Microwave Absorption Mechanism Research Articles

Rational construction of magnetic core-shell structural carbon Nanotubes@Mesoporous N-doped carbon nanofibers for efficient microwave absorption

Magnetic core-shell structural mesoporous carbon materials have an extensive application prospect in microwave absorption because of their comprehensive merits of magnetic function and distinctive mesoporous structure. Herein, magnetic core-shell structural carbon nanotubes@mesoporous N-doped carbon (CoNi/CNTs@mesoNC) nanofibers are successfully fabricated by combining homogeneous coating of mesoporous polydopamine, surface deposition of CoNi-bimetal metal-organic frameworks (MOFs), and in-situ growth of CNTs and CoNi nanoparticles. The resultant CoNi/CNTs@mesoNC nanofibers possess a well-defined hierarchical structure consisting of CNTs core and mesoporous carbon shell distributed with short CNTs and CoNi nanoparticles, high surface area (∼316 m2 g−1), high nitrogen content (∼5.5 wt%), and large pore size (∼10 nm). As expected, the rational design of multifunctional components and hierarchical structure endows CoNi/CNTs@mesoNC composites with excellent microwave absorption performance. Particularly, the minimum reflection loss can reach −52.1 dB at 13.4 GHz with only 1.7 mm thickness and the corresponding effective absorption bandwidth is up to 5.2 GHz (12.8–18.0 GHz), outperforming most reported microwave absorbing materials. The microwave absorption mechanism of this material has been deeply investigated and systematically clarified. This work provides meaningful reference for the design and fabrication of functional core-shell microwave absorbers with distinctive mesoporous structure.

NiFe2O4/coal-based carbon composites with magnetic properties and microwave absorption capacity prepared through microwave radiation and hydrothermal reaction

Nickel ferrite/coal-based carbon (NiFe2O4/CBC) composites were synthesized by using microwave irradiation and simple hydrothermal method. The effects of reaction conditions on particle size, morphology, magnetic, and microwave absorption properties of the NiFe2O4/CBC composites were systematically studied. In all NiFe2O4/CBC composites, NiFe2O4 microspheres with different shapes and sizes were anchored on the surface of CBC. By adjusting size of the NiFe2O4 particles, dielectric and magnetic properties of the NiFe2O4/CBC composites could be optimized simultaneously. For the NiFe2O4/CBC sample with the average particle size of NiFe2O4 to be 4.69 nm, when the thickness was 4.42 mm, the minimum reflection loss (RLmin) could reach − 63.15 dB at 9.89 GHz. Meanwhile, the maximum effective absorption bandwidth (EABmax) was 4.91 GHz (6.31–11.22 GHz) at a thickness of 5 mm, which almost covered the whole X-band. The s-shaped hysteresis loop of the sample revealed that it had typical superparamagnetic characteristics. The possible mechanism of microwave absorption was also discussed. Our NiFe2O4/CBC composites could be used as a new and efficient microwave absorption material.

Hierarchical and Orderly Surface Conductive Networks in Yolk-Shell Fe3 O4 @C@Co/N-Doped C Microspheres for Enhanced Microwave Absorption.

Constructing the adjustable surface conductive networks is an innovation that can achieve a balance between enhanced attenuation and impedance mismatch according to the microwave absorption mechanism. However, the traditional design strategies remain significant challenges in terms of rational selection and controlled growth of conductive components. Herein, a hierarchical construction strategy and quantitative construction technique are employed to introduce conductive metal-organic frameworks (MOFs) derivatives in the classic yolk-shell structure composed of electromagnetic components and the cavity for remarkable optimized performance. Specifically, the surface conductive networks obtained by carbonized ZIF-67 quantitative construction, together with the Fe3 O4 magnetic core and dielectric carbon layer linked by the cavity, achieve the cooperative enhancement of impedance matching optimization and synergistic attenuation in the Fe3 O4 @C@Co/N-Doped C (FCCNC) absorber. This interesting design is further verified by experimental results and simulation calculations. The products FCCNC-2 yield a distinguished minimum reflection loss of -66.39dB and an exceptional effective absorption bandwidthof 6.49GHz, indicating that moderate conduction excited via hierarchical and quantitative design can maximize the absorption capability. Furthermore, the proposed versatile methodology of surface assembly paves a new avenue to maximize beneficial conduction effect and manipulate microwave attenuation in MOFs derivatives.

