy to acquire high EM wave performances for the first time. Benefitting from the special nanostructures, which cause rich dipole polarization, interfacial polarization, multiple scattering centers, reduced specific gravity, three dimensional conductive networks, and proper impedance matching, the NiO/MWCNTs nanocomposites with S-6.5 wt% MWCNTs content display superior microwaves absorption capability. With 30 wt% filler loading, it possesses a strong absorption of − 58.27 dB and a wide absorbing bandwidth of 5.25 GHz at a thickness of only 1.6 mm. Additionally, the broad absorption bandwidth of 16.2 GHz can be obtained in the thickness range of 1.5–5.0 mm. To deeply expose the inner EM wave absorption mechanism, the electronic properties of the hetero-interface (NiO and CNTs) are calculated by density functional theory (DFT). The electronic properties reveal the influence of the polarization on the absorption properties at the atomic level. The combination of experimental and theoretical research clarified the EM wave absorption mechanism of NiO/MWCNTs composites, indicating that NiO/MWCNTs composites can be a high-efficiency absorber with lightweight, ultrathin thickness, broad bandwidth, antioxidation, and strong absorption.

Multifunctional graphene/carbon fiber aerogels toward compatible electromagnetic wave absorption and shielding in gigahertz and terahertz bands with optimized radar cross section

Lightweight absorption-dominated electromagnetic interference (EMI) shielding materials with multifunctional integration of multiband absorption, mechanical durability and thermal insulation are urgently required in the practical application of next-generation communication technology combined with flexible electronics. In this work, ultralight and mechanically durable graphene/carbon fiber composite aerogels (CGAs) are synthesized via solvothermal reaction and freeze-drying. The as-prepared CGAs demonstrate excellent compatible electromagnetic wave absorption and shielding performance in both gigahertz (GHz) and terahertz (THz) bands without addition of magnetic component. Specifically, a broad efficient absorption bandwidth of 8.72 GHz at 2–18 GHz and a high mean absorptivity of 97.4% at 0.3–1.5 THz are achieved, respectively. Furthermore, absorbing coatings with CGAs have been proved to contribute to remarkable radar cross section reduction of 39.06 dBm2 by computer-assisted simulation. Additionally, the compressible CGA demonstrates superior and stable EMI shielding performance under in-situ compression. The EMI shielding effectiveness exceeds 35 dB in X-band when a compression ratio of 78.9% is applied. Moreover, CGAs are thermally insulating and self-extinct, making them reliable in practical application. This work provides a series of promising multifunctional lightweight EMI shielding materials for future high-frequency wireless communication.

Annular hole array design as a high efficiency absorber for photovoltaic applications

In order to benefit from thin-film solar cells cost advantage, increasingly effort is deployed to maximize their harvesting capability. In this work, we focus on improving an a-Si solar thin-film by engraving it with an Annular Hole Array (AHA). The design parameters are fashioned to maximize the absorption across the visible spectral range exploiting the 3D Finite-Difference Time-Domain method (3D−FDTD). When comparing the AHA device to an unpatterned a-Si solar cell, an important absorption enhancement of 64.2% was obtained along with a broad spectral absorption bandwidth with peaks reaching 97.7% at normal incidence over the AM1.5 solar spectrum. It turns out that a proper design optimization highlighted promising results like polarization and almost incidence insensitivity. In fact, an integrated absorption of 90.5% over the AM1.5 solar spectrum was achieved and maintained over 65% for any angle of incidence for the spectral field λ∈[300nm;1000nm]. These results are beneficial for solar energy harvesting and allow this structure to be an advantageous candidate for photovoltaic applications.

Microwave Absorption Performance of Core–Shell rGO/Ni0.5Co0.5Fe2O4@PEDOT Composite: An Effective Approach to Reduce Electromagnetic Wave Pollution

In recent years, the modern technologies working with electromagnetic waves are growing rapidly. Along with this side, malfunctioning in electronic devices and harmful effects of electromagnetic waves on living bodies are observed. Thus, to reduce the electromagnetic radiations pollution and interference problems, electromagnetic wave absorber materials are intensely in demand. Herein, with the aim, the core–shell designed rGO/NiCoFe2O4@PEDOT composites are synthesized through in situ oxidative polymerization method. The structural, morphological, and thermal properties of the composites are studied. The TEM and SEM results confirm the polymerization of PEDOT over the surface of rGO/NiCoFe2O4, i.e., the genesis of core–shell structure formation. The absorption of electromagnetic waves is investigated in the Ku‐frequency band. The maximum microwave absorption and total shielding effectiveness of rGO/NiCoFe2O4@PEDOT composite are estimated as 34.74 dB and 38.79, respectively, with broad absorption bandwidth. The surpassing absorption performance is gained by its characteristic properties such as improved impedance matching, synergic effects of dielectric and magnetic loss, and attenuated behavior exhibited by the material. A comprehensive discussion on the absorption mechanism is presented in this article. The enhanced shielding results of rGO/NiCoFe2O4@PEDOT composite reveal that the material can be used to design lightweight microwave absorbers.

