Effective Microwave Absorption Research Articles

Grow defect-rich bamboo-like carbon nanotubes on carbon black for enhanced microwave absorption properties in X band

• By in-situ growing bamboo-like CNTs on CB, a developed conductive network was constructed and plentiful CB/CNT interfaces were introduced to improve the electromagnetic wave loss ability. • Defect-rich CNTs with open atomic edges can endow nanocarbons with a better balance between good impedance matching and strong loss capacity, causing an effective microwave absorption. • The minimum reflection loss and effective absorption bandwidth of CB-CNT with the CNTs growth time of 40 min reach to −53.6 dB and 4.1 GHz with the matching thickness of 2.7 mm, respectively. Due to the limited electromagnetic wave (EMW) loss capacity and agglomeration, carbon black (CB) gradually fails to meet the increasingly harsh demanding conditions. Herein, defect-rich bamboo-like carbon nanotubes (CNTs) were grown on CB by the process of chemical vapor deposition. CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces. What's more, the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching, thereby causing an effective microwave absorption (MA). Meanwhile, the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability. The influence of CNTs with different growth time on MA performance has been explored. Profiting from the structural merits, the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property, which has the minimum reflection loss of -53.6 dB and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm, covering almost the entire X band. The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB, which provides a rational strategy for the design of high-efficient microwave absorption materials.

Active metasurface microwave absorber with reconfigurable bandwidth and absorption intensity

In this paper, an active metasurface microwave absorber with reconfigurable bandwidth and absorption intensity is proposed. The metasurface unit adopts a metallic-backed structure, and its thickness is approximately 0.08 times the free-space wavelength. As the key feature, the structure with reconfigurable bandwidth and absorption intensity is adopting hollow Jerusalem-cross-shaped pattern-loaded PIN diodes. By virtue of the synergy of the dielectric and ohmic loss, effective and stable microwave absorption is readily achieved, and the simulation results obtained from high frequency structure simulator and advanced design system are in agreement. The reconfigurable absorption bandwidth of the metasurface covers C-band, X-band, and Ka-band, with reconfigurable absorption intensity up to 13 dB range. Then, the sample prototype is fabricated for demonstration, and the measurement result is consistent well with the simulation one. In addition, the structure also has a small reflection in a wide reflection angle space (−60°–60°), which is of great significance for radar stealth.

From waste to wealth: Crumb rubber@carbon nanotube/Fe3O4 composites towards highly effective electromagnetic microwave absorption with wide bandwidth

The reuse of the waste crumb rubber (CR) is of great significance to alleviate the increasingly serious black pollution problem. Herein, low-cost electromagnetic microwave absorption (EMA) CR composites assisted by conductive carbon nanotubes (CNTs) and magnetic Fe3O4 are fabricated with the aid of microwave. The effects of the addition of CNTs and Fe3O4 on the structure and morphology, and EMA properties of the CR@CNT/Fe3O4 composite are evaluated in detail. The resulted composite can exhibit a superior minimum reflection loss (RLmin) of −60.46 dB at 14.19 GHz with a thickness of 2.3 mm, and a wide effective absorption bandwidth of 5.5 GHz (11.2–16.7 GHz) due to the synergy effect of coordinated dielectric and magnetic losses, good interface impedance matching, and internal multiple reflections. This composite recycling from waste tire rubber is expected to become a potential candidate as a low-cost microwave absorber for reducing electromagnetic and black pollution.

Synthesis of super-hydrophobic and self-cleaning magnetic graphene aerogel with excellent microwave absorption properties

The well-established structure and ultra-fine nanoparticles are vital for high-performance microwave absorption materials. Herein, three-dimensional hydrophobic graphene aerogels decorated with ultra-fine Fe3O4 nanocrystals composites (HGAFX, X stands for pyrolysis temperature) were successfully constructed via chemically self-assembly and in situ pyrolysis. Remarkably, the hybrids with only 5% filling contents exhibited excellent microwave absorption performance (MAP) in terms of both minimum reflection loss (RLmin) and effective absorption bandwidth (EAB), outperforming the most reported microwave absorbers. Moreover, the magnetic graphene aerogels composites possess strong hydrophobicity, endowing them attractive functions of self-cleaning, waterproof, anti-icing, and corrosion resistance. Importantly, experimental results and theoretical calculations indicate that superior MAP can be carried out by reasonably regulating the electromagnetic parameters. Considering the excellent absorption capacities, our strategy opened a novel way for anchoring ultra-small nanoparticles on graphene sheets as highly effective synergistic microwave absorbers at low filling contents.

