Microwave Absorption Mechanism Research Articles

Preparation and performance of ultra-wideband high-temperature resistant calcium aluminate cement-based electromagnetic wave absorption cone structural composites

A novel high-temperature resistant calcium aluminate cement-based electromagnetic wave absorption composites were prepared using carbon fibers, Al2O3 hollow spheres, and expanded polystyrene spheres (EPS). EPS, as a pore forming agent, was oxidized as to form pores at high temperatures. The effects of carbon fibers doping levels and various high-temperature treatment on the permittivity of the composites from 0.3-18 GHz were investigated in detail. Additionally, a high-temperature resistant porous cone cement-based electromagnetic wave absorption structure was designed, and its microwave absorption mechanism was explored. The findings indicated that the permittivity of electromagnetic wave absorption composites exhibited stability even after undergoing high-temperature treatments below 350°C, while experiencing a decrease at 500°C. Following cyclic treatments at temperatures of 200°C and 350°C, the cone calcium aluminate porous cement-based composites still exhibited outstanding electromagnetic wave absorption performance, achieving reflection loss (RL) bandwidths below -30 dB of 17.4 GHz and 17.2 GHz, respectively, within the frequency range of 0.3-18 GHz. Furthermore, the RL of the composite from 4-18 GHz after 500°C treatment remained less than -50 dB. Thus, present work associated with the materials and structural design of calcium aluminate porous cone cement-based composites provided a potential insight into the high-temperature electromagnetic wave absorption engineering applications.

Construction of ZIF/CS and ZIF/CS-derivatives with high-efficiency adsorption for dyes/antibiotics and strong microwave absorption performance

Bimetallic Zn/Co-ZIF was in situ loaded onto the surface of chitosan (CS) to form ZIF/CS composites with high-efficiency adsorption of antibiotics (tetracycline (TC)) and dyes (Congo Red (CR), Malachite Green (MG)). The particle size and surface roughness of Zn/Co-ZIF can be effectively adjusted by changing the mass ratio of Zn and Co in ZIF, which helps to regulate the adsorption active sites on the surface of the composites. Meanwhile, the introduction of CS changes the pore structure of the composites, making the molecules of TC, CR and MG easily enter into the pores of ZIF/CS. When the mass ratio of Zn to Co is 1:1, the ZIF/CS composite has the optimal adsorption performance with the ultra-high adsorption capacity qm of 781.3, 1644.2 and 3243.6 mg g−1 for TC, CR and MG, respectively. Impressively, the ZIF/CS-derivative (ZC3–700) from sample ZC3 after calcination at 700 °C under N2 atmosphere owns a good conductive network, which results in its superior microwave absorption performance. Herein, at 30 wt% filler loading, the effective absorption bandwidth and RLmin of ZC3–700 reach 5.28 GHz at 1.90 mm and −68.92 dB at 1.83 mm, respectively. Analyses on microwave absorption mechanism point out the synergistic effect of conduction loss, dipolar polarization and interfacial polarization and magnetic loss on the attenuation of electromagnetic wave. Therefore, ZIF/CS composites and ZIF/CS-derivatives exhibit superior performance on the removal of water pollutants and the absorption of electromagnetic wave, which essentially reveals a multifunctional application of the ZIF/CS composites in the field of environmental protect.

Optimizing microwave energy utilization & heating efficiency: Comparative analysis of susceptor materials for enhanced microwave absorption performance

Susceptors are vital components in microwave heating systems, ensuring efficient, selective, and uniform heating while improving both energy utilization and time effectiveness in various microwave processing applications. The present investigation underlines the microwave absorption performance of various silicon carbide (SiC) susceptors during microwave hybrid heating. The current study also explores methods, including theoretical analysis, simulations, and experiments, to identify most suitable SiC susceptor materials for efficient microwave heating (high microwave absorbing and energy utilization efficiency). Among all susceptor materials, porous nitride-bonded SiC exhibited combination of high properties including permittivity (9.64), loss tangent (0.268), reflection loss (−13.32 dB) and attenuation constant (21.12 Np/m) when microwave heating carried at 1.2 kW, 900 s. Porous nitride-bonded SiC susceptor emerged as optimal choice for most appropriate susceptor material on the basis of theoretical analysis (reflection loss, impedance, microwave attenuation constant, dielectric properties) as compared to other susceptors. The microwave absorption mechanism of various SiC susceptor materials have been established and summarized. The microwave heating behaviour of various SiC susceptors with different compositions were analysed using COMSOL simulations. A higher microwave utilization efficiency was observed by COMSOL simulation for the porous nitride-bonded SiC (95 %) susceptor than dense nitride-bonded SiC (78 %), dense SiC (69 %) and dense oxide-bonded SiC (58 %). The excellent microwave absorption capability of porous nitride-bonded SiC susceptor can be ascribed to synergistic efforts of various polarization mechanisms: dipole polarization, interfacial polarization, multiple reflections and scatterings, defect-induced dipole polarization and conductive loss.