Ion-exchange reaction construction of carbon nanotube-modified CoNi@MoO2/C composite for ultra-intense and broad electromagnetic wave absorption

Structural design and composition adjustment are promising approaches for the preparation of lightweight absorbers with high absorption performance and low matching thickness. In this work, a carbon nanotube-modified CoNi@MoO2/C composite was synthesized by ion-exchange, in-situ growth, and pyrolysis methods. For the synthesized CoNi@CNTs@ MoO2/C composite, the minimum reflection loss value (RLmin) was −63.2 dB at a thickness of 2.3 mm, and the effective absorption bandwidth reached 8.8 GHz (9.2–18 GHz) at a thickness of 2.5 mm. The potential microwave absorption mechanism is attributed to the synergistic effects of polarization relaxation, electron transmission, ferromagnetic resonance, as well as multiple reflections and scattering in the hierarchical nanocomposite. In addition, the radar cross-section (RCS) attenuation was calculated via HFSS to analyze the EMW absorption capacity in the actual far field. The RCS reduction was 36 dB m2 for a scattering angle of 0°. Overall, this work provides theoretical support for the controlled growth of metal-catalyzed CNTs and presents an effective guide for optimizing the electromagnetic and absorption performances of MA materials.

Effects of Gd doping on microwave absorption properties and mechanism for CaMnO3 perovskites

ABO3 type perovskite oxides have been widely studied due to their unique structure and special electromagnetic properties. CaMnO3 is well known for its excellent thermoelectric performance and temperature stability. In this paper, Ca1-xGdxMnO3 (x = 0, 0.1, 0.2, 0.3, 0.4) perovskites were comprehensively studied by first-principles calculations and experimental characterizations on their crystal structure and electromagnetic properties to finally elaborate the microwave absorption mechanism. It is found that Gd doping significantly enhances the dielectric polarization effects, resulting in better electromagnetic wave absorption performance than undoped CaMnO3. Especially for CG2MO perovskite, its reflection loss and bandwidth below −10 dB at 2–18 GHz reaches −31.9 dB and 3.3 GHz approximately, exhibiting excellent microwave absorption property. Moreover, the microwave absorption mechanism of CGMO perovskites involves various modes of conductive loss, resonance loss, multiple reflection and scattering as well as the polarization phenomenon including interfacial polarization, dipole polarization and defect polarization. Among them, polarization effects and conductive loss contributes the most to the microwave absorption performance.

Three dimensional carbon aerogel for microwave absorption from chitosan

3D carbon aerogel is widely used for the fabrication of microwave absorption materials as it is characterized by tunable dielectric properties, ultra-low density, high porosity, and ultra-large specific surface area. We synthesize phenolic aerogels using chitosan as a soft template, phenol and formaldehyde as carbon sources, and acetic acid as a catalyst. We explore the influence of the carbonization temperature on the materials' microstructure, chemical composition, and absorption performance. We also study the mechanism of microwave absorption. The results revealed that carbonized carbon aerogel is characterized by a typical porous structure and a large specific surface area. It was also observed that the degree of carbonization improved with an increase in the carbonization temperature. The minimum reflection loss for the carbon aerogel (carbonized at 700 °C) with a filler loading of 15 wt % is recorded to be −41 dB at 12.24 GHz. The effective absorption bandwidth can reach 5.24 GH at 2.5 mm. The minimum reflection loss for the carbon aerogel (carbonized at 750 °C) with a filler loading of 8 wt % was −36 dB at 13.12 GHz. Under these conditions, the effective absorption bandwidth can reach 4.88 GH. When the thickness is only 1.5 mm, the minimum reflection loss is −14 dB, and the effective bandwidth can reach 4.2 GHz. The fine absorption performance can be attributed to the excellent dielectric constant of the material and the property of impedance matching. The results indicate that the synthesized lightweight and efficient carbon can promote the development and application of microwave-absorbing materials.

