Efficient Microwave Absorption Research Articles

Construction of chiral magnetic structure with enhancement in magnetic coupling for efficient Low-Frequency microwave absorption

Construction of chiral magnetic structure is considered as a promising strategy to achieve efficient low frequency microwave absorption. However, it is not clear that how the magnetic loss is enhanced by the chiral morphology. Herein, a novel chiral magnetic structure containing FeCo2O4-FeCo nanosheets has been constructed by using helical carbon nanocoils (CNCs) as the chiral template. For comparison, the FeCo2O4-FeCo nanosheets are also combined with the linear carbon nanofibers (CNFs). The enhanced magnetic coupling between FeCo2O4-FeCo nanosheets and the magnetic anisotropy induced by the chiral structure are confirmed by the off-axis electron holography and the micro-magnetic simulation. Due to the synergistic effect between chirality, magnetism, and dielectricity, the chiral magnetic structure exhibits superior microwave absorption performance than the linear one with a wide effective bandwidth of 7.1 GHz at an ultra-low filling ratio of 8 %. Meanwhile, the minimum RL value of −60.7 dB is achieved at low frequency (6 GHz). This study provides further evidence of the special mechanisms of the chiral structure for microwave absorption.

Two-phase magnetic nanospheres with magnetic coupling effect encapsulated in porous carbon to achieve lightweight and efficient microwave absorbers

Component selection is crucial for microwave absorbents. Multi-component absorbers are increasingly useful and can be prepared through the rational design and control of various electrical, magnetic, and other auxiliary components. In this paper, Ni3Fe/NiFe2O4 nanospheres with two-phase magnetism were designed for use as a multi-component absorber. Specifically, a Ni3Fe/ NiFe2O4@SPC composite with 3D networks was successfully fabricated by hydrothermal method, high-temperature carbonization for activation, and electrostatic self-assembly. The contact interface and coupling effect between the two magnetic components can promote the attenuation of electromagnetic waves. Moreover, the introduction of porous carbon successfully inhibits the easy aggregation of the magnetic particles. Impressively, with a filling load of 10 wt%, the optimal RL of the prepared Ni3Fe/NiFe2O4@SPC composite reaches −60.6 dB, and the effective absorption bandwidth is 5.2 GHz at 2 mm. The combination of two magnetic components and porous carbon in this multiphase microwave-absorbing composite demonstrates a feasible strategy for designing efficient microwave absorbers in the future.

Glucose derived carbon encapsulated boron nitride core-shell composites for efficient electromagnetic microwave absorption

Hexagonal boron nitride (h-BN) has the advantages of outstanding insulation, high thermal conductivity and excellent chemical stability, which promote the wide application of h-BN in thermal interface electronic packaging and other related fields. However, due to the poor dielectric loss ability of h-BN, which leads to its weak absorption capacity of electromagnetic waves (EMW), so it limits its practical application in related advantageous fields. In this paper, glucose-derived carbon-encapsulated BN core-shell composites (C@BN) were prepared by a simple hydrothermal reaction followed by high-temperature pyrolysis. The dielectric loss capacity of the C@BN was investigated by manipulating the concentration of glucose solution and pyrolysis temperature. Specifically, by adjusting the glucose derived carbon defect to induce polarization loss and impedance matching performance, so that more EMW entering the interior of the composite is absorbed and dissipated. The results show that C@BN obtained at 800 °C shows the best EMW absorption performance when the concentration of glucose solution is 3.6 wt%. The minimum reflection loss value (RLmin) is −43.5 dB and the maximum width effective absorption bandwidth (EABmax) of 6.72 GHz. Therefore, this study provides a reliable reference for the preparation of h-BN based EMW absorbing materials.

Co-Doped Porous Carbon/Carbon Nanotube Heterostructures Derived from ZIF-L@ZIF-67 for Efficient Microwave Absorption.

