Improved Microwave Absorption Properties Research Articles

A three-dimensional BaFe11.6(ZrSm)0.2O19/rGO composite aerogel with superior microwave absorption properties

The combination of dielectric and magnetic materials can significantly improve microwave absorption properties. In this work, we introduce a novel Zr-Sm doped barium ferrite BaFe11.6(ZrSm)0.2O19, which is compounded with rGO aerogel and presents superior microwave absorption properties. The results show that the BaFe11.6(ZrSm)0.2O19/rGO composite aerogel exhibits a unique three-dimensional porous network structure which enhances the reflection and scattering of electromagnetic waves. Meanwhile, the addition of BaFe11.6(ZrSm)0.2O19 abounds the folds and defects on the surface of rGO sheet layer, generating a large amount of polarisation and relaxation. In addition, with the increase of BaFe11.6(ZrSm)0.2O19 content, the permeability gradually increases, while the dielectric constant gradually decreases. At a certain content, both of them can be well balanced to obtain high attenuation constants and great impedance matching, which regulates the wave-absorbing properties of the material. The minimum reflection loss (RLmin) of BaFe11.6(ZrSm)0.2O19/rGO composite aerogel can reach -53.17 dB at a matching thickness of 2.9 mm, and the absorption bandwidth reaches 7.04 GHz, which has been improved by 40% than pure BaFe11.6(ZrSm)0.2O19. Therefore, it is expected to be a candidate for lightweight, thin, high loss, large bandwidth microwave absorbing materials.

Bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles for improved microwave absorption properties

High reflection loss and wide absorption bandwidth materials are in great demand to prevent electromagnetic pollution and military applications. The composites prepared by combining different components with good dielectric and magnetic losses are expected to achieve ideal absorbing performance. In this study, a composite of cobalt nanoparticles enveloped in nitrogen-doped bamboo-like carbon nanotubes (Co@N-CNTs) was prepared by one-step annealing the mixture of melamine and cobalt nitrate at 800 °C in a mixed atmosphere of hydrogen and argon. Co nanoparticles derived from the reaction between H2 and cobalt nitrate during the sintering process were used as catalysts to prompt the carbonization of melamine and the formation of the bamboo-shaped N-doped carbon nanotubes, thus forming the composite structure of bamboo-shaped N-doped carbon nanotubes encapsulated with Co nanoparticles. This Co@N-CNTs composite not only had an excellent dielectric loss and magnetic loss but also greatly improved its impedance matching, thus having good electromagnetic wave absorption performance. The coating made from the Co@N-CNTs composite had a maximum reflection loss (RL) of −35.89 dB at only 1.8 mm thickness at 14.1 GHz and possessed an effective absorption bandwidth of up to 4.91 GHz (12.35–17.26 GHz), suggesting it a high-performance and wide-absorption bandwidth composite material.

Construction of Fe3O4/PANI composites with hollow 0D/1D structures for efficient microwave absorption

In this study, a novel microwave absorber ferric oxide/polyaniline (Fe3O4/PANI) composite was successfully fabricated with 0-dimensional (0D) hollow Fe3O4 nanospheres and 1-dimensional (1D) hollow polyaniline (PANI) nanotubes using hydrothermal treatment and chemical oxidative polymerization. The results demonstrate that the prepared Fe3O4/PANI composites exhibit remarkable microwave absorption (MA) properties. It possesses a minimum reflection loss (RLmin) of −55.03 dB and an effective absorption bandwidth (EAB) of 4.88 GHz with a thickness of 1.84 mm. When the thickness is increased to 1.88 mm, the composite achieves a maximum EAB (EABmax) of 5.16 GHz (12.84–18 GHz) and an RL of −40.47 dB. The hollow structures of Fe3O4 and PANI reduce the weight of the absorber and also enhance the synergistic loss effects, including interfacial polarization loss and multiple reflection and scattering loss, resulting in improved MA properties. The combination of hollow 0D/1D structures provides a novel approach in designing lightweight and efficient composite MA materials.