Biomass-derived ultralight superior microwave absorber Towards X and Ku bands

Biomass-derived microwave absorbers have attracted extensive attention due to their natural abundance, low cost and eco-friendliness. However, it is still a challenge to achieve superior absorptivity under the extremely low filler content in such absorbers. Herein, we engineer a hybrid of Co3Fe7 alloy nanoparticles (NPs) anchoring on the biomass shaddock peel derived porous carbon nanosheets (CNs) for superlight and efficient microwave absorption. The CNs exhibit attractive graphene-like morphology with Co3Fe7 alloy NPs uniformly dispersing throughout the CNs. It is revealed that the EM parameters could be well controlled by tailoring the deposition ratio of Co3Fe7 NPs to optimize impedance matching. Specifically, the sample with relatively sparse Co3Fe7 NPs exhibit a reflection loss (RL) of –22.3 dB and broad absorption bandwidth of 5.3 GHz in Ku band under the ultralow filler content of only 8.0 wt%. As the deposition ratio of magnetic Co3Fe7 NPs increases, the optimized absorption peak moves to X band with −50.6 dB of RL value and 4.5 GHz of effective absorption, completely covering the whole X band. The elaborative studies demonstrate the significant influence of impedance matching on the ultimate absorption performance. This work paves a new way for the development of biomass-derived composites as superlight and tunable microwave absorber.

Lithography-free wide-angle polarization-independent ultra-broadband absorber based on anti-reflection effect.

We propose a lithography-free wide-angle polarization-insensitive ultra-broadband absorber by using three pairs of tungsten (W) and calcium fluoride (CaF2) films. The simulation results show that the absorptivity is larger than 0.9 with normal incidence in the wavelength range from 400 nm to 1529 nm. By adding a pair of CaF2-W films, we can get a broader absorption bandwidth with absorptivity larger than 0.9 over the wavelength of 400-1639 nm. In addition, the absorption performance is insensitive to the polarization and angle of incidence. The electric field distributions at the absorption peaks show that the absorption is originated from the destructive interference between the reflection waves from the top and bottom interfaces of the multilayer CaF2-W films. Furthermore, the ultra-broad bandwidth is attributed to the anti-reflection effect from the increased effective refractive index from top to down of the proposed absorber. Such physical mechanism of broadening bandwidth based on anti-reflection effect provides a new idea for the design of broadband absorber. Meanwhile, this broadband absorber is a good candidate for potential applications such as detection and energy harvesting.

Growth of magnetic metals on carbon microspheres with synergetic dissipation abilities to broaden microwave absorption

• Facile electrostatic assembly approach for preparation of core-shell C/magnetic metal composite microspheres. • Excellent microwave absorption performance including a maximum reflection loss value of −54.1 dB and a broad effective absorption bandwidth of 6.7 GHz. • Profound magnetic coupling effect and magnetic-dielectric synergy mechanism for enhancing microwave absorption performance. Microwave absorption (MA) materials have been captured extensive attentions due to the serious electromagnetic (EM) pollution. Numerous interests focus on the MA performances of core-shell structural composites with magnetic constituents as cores and dielectric constituents as shells, which inevitably suppressed the magnetic coupling causing the decrease of magnetic loss to some extent. Herein, the core-shell structural carbon (C) microsphere/magnetic metal composites were fabricated through the combination of an electrostatic assembly approach and subsequent in-situ reduction reaction. The complex permittivity and permeability of core-shell C@magnetic metal composite system can be effective adjusted by the constituent and microstructure of shells. Thanks to the distinct magnetic coupling from the subtle designed structures and the promotion of the magnetic-dielectric synergy, the C@magnetic metal composite exhibited enhanced MA properties. The optimal reflection loss (RL) of C@Ni composite was -54.1 dB with a thickness of 3.4 mm, meanwhile the effective absorbing band could reach over 5.5 GHz at only a 1.8 mm thickness. Broad absorption bandwidth with RL below -10 dB could achieve 6.0 GHz and 6.7 GHz for C@Co and C@NiCo composites with a thin 2.1 mm thickness, respectively. Our exciting findings might lead a guide on the novel structure design for the functional core-shell structural composites used for microwave absorption. Graphical Abstract .

Additive manufacturing of nanocellulose/polyborosilazane derived CNFs-SiBCN ceramic metamaterials for ultra-broadband electromagnetic absorption