Carbon-based magnetic metal composites derived from metal-organic frameworks (MOFs) are promising materials for the preparation of broadband microwave absorbers. In this work, the leaf-like co-doped porous carbon/carbon nanotube heterostructure was obtained using ZIF-L@ZIF-67 as precursor. The number of carbon nanotubes can be controlled by varying the amount of ZIF-67, thus regulating the dielectric constant of the sample. An optimum reflection loss of -42.2 dB is attained when ZIF-67 is added at 2 mmol. An effective absorption bandwidth (EAB) of 4.8 GHz is achieved with a thickness of 2.2 mm and a filler weight of 12%. The excellent microwave absorption (MA) ability is generated from the mesopore structure, uniform heterogeneous interfaces, and high conduction loss. The work offers useful guidelines to devise and prepare such nanostructured materials for MA materials.

Multidimensional and hierarchical design of biomass-derived carbon nanofiber networks for efficient microwave absorption

Carbon materials have gained significant attention for their potential as highly efficient microwave absorbers. However, it remains a challenge to attain a perfect integration of thin thickness, wide frequency bandwidth, lightweight and strong absorption through structural design of carbon materials. Herein, we design multidimensional and hierarchical carbon nanofiber networks consisting of core-shell carbon nanofibers wrapped by hollow carbon nanoparticles, named CPDA@RCNFs. CPDA@RCNFs which are derived from cellulose and polydopamine (PDA) were prepared by electrostatic spinning, deacetylation, self-polymerization, and carbonization, successively. Thanks to the cooperation of three-dimensional conductive networks, core-shell/hollow/porous structures, as well as doped nitrogen and oxygen heteroatoms, CPDA@RCNFs exhibit excellent comprehensive microwave absorption performance. Specifically, an ultra-strong reflection loss value of −63.31 dB and a wide frequency bandwidth of 5.60 GHz (12.32–17.92 GHz) are achieved at a very thin thickness of 1.8 mm with an ultra-low filler loading of 5 wt%. This work provides a new insight into the structural design of advanced high-performance microwave absorption carbon materials.

Fe3O4-CuO-MgNb2O6 Ternary Ceramics with Heterogeneous Interfaces for Efficient Microwave Absorption

Fe3O4-CuO-MgNb2O6 Ternary Ceramics with Heterogeneous Interfaces for Efficient Microwave Absorption

MXene/cobalt ferrite/carbon materials based composites for efficient microwave absorption

In the present study, cobalt ferrite (CF) nanoparticles were in-situ grown on MXene/carbon-based materials (activated carbon (AC), MWCNT, and GO) to develop composites via facile hydrothermal route. The MXene/CF/MWCNTs composite (FMCNT4) achieved an excellent maximum reflection loss (RLmax) of −67.04 dB at 16.24 GHz & a thickness of 5.94 mm, whereas at the thickness of 5.86 mm, the FMCNT4 obtained a maximum effective absorption bandwidth (EAB, RL < −10 dB) of 2.73 GHz. On the other hand, replacing MWCNTs with AC in the composite (FMAC4) showed RLmax of −46.52 dB at 18 GHz and 5.1 mm thickness, it also got an EAB of 2.54 GHz at 5.5 mm thickness. The MXene/CF/GO composite (FMGO5) obtained RLmax = −17.31 @ 17.12 GHz & 6 mm. The composite having MWCNTs showed the best performance, and the reason for this remarkable MW absorption performance originated from the high impedance matching followed by dielectric polarization and magnetic losses in the composite. The formation of multiple heterointerfaces between MXene, CF, and MWCNTs enhanced the interfacial polarization, whereas the conducting MXene and MWCNTs also contributed to conduction polarization. Thus, the present investigation showcases FMCNT as an excellent synergetic nanocomposite for MW absorption applications.