Tunable microstructure and microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbent prepared via a reduction diffusion method

Magnetic materials with highly efficient microwave absorption properties, crucial for dealing with the advanced wireless communications and radar detections, have been garnering significant attentions. Rare-earth transition-metal compounds were researched as the potential candidates but still suffer from the disadvantages of complex powder metallurgy process and low serving frequencies. In this work, the novel magnetic composites consisting of SmCo5 and Sm2Co17 are developed by a reduction diffusion method. The micromorphology and the binary phase ratios of the SmCo5/Sm2Co17 could be easily modulated by simply altering the reactant concentrations. Consequently, an optimum reflection loss of − 50.2 dB and broad absorption bandwidth of 4.95 GHz at a thickness of only 2.0 mm are achieved. The improved microwave absorption properties of the SmCo5/Sm2Co17 binary-phase magnetic absorbents can be attributed to their adjustable magnetic phases and the distinctive flaky particle shape, which greatly enhance microwave absorption capabilities. This work demonstrated a feasible reduction diffusion method and proposed a new strategy of designing binary-phase magnetic materials to achieve high microwave absorption properties.

Improved microwave absorption properties of ferrite-rGO composites by covalent bond

In this work, to investigate the effect of electron motion mode on the microwave absorption performance, ferrite Fe3O4 and graphene oxide (GO) were united by covalent bonding and subsequent reduction to fabricate microwave absorbing material (MAM) with excellent impedance matching characteristics and superb attenuation ability. Under the synergistic effect of the magnetic and dielectric properties, the Fe3O4-rGO hybrid nanocomposites present high absorption performance. Its minimum reflection loss (RLmin) reached –47.46 dB when the thickness was 3.5 mm. The effective absorption bandwidth (EAB) was 5.86 GHz when the thickness was only 2.0 mm. XPS and FT-IR spectroscopy indicate the formation of amide bonds between the modified Fe3O4 and functional GO. SEM, EDS, TEM and Raman spectroscopy were used to analyze the morphology and structure of the hybrid nanocomposites. The effects of bonding modes and component fractions on the electron motion and the resulting impedance matching of the hybrid nanocomposites were discussed.

Hard Carbon Embedded with FeSiAl Flakes for Improved Microwave Absorption Properties.

Carbon-based composites have been proven to be strong candidates for microwave absorbers in recent years. However, as an important member, magnetic hard carbon (HC)-based composites have rarely been studied in the field of microwave absorption. In this study, HC embedded with FeSiAl (FeSiAl@HC) was synthesized by pyrolyzing a mixture of FeSiAl flakes and phenolic resin (PR). The as-synthesized HC-FeSiAl exhibited a layered structure, and the detailed microstructures were modified by changing the mass ratio of FeSiAl flakes and PR. Thus, the as-synthesized HC-FeSiAl exhibited tunable magnetic properties, wealthy functional groups, excellent thermal stability, and enhanced microwave absorption properties. The optimal minimum reflection loss is lower up to −36.1 dB, and the effective absorption bandwidth is wider up to 11.7 GHz. These results indicated that HC-FeSiAl should be a strong candidate for practical applications of microwave absorption, which may provide new insight into the synthesis of magnetic HC-based composites.

Solid-state reaction induced defects in multi-walled carbon nanotubes for improving microwave absorption properties

• Defect structures and contents of MWCNTs have been optimized. • MA property of MWCNTs could be optimized by the defect engineering. • Dipole polarization can effectively improve MA performance. • Permeability-to-permittivity transformation is another MA mechanism. Dielectric polarization performance induced by defect engineering approach has been proved to be an effective way for improving the microwave absorption property of carbon-based materials. Assisting by the solid-state reaction, the structural integrity of multi-walled carbon nanotubes (MWCNTs) would be broken along with the volume expansion and etching process of cobalt oxides. Therefore, the defects could be obtained and result in the enhancement of microwave absorption property. Ascribing to the broken wall structures, the defect-distances ( L D ) and concentrations ( n D ) have been optimized to be 9.80 nm and 3.37 × 10 11 cm −2 . The minimum reflection loss ( RL ) had reached -54.6 dB at 4.5 GHz with a thickness of 4.13 mm and the corresponding effective absorption bandwidth (EAB <-10 dB ) was analyzed to be 14.6 GHz. Such enhancement is correlated to the dielectric polarization and the permeability-to-permittivity transformation raised from the defect structures and concentrations. The present work demonstrates an effective strategy for tailoring the microwave absorption property of MWCNTs by engineering defect concentrations, and could be further extended to other carbon-based absorbents.

Intense nonlinear dielectric and magnetic resonances of core–shell Ni@graphene composites and their improved microwave absorption properties

Core/shell Ni@graphene composites are prepared by an in situ CVD process using PMMA precursors. The composites exhibit intense nonlinear dielectric and magnetic resonances at Ku-band frequency range, which are benefit to the absorption of microwave.

