Tunable High-performance Microwave Absorption Research Articles

Hierarchical porous carbon fibers for broadband and tunable high-performance microwave absorption

Constructing multiple polarization losses and improving impedance matching in carbon materials is essential for improving electromagnetic wave absorption performance of carbon materials. Meanwhile, surface contamination of electromagnetic wave absorbers has a significant impact on their absorption performance. Herein, a pod-like macroporous carbon nanofibers with self-cleaning function are successfully prepared by Electrospinning-etching strategy. Through the adjustment of SiO2 and pore structure, conduction loss, dipole polarization loss, interface polarization loss, and impedance matching of carbon nanofibers are optimized simultaneously. The optimized a pod-like macroporous carbon nanofibers has strong absorption and wide effective absorption bandwidth. With a cavity content of 4 %, the minimum reflection loss at 2.29 mm is -49.36 dB, and the effective absorption bandwidth is 7.6 GHz and the matched thickness is 2.16 mm. This result indicates that cavity and pod-like structure can significantly improve dielectric properties and enhance interface polarization loss and conductivity loss. The simulation results verify that the pod structure has a greater impact on surface electric field distribution, which shows that interface polarization is caused by the cavity structure. In addition, the contact angle of absorber is 105 °, which proves its self-cleaning ability. This functional absorbing material has potential to meet future practical applications.

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.

Tunable high-performance microwave absorption of cobalt nanoparticles wrapped in N-self-doped carbon nanofibers at ultralow filler loadings

Manufacturing lightweight, ultralow filler loading, broad bandwidth and highly efficient microwave absorbers is still a challenge. Herein, we have synthesized Co nanoparticles decorated N-self-doped carbon nanofibers (Co@NCNFs) composite by electrospinning followed by a two-step heat treatment and investigated its electromagnetic (EM) and microwave absorption performances under different filler contents (from 2.5 to 7.5 wt%) in paraffin wax matrix. It is found that the Co@NCNFs composite has strong ferromagnetism and moderate graphitization degree as well as abundant polar groups and defects, and Co nanoparticles encapsulated by graphitic carbon layers with sizes around 45–115 nm are uniformly dispersed in the NCNFs. With increasing the filler loading, the EM attenuation ability is gradually strengthened while the impedance matching level is just the opposite. The EM absorbing properties of the composites are more superior within 5.0 wt% Co@NCNFs loading owing to the synergy of improved impedance matching and satisfactory EM dissipation ability. Under an ultralow filler loading of 2.5 wt%, the optimal reflection loss (RL) can reach as strong as −49.3 dB at 17.83 GHz with a thin thickness of 1.61 mm and the maximum effective absorption bandwidth (EAB, RL<−10.0 dB) is as wide as 5.44 GHz (12.56–16.99 GHz) at 1.92 mm. When the filler loading is only 5.0 wt%, a minimum RL value of −52.3 dB is achieved at 6.36 GHz with the thickness of 3.03 mm and the maximum EAB is 4.64 GHz (13.36–18.00 GHz) at 1.42 mm. Compared to other Co/C composite absorbers, the as-prepared Co@NCNFs composite with well-designed constitute and structure demonstrates the better comprehensive absorption performance at a much lower filler loading. Therefore, the present Co@NCNFs may be more promising for practical applications as lightweight and high-performance EM wave absorbers especially in the medium and high frequency range.

Fe/Fe3O4/biomass carbon derived from agaric to achieve high-performance microwave absorption

Recently, biomass carbon materials as electromagnetic wave-absorbing materials have received widespread attention due to their easy availability, low cost, and environmental friendliness. However, for the vast majority of microwave absorbing materials that possess only dielectric losses, it is difficult for them to achieve satisfactory microwave absorbing performance. This paper proposes a new strategy to prepare a magnetic biomass composite material with tunable high-performance microwave absorption using agaric as the biomass carbon precursor and ferric nitrate as the magnetic precursor. When the carbonization temperature is 800 °C, the Fe/Fe3O4/biomass carbon (Fe/Fe3O4/BC) composite exhibits excellent microwave absorption performance in the X-band. At a thickness of 2.06 mm and a frequency of 9.63 GHz, its minimum reflection loss reaches −30.41 dB, and the effective absorption bandwidth is 2.45 GHz. In the carbonization process, ferric nitrate is transformed into magnetic Fe3O4 and Fe nanoparticles. The magnetic losses generated by Fe/Fe3O4 and the dielectric losses of biomass carbon, interfacial polarization, dipole polarization and multiple reflection synergies improve the impedance matching characteristics of the composite and improve the microwave absorption performance. Therefore, the prepared Fe/Fe3O4/BC composite material has exhibits great potential as a high-efficiency microwave absorber.