Biomimetic artificial nacre-like microfiber of Co/C modified cellulose nanofiber/Ti3C2Tx MXene with efficient microwave absorption

Although considerable efforts have been made in the fabrication of MXene-based composites for microwave absorption (MA), there is a great challenge to assemble MXene into regularly arranged microfibers prepared by wet-spinning technique for application in the field of MA due to insufficient interlayer interactions between Ti3C2Tx flakes. Heterogeneous interface design by optimizing material components to construct ingenious microstructure is crucial for efficient microwave absorbers. Herein, artificial nacre-like supramolecular microfibers of Co/C modified cellulose nanofiber/Ti3C2Tx MXene (Co/C/CNF/Ti3C2Tx) with plenty of heterogeneous interfaces were prepared by a simple wet-spinning technology through a self-assembly process induced by hydrogen bonding interactions between CNF and Ti3C2Tx. The artificial nacre-like microfibers with layered structure possess abundant heterogeneous interfaces, which facilitate multiple reflections/scattering of electromagnetic waves (EMW) between these interfaces, and at the same time promote interfacial and dipole polarization. The introduction of magnetic Co/C nanoparticles not only offer additional magnetic loss ability and improved impedance matching, but also enhance conductivity loss and polarization loss. Benefiting from these advantages, Co/C/CNF/Ti3C2Tx (1:1:1) fiber exhibits superior MA performance with a minimum reflection loss (RLmin) of up to −62.32 dB (>99.9999 % energy absorption) and a broad effective absorption bandwidth (EAB) of 5.86 GHz. The work provides a promising method for the preparation of biomimetic artificial nacre-like MXene-based microfibers with efficient MA performance, which is expected to be applied in the field of flexible wearable electromagnetic protection.

Facile synthesis of Fe3O4/CoCO3 nanoparticles anchored on reduced graphene oxide for highly efficient microwave absorption

Facile synthesis of Fe3O4/CoCO3 nanoparticles anchored on reduced graphene oxide for highly efficient microwave absorption

Hollow Fe3O4/Fe@C nanocubes for broadband microwave absorption spanning low- and high-frequency bands

Rationally constructing hollow structures with heterogeneous interface is usually an effective strategy to regulate the electromagnetic response behavior for lightweight and strong absorption, but achieving low-frequency and broadband absorption is a major challenge. This work adopts a novel Fe(II)/Fe(III) ions regulation strategy to design and synthesize hollow Fe(OH)X (x = 2, 3) nanocubes, which addresses the disadvantages of time-consuming or using etchant. Subsequently, a unique hollow Fe3O4/Fe@C nanoboxes with adjustable magnetic composition and uniformly coated shell have been successfully synthesized by in-situ carbonization with the assistance of phenolic resin and hydrogen thermal reduction. Notably, the different magnetic components induce the magnetic coupling assembly and play a crucial role in determining its electromagnetic parameters, whereas Fe3O4 contributes to more dipole polarization and stronger low-frequency response characteristics. For Fe3O4@C hollow nanoboxes, the minimum reflection loss (RLmin) is as low as –119.9 dB at 2.3 mm, and extremely wide effective absorption bandwidth (EAB) of 11.4 GHz is achieved spanning low-frequency band of 2.8 ∼ 7.2 GHz and high-frequency band of 11.0 ∼ 18 GHz at 5.0 mm. Surprisingly, the Fe3O4@C also has satisfactory EAB20 (RL＜ –20 dB) reaching 7.1 GHz (14.9 ∼ 18 GHz) at a thin thickness of 1.8 mm. The RLmin of other hollow nanoboxes is also below –30 dB, and the EAB is greater than 9 GHz. This study provides a competitive candidate for efficient microwave absorption in complex frequency bands, especially low-frequency bands.

Coupling RGO with magnetic components derived from basic ferric cobalt carbonate (BFCC) for efficient microwave absorption

In this work, reduced graphene oxide (RGO)-based composites loaded with magnetic CoFe2O4 (CFO) and CoFe were successfully synthesized via heat treatment of basic ferric cobalt carbonate (BFCC) under different temperatures. The impact of adding CFO and CoFe on the electromagnetic parameters and absorption properties was investigated. When 40 wt% CFO flakes and CoFe particles are added to the RGO matrix and the filler content is 20 wt% in paraffin, there gives a reflection loss of −48 dB with a 5.5 GHz absorption bandwidth at 2.1 mm thickness, and −50 dB with 4.8 GHz at 2.9 mm, respectively. The coupling of a magnetic medium can change the electromagnetic loss mechanism in the material, which ultimately affects the absorption properties of the material. This study provides a good basis for the design of composite materials of RGO as microwave absorbing materials, enabling large-scale production of high-performance absorption materials.