SYNTHESIS OF REDUCED GRAPHENE OXIDE - Mn0.8Zn0.2Fe2O4 - POROUS POLYANILINE NANOCOMPOSITE MATERIALS FOR EFFECTIVE MICROWAVE ABSORPTION IN X-BAND

In this paper, a composite of reduced graphene oxide (RGO), manganese/zinc ferrite (Mn0.8Zn0.2Fe2O4 - MZF) nanoparticles, and porous polyaniline (PANI) was successfully synthesized to improve microwave absorption properties exclusively in X-band. The experimental results demonstrate that the synthesized ternary composite had RGO nanosheets decorated mostly with MZF nanoparticles, and porous PANI was uniformly coated onto the surface of RGO-MZF. The strong reflection loss value of -60.4 dB at 10 GHz and wide effective bandwidth are effectively achieved with the sample which had thicknesses of 2 mm and contained 33 weight % of product. The marked display of the microwave absorption properties of this composite was associated with their notable structure.

Carbon Coated Core-Shell FeSiCr/Fe3C Embedded in Carbon Nanosheets Network Nanocomposites for Improving Microwave Absorption Performance

Development of microwave absorbing materials with tunable thickness and bandwidth is particularly important for practical applications, but its realization remains a great challenge. Here, we report carbon coated core-shell FeSiCr/Fe3C embedded in two-dimensional carbon nanosheets network (FeSiCr/Fe3C@C/C) nanocomposites fabricated by plasma arc-discharging method. FeSiCr/Fe3C@C/C has the best microwave absorption properties in which the minimum calculated reflection loss (RL) can reach [Formula: see text][Formula: see text]dB at 11.5[Formula: see text]GHz with a coating thickness of 2.4[Formula: see text]mm and the efficient absorption bandwidth (RL[Formula: see text][Formula: see text]dB) almost covers 4.5–18[Formula: see text]GHz range by adjusting the coating thicknesses from 1.3 to 5.0[Formula: see text]mm. The improved microwave absorption properties could be ascribed to the optimized impedance matching and enhanced polarization loss, conduction loss and internal reflections of the propagated microwave.

Effects of Sm-doping on microstructure, magnetic and microwave absorption properties of BiFeO3

In this paper, polycrystalline samples of Bi1–xSmxFeO3 (x = 0, 0.05, 0.1, 0.15) were successfully synthesized by sol-gel method. The effects of Sm concentration on the crystal structure, morphology, chemical states, magnetic properties and microwave absorption performance were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), a vibrating sample magnetometer (VSM) and a Vector network analyzer (VNA), respectively. The results show that the rare earth Sm doping causes the crystal structure to change. When x ≤ 0.1, Bi1–xSmxFeO3 is the distorted rhombohedral structure with space group R3c. With the increase of Sm doping amount to x = 0.15, the phase structure of Bi1–xSmxFeO3 changes from rhombohedral structure to cubic structure with the space group Pm3¯m. The particle size decreases with the increase of the Sm doping amount. The analysis results show that Sm doping can effectively reduce the oxygen vacancies and significantly improve its magnetic properties. The results exhibit that moderately doped rare earth Sm element can effectively improve microwave absorption properties of Bi1–xSmxFeO3 powders. When Sm doping amount of x is 0.1, the Bi0.9Sm0.1FeO3 compound has good microwave absorption performance, and the minimum reflection loss value of Bi0.9Sm0.1FeO3 powder reaches about −32.9 dB at 11.7 GHz, and its effective absorption bandwidth (RL < −10 dB) is 2.6 GHz with the optimal matching thickness of 2.0 mm.

Influence of heat treatment on the microwave absorption properties of flaky carbonyl iron powder

High-energy ball milling is a very common method to produce materials with high magnetic permeability due to its ability to produce flaky shape particles on the nano-scale. It is an efficient technique to improve microwave absorbing properties. Therefore, this study aims to achieve an ideal microstructure and improve microwave absorption properties of flake carbonyl iron powder fabricated by high-energy ball milling. The influence of pre-heating at different times/temperatures on magnetic absorbing properties is also investigated. Further, the relationship between heat treatment temperature, permeability is analyzed. Microstructural analyses reveal that the phase of the material does not change with the change of pre-heating temperature. However, the material made by ball-milling has a finer grain size and a higher flattening ratio. The results show that the length to diameter ratio of the flake material can be increased by pre-heating, and thus improve the magnetic permeability and absorbing performance of the material. The optimal parameters of pre-heating are obtained at the temperature and time of 200 °C and 2 h, respectively, wherein the real part of the permeability reaches up to 3.20 at 2 GHz, the imaginary part reaches 1.61 at 6.2 GHz.