Preparation of microcrystalline graphite/zinc ferrite composites with enhanced and tunable electromagnetic wave absorption using a high-temperature ball milling method

Microcrystalline graphite (MG)/zinc ferrite (ZFO) composites were prepared by a high-temperature ball milling method. The magnetic and microwave absorption properties of MG/ZFO composites were analyzed in the frequency range of 2.0–18.0 GHz. The results showed that MG has a favorable impact on the microwave absorption capacity of ZFO. The composites containing 10 wt% MG had a minimum reflection loss of −62.90 dB, which is almost a factor of 12 higher than for pure ZFO, and their effective absorption bandwidth (EAB, RL<−10 dB) covers frequency range of 5.84–7.92 GHz for a matching thickness of 3.9 mm, and for a matching thickness of 1.8 mm, the EAB covers frequency range of 12.87–17.70 GHz. A probable mechanism of microwave absorption for MG/ZFO composites is based on a synergistic combination of dielectric and magnetic losses. The attractive properties of prepared composites indicate that they are promising and competitive materials for use in microwave absorption.

MnFe2O4/ rGO/Diatomite composites with excellent wideband electromagnetic microwave absorption

Electromagnetic interference has become one urgent problem in the current society. Efficient preparation of materials with excellent electromagnetic wave absorption is challenging but urgently needed. In this work, MnFe2O4/rGO/Diatomite (M/rGO/DT) cladding structure composites were prepared using a direct, one-step hydrothermal technique. The ternary composite has many microwave absorption mechanisms, including interfacial dipole polarization, conductive loss, natural resonance, flux loss, huge kudos to the three-dimensional cladding cross-linked structure and close-packed MnFe2O4 particles. As a result, compared with unitary or binary composites this ternary composite offers superior capabilities in low and medium frequency microwave absorption. The composite's minimum reflection loss (RLmin) is − 76.56 dB at 7.9 GHz, its thickness is 2.485 mm, and its effective absorption bandwidth (EAB) is up to 3.61 GHz. The remarkable electromagnetic wave attenuation ability of the generated ternary composite shows that the work in this research may provide an innovative and simple technique for the preparation of superior microwave absorbing materials (MAMs).

Comparison of the microwave absorption performance of core–shell SiO2@C and hollow carbon nanospheres with different sizes

Microwave absorption performance and mechanisms of core–shell SiO2@C and hollow carbon nanospheres with different sizes.

In situ synthesis of Fe3O4 coated on iron-based magnetic microwave absorbing materials and the influence of oxide magnetic materials on microwave absorption mechanism

Fe3O4 coated iron-based magnetic microwave absorbing materials were prepared by heat treatment in controllable oxygen atmosphere. The obtained core-shell microstructure improved the absorbing properties by enhancing the dielectric loss capability and optimizing the impedance matching. The effective absorption bandwidth (nearly reach -20 dB) of the composite material covers 3-18 GHz by adjusting the coating thickness from 1.5∼5.0 mm. The shell Fe3O4 improves the microwave absorbing properties and broadens the effective absorption frequency band of the iron-based material. In addition, the oxide layer improves the stability and environmental adaptability of the iron-based materials, which would provide reference idea for iron-based absorbing materials in industrial production.

Nanowires/nanohelices hybrid carbon aerogels as the lightweight and hydrophobic microwave absorbers with excellent electrothermal properties

To extend the operational life of electronic equipment under a complex environment and introduce protection for human health against electromagnetic pollution, it is urgent to construct lightweight microwave absorption materials (MAMs) with hydrophobicity and electrothermal properties. Herein, we have fabricated creatively the nanowires/nanohelices hybrid carbon (CNWs/CNHs) aerogels via growing and carbonizing nanohelices in bacterial cellulose (BC) matrix, forming intertwined and interconnected conductive network. In addition, we investigated systematically the detailed structure and microwave absorption mechanism of the new type of CNWs/CNHs aerogels. Such novel structure was found to promote multiple relaxation and interface polarization due to the electromagnetic cross polarization, which in turn ameliorates remarkably the microwave absorption intensity and broadens the effective absorption bandwidth (EAB). The optimal CNWs/CNHs aerogels can show an excellent microwave absorption intensity of −56.90 dB at 13.76 GHz at a filling content of 5 wt%, and extend its maximum EAB to 6.32 GHz at a thickness of just 2.00 mm. At the same time, the CNWs/CNHs aerogels also have a superior self-cleaning function and a good electrothermal conversion performance. Therefore, the CNWs/CNHs aerogels may be adopted as the lightweight and hydrophobic MAMs with excellent electrothermal properties to satisfy the practical applications in complex low-temperature environment.