A facile molten salt synthesis route for a C/MoS2/Co9S8 complex with multiple heterogeneous interfaces and excellent dielectric and magnetic properties for effective microwave absorption

Electrical conductivity, interfacial polarization, and magnetic properties are key factors in designing efficient microwave absorbing (MA) materials. In this study, we report a one-step route to synthesize multicomponent C/MoS2/Co9S8 composite via the molten salt strategy (MSS) and systematically investigate the MA performance of the C/MoS2/Co9S8 composite. The excellent dielectric property is related to the conductive carbon network. In addition, magnetic Co9S8 improves the impedance matching performance of the composite. Abundant heterointerfaces, such as C/MoS2, C/Co9S8 and MoS2/Co9S8, exist in the C/MoS2/Co9S8 composite, which leads to a great interface polarization effect. The synergy of these factors results in the effective MA performance of the C/MoS2/Co9S8 composite. The results show that the EAB reached 6.0 GHz (12.0–18.0 GHz). In addition, the maximal MA performance of the C/MoS2/Co9S8 reached – 62.1 dB. This research expands the application of MSS in MA materials, especially the preparation of multicomponent MA composites.

Huygens’ Metasurface Based on Induced Magnetism: Enhance the Microwave Absorption Performance of Magnetic Coating

AbstractDespite great efforts in material design and modification, there are still obstacles to improve the effective microwave absorption, which hinders the development of stealth materials. By introducing a magnetically induced Huygens’ metasurface with Fibonacci spiral meta‐atom, a hierarchical absorber with carbonyl iron particle coating is designed and prepared, of which the total effective absorption bandwidth (EAB, reflection loss≤−10 dB) amazingly reaches 9.41 GHz, exceeding 199% of the original coatings', and the absorption peak value declines from−15.91 to−32.12 dB. The overall thickness of the absorber is 7 mm, only 0.17 over the minimum thickness dictated by the causality limit. A conceptual basis for the proposed design is provided, that is, the balance of effective surface current and magnetic current induced simultaneously will enhance the electromagnetic (EM) wave transmission, which contributes to broadening the absorption bandwidth with promising impedance matching. The system is validated numerically and experimentally, suggesting a novel route to obtain high‐performance microwave absorption materials for the EM stealth technology.

Ru doped magnetic nanoparticles embedded in mesoporous silica for effective microwave absorption by interface engineering and DFT calculations

Strong absorption, thin thickness, wide-bandwidth as well as lightweight of microwave absorption materials (MAMs) are highly desirable. In this study, the mesoporous silica skeleton embedded by FeRu/(Fe, Ru)3O4 magnetic nanoparticles (FR/FRO-mSiO2) were designed and fabricated by vacuum impregnation and reduction sintering methods. The minimum reflection loss (RLmin) of the FR/FRO-mSiO2 composite with a metal mass ratio of 46% was −61.1 dB at a thickness of 2.0 mm, and the covered absorption bandwidth (RL < −10 dB) reached 6.8 GHz. In combination of Density functional theory (DFT) calculation, microstructure characterizations and electromagnetic characteristics, we found that the interface polarization and magnetic enhancement at the interfaces of FeRu-(Fe, Ru)3O4, the local dipole moment, and the abundant propagation channels for the incident microwaves, endowed by the unique component and construction of FR/FRO-mSiO2, contributed together to the excellent microwave absorption capability of FR/FRO-mSiO2. This work provides a promising porous structure to broaden efficient bandwidth and strengthen microwave absorption intensity with lightweight.

