Broadband Microwave Absorption Research Articles

Graphene-Wrapped Magnetic Multichamber Ti3C2Tx Spheres for Stable Broadband Microwave Absorption.

Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

Capping Agent–Induced ZIF-8-Based ZnO/Magnetic Carbon Nanocomposites for Enhanced Broadband Microwave Absorption

Capping Agent–Induced ZIF-8-Based ZnO/Magnetic Carbon Nanocomposites for Enhanced Broadband Microwave Absorption

Multi-scale structural design of multilayer magnetic composite materials for ultra-wideband microwave absorption

Broadband microwave absorbing (MA) materials have important applications in reducing electromagnetic radiation pollution and realizing low scattering characteristics. However, current MA materials with single-layer structure generally cannot meet this requirement due to the difficulty in achieving good impedance matching. Here, we design a multilayer-structured MA material, which consists of a wave transmitting layer, a carbon-magnetic material composite absorbing layer, a strong magnetic absorbing layer and a reflector layer. Hollow Co/CoFe@C composite particles prepared using CoCoPBA as templates are used as fillers to design carbon-magnetic material composite absorbing layer. The Co/CoFe bimagnetic phases enhance permeability while the hollow structure optimizes permittivity, which endows this absorbing layer with strong microwave absorption ability with a reflection loss of -47.18 dB. The introduction of a strong magnetic absorbing layer that combines FeSiAl with high permeability and SmFeB with high coercivity further significantly improves the overall impedance matching of the material. Benefitting from the multi-scale structural design, the obtained multilayer MA material achieves strong microwave absorption in both low and high frequency ranges, and the effective absorption bandwidth reaches 12.85 GHz, far superior to the traditional single-layer MA material.

Controllable and lightweight ZIF-67@PAN derived Co@C nanocomposites with tunable and broadband microwave absorption

Metal-organic framework-based carbon–carbon composite represent a novel class of microwave-absorbing materials (MAMs). However, obtaining lightweight and highly efficient absorbers with a lower filling ratio and larger effective absorption bandwidth (EAB) poses a challenge. In this study, we developed a controllable preparation method for ZIF-67 template polyacrylonitrile-wrapped nanocomposite (ZIF-67@PAN) precursor. This was achieved through radical polymerization of acrylonitrile (AN) initiated by azobisisobutyronitrile (AIBN). Subsequent annealing at high temperatures produced a lightweight nitrogen and oxygen-doped graphite layer-wrapped Co@C smart material (Co@C1, Co@C2, and Co@C3) with tunable microwave absorption properties (MAP). The results demonstrate that Co@C2 achieved a minimum reflection loss (RLmin) value of −50.20 dB at a thickness of 2.0 mm with an EAB of 6.1 only at a filler content of only 13 %. Therefore, this work offers a controllable preparation method and introduces a simple and facile approach for creating efficient, lightweight micro and nano-sized microwave-absorbing materials.

Multi-material fused deposition modelling of structural–functional integrated absorber with multi-scale structure possessing tunable broadband microwave absorption

Designing and manufacturing advanced structural microwave absorbers is one of the most feasible methods to address the growing electromagnetic stealth and protection challenges in both military and civilian domains. To this end, under the application context of structural–functional integration, a series of nanocomposites with varying ratios were prepared using multi-walled carbon nanotubes (MWCNTs) and inexpensive thermoplastic polypropylene as raw materials. The dispersion of nanofillers, rheological properties, thermal properties, and mechanical properties were evaluated. The research found that the impedance matching factor of the electromagnetic wave absorbers plays a more critical role in determining the material’s absorption capacity compared to the loss factor. Simple structural layering by changing the composition and design can effectively increase the effective absorption bandwidth (EAB) of the absorbers, with microwave attenuation primarily arising from conductive loss, interfacial polarization, dipole polarization, and multiple reflections. Finally, a multi-scale quasi-honeycomb absorber was fabricated using multi-material 3D printing with a structured design. Both simulation and experimental results showed consistent trends, demonstrating low sensitivity to the incident azimuth angle. This research features simplicity, low cost, and strong design capability, providing a new strategy for the preparation of functionally graded materials with potential applications in electromagnetic wave absorption.