Effect of metal doping on the microwave absorption performance of multi-element (metal, N, and Cl) doped carbon composites

Multi-element-doped carbons are actively being pursued as efficient lightweight microwave absorbers. In this work, metal, nitrogen and chlorine codoped carbons (metal,N,Cl–C, where metals = Ni, Co, Mn, or Zn) were synthesized through the high-temperature carbonization of polypyrrole doped with hydrochloric acid (PPy-HCl) and prepared in the presence of certain metal chloride salts (NiCl2, CoCl2, MnCl2, or ZnCl2). The dielectric parameters and microwave absorption properties of the metal,N,Cl–C composites could be regulated by simply altering the type of metal salt. Compared with N,Cl–C, it was discovered that Co,N,Cl–C and Ni,N,Cl–C possessed higher graphitization degrees, smaller particle sizes and more surface chemical functional groups (metal−N), which significantly improved the conduction loss and polarization loss effects including interfacial polarization and dipole polarization. At a filler ratio of 9.0 wt%, Ni,N,Cl–C displayed a wide effective absorption bandwidth (EAB, RL ≤ −10 dB) of 7.1 GHz at a thickness of 2.5 mm and a minimum reflection loss (RLmin) of −29.7 dB at 9.7 GHz and 3.5 mm thickness. Similarly, Co,N,Cl–C offered an RLmin value of −48.2 dB at 11.3 GHz and a thickness of 3.0 mm and an EAB of 6.0 GHz at a thickness of 2.5 mm. These results showcase the advantages of metal,N,Cl–C composites as microwave absorbers.

Design of morphology-controlled cobalt-based spinel oxides for efficient X-band microwave absorption

The cobalt-based spinel structure oxides with synergistic effect of magnetic loss and dielectric loss have important applications in electromagnetic wave absorption. And the excess 0.5 oxygen atoms in MnCo2O4.5 provide more vacancies than traditional MnCo2O4 spinel structure and improve the electrical conductivity. In the current study, MnCo2O4.5 microsphere clusters, MnCo2O4.5 microcubic spheres and MnCo2O4.5 flowery spheres were prepared by solvothermal method and annealing process. Among the final samples with different morphologies, MnCo2O4.5 microcubic spheres showed outstanding microwave absorption capabilities, with a minimum reflection loss (RLmin) of -51.52 dB at 2.2 mm. When the thickness was further increased to 2.3 mm, the effective absorption bandwidth could be as wide as 5.36 GHz, covering most of the X-band. The excellent absorption performance of electromagnetic waves is related to the modulability of the complex dielectric parameters, the optimization of impedance matching, and the enhancement of the polarization relaxation process through the improvement of the morphologies. This work provides guidance and support for refining the electromagnetic wave absorption potential of cobalt-based spinel oxides and for designing highly efficient electromagnetic wave absorbers in the X-band.

Rational design of hollow bimetallic sulfide@carbon with abundant heterogeneous interfaces and conductive network synergies for efficient microwave absorption

Developing composites with rational structural design and multicomponent synergistic effects is regarded as a promising strategy for achieving excellent impedance matching and high intensity attenuation performance. Herein, a hierarchical and multifunctional hollow porous Co3S4@NiCo2S4@BPC composite with integrated strong microwave absorption (MA) and self-cleaning properties was designed. The resultant composite exhibits remarkable EMW absorption behavior with a minimum reflection loss (RLmin) of −68.1 dB at 2.3 mm. The multicomponent synergy achieves a satisfactory heterogeneous structure, invoking intense interfacial polarization. Additionally, the residual functional groups and lattice defects induced by S doping further enhance the microwave attenuation. Meanwhile, the hierarchical hollow porous structure facilitates the impedance matching between the absorber and air. Notably, the composite has ideal radar cross-section (RCS) reduction and excellent hydrophobicity, demonstrating its outstanding MA properties as well as the potential applications in complex environment. Therefore, this work provides a novel strategy for the rational design of high-performance absorbers.

