Low-frequency Microwave Absorption Research Articles

Self-Templating Engineering of Hollow N-Doped Carbon Microspheres Anchored with Ternary FeCoNi Alloys for Low-Frequency Microwave Absorption.

Rational design and precision fabrication of magnetic-dielectric composites have significant application potential for microwave absorption in the low-frequency range of 2-8GHz. However, the composition and structure engineering of these composites in regulating their magnetic-dielectric balance to achieve high-performance low-frequency microwave absorption remains challenging. Herein, a self-templating engineering strategy is proposed to fabricate hollow N-doped carbon microspheres anchored with ternary FeCoNi alloys. The high-temperature pyrolysis of FeCoNi alloy precursors creates core-shell FeCoNi alloy-graphitic carbon nano-units that are confined in carbon shells. Moreover, the anchored FeCoNi alloys play a critical role in maintaining hollow structural stability. In conjunction with the additional contribution of multiple heterogeneous interfaces, graphitization, and N doping to the regulation of electromagnetic parameters, hollow FeCoNi@NCMs exhibit a minimum reflection loss (RLmin) of -53.5dB and an effective absorption bandwidth (EAB) of 2.48GHz in the low-frequency range of 2-8GHz. Furthermore, a filler loading of 20wt% can also be used to achieve a broader EAB of 5.34GHz with a matching thickness of 1.7mm. In brief, this work opens up new avenues for the self-templating engineering of magnetic-dielectric composites for low-frequency microwave absorption.

Construction of Chiral-Magnetic-Dielectric Trinity Structures with Different Magnetic Systems for Efficient Low-Frequency Microwave Absorption.

The fabrication of carbon nanocoil (CNC)-based chiral-dielectric-magnetic trinity composites holds great significance in low-frequency microwave absorption fields. However, it is not clear that how the different magnetic systems affect the magnetic and frequency responses of the composites. Herein, four types of magnetic metals, FeCo, CoNi, FeNi, and FeCoNi, are selected to be combined with the chiral templates respectively, resulting in four types of chiral-dielectric-magnetic composites with similar morphology. The CNC templates endow all the composites with excellent dielectric loss. Further permeability analysis and the micro-magnetic simulation confirm that the frequency response region can be well adjusted by changing the magnetic systems with specific magnetic resonance modes and magnetic domain motion. Due to the synergistic effect between magnetism, chirality, and dielectricity, the FeNi-based composites exhibit the best low-frequency microwave absorption performance. The minimum RL of -60.7 dB is achieved at 6.7 GHz with an ultra-low filling ratio of 10%, and the EAB value in low-frequency region is extended to 3.7 GHz. This study provides further guidelines for the design of the chiral-dielectric-magnetic trinity composites in low-frequency microwave absorption.

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.

Suppressed conductive loss of flower-like NiCo2O4-wrapped flaky FeSiAl for excellent low-frequency microwave absorption

Flaky FeSiAl is a high potential absorbent for low-frequency microwave applications. However, impedance mismatching due to its excessively high complex permittivity presents a challenge. Herein, inspired by the surface modification strategy, flaky FeSiAl wrapped with flower-like NiCo2O4 (NiCo2O4@flaky FeSiAl) was developed via a hydrothermal method. The introduction of a surface NiCo2O4 insulating layer was expected to reduce the complex permittivity and increase the high complex permeability in the NiCo2O4@flaky FeSiAl composite. Subsequently, an excellent low-frequency microwave absorption performance was achieved. The designed NiCo2O4@flaky FeSiAl displayed a robust minimum refection loss (RL min) of −33.41 dB at 6.32 GHz and increased the effective absorption bandwidth (EAB, RL < −10 dB) to 4.08 GHz when the matching thickness was 1.6 mm. The enhanced low-frequency microwave absorption performance was mainly attributed to the improvement in impedance matching, which originated from the collaborative regulation of electromagnetic parameters. This study provides a promising approach for designing flaky FeSiAl-based composites and high-performance low-frequency microwave absorbents.