Broadband and tunable high-performance microwave absorption properties by Ni-coated carbon fibers

Composites of carbon fibers (CFs) and magnetic metals have concerned attention for tunable microwave absorption materials (MAMs). In this work, magnetic nickel (Ni) particles were coated on the CFs surface by an electroplating technique. Different morphology of Ni-coated CFs was established by setting the plating time. The microstructure, electric and magnetic properties, complex permittivity and permeability, and reflection loss (RL) of the Ni-coated CFs were specified as a function of the surface morphology of composites. SEM and EDX results displayed that Ni particles are uniformly deposited on the surface of CFs. Moreover, the Ni-coated CFs with different coating morphologies exhibit different microstructure. The creation of a magnetic Ni layer onto CFs improved composite properties, not only raising the saturation magnetization (17–46 emu/g) but also enhancing electrical conductivity (361–594 S/cm). The electromagnetic parameters and RL values of the Ni-coated CFs were investigated over the 2.0–18.0 GHz frequencies. The minimum RL could reach up to −64.8 dB at 14.9 GHz with 2.0 mm matching thickness and high effective bandwidth of 2.2–18.0 GHz. It has been displayed that the properties of Ni-coated CFs can be effectively controlled by changing the morphology of the Ni layer, which provides a novel route to fabricate Ni-coated CFs with tunable and broadband microwave absorption properties.

Strong and thermostable hydrothermal carbon coated 3D needled carbon fiber reinforced silicon-boron carbonitride composites with broadband and tunable high-performance microwave absorption

Excellent electromagnetic wave (EMW) absorbing materials with high-temperature stable and superior mechanical properties are among the most promising candidates for practical application. Here, novel hydrothermal carbon coated three-dimensional (3D) needled carbon fiber reinforced silicon-boron carbonitride (HC-CF/SiBCN) composites with a hierarchical A (CF)/B (HC)/C (SiBCN) structure were constructed and prepared for the first time by combining hydrothermal transformation and precursor infiltration and pyrolysis (PIP) process. The thickness of the HC coating controlled by the glucose concentration played a crucial role in tailoring the EMW capacity of the composite. The incorporation of SiBCN could not only effectively improve the oxidation resistance but also actively enhance the mechanical properties of the HC coated CF structure. Compared to the weak high-temperature oxidation resistance and mechanical properties of pristine 3D needled CF felt, the composites after the introduction of HC and SiBCN were thermostable in air atmosphere beyond 1000 °C to about above 70% weight retention, and the maximum flexural and compression strength of the composites could reach to 23.51 ± 1.37 and 12.22 ± 1.12 MPa, respectively. A substantial enhancement of EMW absorption ability was achieved through incorporation of HC and SiBCN, which could be attributed to the matched characteristic impedance and enhanced loss ability, whose optimization EMW absorption performance was the minimum reflection loss (RLmin) of −52.08 dB and effective absorption bandwidth (EAB) of 7.64 GHz for the composite obtained by two PIP cycles with 24 wt% glucose solution, demonstrating that the HC-CF/SiBCN composites with high-temperature stable, excellent mechanical and superior EMW absorption properties could be considered as a promising candidate for the applications in harsh environments.