Controllable synthesis of pine leaf-like CoO/3D carbon foam composites as efficient microwave absorbers

The development of high-performance microwave absorbing materials (MAMs) is an effective and sustainable solution for mitigating electromagnetic pollution. Inspired by the radiation-resistant structure of pine leaves, CoO/Carbon foam composites (COCF) with 3D network structures were constructed using alkali treatment and in situ hydrothermal and carbothermal reduction strategies. The 3D-structured carbon foam effectively prevents the agglomeration of CoO in COCF composites, improves the electron transfer efficiency, and enriches the heterogeneous interfaces; in this way, a superb microwave attenuation capability is realized. The optimum reflection loss (RLmin) reaches -90.67 dB, and the effective absorption bandwidth (EAB, RL<-10 dB) is 4.18 GHz at a thickness of 1.34 mm. The total EAB included almost all four bands, namely S, C, X, and Ku. Moreover, the present study offers new ideas for optimizing transition metal oxides (TMOs) and carbon materials combinations and for the structural design of MAMs with multiscale fine micro-nanostructures.

Three-dimensional porous, flexible and lightweight reduced graphene oxide/Li0.35Zn0.3Fe2.35O4@SiO2 nanofibers aerogel for efficient microwave absorption

The development of flexible, lightweight, broadband EMW-absorbing materials is necessary for individual protection. However, balancing the mechanical properties and high absorbent performance of aerogel materials is challenging. We hypothesized that lightweight RGO/LZFO@SiO2 NFs flexible composite aerogels with three-dimensional (3D) porosity, flexibility and a high absorption capacity could be prepared via a simple preparation strategy combining electrospinning, freeze-drying, and heat curing. First, flexible LZFO@SiO2 NFs were prepared via sol–gel electrospinning, whereby LZFO particles were embedded in the SiO2 NFs. Subsequently, the LZFO@SiO2 NFs and graphene oxide (GO) were homogenized in deionized water with the addition of a crosslinker along with vigorous stirring. Finally, aerogels with cross-linked structures were obtained after freeze-drying and calcination treatments. Under 30% strain, the stress undergone by RGO/LZFO@SiO2 NFs-2 reached 32 kPa. After 200 anti-fatigue tests, the plastic deformation was 15%. The combined action of the RGO conductive elements and LZFO@SiO2 NFs magnetic elements cooperate to improved the impedance-matching imbalance, and the two were bonded to produce form a rich interface effect. The RGO/LZFO@SiO2 NFs-2 aerogel exhibited a minimum reflection loss (RLmin) of −55.1 dB (2.2 mm) and an effective absorption bandwidth (EAB) of 4.3 GHz.

Simultaneous manipulation of constituent and structure toward MOFs-derived hollow Co3O4/Co/NC@MXene microspheres via pyrolysis strategy for high-performance microwave absorption