Well-Dispersed CoNiO2 Nanosheet/CoNi Nanocrystal Arrays Anchored onto Monolayer MXene for Superior Electromagnetic Absorption at Low Frequencies

Developing microwave absorbers with superior low-frequency electromagnetic wave absorption properties is one of the foremost important factors driving the boom in 5G technology development. In this study, via a simple hydrothermal and pyrolysis strategy, randomly interleaved CoNiO2 nanosheets and uniformly ultrafine CoNi nanocrystals are anchored onto both sides of a single-layered MXene. The absorption mechanism demonstrated that the hierarchical heterostructure prevents the aggregation of MXene nanoflakes and magnetic crystallites. In addition, the introduction of the double-magnetic phase of CoNiO2/CoNi arrays can not only enhance the magnetic loss capacity but also generate larger void spaces and abundant heterogeneous interfaces, collectively promoting impedance-matching and furthering microwave attenuation capabilities at a low frequency. Hence, the reflection loss of the optimal absorber (M–MCNO) is −45.33 dB at 3.24 GHz, which corresponds to a matching thickness of 5.0 mm. Moreover, its EAB can entirely cover the S-band and C-band by tailoring the matching thickness from 2 to 7 mm. Satellite radar cross-section (RCS) simulations demonstrated that the M–MCNO can reduce the RCS value to below −10 dB m2 over a multi-angle range. Thus, the proposed hybrid absorber is of great significance for the development of magnetized MXene composites with superior low-frequency microwave absorption properties.

Low-frequency and dual-band microwave absorption properties of novel VB-group disulphides (3R–TaS2) nanosheets

As electromagnetic technology advances and demand for electronic devices grows, concerns about electromagnetic pollution intensify. This has spurred focused research on innovative electromagnetic absorbers, particularly chalcogenides, noted for their superior absorption capabilities. In this study, we successfully synthesize 3R–TaS2 nanosheets using a straightforward calcination method for the first time. These nanosheets exhibit significant absorption capabilities in both the C-band (4–8 ​GHz) and Ku-band (12–18 ​GHz) frequency ranges. By optimizing the calcination process, the complex permittivity of TaS2 is enhanced, specifically for those synthesized at 1000 ​°C for 24 ​h. The nanosheets possess dual-band absorption properties, with a notable minimum reflection loss (RLmin) of −41.4 ​dB in the C-band, and an average absorption intensity exceeding 10 ​dB in C- and Ku-bands, in the absorbers with a thickness of 5.6 ​mm. Additionally, the 3R–TaS2 nanosheets are demonstrated to have an effective absorption bandwidth of 5.04 ​GHz (3.84–8.88 ​GHz) in the absorbers with thicknesses of 3.5–5.5 ​mm. The results highlight the multiple reflection effects in 3R–TaS2 as caused by their stacked structures, which could be promising low-frequency absorbers.

Heterogeneous interface engineering of bionic corn-structured ternary nanocomposites for excellent low-frequency microwave absorption

Achieving strong low-frequency microwave absorption is an important research direction, and heterogeneous interface engineering is emerging as a promising strategy. In this work, drawing inspiration from corn, bionic corn-structured ternary nanocomposites were designed and prepared. The obtained Co2NiO4/Fe2O3/Fe3O4 ternary nanocomposites mimic corn kernel structures, and create abundant heterogeneous interfaces, large specific surface area (SSA), and pores. These features effectively enhance interface polarization, optimize impedance matching, and also induce low-frequency natural resonance and high-frequency eddy current loss. The internal defects in the material can promote dipole polarization. The heterogeneous interface engineering of the corn-structured ternary nanocomposites enhances the synergistic effect of dielectric and magnetic loss in the low-frequency region. This optimization achieves an excellent microwave absorption capability of −55.16 dB at a low frequency of 4.40 GHz. Furthermore, radar cross section (RCS) simulations also verified its immense potential for practical applications. This work fabricates an original bionic nanostructure and proposes a performance optimization strategy that will provide useful guidance for the design and fabrication of low-frequency microwave absorbers.

Strong microwave absorption performance of simply grinding FAPbI3/CNTs composite absorbers

The distinctive physical and chemical characteristics of organic-inorganic lead halide perovskite make it a promising candidate for microwave absorption applications. However, the high-efficiency microwave absorption of halide perovskite-based composites is concentrated at high frequencies, while electronic equipment operates at low-frequency bands. Exploring simple and efficient methods to achieve optimal microwave absorption efficiency at low frequencies continues to pose a considerable challenge. Here, FAPbI3 was synthesized by a simple solvent-free hand grinding method and mixed with carbon nanotubes (CNTs) to obtain a series of FAPbI3/CNTs (FC) composites. By modulating the mass ratio of the components, FAPbI3 modulates the absorption bands, CNTs can effectively establish a conductive network to enhance both polarization loss and conductive loss and regulate impedance matching. The lower permittivity of FAPbI3 gives FC an advantage in terms of low-frequency microwave absorption. The FC-4 composite exhibits a minimum reflection loss (RLmin) of −55.67 dB at a low frequency of 6.88 GHz with a thickness of 3.5 mm. Meanwhile, microwave absorption performance can reach 99 % covering almost the entire C band when utilizing a thickness ranging from 3 to 5 mm. Additionally, according to adjusting the load of FAPbI3 in the mixture, the FC-3 composite displays the highest microwave absorption value among the composites based on halide perovskites. With a thickness of 1.4 mm, the reflection loss at 17.4 GHz reaches an impressive minimum value of −71.89 dB. This study represents the first research specifically focused on FAPbI3 perovskite in the domain of microwave absorption. FC composites display remarkable capabilities in absorbing microwaves, indicating their promising prospects for advancement within the realm of microwave absorption. This research may provide valuable insights for the design of low-frequency and high-efficiency microwave absorbers.