Strong and Thermostable Boron-Containing Phenolic Resin-Derived Carbon Modified Three-Dimensional Needled Carbon Fiber Reinforced Silicon Oxycarbide Composites with Tunable High-Performance Microwave Absorption Properties

This paper focuses on the preparation of boron-containing phenolic resin (BPR)-derived carbon modified three-dimensional (3D) needled carbon fiber reinforced silicon oxycarbide (SiOC) composites through a simple precursor infiltration and pyrolysis process (PIP), and the influence of PIP cycle numbers on the microstructure, mechanical, high-temperature oxidation resistance. The electromagnetic wave (EMW) absorption properties of the composites were investigated for the first time. The pyrolysis temperature played an important role in the structural evolution of the SiOC precursor, as temperatures above 1400 °C would cause phase separation of the SiOC and the formation of silicon carbide (SiC), silica (SiO2), and carbon. The density and compressive strength of the composites increased as the PIP cycle number increased: the value for the sample with 3 PIP cycles was 0.77 g/cm3, 7.18 ± 1.92 MPa in XY direction and 9.01 ± 1.25 MPa in Z direction, respectively. This composite presented excellent high-temperature oxidation resistance and thermal stability properties with weight retention above 95% up to 1000 °C both under air and Ar atmosphere. The minimal reflection loss (RLmin) value and the widest effective absorption bandwidth (EAB) value of as-prepared composites was −24.31 dB and 4.9 GHz under the optimization condition for the sample with 3 PIP cycles. The above results indicate that our BPR-derived carbon modified 3D needled carbon fiber reinforced SiOC composites could be considered as a promising material for practical applications.

Tunable High-Performance Microwave Absorption and Shielding by Three Constituent Phases Between rGO and Fe3O4@SiO2 Nanochains.

With the aim of achieving high microwave absorption and electromagnetic shielding performance, reduced graphene oxide (rGO) and Fe3O4@SiO2 nanochains are successfully combined at various mass ratios. By selecting the right mass ratio, an rGO/Fe3O4@SiO2 composite with excellent microwave absorption properties is obtained, and, due to the addition of highly conductive rGO, the desired shielding effectiveness is also achieved. The reflection loss (RL) value of the composite can reach −48.34 dB with a mass ratio of 1:1, and the effective bandwidth (<-10 dB) can cover 4.88 GHz at a thickness of 2.0 mm. Moreover, the composite with a mass ratio of 4:1 exhibits outstanding electromagnetic shielding performance, which also broadens its fields of application. This outstanding microwave absorption and electromagnetic shielding performance indicate that the composite can potentially be employed as a multi-functional material.

Electrospun generation of Ti3C2Tx MXene@graphene oxide hybrid aerogel microspheres for tunable high-performance microwave absorption

Constructing different 2D nano-materials into hybrids is an effective way to fabricate high-performance microwave absorbing (MA) materials. The formed heterointerfaces offers new loss mechanisms to make up the shortages of sole material in attenuating electromagnetic energy. For practical utilizations, microwave absorbers perform at low-frequency band with light-weight and thinness are more desirable. Here, hybrids aerogel microspheres constructed from graphene oxide (GO) and Ti3C2Tx MXene are manufactured by rapid freezing assisted electrostatic-spinning. Combined with the disparities of conductivity between Ti3C2Tx MXene and GO, and the newly generated heterointerfaces and abundant surface groups, the Ti3C2Tx [email protected] hybrid aerogel microspheres ([email protected]) exhibit optimized impedance matching and improved MA performance. Besides, the unique aerogel structure not only offers light weight merit for this absorber but also elongates the attenuating paths when electromagnetic waves inject in. With a rather low filler loading of 10.0 wt% and a thickness of 1.2 mm, the optimized [email protected] exhibit reflection loss (RL) of −49.1 dB at 14.2 GHz. More importantly, the [email protected] present effective MA at S-band, and the RL reaches −38.3 dB at 2.1 GHz with a thickness of 5.0 mm. We believe the [email protected] provides new opportunities for designing efficient MA absorbers, especially for the low-frequency.