Oxygen-sulfur Co-substitutional Fe@C nanocapsules for improving microwave absorption properties

Heteroatom substitution has been investigated to be a feasible way to optimize microwave absorption properties of core-shell structural nanocapsules at gigahertz. Although dielectric capacity has been increased at specific frequency with substituted absorbents, its broadband absorption performance is still relatively poor ascribed to the low dipole oscillation amplitude of single substituted heteroatom. In this study we demonstrate that sulfur and oxygen co-substituted heterostructure leads to high microwave absorption property of core-shell structural Fe@C nanocapsules at broadened frequency range, comparable to the single sulfur substitutional Fe@C nanocapsules. Experimental characterizations coupled with first-principles calculations reveal that the microwave absorption enhancement is triggered by the sulfur-oxygen co-substitution, which results in the serious symmetry breaking and thus leads to the charge separation at the co-substituted area. In particular, the nanocapsules exhibt the minimum reflection loss capcacity R(dB) of −52 dB at 6.8 GHz and the bandwith for R(dB) <−20 dB is in the frequency range of 3.1−12.7 GHz. The present study not only offers a deep insight into the relationship between heteroatom and microwave absorption property, but also puts forward a mentality for further designing microwave absorbents.

Research on Broadband Microwave Absorber Containing a 2D Artificial Electromagnetic Material Composed of Cross Section Resonator Sub-Unit Cells Inserting Ferromagnetic Materials

This paper provides a new method to improve microwave absorption properties of ferromagnetic materials. A 2D artificial electromagnetic material is designed using a square combination of cross section resonator sub-unit cells, and then inserted into carbonyl iron powder layers to realize a broadband microwave absorber. Both the simulation and experiment results show that the absorber can realize the wideband and high efficiency absorption.

The influence of Nd substitution in Ni–Zn ferrites for the improved microwave absorption properties

Nanocrystalline Ni–Zn ferrites with different neodymium contents (Ni0.5Zn0.5NdxFe2-xO4) were synthesized by sol-gel route combined with self-propagating combustion (SPC) method. The presence of surface functional groups, crystal structure and morphology of the samples were studied by FT-IR, XRD and SEM. The results show that the prepared samples are composed of spinel phase under the condition of low neodymium content, like the pure Ni–Zn ferrite. While neodymium oxide appears after the content of Nd3+ exceeds a certain limit (x > 0.04) and there exist two phases in the ferrite. The results of vibrating sample magnetometer (VSM) and vector network analyzer (VNA) show that adjusting the content of Nd is significant in improving the dielectric properties and microwave absorption capacity of the materials, specifically at low frequencies. When x < 0.04, the enhancement of dielectric loss ability of spinel ferrites by doping Nd3+ is the dominant factor affecting microwave absorption ability of samples. The secondary phase Nd2O3 hardly appears under this condition, thus the weakening effect of Nd3+ addition on magnetic loss ability is not obvious. When x = 0.04, the optimal absorption peak of the material reaches −20.8 dB at 4.4 GHz with a thickness of 8.5 mm and the effective absorption bandwidth (RL < −10 dB) was 3.2 GHz. On the contrary, when x > 0.04, the magnetic loss ability decreases rapidly (e.g., Ms decreases from 82.47 emu/g to 59.77 emu/g). Meanwhile, the dielectric loss increases slowly and the microwave absorption capacity decreases.