Facile and precise synthesis of core-shell ZnO/C nanorods with excellent microwave absorption

Carbonaceous materials have great prospects in microwave absorption due to their lightweight and corrosion resistance. However, their high conductivity leads to poor impedance matching, posing a significant challenge for obtaining outstanding microwave absorption (MA) materials from carbonaceous materials. In this work, the core-shell ZnO/C nanorods (ZCNs) are prepared by covering conductive carbon on the surface of ZnO nanorods through a simple stirring process in ambient temperature and calcination treatment. The thickness of carbon shell is carefully regulated to realize appropriate impedance matching and strong microwave dissipation capability. ZCN with 30.2 nm of carbon shell achieves outstanding microwave absorption in low frequency and broadband microwave absorption because of the synergies of optimized impedance matching and enhanced dielectric loss: the reflection loss of 49.9 dB at 6.32 GHz, and the effective absorption bandwidth of 6.4 GHz at a corresponding thickness of 2.0 mm. RCS simulation results have verified its excellent performance in practical application. This study proposes a simple and effective idea for the efficient utilization of carbonaceous materials in microwave absorption.

Preparation of cellulose derived carbon/reduced graphene oxide composite aerogels for broadband and efficient microwave dissipation

The development of cellulose derived carbon-based composite aerogels with light weight, broad bandwidth and strong absorption remains a challenging task. In this work, the cellulose derived carbon/reduced graphene oxide composite aerogels were prepared by a two-stage process of chemical crosslinking and high-temperature carbonization. The results revealed that the as-fabricated binary composite aerogels had a unique lightweight characteristic and three-dimensional porous network structure, which was chemically crosslinked by epichlorohydrin. Furthermore, the weight concentration of graphene oxide (GO) had a notable influence on the electromagnetic parameters and microwave absorption properties of the composite aerogels. The obtained binary composite aerogel possessed the optimal microwave dissipation capability when the concentration of GO was 1.5 mg/mL. Remarkably, the minimum reflection loss reached −50.42 dB at a thickness of 2.47 mm and a filling ratio of 17.5 wt%. Concurrently, the composite aerogel with a comparable thickness of 2.73 mm showed a wide effective absorption bandwidth of 7.28 GHz, spanning the total Ku-band and extending into a portion of the X-band. The radar cross section contribution of binary composite aerogels in the far-field was also simulated by computer simulation technique. In addition, the potential microwave attenuation mechanism was proposed. It was believed that the results of this paper would offer a reference for the preparation of cellulose derived carbon-based composite aerogels as efficient and broadband microwave absorbers.

Carbon nanofiber aerogel microspheres with heterogeneous skin-core structure for broadband electromagnetic wave absorption

The advancement in the miniaturization of carbon aerogels into micro-sized spheres represents a significant development in the creation of ultralight, broadband microwave absorbers. Notwithstanding this innovation, there is still a considerable challenge in optimizing microwave absorption (MA) performance through heterointerface engineering within aerogel microspheres. Herein, we have developed skin-core heterogeneous aerogel microspheres by the in situ generation of ZIF-67 nanocrystals on the wet-spun aramid nanofiber (ANF) aerogel microspheres, followed by a high-temperature carbonization process. The resulting Co@C nanoparticle-enshrouded ANF-derived carbon nanofiber aerogel microspheres (Co@C/CNFAMs) demonstrate an exceptional equilibrium between impedance matching and multi-faceted attenuation. Remarkably, the Co@C/CNFAM2 sample attains a maximum effective absorption bandwidth of 8.72 GHz, while maintaining an ultralow filler proportion of 1.5 wt%. Moreover, the Co@C/CNFAM3 sample achieves a minimum reflection loss of −72.34 dB with a filling ratio of 1.2 wt%. Our findings offer a refined approach to the intricate engineering of heterostructures, along with the strategic macrostructural design, paving the way for the development of aerogel-based microwave absorbers that represent the next step in material science innovation.

Green-prepared high-performance electromagnetic wave absorption Ni6W6C/Co2O3@C composites and related broadband absorption device

In recent years, the synthesis of absorbing materials using green and environmentally friendly natural raw materials have become a research topic, but green and environmentally friendly materials with both high performance and simple synthesis steps still need to be developed. In this work, glucose and metal organic framework (MOF) were used to prepare composite materials with strong absorbing ability and low cost. We chose glucose, which is convenient to purchase on the market, as the raw material and constructed MOF derivatives with carbon shell skeleton nanostructures through a simple method of hydrothermal and annealing. Compared to the raw materials of traditional absorbing materials, glucose has environmentally friendly, low-cost and green characteristics. We characterized the microstructure and morphology of the material. In addition, we also analyzed the material composition and absorption mechanism of Ni6W6C/Co2O3@C. We have found from the theoretical analysis and simulation results of transmission lines that the minimum reflection loss (RLmin) value of Ni6W6C/Co2O3@C material at 5.43 GHz and 4.76 mm is −56.68 dB. And the effective absorption bandwidth (EAB) at 2.04 mm can reach 7.12 GHz. We load the best sample to the honeycomb structure, a broadband microwave absorber was designed for simulation. The results show that the broadband microwave absorber can achieve an average electromagnetic wave (EMW) loss of more than 99 % in the 0.3–16.04 GHz frequency band (RL value is less than −20 dB), and an average EMW loss of more than 90 % in the 16.04–18 GHz frequency band (RL value less than −10 dB). The composite structure of glucose and MOF derivatives enhances the dielectric loss of the material and enriches various EMW loss mechanisms. Finally, a green, environmental-friendly, high-performance absorbing material with a simple synthesis method is prepared. These results provide insights into the research on EMW absorption of composite materials and new methods for referring.