Wheat straw-derived magnetic carbon foams: In-situ preparation and tunable high-performance microwave absorption

Recently, biomass-derived three-dimensional (3D) porous carbon materials have been gaining more interest as promising microwave absorbers due to their low cost, vast availability, and sustainability. Here, a novel 3D interconnected porous magnetic carbon foams are in-situ synthesized via a combination of sol-gel and carbonization process with wheat straw as the carbon source and FeCl3·6H2O as the magnetic regulating agent. During the process of foams formation, the lignocelluloses from the steam-exploded wheat straw are converted into interconnected carbon sheet networks with hierarchical porous structures, and the precursor FeCl3·6H2O is converted into magnetic nanoparticles uniformly embedded in the porous carbon foams. The generated magnetic nanoparticles are benefit to enhance the interface polarization and magnetic loss ability to improve the efficient complementarities between the dielectric and magnetic loss, thus increasing the impedance matching. The obtained sample treated at 600 °C displays the best microwave absorption (MA) performance. It presents a minimal reflection loss (RL) of −43.6 dB at 7.1 GHz and the effective bandwidth (RL < −10 dB) is 3.3 GHz with the thickness of 4.7 mm. The 3D porous structure, multi-interfaces and the synergy of dielectric loss and magnetic loss make great contribution to the outstanding MA performance.

Broadband and tunable high-performance microwave absorption composites reduced graphene oxide-Ni

Reduced graphene oxide (RGO)/Ni composites with high-performance microwave absorption were successfully synthesized through the electroless plating. The structures and morphologies of the materials were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy as well as scanning electron microscope. Results show that spherical pure nickel particles are uniformly distributed on the surface of RGO. The complex permittivity and permeability of the composite were measured by mixing RGO/Ni with paraffin, the minimum reflection loss could reach − 51.1 dB, and from 7.28 to 11.28 GHz, the reflection loss is less than − 10 dB. Through the analysis of the absorbing mechanisms, it is found that the quarter wavelength theory contributes more to the absorbing performance than the impedance matching. In addition, changing the electroless plating time is a feasible method to adjust the absorbing properties of the materials. RGO/Ni is an excellent microwave absorption material with a strong tunable absorbing property at its own low content.

Interface Modulating CNTs@PANi Hybrids by Controlled Unzipping of the Walls of CNTs To Achieve Tunable High-Performance Microwave Absorption.

Making full use of the interface modulation-induced interface polarization is an effective strategy to achieve excellent microwave absorption (MA). In this study, we develop an interfacial modulation strategy for achieving this goal in the commonly reported dielectric carbon nanotubes@polyaniline (CNTs@PANi) hybrid microwave absorber by optimizing the CNT nanocore structure. The heterogeneous interfaces from PANi and CNTs can be well regulated by longitudinal unzipping of the walls of CNTs to form 1D CNT- and 3D CNT-bridged graphene nanoribbons and 2D graphene nanoribbons. By controlling the oxidation peeling degree of CNTs, their interface area and defects are enhanced, thus producing more polarization centers to generate interfacial polarization and polarization relaxation, and also introducing more PANi loadings. Furthermore, more interface contact area can be produced between CNTs and PANi. This could induce a strong dielectric resonant and further improve the impedance matching, leading to significant enhancement of MA performance. With filler loading of only 10 wt % and a thinner coating thickness of 2.4 mm, the optimized CNTs@PANi exhibits excellent MA performance with the minimum reflection loss (RLmin) value of -45.7 dB at 12.0 GHz and the effective bandwidth is from 10.2 to 14.8 GHz. Meanwhile, the broadest effective bandwidth reaches 5.6 GHz, covering the range of 12.4-18.0 GHz with a thin thickness of 2.0 mm and its RLmin reaches -29.0 dB at 14.6 GHz. It is believed that the proposed interfacial modulation strategy can provide new opportunities for designing efficient MA absorbers.

Carbonized Design of Hierarchical Porous Carbon/Fe3O4@Fe Derived from Loofah Sponge to Achieve Tunable High-Performance Microwave Absorption

Recently, three-dimensional (3D) porous carbon materials derived from biomass have been gaining interest as promising microwave absorbers due to their low cost, vast availability, and sustainability of biomasses. Herein, a novel strategy of utilizing loofah sponge as 3D hierarchical porous carbon precursors and ferric nitrate as magnetic precursor to prepare magnetic hierarchical porous carbon composites, which exhibit tunable high-performance microwave absorption (MA). During the carbonization process, the 3D-bundled microtube structure of loofah sponge changes into interconnected networks with hierarchical porous structures, and the precursor ferric nitrate converts into magnetic Fe3O4@Fe nanoparticles. As expected, the as-obtained loofah sponge-derived 3D porous carbon/Fe3O4@Fe composites treated at 600 °C exhibit outstanding MA performance. It displays the minimum reflection loss (RL) of −49.6 dB with a thickness of 2 mm, and the effective absorption bandwidth (RL≤ 10 -dB) can reach 5.0 GHz (from 13 t...