Like-hydrangea Fe3O4@MoS2 composites towards high-efficiency electromagnetic wave absorption

Presently, electromagnetic wave absorbing materials are rapidly developing towards the direction with thin, light, wide, and strong characteristics. Based on this target, the like-hydrangea Fe3O4@MoS2 composites were synthesized using facile hydrothermal technology. In this work, the effect of molar ratio between MoS2 and Fe3O4 as well as micro-morphology on electromagnetic wave absorption properties was discussed emphatically. As a result, when the molar ratio was 1:2 and match thickness of sample was 2.5 mm, the minimum reflection loss (RLmin) achieved −96.77 dB at 10.64 GHz. At the same time, the effective absorption bandwidth (EAB) was 10 GHz ranging from 7.6 to 17.6 GHz. In final, the microwave absorption mechanisms of like-hydrangea Fe3O4@MoS2 composites were proposed.

Microwave absorption properties and mechanism analyses of core-shell structured high-entropy oxides coated with PPy

For HEO@PPy composites, there are mainly eddy current loss and hysteresis loss in the high-entropy oxides. For the effect on the magnetic loss performance, it is weakening for Fe, Ni, and Co successively. The composite of HEO(1)-FeNi@PPy has the largest reflection loss with a minimum RL value of −32.04 dB and an effective absorption bandwidth of 5.8 GHz, and the corresponding thicknesses are almost the same, which enables the optimization of both parameters simultaneously. The sample also has the optimal waveband-thickness absorption characteristics. A reciprocal relationship was found between magnetic loss and dielectric loss. By incorporating the HEO(1)-FeNi@PPy powder into paraffin, it was found that the greater the amount of powder material, the higher the electric conduction loss and polarization loss, and the magnetic loss would decrease. The microwave frequency f was found to be the main variable affecting the magnetic permeability and dielectric constant.

Fabrication of nitrogen-doped reduced graphene oxide/tricobalt tetraoxide composite aerogels with high efficiency, broadband microwave absorption, and good compression recovery performance

The fabrication of advanced graphene-based microwave absorbing materials with thin thickness, wide bandwidth, strong absorption strength, and low filling ratio remains a huge challenge. In this paper, nitrogen-doped reduced graphene oxide/tricobalt tetraoxide (NRGO/Co3O4) composite aerogels were synthesized by a three-step method of solvothermal reaction, high-temperature calcination, and hydrothermal self-assembly. The results showed that the attained NRGO/Co3O4 composite aerogels had a unique three-dimensional porous network structure, extremely low bulk density, and good compression recovery. Furthermore, the effect of the addition amounts of flower-like Co3O4 on the complex dielectric constant and microwave absorption properties of NRGO/Co3O4 composite aerogels was investigated. When the addition amount of Co3O4 was equal to 15 mg, the prepared binary composite aerogel showed the strongest absorption strength of –62.78 dB and a wide absorption bandwidth of 5.5 GHz at a thin thickness of 2.13 mm and a low filling ratio of 15 wt.%. It was worth noting that the maximum absorption bandwidth could reach 6.32 GHz (11.68–18 GHz, spanning the entire Ku-band) at a thickness of 2.24 mm. In addition, the possible microwave absorption mechanism of NRGO/Co3O4 composite aerogels was also proposed. Therefore, this paper will provide a new and simple strategy for preparing RGO-based porous nanocomposites as lightweight, efficient, and broadband microwave absorbers.