Construction of multi-interface magnetic FeMnC modified carbon/graphene aerogels for broadband microwave absorption

Magnetic carbon-based aerogels with low-density and strong attenuation, have attracted significant attention as microwave absorbing materials, but still face huge challenges. Herein, magnetic FeMnC modified carbon/Graphene aerogels (NCMF) were synthesized utilizing freeze casting following a carbothermal reduction process. The conductivity, defects density, material component and electromagnetic properties can be regulated by the temperature. The NCMF aerogels exhibit remarkable microwave absorption properties, with an effective absorption bandwidth of 5.76 GHz at a thickness of 2.1 mm and a minimum reflection loss as low as −50.8 dB at 7.52 GHz with a fill ratio of only 5 wt%. The exceptional microwave absorption capabilities of NCMF aerogels are attributed to the synergistic effects of dielectric loss, magnetic loss, three-dimensional (3D) carbon conductive network, and the optimal impedance matching. Consequently, this research paves a way for the development of microwave absorbing materials with lightweight, broadband and strong microwave absorption at low loading.

Zirconium carbide modified SiOC composites with porous lamellar structures for broadband microwave absorption and thermal stability

The inherent dielectric properties and thermal stability of transition metal carbides (TMCs) have generated significant interest because of their potential use in electromagnetic (EM) wave applications at various temperatures. However, the high relative complex permittivity and conductivity of TMCs can cause impedance mismatch issues when utilized as absorbers, thereby limiting their effectiveness in absorbing EM waves. To solve these problems, ZrC/ZrO2–SiOC composites with a porous lamellar structure were prepared using polymer-derived ceramics (PDC) technology, which involved dispersing zirconium carbide (ZrC) into modified polysiloxane (PSO). The resulting ZrC/ZrO2–SiOC composite (with 5 wt% ZrC content sintered at 900 °C) achieved remarkable EM wave absorption performance, with a minimum reflection loss (RLmin) of −33.52 dB at 13.0 GHz and an effective absorption bandwidth (EAB) extending up to 7.75 GHz. This exceptional absorption of EM waves is due to the synergistic interplay of various factors such as interface polarization, dipole polarization, and conduction loss. Moreover, the composites exhibit a minimal weight loss of less than 2 % when exposed to air at temperatures ranging from 25 to 1200 °C. This study not only broadens the application possibilities of TMC materials in microwave absorption but also highlights their potential for further improvement and deployment in high-temperature environments.

Preparation and electromagnetic wave absorption properties of CAU-Al MOF and graphene oxide aerogel composites

The application of microwave technology has penetrated all aspects of life, but also lead to the electromagnetic pollution, therefore the research of high efficiency microwave absorption materials has been widely concerned. In this work, a new type of Al based CAU-10-H MOF was prepared by hydrothermal method. The particles were polyhedral in size of 2 [Formula: see text]m. After high temperature annealing, the interplanar spacing increased with the annealing temperature, and the lattice structure was destroyed at 400°C. CAU-Al/rGO aerogels were prepared by freeze-drying of hydrogels. With the increase of CAU-Al content and the annealing temperature, the carbon crystallinity decreases, and the pores of the aerogels became larger and fluffier. The real parts of permittivity of CAU-Al/rGO aerogels were between 5 and 30, which can be tuned by the annealing temperature and CAU-Al content. For the microwave absorption performance, the CAU-Al/rGO aerogel with a ratio of 3:1 achieved the minimum reflection loss of −37.8 dB at 3 mm. Moreover, the CAU-Al/rGO aerogels showed a wide effective bandwidth, which reached 5.1 GHz under the thickness of 2.5 mm. Therefore, the CAU-Al/rGO aerogels could be used as a kind of broadband microwave absorber with excellent microwave absorption performance.