Microwave Parameters of Components of Shielding Composites. Part 2: Mechanisms of Microwave Absorption

Microwave Parameters of Components of Shielding Composites. Part 2: Mechanisms of Microwave Absorption

Microstructure evolution and microwave absorbing properties of novel double-layered SiC reinforced SiO2 aerogel

In this paper, a novel double-layered SiC reinforced SiO2 aerogel (SSA) was successfully synthesized by a facile route. The porous double-layered SiC microstructure was constructed by chemical vapor deposition (CVD) technology, and SiO2 aerogel was introduced by sol-gel method to adjust the dielectric properties. The microstructures of the interconnected double-layered SiC structure remained intact after SSA formation. The porous SiO2 aerogel particles were filled between the double-layered SiC structure, and the stem segments of the double-layered SiC structure were wrapped by SiO2 aerogel. In addition, SiO2 aerogel spread into the hollow pores of the double-layered SiC, forming a large number of interfaces. As expected, SSA could be used as an absorber. The minimum reflection loss (RL) value of SSA achieved − 22.80 dB at 15.77 GHz at the thickness of 3.57 mm. The optimal effective absorption bandwidth (fE) of 6.8 GHz was recorded at a 4.0 mm absorber thickness. The absorber thickness of 3.5–5.0 mm was easy to obtain wider fE and smaller RL, which provided practical guidance for the application of SSA. Finally, the microwave absorbing mechanism of SSA was studied deeply. The importance of attenuation constant (α) was more significant than the impedance matching ratio (Zr) for the microwave absorption performance of SSA. The higher Zr ascertained that a large proportion of the electromagnetic waves entered the SSA absorber, and then the α supported the microwave absorbing mechanisms.

Tuning layer thickness and layer arrangement in a GdMnO3 and GdMnO3-MoSe2 bi-layer absorber to cover the S, C, and X band frequency range

The bi-layer absorber's microwave absorption performance can be enhanced by adjusting and manipulating the layers' composition, layer thickness, and layer arrangement. Herein, two magnetic and magneto-electric components, GdMnO3 (G) and GdMnO3-50 wt.% MoSe2 (GM), were prepared via a solvothermal method. In particular, the impact of filler loading and layer thickness on microwave absorption characteristics was examined. The findings indicate that a single-layer absorber sample containing G or GM components independently did not have good microwave absorption capability. On the other hand, a bi-layer absorber sample with G as the matching layer (1.5 mm thickness) and GM as the absorber (0.5 mm thickness) possesses exceptional -44 dB reflection loss with 9 GHz of effective absorption bandwidth, which covers S, C, and almost the whole X band frequency range. The optimal 3D network architecture of the G particles' rod-like morphology, which improves the impedance matching property, may be to blame for this phenomenon. Additionally, this special 3D network architecture gives an abundance of interfaces to disperse electromagnetic waves in addition to many channels for microwave reflecting and scattering. More crucially, the composites' microwave absorption mechanism is investigated and studied, which offers a trustworthy guide for making a bi-layer absorber.