Enhancement of low-frequency microwave absorption in TiO2@Fe-based amorphous alloy composite powders

Enhancement of low-frequency microwave absorption in TiO2@Fe-based amorphous alloy composite powders

Dimensional design of Fe0.9Co0.1 nano-alloys with enhanced low-frequency microwave absorption

Low-frequency microwave absorbing materials are critical for enabling radar stealth and interference resistance in gigahertz communication devices and electronic equipment. However, long-wavelength electromagnetic waves are not easily attenuated, due to the limitations of current absorbing materials, including low permeability and a lack of electromagnetic wave loss mechanisms at low frequencies. Herein, we design and prepare one- and two-dimensional Fe0.9Co0.1 nanoalloys with high permeability through an organic templating method combined with a constrained transformation strategy. We systematically investigate the impact of the anisotropy of monodisperse Fe0.9Co0.1 nanoalloys on low-frequency microwave absorption performance. The generous specific surface area of Fe0.9Co0.1 nanosheets facilitate multiple reflections and the scattering of electromagnetic waves within the absorber. This phenomenon, coupled with dielectric resonance, culminates in a maximum reflection loss value of − 48.7 dB at 4.2 GHz. More significantly, Fe0.9Co0.1 nanorods exhibit an absorption intensity of − 35.3 dB at a notably lower frequency of 2.5 GHz, outperforming existing materials, in addition to an efficient absorption bandwidth of 4.2 GHz at a thickness of only 0.7 mm. Through a combination of experimental investigations and finite element simulations, we identify that highly anisotropic magnetic nanorods demonstrate a robust magnetic coupling interaction, substantial interface polarization and quasi-antenna effect. These characteristics result in enhanced low-frequency electromagnetic losses. Our findings indicate that the high anisotropy of the Fe0.9Co0.1 nanoalloys significantly improves their microwave absorption performance, thus emphasizing their substantial potential in the development of efficient low-frequency microwave absorbers.

Porous metal microsphere M@C-rGO (metal = Mn, Fe, Co, Ni, Cu) aerogels with high low-frequency microwave absorption, strong thermal insulation and superior anticorrosion performance

Porous metal microsphere M@C-rGO (metal = Mn, Fe, Co, Ni, Cu) aerogels with high low-frequency microwave absorption, strong thermal insulation and superior anticorrosion performance are successfully constructed.

Ni-Carbon Microtube/Polytetrafluoroethylene as Flexible Electrothermal Microwave Absorbers.

Flexible microwave absorbers with Joule heating performance are urgently desired to meet the demands of extreme service environments. Herein, a type of flexible composite film is constructed by homogeneously dispersing a hierarchical Ni-carbon microtube (Ni/CMT) into a processable polytetrafluoroethylene (PTFE) matrix. The Ni/CMT are interconnected into a 3D conductive network, in which the huge interior cavity of thecarbon microtube (CMT) improves impedance matching and provides additional hyper channels for electromagnetic (EM) waves dissipation, and the hierarchical magnetic Ni nanoparticles enhance the synergistic interactions between confined heterogeneous interfaces. Such an ingenious structure endows the composites with excellent electrothermal performance and improves their serviceability for application under extreme environments. Moreover, under a low fill loading of 3wt.%, the Ni/CMT/PTFE (NCP) can achieve excellent low-frequency microwave absorption (MA) property with a minimum reflection loss of -59.12dB at 5.92GHz, which covers almost the entire C-band. Relying on their brilliant MA property, an EM sensor is designed and achieved by the resonance coupling of the patterned NCP. This work opens up a new way for the design of next-generation microwave absorbers that meet the requirements of EM packaging, proofing water and removing ice, fire safety, and health monitoring.