Generation of graphene-based aerogel microspheres for broadband and tunable high-performance microwave absorption by electrospinning-freeze drying process

Despite recent progress in the synthesis and application of graphene-based aerogels, some challenges such as scalable and cost-effective production, and miniaturization still remain, which hinder the practical application of these materials. Here we report a large-scale electrospinning method to generate graphene-based aerogel microspheres (AMs), which show broadband, tunable and high-performance microwave absorption. Graphene/Fe3O4 AMs with a large number of openings with hierarchical connecting radial microchannels can be obtained via electrospinning-freeze drying followed by calcination. Importantly, for a given Fe3O4:graphene mass ratio, altering the shape of aerogel monoliths or powders into aerogel microspheres leads to unique electromagnetic wave properties. As expected, the reflection loss of graphene/Fe3O4 AMs-1:1 with only 5 wt.% absorber loading reaches −51.5 dB at 9.2 GHz with a thickness of 4.0 mm and a broad absorption bandwidth (RL < −10 dB) of 6.5 GHz. Furthermore, switching to coaxial electrospinning enables the fabrication of SiO2 coatings to construct graphene/Fe3O4@SiO2 core‒shell AMs. The coatings influence the electromagnetic wave absorption of graphene/Fe3O4 AMs significantly. In view of these advantages, we believe that this processing technique may be extended to fabricate a wide range of unique graphene-based architectures for functional design and applications.

Erratum to: Generation of graphene-based aerogel microspheres for broadband and tunable high-performance microwave absorption by electrospinning-freeze drying process

The name of the third author in the original version of this article was unfortunately wrongly written on the first pages of the main text and the ESM. Instead of Wei It should read Wei Wei

Tunable high-performance microwave absorption for manganese dioxides by one-step Co doping modification

The frequencies of microwave absorption can be affected by the permanent electric dipole moment which could be adjusted by modifying the crystal symmetry of the microwave absorbing materials. Herein, we corroborate this strategy experimentally and computationally to the microwave absorption of manganese dioxides. Nanosized Co-doped cryptomelane (Co-Cryp) was successfully synthesized by a one-step reaction. The introduction of Co(III) induced a change of crystal symmetry from tetragonal to monlclinic, which could lead to an increase of its permanent electric dipole moment. As a result, the frequencies of maximum microwave absorption were regulated in the range of 7.4 to 13.9 GHz with a broadened bandwidths. The results suggested that microwave absorption of manganese dioxides can be tailored with Co doping to expand their potential uses for abatement of various microwave pollutions.

Self-Supported Construction of Three-Dimensional MoS2 Hierarchical Nanospheres with Tunable High-Performance Microwave Absorption in Broadband

The three-dimensional (3D) MoS2 hierarchical nanospheres which assembled spontaneously by two-dimensional (2D) lamina have been successfully designed and fabricated in large scale via a simple hydrothermal process. Subsequently, the electromagnetic wave absorption properties of hierarchical MoS2 nanospheres compounded with polyvinylidene fluoride (PVDF) were investigated in a broad frequency range of 2–40 GHz. The results indicated that the MoS2/PVDF nanocomposites possess adjustable and enhanced wave absorption performance. Furthermore, the MA performance can be effectively tuned by the absorber’s thickness and filler content. In addition, the peculiar hierarchical nanostructure of MoS2 is beneficial to microwave absorption property compared with the bulk MoS2 and micrometer-sized MoS2. Moreover, the main microwave absorption mechanism including various polarization, destructive interference theory, and multiple reflection has been described in detail.

Broadband and tunable high-performance microwave absorption of an ultralight and highly compressible graphene foam.

The broadband and tunable high-performance microwave absorption properties of an ultralight and highly compressible graphene foam (GF) are investigated. Simply via physical compression, the microwave absorption performance can be tuned. The qualified bandwidth coverage of 93.8% (60.5 GHz/64.5 GHz) is achieved for the GF under 90% compressive strain (1.0 mm thickness). This mainly because of the 3D conductive network.