Recent progress in carbon-based materials and loss mechanisms for electromagnetic wave absorption

The burgeoning advancement of electronic technology and wireless communications has opened up an unprecedented era of electromagnetic wave applications, but the accompanying issues of electromagnetic pollution are equally deserving of profound attention. In recent years, a variety of novel electromagnetic absorbers have been ingeniously designed and actively emerged, among which carbon-based materials have become one of the most promising alternatives for next-generation electromagnetic functional materials, owing to the low density, tunable electrical properties, high stability, and chemical tolerance. This article comprehensively reviews the current research status and frontier science of carbon-based absorbing materials serving in microwave frequency band, and discusses in detail the microwave absorption mechanisms of various carbon-based systems as well as the critical factors affecting microwave attenuation. Furthermore, strategies to optimize microwave absorption performance of carbon-based materials through component design, structural modification, morphology modulation, and composite approaches will be discussed, with particular emphasis on their intrinsic correlation with magnetic-dielectric loss characteristics. Finally, the urgent requirements for improving carbon-based absorbing materials and insights into future development are provided, covering from material design to performance optimization to device-based applications. This review endeavors to support valuable references for research on carbon-based microwave absorbing materials and to stimulate further innovative thinking.

Kapok derived microtubular FeCo/CMT with high specific surface area for broadband microwave absorption

Since biomass-derived carbon materials possess the advantages of peculiar morphology and low density. They have received significant attention on microwave absorption materials. We synthesize a one-dimensional hollow FeCo/carbon microtubule (FeCo/CMT) derived from homogeneous kapok fiber using a feasible solvothermal method and calcination process. The graphitization degree and magnetic properties of FeCo/CMT could be controlled by manipulating the calcination temperature. The FeCo/CMT composite with the calcination temperature of 600 °C demonstrated exceptional microwave absorption performance, characterized by strong absorption (−50.6 dB), broadband absorption (12.4–18.0 GHz), thin thickness (2.5 mm), and low loading (10 wt%). The hollow structure, interfacial polarization, and the synergistic effect between FeCo and CMT collectively account for the microwave absorption mechanisms. Considering its outstanding comprehensive characteristics and performance, the biomass-derived hollow FeCo/CMT shows great potential for widespread application as a high-performance microwave absorption material.

Assembling of the novel Sm2O3@Co magnetic composites for highly efficient electromagnetic wave absorption

Magnetic metals have attracted extensive attention in microwave absorption for comprehensive merits of high magnetic loss and suitability for mass productions. Nevertheless, the applications have been limited by shortcomings of high conductivity and inadequate impedance matching. In this study, we have successfully synthesized a biphasic magnetic Sm2O3@Co composite through a facile one-step precipitation method. The resultant features a well-designed structure with spherical cores and flaky shells, exhibiting highly-tunable absorption performance over 2–18 GHz. Particularly, under 20 wt% filling ratio with paraffin, the Sm2O3@Co composite achieved minimum reflection loss (RLmin) of −30.1 dB and effective absorbing bandwidth (EAB) of 6.22 GHz at only 1.7 mm. The dielectric and magnetic losses could be easily modulated by simply changing the induced Co ratios. Through a systematic study, the microwave absorption mechanisms of the Sm2O3@Co magnetic composite have been comprehensively elucidated. This research offers a fresh perspective on developing highly efficient electromagnetic wave absorbents based on traditional magnetic metals.

Ni1−xZnxFe2O4/coal-based carbon composites with tunable electromagnetic wave absorption properties prepared with microwave irradiation and hydrothermal reaction

A simple hydrothermal method combined with microwave irradiation was used to synthesize nickel-zinc ferrite/coal-based carbon (Ni1−xZnxFe2O4/CBC) composites. The influences of Zn2+ concentration on the magnetism and microwave absorption characteristics of Ni1−xZnxFe2O4/coal-based carbon composites were examined. The Ni1−xZnxFe2O4 particles were equally anchored on the coal-based carbon within the Ni1−xZnxFe2O4/CBC composites. The dielectric and magnetism characteristics of Ni1−xZnxFe2O4/CBC composites can be improved simultaneously by adjusting the Zn2+ concentration. The minimum reflection loss (RLmin) for the sample at x = 0.4 is −65.5 dB for a thickness of 4.0 mm. The samples also have typical soft magnetic properties. Furthermore, some possible mechanisms of microwave absorption are investigated. Our Ni1−xZnxFe2O4/CBC composites show great potential for microwave absorption applications.