Dielectric response and microwave absorption properties of SiC whisker-coated carbon fibers

SiC whisker-coated carbon fibers with improved microwave absorption properties were synthesized by catalysis chemical vapor deposition. Dielectric response and microwave absorption properties of SiC whisker-coated carbon fibers were investigated at the frequency range of 2–18 GHz. 8 and 18 wt% SiC whiskers were grown on carbon fibers after depositing for 2 and 3 h, respectively, and the whiskers grew thicker and more compact with prolonged deposition time. Many stacking faults formed during the growth of SiC whiskers. Moreover, carbon fibers coated with 8 and 18 wt% SiC whiskers both presented decreased complex permittivity. Although their electromagnetic wave attenuation capability slightly decreased, impedance matching clearly improved. The minimum reflection loss of carbon fibers significantly increased from around − 2 to − 19.8 dB after coating with 18 wt% SiC whiskers at a thickness of 2.0 mm. Carbon fibers coated with 18 wt% SiC whiskers also exhibited remarkably enhanced microwave absorbing properties of − 44.53 dB at 7.4 GHz at a thickness of 3.0 mm.

Foam structure to improve microwave absorption properties of silicon carbide/carbon material

Foam structure materials are well known for their lightweight, efficient, and broadband microwave absorption properties compared to bulk material. However, little has been understood about the effect of a foam structure on the absorption performance of the foam material. In this study, the role of foam structure properties of the silicon carbide/carbon (SiC/C) foam material on microwave absorption is explored using experiment and simulation. We find that the foam structure of SiC/C foam material causes diffraction, multiple reflections, improves the interfacial polarization, and compatibilization. The absorption performance of SiC/C foam material is also studied. The -10 dB effective absorption bandwidth can be adjusted from 4.0 GHz to 18 GHz by tuning SiC/C foam material thickness to 3–7 mm. Therefore, the foam structure design is an effective way to improve the absorption performance of the SiC/C foam material.

Nanolayered flaky Fe-based amorphous-nanocrystalline/graphite sheet composites with enhanced microwave absorbing properties

Nanolayered flaky Fe-based amorphous-nanocrystalline/graphite sheet composites with excellent microwave absorbing properties are fabricated by ball milling the Fe-based amorphous alloy and graphite. The obtained composites consist of Fe-based amorphous-nanocrystalline flakes and graphite sheet coating, which exhibit good impedance matching. The modified magnetic and dielectric properties, especially the large coercivity, high permeability and the interfacial polarization are responsible for the significantly improved microwave absorption properties with minimum reflection loss of −67.95 dB at thin thickness of 1.6 mm and bandwidth of 5.36 GHz. The facile composites with excellent microwave absorbing properties are potential materials for high-performance microwave absorbers.

Synthesis and Characterization of Ternary Polyaniline/Barium Ferrite/Reduced Graphene Oxide Composite as Microwave-Absorbing Material

A microwave-absorbing composite with polyaniline (PANI), barium ferrite (BaFe12O19) and reduced graphene oxide (rGO) by co-precipitation and in situ polymerization is presented, consisting of three different microwave-absorbing materials. The structure characterization, the microstructure of the fabricated composites and their related thermal and microwave absorption properties have been investigated. The thermogravimetric analysis and vector network analyzer measurements indicated that both the thermal stabilities and the microwave-absorption properties of this ternary composite were significantly enhanced due to the synergistic effects of PANI, BaFe12O19 and rGO. The minimum reflection loss of PANI/BaFe12O19/rGO was − 22.05 dB at 8.6 GHz, and the effective microwave-absorption bandwidth for reflection loss below − 10 dB was 0.9 GHz from 8.2 GHz to 9.1 GHz with the thickness of 2.6 mm. The improved microwave-absorption properties could be mainly due to the impedance matching by integration of dielectric loss and magnetic loss, and interfacial polarization between the three components. The remarkable microwave-absorption properties suggests its promising application for microwave absorption.

Nanofiber network with adjustable nanostructure controlled by PVP content for an excellent microwave absorption

Carbon nanofibers were widely utilized to improve microwave absorption properties since they are a promising lightweight candidate. Adjustable conductive nanostructures of carbon nanofibers were synthesized by electrospinning technique. The conductive network is controlled by the polyvinyl pyrrolidone (PVP) content due to the special hygroscopicity of PVP. The increased adhesive contacts of nanofibers provide more transmission paths for electrons to reduce the effect of air dielectric. Satisfactorily, the carbon nanofibers that carbonized from the polyacrylonitrile (PAN) and PVP (the mass ratio is 6:4) show excellent microwave absorption performance. The minimum reflection loss (RL) value is −51.3 dB at 15.2 GHz and the maximum effective absorption frequency width (<−10 dB) is 5.1 GHz with the matching thickness of only 1.8 mm. Thereby, we believe that this research may offer an effective way to synthesize lightweight carbon nanofibers microwave absorbents.