The development of microwave absorbing materials with high performance is one of the effective strategies to solve the increasingly serious electromagnetic pollution problem, and has received the attention of researchers. Herein, the structure and composition manipulation of Ti3C2Tx MXene and MOFs derivatives are investigated. It is found that the TiO2 produced by oxidation of Ti3C2Tx MXene, as a low dielectric material, can effectively solve the impedance mismatch caused by the high conductivity of Ti3C2Tx MXene. Additionally, MOFs derivatives with excellent dielectric-magnetic properties are often obtained by high temperature pyrolysis, which also aids in the oxidation of Ti3C2Tx MXene. Here, we successfully synthesized ZIF-67 nanoparticles on the surface of a three-dimensional spherical skeleton supported by Ti3C2TX MXene nanosheets through template method and electrostatic self-assembly, and obtained Co3O4/Co/NC@MXene microspheres with an obvious hollow structure after one-step pyrolysis. This magnetic carbon heterostructure could effectively optimize the impedance matching and achieve efficient microwave absorption. The HCCM-800 sample had a minimum reflection loss value of −71.60 dB with thickness of 2.25 mm and a maximum effective absorption bandwidth achieved 5.14 GHz at 1.85 mm. Meanwhile, the radar cross section (RCS) simulation revealed that the HCCM-800 sample’s RCS reduction value could reach 20.2 dBm2 at 0° incidence angle. It is believed that this research will pave the way for further vigorous development in the field of microwave absorption.

Non-magnetic hollow ZnO/C fabricated by a novel ZnO self-sacrificial template hollow engineering for efficient microwave absorption

Non-magnetic hollow ZnO/C fabricated by a novel ZnO self-sacrificial template hollow engineering for efficient microwave absorption

Ni-doped Co3O4 with micro-nano porous structure as a highly efficient microwave absorber

This article employs a hydrothermal method combined with a calcination process to prepare Co3O4 microsheets with varying Ni doping concentrations. Microstructural analysis reveals that the obtained samples are single-phase, free from other impurities, and exhibit a unique self-assembled porous micro-nanostructure. The micron-sized secondary aggregates consist of small nanometer-sized particles with many voids. The nanoscale pores between the nanoparticles contribute to the dissipation of incident microwaves. The dielectric and magnetic properties of Co3O4 microplates can be effectively tuned by adjusting the Ni doping concentration. Comparative results indicate that the Ni-doped Co3O4 microsheets with 0.03 mol% Ni exhibit the minimum reflection loss (RLmin) of −34.7 dB at 16.56 GHz, with a thickness of just 1.4 mm. Simultaneously, the effective absorption bandwidth (EAB) reaches 4.32 GHz within the frequency range of 13.68–18 GHz. With an absorber thickness of 1.5 mm, the EAB can reach 5.2 GHz from 12.8 to 18 GHz. By adjusting the matching thickness of the absorber in the range of 1.4–4.5 mm, the EAB of Ni-doped Co3O4 can cover multiple frequency bands from 3.6 to 18 GHz. The outstanding microwave absorption performance primarily stems from the unique porous micro-nanostructure and enhanced dielectric and magnetic losses. The results provide an effective component regulating strategy to promote microwave absorption, meanwhile suggest that the low-cost Ni-doped Co3O4 is a promising microwave absorption material.

Cation Bimetallic MOF Anchored Carbon Fiber for Highly Efficient Microwave Absorption.

Carbon fiber (CF) is a potential microwave absorption (MA) material due to the strong dielectric loss. Nevertheless, owing to the high conductivity, poor impedance matching of carbon-based materials results in limited MA performance. How to solve this problem and achieve excellent MA performance remains a principal challenge. Herein, taking full advantage of CF and excellent impedance matching of bimetallic metal-organic frameworks (MOF)derivatives layer, an excellent microwave absorber based on micron-scale 1D CF and NiCoMOF (CF@NiCoMOF-800)is developed. After adjusting the oxygen vacancies of the bimetallic MOF, the resultant microwave absorber presented excellent MA properties including the minimum reflection loss (RLmin ) of -80.63dB and wide effective absorption bandwidth (EAB) of 8.01GHz when its mass percent is only 5wt.% and the thickness is 2.59mm. Simultaneously, the mechanical properties of the epoxy resin (EP)-based coating with this microwave absorber are effectively improved. The hardness (H), elastic modulus (E), bending strength, and compressive strength of CF@NiCoMOF-800/EP coating are 334MPa, 5.56GPa, 82.2MPa, and 135.8MPa, which is 38%, 15%, 106% and 53% higher than EP coating. This work provides a promising solution for carbon materials achieving excellent MA properties and mechanical properties.