Phase-incorporation-induced electromagnetic coupling of NFS@1T/2H–MoS2 for enhanced microwave absorption

Herein, we propose a combination strategy to induce robust room-temperature electromagnetic coupling in non-magnetic MoS2 semiconductor (2H–MoS2). The introduction of ascorbic acid (AA) is intended to introduce sulfur vacancies (sv) in the process of 2H–MoS2 nano-sheet shells coating on the surface of three-dimensional (3D) matrix. It promotes the transformation of local lattice (2H–MoS2) into metal phase (1T-MoS2). The transformed 1T-MoS2 phase improves the conductivity (σ) of the composite by 1.48 times. Due to the Mo4+4d energy state within the bandgap, the exchange interaction between the sv and the Mo4+4d bandgap state produces a robust intrinsic electromagnetic response of more than 1.2 emu/g. Density functional theory (DFT) calculations are used to analyze the above results, and a novel electromagnetic-coupling-enhanced microwave absorption mechanism is proposed. The results indicates that microwave absorption performance can be effectively improved by the phase-incorporation effect. The minimum reflection loss (RLmin) reaches −53.1 dB (1.7 mm) and the adjustable effective absorption bandwidth (EAB) covers 14.5 GHz (3.5–18 GHz) at the various matching thicknesses. This work might shed light on a new possibility of manipulating electromagnetic interaction to promote microwave absorption.

Hafnium boride whiskers prepared by boro/carbothermal reduction for high-performance electromagnetic wave absorption

In this study, a chloride-assisted boro/carbothermal reduction method was employed to prepare HfB2 whiskers, aiming to address the challenges associated with large-scale preparation of HfB2 whiskers and the development of high-temperature resistant electromagnetic wave absorbing materials. When the precursors were mechanically stirred, the resulting mixture underwent calcination at 1450 °C for 3 h, leading to the formation of single-phase HfB2 whiskers. The as-synthesized HfB2 whiskers showed exceptional resistance to oxidation at temperatures up to 700 °C. The microwave absorption performance and mechanism of the HfB2 whiskers/paraffin composite were also investigated. The results revealed that the composite achieved a minimum reflection loss of −41.29 dB when the HfB2 whiskers content reached 80 wt%, while the widest effective absorption bandwidth of the composite reached 3.6 GHz when the HfB2 whiskers content increased to 82.5 wt%. This work presents a novel candidate for high-temperature resistant materials used in absorbing electromagnetic wave.

Spongy ternary nano-composites with optimized impedance matching and synergistic effect for broadband and strong microwave absorption

To counter the negative effects of electromagnetic radiation on the immunity of precision instruments, the stealthiness of military equipment, and human health, the preparation of porous multi-component nano-composites is considered an effective strategy to obtain efficient microwave absorption. In this work, the spongy ternary nano-composites (STC) with large specific surface area (SSA) and pore volume obtained by adjusting the calcination temperature, the porous effectively improves the impedance matching. The ternary composition of FeCo/Fe0.45Ni0.55/C, large SSA and pore volume provide abundant specific surface/interface for polarization and magnetization, the continuous conductive network is established, the strong dielectric and magnetic loss achieve a synergistic effect, realizing strong absorption in the low-frequency, greatly reducing the minimum reflection loss (RLmin, −56.37 dB) and broadening the effective absorption bandwidth (EAB, 7.45 GHz). The microwave absorption mechanism has been analyzed in detail and its great potential for practical applications has been verified by RCS signal simulations. This research provides an effective method for fabricating high-performance ternary nano-composite microwave absorbers.

The novel Co-doped MoO3 microwave absorber prepared by heat treatment

The Co doped α-MoO3 microwave absorbers were prepared by heat treatment technology. The oxygen vacancy, conductivity, and electromagnetic (EM) parameters of the material could be manipulated by changing the heat treatment temperature. The microwave absorption mechanism was explored. X-ray diffraction, Raman, scanning electron microscopy, x-ray photoelectron spectroscopy, and vector network analyzer were used to characterize the Co-doped α-MoO3 samples. The orthorhombic phases and scale-layer rod-like structure were observed to favor absorption via multiple transmission paths to EM waves. Notably, the material prepared by heat treatment at 500 °C exhibits a synergistic effect of magnetic and dielectric loss, due to its proper conductivity, rich interfaces and magnetism. The effective absorption bandwidth reaches 2.4 GHz.