Enhanced low-frequency microwave absorption of N-doped biomass derived carbon

Hierarchical porous undoped and N-doped carbon derived from the natural spinach roots was prepared by a facile carbonization process at 600–800 ℃ respectively. The electromagnetic properties were carefully investigated in the range of 1–18 GHz in order to study the effect of the tunable permittivity on the microwave absorbing and shielding performance by modulating the intrinsic polarization of the biomass carbon. Compared with the other samples, the undoped one sintered at 650 ℃ shows the minimum reflection loss (RL) of − 42.93 dB at 16.72 GHz with a thickness of 2.0 mm, while the effective absorbing bandwidth achieves 6.46 GHz at 2.4 mm. With the N-doping, the permittivity is obviously affected by the nitrogen-containing groups and compounds induced dipolar and interfacial polarization. The RLmin of the N-doped carbon sample sintered at 700 ℃ has arrived at − 49.96 dB at 15.88 GHz with a very thin thickness of 1.5 mm. Besides, the impedance matching bandwidth can cover the L-C band in the N-doped carbon with the excellent RL of − 43.195 dB at d= 8.4 mm and f= 2.4 GHz. The competitive and tunable mechanism of the dielectric property are also studied for the tunable impedance and microwave absorption.

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption.

Graphene-based aerogels have garnered considerable attention for their lightweight and efficient microwave absorption (MA) properties; however, optimizing the relationship between impedance matching and attenuation capability at low frequencies remains a challenge. In this study, a three-dimensional (3D) silicon carbonitride (SiCN) nanoceramic-coated graphene aerogel with conformal heterogeneous interfaces is constructed by precursor infiltration and pyrolysis to optimize MA performance at low frequencies. Thanks to the enhanced impedance matching and significant interfacial polarization of the two-dimensional sandwiched SiCN/graphene/SiCN cell walls and multiple scattering occurring within the 3D porous skeleton, the aerogel achieves a minimum reflection loss of -57.9 dB at an ultralow frequency of 4.92 GHz (C-band) and a broad bandwidth of 5.0 GHz at an ultralow thickness of 1.7 mm. The strategy developed here provides a method for enhancing dielectric polarization loss in graphene aerogels by the joint optimization of interfacial polarization and impedance matching, inspiring the design of high-performance graphene-based materials for low-frequency MA.

Ultrafine well-dispersed Co nanocrystals onto crumpled sphere-like rGO for superior low-frequency microwave absorption

Nowadays, it is challenging to construct strong absorption materials for addressing low-frequency electromagnetic pollution from electronic equipment. In this work, Co nanocrystals anchored onto crumpled sphere-like reduced graphene oxide are fabricated via a stepwise spray drying-calcination strategy. The crumpled sphere-like architecture prevents the agglomeration of graphene sheets and magnetic nanoparticles while ensuring appropriate exposure of polar functional groups on graphene surfaces. Meanwhile, the addition of magnetic components results in increased magnetic loss capacity, and the crumpled sphere-like structure generates large void spaces and bountiful heterogeneous interfaces, together promoting dielectric polarization loss and impedance matching. Consequently, the optimal absorber achieves a strong reflection loss of −43.3 dB at 3.5 GHz, which can fulfill the ∼85% coverage of the S and C bands by adjusting the thickness from 3.6 to 7.0 mm. This work paves a time-saving and scale-up path for preparing graphene-magnetic materials with superior low-frequency microwave absorption.

Oblique incidence-insensitive metamaterial absorber using strong magnetic coupling resonance for low-frequency microwave absorption

In this work, we presented an oblique incidence-insensitive metamaterial absorber (MA) based on the strong magnetic coupling resonance using the printed circuit board process, and the spacer is produced by a typical magnetic absorber material (MAM). As for reflection loss (RL) at oblique angles, it can achieve high-efficiency absorption for both transverse-electric (TE) and transverse-magnetic (TM) polarizations with a wide angular range from 0° to 60° in the low frequency of 2.33 GHz to 3.44 GHz. In addition, the magnetic coupling mechanism of the metamaterial absorber was deeply analyzed. Comparing the results of the simulation and experiment, it displays excellent absorption performance of the proposed absorber in TE and TM modes under large oblique incidence angles.