A two-dimensional semiconductive Cu-S metal-organic framework for broadband microwave absorption

Electromagnetic radiation and pollution are urgent and crucial problems to be solved. Metal-organic framework (MOF) derivates play an important role in the attenuation of electromagnetic waves efficiently. However, limited by the complex pyrolysis process, the chemical composition and crystal structure of MOF were totally destroyed. Inspired by the electrical window (10−6–10 S·cm−1) of microwave absorption materials (MAMs), semiconductive MOF with precise crystal structure is potential to be an ideal microwave absorbent. This work reports a two-dimensional (2D) semiconductive MOF (Cu-S-MOF) as broadband high-performance MAMs. The effective absorption bandwidth (EAB) of the Cu-S-MOF can reach 6.72 GHz (9.68–16.4 GHz) at a thickness of 1.5 mm, and a minimum reflection loss (RLmin) value of −52.8 dB at 1.69 mm. Due to the absence of the pyrolysis process, a well-defined single-crystal structure of Cu-S-MOF can be obtained. A density functional theory (DFT) calculation was performed to illuminate the microwave absorption mechanism. Resistance loss and interfacial polarization loss between the Cu-S layers mainly contribute to the Cu-S-MOF MAMs. The semiconductive MOF towards MAMs provides a facile and effective strategy to tune microwave absorption performance, which can be applied in the electromagnetic protection field.

Recent research progress of carbon-based and their composites for electromagnetic waves absorption

With the rapid development of electromagnetic (EM) technology and the wide application of mobile electromagnetic equipment, electromagnetic radiation pollution is increasingly aggravated, electromagnetic pollution has become another pollution source after air, water, and noise pollution, so electromagnetic protection for civil and military is of great significance. As the functional medium of electromagnetic energy sustainable transformation, microwave absorption (MA) materials are widely used in electromagnetic pollution prevention and control. Carbon-based materials have the advantages of low density, light weight, good electrical conductivity, good physical and chemical stability, etc., which can be combined with magnetic loss type, dielectric loss type, and multi-component to improve the absorbing performance. According to the dimensions, carbon-based materials can be divided into zero-dimensional (carbon spheres), one-dimensional (carbon nanotubes), two-dimensional (graphene), and three-dimensional (porous carbon) carbon materials. This paper briefly introduces the mechanism of microwave absorption and its performance evaluation index. Then, the research status of carbon materials with different dimensions is introduced. Then the application and research progress of carbon matrix composites in electromagnetic waves (EMW) absorption are reviewed. Finally, the future development prospect of carbon-based absorbing materials has been prospected.

Constructing 3D Tent-Like frameworks in melamine hybrid foam for superior microwave absorption and thermal insulation

Taking serious electromagnetic pollution and practical application requirements into consideration, it’s imperative to develop multifunctional microwave absorption materials. In this work, the phenol–formaldehyde resin (PF) successfully adheres to melamine–formaldehyde foam (MF) as three-dimensional (3D) porous frameworks, and subsequently the substrate anchors few-layered MXene nanosheets by dripping-squeeze-drying procedures. According to the results, the hollow tent-like structure of MXene/PF@MF (MPM) shows a significant effect on microwave absorption capability, including extending heterogeneous interfaces for polarization relaxation and prolonging microwave propagation paths for energy dissipation. Based on the synergy of multiple components and rational structure, MPM exhibits a minimum reflection loss (RLmin) value of −58.8 dB at 2.2 mm and achieves an effective absorption bandwidth (EAB) of 6.74 GHz covering the entire Ku band. The microwave absorption mechanism reveals that the superior microwave absorption capability results from high conduction loss, polarization relaxation, multiple attenuations, and appropriate impedance matching. Furthermore, the MPMs possess lightweight features (32.7–48.7 g cm−3) and low thermal conductivity (0.0309–0.0318 W m−1 K−1) benefitting the unique 3D porous structure. Meanwhile, the low thermal conductivity endows MPMs with infrared stealth, which broadens the application in military fields. This work proposes a facile strategy for constructing highly efficient microwave absorbers with multiple functions.

Lightweight Chain-Typed Magnetic Fe3O4@rGO Composites with Enhanced Microwave-Absorption Properties.