Recent progress on the electromagnetic wave absorption of one-dimensional carbon-based nanomaterials

The rapid development of electronic information technology and the use of high-power electrical equipment have led to the increasingly serious problem of electromagnetic interference (EMI). Therefore, it is of great significance to study electromagnetic wave absorbing (EWA) materials with good absorbing properties. Compared with other wave absorbing materials, carbon-based nanomaterials such as silicon carbide (SiC), carbon nanotube (CNT), carbon nanowire (CNW) and carbon nanofiber (CNF) have the advantages of low density, large specific surface area/aspect ratio and excellent dielectric properties, which make them stand out. However, impedance mismatch caused by high conductivity and a single microwave loss mechanism seriously affect the absorption performance. In order to overcome the above shortcomings, surface modification, component control, structural design and other methods have been widely used in EWA materials in recent years to improve their absorption performance. In this review, we introduce the mechanism of microwave absorption and summarizes the research progress of one-dimensional carbon based nanomaterials and their composites. The preparation methods and microwave absorption properties of one-dimensional carbon based nanocomposites with different components, morphologies, and microstructures were discussed in detail. Finally, the challenges and future development prospects of one-dimensional carbon based nanomaterials were summarized, providing reference for the development of high-performance microwave absorbing materials.

Three-dimensional RGO/CNTs/GDY assembled microsphere: Bridging-induced electron transport enhanced microwave absorbing mechanism

As a new type of carbon allotrope, graphdiyne (GDY) is a promising material with highly conjugated conductive structure and excellent chemical stability. This indicates the great potential of GDY as a microwave absorbing material. Herein, we realize the simple one-step assembly of zero-dimensional GDY particles, one-dimensional carbon nanotubes (CNTs) and two-dimensional reduced graphene oxide (RGO) through ultrasonic spray method and carbonization technology, and obtained RGO/CNTs/GDY microspheres (RCG) with three-dimensional porous structure. CNTs can bridge RGO and GDY, forming a complete conductive network and providing pathways for electron migration. Benefiting from the unique three-dimensional assembly structure, high specific surface area, suitable impedance matching and strong dissipation ability, RCG shows excellent microwave absorption performance. By adjusting the assembly ratio and optimizing the filler loading, RCG-2 (RGO: CNTs: GDY = 4:1.5:1, 17.5%) with outstanding microwave absorption properties is obtained. The minimum reflection loss (RLmin) reached −51.8 dB at the matching thickness of 1.6 mm and the maximum effective absorption bandwidth (EAB) covered 5.4 GHz. The novel loss mechanism of bridge-induced electron transfer enhanced microwave absorption is proposed. It provides a new way to manufacture advanced microwave absorbers.

One-dimensional core–shell CoC@CoFe/C@PPy composites for high-efficiency microwave absorption

In recent years, electromagnetic pollution has become more and more serious, and there is an urgent need for microwave absorbing materials with superior performance. Prussian blue analogue (PBA) is a metal organic framework material with the advantages of diverse morphology and tunable composition. Therefore, PBA has attracted a lot of attention in the field of microwave absorption. In this work, PBA was coated on the surface of carbon composites by hydrothermal method, and then PPy was compounded on its surface after carbonization treatment to construct hierarchical core–shell CoC@CoFe/C@PPy fibers. The fibers have Co-doped C composites as the core and CoFe/C decorated with PPy as the shell. This unique hierarchical structure and various microwave absorption mechanisms are described in detail. The microwave absorption performance is optimized by adjusting the filling of the sample. The best microwave absorption performances are achieved at 25 wt% filling of CoC@CoFe/C@PPy. At a thickness of just 1.69 mm, CoC@CoFe/C@PPy fiebrs have a minimum reflection loss (RLmin) of −64.32 dB. When the thickness is 1.88 mm, CoC@CoFe/C@PPy achieves a maximum effective absorption bandwidth (EABmax) of 5.38 GHz. The results indicate that the CoC@CoFe/C@PPy composite fibers have a great potential in the field of microwave absorption.

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.