• Defect-rich CNFs were developed as electromagnetic absorbents. • Metamaterials were developed by the combination of 3D printing and PDC route. • Cole-Cole circle plots indicates the materials possess strong polarization capability. • Ultra-broad EAB of 32.4 GHz was achieved by multi-scale design. Electromagnetic absorption materials that possess efficient absorption performance and broad absorption bandwidth are needed to combat the electromagnetic interference (EMI). SiBCN ceramic-based metamaterials modified with defect-rich carbon nanofibers (CNFs) were developed by combining the additive manufacturing technique and polymer derived ceramic route. Meta-structures were patterned by additive manufacturing of preceramic polymer and followed by thermolysis of the green bodies. Defect-rich CNFs were in-situ generated by thermolysis of nanocellulose introduced into the preceramic green bodies. When the content of cellulose is 6.0 wt% and the annealing temperature is 1200 °C, the real and imaginary part of permittivity can reach as high as 17.0 and 7.0, respectively. Cole-Cole circle plots indicates that the CNFs-SiBCN ceramics possess strong polarization capability due to the defect-rich structure of CNFs. At the thickness of 1.8 mm, the minimal reflection loss (RL min ) can reach −20.0 dB while the effective absorption bandwidth reached 2.85 GHz. Through multi-scale (nano and macro) designing, a simulated ultra-broad effective absorption bandwidth of 32.4 GHz from 7.6 GHz to 40 GHz was achieved, where the RL min reached −46.0 dB at the frequency of 26.8 GHz. This work finds innovative route for the development of ceramic-based broadband electromagnetic absorption materials and new application for the polymer derived ceramics.

Impedance amelioration of coaxial-electrospun TiO2@Fe/C@TiO2 vesicular carbon microtubes with dielectric-magnetic synergy toward highly efficient microwave absorption

An impedance-optimized hierarchical TiO 2 @Fe/C@TiO 2 vesicular carbon microtube is constructed for the first time via coaxial electrospinning and solvothermal method. Benefit from the integration of cavities, highly dispersed magnetic nanoparticles, and dielectric coating, the impedance is effectively improved by dielectric-magnetic synergy. The unique structure simultaneously fulfills a dual-network of micron-scale magnetic interaction and charge transfer, embedding the composite with enhanced magnetic and dielectric loss. The interfacial polarization and multiple reflections further promote microwave absorption. • 1D vesicular structure was successfully constructed via coaxial electrospinning. • Structural and compositional integration progressively improved impedance. • Strong magnetic-dielectric synergy of quaternary components in this absorber. • Electron holography confirmed magnetic coupling and charge transfer dual-network. Impedance matching ( Z ) is a key issue requested by high-efficient microwave absorption materials, which remains a major challenge. Lacking magnetic loss capacity and electromagnetic impedance balance, the microwave attenuation capacity of carbon-based absorbers urgently needs to be improved. Herein, a TiO 2 @Fe/C@TiO 2 vesicular carbon microtube was reasonably constructed by coaxial electrospinning. The characteristic impedance was gradually improved by introducing cavities, magnetic Fe particles and dielectric TiO 2 coating. The composite achieves an enhanced microwave performance with a maximum reflection loss of as strong as − 60.98 dB and a broad absorption bandwidth of 4.8 GHz at only 2.0 mm thickness. Such a well-integrated hierarchically vesicular carbon microtube with a tubular porous structure endows the assembly with high magnetic anisotropy and multiple interfaces, further offers the composites: i) the dual-networks of micron-scale 1D anisotropic magnetic coupling and charge conduction, ii) dielectric-magnetic synergy of quaternary components, iii) progressively matched impedance, proved by micromagnetic simulation and electron holography. This finding might have great significance in the impedance matching control of high-performance microwave absorbents.

Achieving broad absorption bandwidth of Ba2Co2Fe12O22 ferrites by adjusting the sintering temperature

The Ba2Co2Fe12O22 (Co2Y) ferrites were prepared via the sol–gel method, and the dielectric and magnetic properties were tuned by changing sintering temperature (Ta). It can be noted that the nature resonance frequency of Co2Y decreases form 10.2 GHz to 1.9 GHz with increasing sintering temperature, and the resonance peaks ascribed to exchange coupling between Fe2+ ions and Fe3+ ions appear in 13–17 GHz. Due to the synergy of Fe2+ ions and oxygen vacancies, the real part of complex permittivity (ε′) of Co2Y ferrites decreases firstly, and then increases with increasing sintering temperature. The excellent microwave absorption properties are obtained at Ta = 1100 °C, its effective absorption bandwidth (EAB) reaches 7.3 GHz at a thickness of only 1.4 mm. The outstanding properties are mainly ascribed to a combination of multiple reflections, dipole polarization, natural resonance, exchange resonance and good impedance matching. Our research provides an efficient approach for obtaining the thin and broadband microwave absorbers by adjusting the sintering temperature of Co2Y ferrites.

Microstructure Evolution at High Temperatures for Co-MOF-74 as High-Efficiency Electromagnetic Absorbers

Increasing demands of microwave absorbents require new approaches to enhance the absorbing performance. Metal−organic frameworks (MOFs) could be developed as effective absorbers owing to their outstanding features including intrinsic porosity and high specific area. Herein, novel nanostructured Co-MOF-74 composites have been successfully fabricated via a simple solvothermal method. Excellent absorption performance was achieved for the composite with a minimum reflection loss (RL) of −25.5 dB at 2.5 mm and a broad absorption bandwidth (RL &lt; −10 dB) of 6.7 GHz. Such absorber could be developed as lightweight and high-efficiency absorbing materials, and this work provides inspiration for the design of advanced absorbers with strong dissipation capacity and broad effective bandwidth.