An ultra-wideband magnetic composite metamaterial microwave absorber embedded with multilayered graphene FSS

Nowadays, it is still challenging to develop high-efficiency broadband microwave absorption materials for electronic equipment and communication facilities. Herein, an ultra-wideband metamaterial microwave absorber (MMA) composed of CoNi@CNH/epoxy composite absorption substrates and the multilayered graphene frequency selective surface (FSS) is designed and fabricated. Thanks to the effective synergies of the multilayered graphene FSS with impressive tunable frequency features and magnetic absorption substrates with distinguished broadband absorption capacity, the obtained MMA showcases an effective absorption bandwidth from 4.5 GHz to 18 GHz. Meanwhile, an equivalent circuit model is proposed to explain its physical absorption mechanism. The designed MMA exhibits the insensitivity to both polarization modes and oblique incidences, and a significant radar cross-section reduction. The experimental results of the as-fabricated sample match well with the simulation values. Furthermore, the as-designed MMA possesses a simple fabrication process and an ultralight feature of 2.7 kg/m2. All these excellent properties make this MMA a high application prospect in both military stealth and civil fields.

Facile Fabrication of Melamine/MXene/FeNi‐PBA Composite Derived Multi‐Interface Magnetic Carbon Foam for High‐Efficiency Microwave Absorption

AbstractThe development of novel materials with high‐efficiency microwave absorption is crucial for mitigating the adverse impacts of electromagnetic pollution. In this study, MXene and FeNi Prussian blue analogs (PBA) are assembled onto a melamine foam using self‐assembly and in situ growth technique. Subsequently, magnetic carbon foam, comprising FeNi alloys, TiN and carbon with various morphologies, is synthesized via carbothermal reduction reaction. The surface morphology electromagnetic properties are significantly influenced by the pyrolysis temperature. The results revealed that the magnetic carbon foam composite demonstrated an effective microwave absorption bandwidth of 4.72 GHz at a thickness of only 1.5 mm, with a minimum reflection loss of −24.83 dB at 1.3 mm. The outstanding microwave absorption performance can be attributed to the 3D conductive network formed by N‐doped carbon, as well as the contributions from polarization loss, magnetic loss, and suitable impedance matching. Furthermore, the corresponding absorber coating demonstrated a maximum reduction value of radar cross‐section (RCS) by 13.16 dB m2. This research offers novel insights for the development of lightweight and efficient low‐filled electromagnetic composite for broadband microwave absorption.

MnFe2O4/Fe3O4/PANI/rGO heterogeneous nanocomposites: Outstanding dual-broadband nano-coating microwave absorbers

In this study, MnFe2O4/Fe3O4/PANI nanocomposites were synthesized via hydrothermal and coprecipitation methods and decorated on reduced graphene oxide (rGO) sheets with three weight ratios (1:1), (2:1), and (3:1) for MnFe2O4/Fe3O4/PANI versus rGO. FESEM images indicate a random distribution of MnFe2O4/Fe3O4 and PANI components on the rGO sheets. The designed superparamagnetic nanocomposites, MnFe2O4/Fe3O4/PANI/rGO, exhibit multi-reflections, strong interfacial polarizations, scattering of incident microwaves, and multiple magnetic resonances, which results in superior absorption performance. This is due to the structural design and distribution of different components providing various interfaces, high specific surface area, and different magnetic and dielectric components. The microwave absorption properties are evaluated in the frequency range of 1–18 GHz (L, S, C, X, and Ku bands), from electromagnetic parameters according to transmission line theory. Our results show that (MnFe2O4/Fe3O4/PANI)/rGO (1:1) presents the highest reflection loss, −108.71 dB, at 17.8 GHz with a thickness of 4.2 mm and bandwidth of 3.2 GHz. Interestingly, (MnFe2O4/Fe3O4/PANI)/rGO (3:1) shows a broad absorption bandwidth of 5.6 GHz for a thickness of only 2.2 mm, having a remarkable reflection loss of −95.52 dB at 17.8 GHz. Our study introduces a novel approach for the successful design and preparation of multi-dimensional graphene-based quaternary nanocomposites compromised from lightweight microwave absorbers, with numerous heterogeneous interfaces and defects resulting from interfacial engineering that have promising potential applications in broadband microwave absorption.