A lightweight microwave-absorbing material with a strong electromagnetic-absorption capability of practical significance in the field of electromagnetic compatibility was obtained by adjusting the ratio of Fe3O4 and rGO. A nanoparticle material with a chain-typed structure consisting of a combination of Fe3O4 and rGO was produced by a hydrothermal method under an applied magnetic field. The electromagnetic loss property of the Fe3O4@rGO composites is studied in the frequency range from 2 to 18 GHz. In addition, the reflection loss and the mechanism of microwave absorption are explored. By changing the amounts of rGO, the electromagnetic loss of the Fe3O4@rGO composites can be effectively regulated, which obtain better reflection loss. The minimum reflection loss of the Fe3O4@rGO composites is −49.4 dB at 16.2 GHz only with a thickness of 1.75 mm. Thus, the Fe3O4@rGO composites have an extremely thin thickness and a strong electromagnetic wave absorption capacity, which is a candidate for the development of lightweight magnetic absorbing materials.

Effect of Particle Size and MWCNTs Content on Microwave Absorption Characteristics of Cobalt

In today’s ever-developing electronic world, tremendous efforts are being made to develop highly efficient microwave absorbing materials with thin thickness and broad bandwidth while maintaining a simple manufacturing procedure. Since so much study is devoted to structural and component designing of microwave absorbers, the mechanism of microwave absorption still has potential for improvement. It is critical to have fundamental mechanistic knowledge of microwave absorption by absorbing materials with diverse types of geometries and components. It is also important to explore the influence of different physical/chemical characteristics of absorbing materials on microwave absorption performance. The methodical and thorough examination of these issues may provide internal information on the interaction of the microwave absorber’s components and subsequent structural design. Therefore, in this article, by taking cobalt (Co) as the base material, an attempt has been made to comprehend the microwave absorption mechanism of Co milled at various times, which results in changes in particle size and morphology. A significant change in the microwave absorption of Co has been observed with changed morphology after milling. The enhancement in microwave absorption characteristic of milled Co with the addition of different wt% of multiwall carbon nanotubes (MWCNTs) has also been analyzed. MWCNTs in milled Co increase interfacial polarization and multiple reflections in the sample, resulting in microwave attenuation. The prepared Co/MWCNTs composite samples yielded excellent bandwidth with low coating thickness. The effective bandwidth of 10 GHz (3.73–13.73 GHz) was obtained for the composite of 20 h wet-milled Co and 2 wt% MWCNTs, with a coating thickness of 2.5 mm. To further enhance the microwave absorption bandwidth and reduce coating thickness, a genetic algorithm (GA)-assisted multi-layering approach has been implemented for designing triple-layer microwave absorbers. The optimized triple-layer result for combination 5W4–10W1–20W2 shows an effective bandwidth of 13.65 GHz (4.35–18 GHz), with an overall coating thickness of 2.31 mm.

Recent progress in MXene and graphene based nanocomposites for microwave absorption and electromagnetic interference shielding

There is widespread use of telecommunication and microwave technology in modern society, and raised the electromagnetic interference (EMI) issue to alarming situation due to apprehensive demand and growth of 5G technology undesirably disturbing the human health. The two dimensional (2D) materials including graphene and MXenes are already been used for variety of electronic devices due to their exceptional electrical, mechanical, optical, chemical, and thermal properties. MXene is composed of metal carbides, in which mainly metals are the building blocks for dielectrics, semiconductors, or semimetals. However, the strong interfaces with electromagnetic waves (EM) are variable from terahertz (THz) to gigahertz (GHz) frequency levels and are widely used in EMI and Microwave absorption (MA) for mobile networks and communication technologies. The use of different organic materials with metal, organic, inorganic fillers, polymers nanocomposite and MXene as a novel material has been studied to address the recent advancement and challenges in the microwave absorption mechanism of 2D materials and their nanocomposites. In this concern, various techniques and materials has been reported for the improvement of shielding effectiveness (SE), and theoretical aspects of EMI shielding performance, as well stability of 2D materials particularly MXene, graphene and its nanocomposites. Consequently, various materials including polymers, conducting polymers, and metal–organic frameworks (MOF) have also been discussed by introducing various strategies for improved MA and control of EMI shieling. Here in this comprehensive review, we summarized the recent developments on material synthesis and fabrication of MXene based nanocomposites for EMI shielding and MA. This research work is a comprehensive review majorly focuses on the fundamentals of EMI/MA. The recent developments and challenges of the MXene and graphene based various structures with different polymeric composites are described in a broader perspective.