Large aspect ratio makes high low-frequency microwave absorption performance via a unique roll grinding method for flake FeSiAl

Increasing aspect ratio for flake magnetic alloy to facilitate microwave absorption capability in low-frequency is highly desired but remains changes by conventional methods. Here we report a unique roll grinding method to fabricate flake FeSiAl alloys with large aspect ratio of 40–100, which is beyond the limit of traditional ball milling method (< 40). As a result, such roll ground flake FeSiAl obtains a 3 times larger low frequency reflection loss (RL= −56.2 dB at 3.47 GHz) than that of ball milled one. Furthermore, the fabricated microwave absorber shows an ultra-wide effective absorption band of 14 GHz (RL < −20 dB, 2.3–16.3 GHz) with the thin coating thickness of 1.6–6.0 mm. Further analysis showed its exceptional properties stem from large aspect ratio induced satisfied impedance matching, enhanced magnetic loss, and intense dielectric loss. Our findings provide an easy industrial preparation method for making flake magnetic alloys that possess unconventional and technologically important electromagnetic properties.

Hollow structured (Ni/C)/ZnFe2O4 composite with enhanced low-frequency microwave absorption performance

To enhance the low-frequency (2–10 GHz) microwave absorption performance of hollow magnetic metal–carbon composites, hollow (Ni/C)/ZnFe2O4 composite was prepared by introducing submicron ZnFe2O4 into hollow Ni/C microspheres. With the increased addition of ZnFe2O4, the low-frequency microwave absorption performance of the composites was gradually enhanced. When the addition of ZnFe2O4 was 12 wt%, the minimum reflection loss (RL) of −38.64 dB could be obtained at 5.33 GHz and the effective absorption bandwidth was 3.45 GHz. As the ZnFe2O4 addition increased to 18 wt%, the minimum RL reached −55.39 dB at 4.26 GHz and the effective absorption bandwidth was 3.82 GHz. The enhanced low-frequency microwave absorption performance can be attributed to the introduction of ZnFe2O4 improved attenuation coefficient and optimized impedance matching of the (Ni/C)/ZnFe2O4 composite. This work provides an effective idea to improve the low-frequency microwave absorption performance of hollow magnetic metal/carbon composites, and the prepared (Ni/C)/ZnFe2O4 composite can be used for microwave absorption in the low-frequency band.

Fe3O4@C 3D foam for strong low-frequency microwave absorption

Low-frequency microwave absorbing materials have been challenging for many years. Three-dimensional dielectric/magnetic porous materials are beneficial for improving the low-frequency microwave absorbing performance because of natural resonance and improved impedance matching. In this study, Fe3O4@C 3D foam was prepared by carbothermal reduction method and the microwave attenuation performances and mechanisms were studied. By adjusting the content of Fe3O4@C 3D foam in paraffin composites, the low-frequency microwave attenuation capacity could be effectively optimized. The minimum reflection loss (RLmin) of paraffin composite with 40% (in mass fraction) loading exhibits −54.7 dB at 4.1 GHz for a thickness of 4.0 mm. Surprisingly, the paraffin composite with 50% (in mass fraction) loading could almost cover 2–4 GHz (S-band) in the thickness range of 3.5–5.5 mm. The strong low-frequency microwave attenuation property of Fe3O4@C 3D foam is mainly attributed to excellent low-frequency impedance matching, natural resonance, interfacial/dipole polarization, multiple reflection and scattering. This method provides a new perspective for preparing lightweight and high performance low-frequency microwave absorbing materials.

Reduced graphene oxide loaded with magnetic nanoparticles for tunable low frequency microwave absorption

Graphene-based microwave absorption materials have been profoundly and extensively investigated because of their excellent properties and is potential absorbing material. However, graphene-based absorbing materials about low-frequency remain to be researched and developed. Here we obtain that Reduced Graphene Oxide (RGO) modified with magnetic xNi/yNiO nanoparticles by a simple hydrothermal method, which presents a large reflection loss (RL) in S-band. The electromagnetic parameters, attenuation constants and impedance matching of xNi/yNiO/RGO composite were analyzed to determine the appropriate ratio of magnetic xNi/yNiO nanoparticles and GO. The maximum RL can reach −46.5 dB with a thickness of 3.6 mm at 3.57 GHz with a loading wax ratio of 15 wt%. The probability of falling on EAB is maximized to cover 94.5% of the S-band. Notably, the RL and efficient absorption bandwidth (EAB) of xNi/yNiO/RGO composite material can be adjusted according to the quarter wavelength matching theory. All the results indicate that xNi/yNiO/RGO composite has a great potential of low frequency absorbing material for low frequency absorbing material research on practical. • xNi/yNiO/RGO was prepared by simple hydrothermal method. • The maximum reflection loss can reach −46.6 dB with a thickness of 3.6 mm at 3.57 GHz. • The probability of falling on EAB is maximized cover 94.5% of S-band. • According to the practical adjustment of raw material proportion to get the required absorbing material.