Boosting magnetic loss and impedance matching based on laminated structure for balancing low-/high-frequency broadband microwave absorption

Balancing low-/high-frequency broadband absorption is significantly essential for realizing ultra-wideband microwave absorption but mains challenging. In this work, laminated dielectric@magnetic FePO4/CrPO4@FeSiCr flakes have been created using facile vertical ball milling technique and subsequent phosphate passivation process. The flaky morphology provides the strong magnetic loss ability for boosting a lower-frequency microwave absorption. The dielectric@magnetic structure contributes good impedance matching and sufficient double loss mechanism for ensuring a wideband higher-frequency microwave absorption. The unique laminated structure is benefit for multi-scattering and reflection, which can balance the low-/high-frequency broadband absorption. With 6 h ball milling, FePO4/CrPO4 hybrid layer covers FeSiCr flakes deliver effective absorption bandwidth (EAB) of 1.6 GHz covering 2.4–4.0 GHz (S-band) with 3.2 mm, EAB of 3.52 GHz covering 4.40–7.92 GHz (C-band) with 1.9 mm and EAB of 8.24 GHz covering 9.36–17.6 GHz (X+Ku band) with 1.1 mm. Generally, an easy pathway is provided in this work for developing ultra-wide microwave absorbers that balance low-/high- frequencies.

Nd-, La-induced precipitate/defect in cobalt-iron magnetic alloy for strong and broadband microwave absorption

Soft magnetic microwave absorbents have merits of sufficient magnetic loss and unique magnetism-frequency response characteristics, yet are limited by the low natural resonance frequencies and simplex loss mechanism. Introducing second phase has been proven to be efficient in evoking structure, magnetism and conductivity changes, but the effects on the microwave absorption is still unbeknown. In this work, the Co0.72Fe0.28 alloy magnetic absorbents with dispersedly distributed NdCo5/LaCo5 nano precipitates were prepared. By fine-tuning the doping ratios of the rare earth (RE) of Nd/La, the coercivity and conductivity show an upward trend with enhanced magnetic and dielectric losses on 2–18 GHz. On one hand, the high magneto-crystalline anisotropic RECo5 phases uplifted the holistic resonance frequency ranges and enhanced the C/X/Ku band attenuations. On the other hand, the as-spawn vacancies, heterogeneous interfaces and dislocations boosted the conductive/polarization losses of the individual magnetic alloys. As a result, the high-frequency performance was significantly improved when ensuring the impressive low-frequency loss. A remarkable minimum reflection loss (RLmin) of −76 dB was achieved in the S band, and the effective absorption bandwidth (EAB) of 7.34 GHz was obtained at only 1.7 mm, covering most of the X/Ku bands. The performance sets it apart as the highest among the reported RE-transitional alloy absorbents so far. Overall, this work provides a feasible way and novel strategy for improving the microwave absorption properties for the traditional metal alloys and their compounds.

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.

Lightweight Fe-doped MnO2@C hollow nanocubes for ultra-broadband microwave absorption

The rational structural design and compositional merits as well as the synergistic coupling effect can break the properties of single material and broaden the microwave absorption band. Herein, the unique lightweight Fe-doped MnO2@C hollow nanocubes are rationally designed and successfully synthesized via a scalable wet chemical process and polydopamine coating followed by high-temperature calcination. By virtue of the unique structure and compositional merits, the as-obtained Fe-doped MnO2@C hollow nanocubes (Fe–MnO2@C-HNBs) displayed notable microwave absorption performance (MAP), simultaneously achieving ultra-broad absorption bandwidth and strong absorption characteristics at a low thickness of 2.3 mm (the reflection loss of −41.02 dB and the effective absorption bandwidth of 5.86 GHz). Surprisingly, the effective absorption bandwidth (RL < −10 dB) could reach up to 8.08 GHz and the minimum reflection loss (RLmin) was −38.20 dB at the thickness of 2.7 mm. The results further confirmed that the excellent microwave attenuation ability of the as-prepared Fe–MnO2@C-HNBs composites benefitted from the special “air@core-shell” structure and multiple heterointerfaces as well as multi-component recombination. These results demonstrated that the as-obtained Fe–MnO2@C-HNBs composites could be attractive candidates for broadband microwave absorption materials.

Lightweight titanium dioxide/carbon nanotube composites prepared by atomic layer deposition for broad-band microwave absorption

The microwave absorbing material with appropriate impedance matching and excellent attenuation ability can be applied to resist electromagnetic radiation. In this work, carbon nanotubes were modified by titanium dioxide via the atomic layer deposition method, to prepare lightweight composites with high microwave absorption performance. The impedance matching and attenuation ability of titanium dioxide/carbon nanotube (TiO2/CNT) composites could be precisely controlled by adjusting the number of titanium dioxide deposition cycles. The relationship between the microstructure and microwave absorption performance of the composite was analyzed in detail. When the number of TiO2 deposition cycles was 100, the composite displayed outstanding microwave absorption performance, due to appropriate impedance matching and strong attenuation ability. The maximum effective absorption bandwidth of the composite reached 5.19 GHz (1.6 mm), which almost covered the Ku band. The microwave attenuation mechanism of the composite has also been investigated. This work provided a new idea for fabricating lightweight microwave absorption materials.