Construction of Ni-based alloys decorated sucrose-derived carbon hybrid towards: effective microwave absorption application

Construction of Ni-based alloys decorated sucrose-derived carbon hybrid towards: effective microwave absorption application

Microwave absorption in epoxy composites filled with MoS2 and carbon nanotubes

In this study, the microwave absorbing properties of epoxy composites filled with micro-sized MoS2 and carbon nanotubes (CNT)/MoS2 were investigated in the frequency range of 1–67 GHz. Sample characterization was performed using electron microscopy and Raman spectroscopy methods. Direct current (DC) conductivity, complex permittivity, and shielding properties of composite materials with 50 wt. % of MoS2 and 1.5–2 wt. %CNT/50 wt.%MoS2 were measured. The permittivity of 50 wt. % MoS2/epoxy composite was found to be equal to 7.3, decreasing monotonically down to 4.5 at 67 GHz, while the imaginary part is equal to 1 and does not change. The addition of 2 wt. % of CNTs increases the real part of permittivity εr′ up to 30 at 1 GHz (13 at 67 GHz) and also leads to a large increase of the imaginary part of permittivity, with the most pronounced relaxation peak εr′′=10 at 10 GHz. Such an increase of dielectric loss correlates with the increase of DC conductivity up to 3.2 × 10−5 S/m as compared to the two-phase composite 50 wt. %MoS2/epoxy (σdc = 1.7 × 10−9 S/m). It was shown that 50 wt. %MoS2/epoxy composite exhibited an effective microwave absorption bandwidth of 9.9 GHz at the sample thickness of 2.0 mm with reflection loss minimum of -20.0 dB at 51.5 GHz. 2 wt. %CNT/50 wt. %MoS2/epoxy composite with a thickness of 0.9 mm showed a reflection loss minimum of −38 dB at 20.2 GHz with the absorption bandwidth of 3.68 GHz. The influence of sample thickness on position, width, and depth of EMR absorption maximums for the composites filled with MoS2 and mixed filler CNT/MoS2 was also determined.

Microwave absorption analysis of graphene-based hybrid nanocomposites: experimental, numerical and component level testing studies

ABSTRACT An effective nanocomposite-based microwave absorber made of polyurethane /graphene/glass/epoxy with different weight percentages of graphene (0 to 2.5 wt%) is proposed. Microstructural characterization of samples is done with the help of XRD, FESEM and TEM. Graphene crystalline structure maximum diffraction peak is observed at 26o associated interlayer d-spacing is 0.341 nm (plane 002), the same affirmed with TEM analysis. Graphene flake structure is identified from FESEM results. Firstly, experimental investigation is done using wave guide setup, later numerical model is developed using RF module in COMSOL. The experimental results reveal more than 90% absorption capability in broad bandwidth i.e., 3 GHz and maximum Reflection loss -35.9 dB is attained at 12.1 GHz. Also, maximum shielding effectiveness is -47 dB for 2.5 wt% PU/graphene composite due to its semi conduction. Further, a composite concrete block using 2.5 wt% PU/graphene is analysed using numerical model for the application of anechoic.

Integration of efficient microwave absorption and shielding in a multistage composite foam with progressive conductivity modular design.

Ultra-efficient electromagnetic interference (EMI) shielding composites with excellent microwave absorbing properties are the most desirable solution for eliminating microwave pollution. However, integrating absorbing and electromagnetic shielding materials is a difficult challenge because they have different design strategies. In this work, the compatibility of high absorption and shielding capability based on progressive conductivity modular design was realized. Reduced graphene oxide@ferroferric oxide/carbon nanotube/tetraneedle-like ZnO whisker@silver/waterborne polyurethane (rGO@Fe3O4/CNT/T-ZnO@Ag/WPU) multistage composite foams with aligned porous structures were fabricated, which exhibited an excellent average EMI SE > 92.3 dB and remarkable microwave absorption performance with reflection loss < -10 dB in the frequency range of 8.2-18.0 GHz. The average shielding effectiveness of reflection (SER) and reflectivity (R) are as low as 0.065 dB and 0.015, respectively. Besides, the correlations between the morphology and structure of the composite foam and the electromagnetic wave attenuation mechanism were established via electromagnetic simulation. Significantly, the integration of efficient absorbing and shielding materials was realized for the first time. Such composite foams with electromagnetic wave absorption and shielding characteristics are light weight and structurally designable with an adjustable shielding mechanism, and exhibit low filler consumption and high performance. They display promising applications in demanding electromagnetic environments. Our work provides a new strategy to design ultra-efficient EMI shielding materials with reliable absorption-dominated features.

Core-Shell Cuco2s4 Based Microspheres Decorated with Carbon Black Nanoparticles for Effective Microwave Absorption

Core-Shell Cuco2s4 Based Microspheres Decorated with Carbon Black Nanoparticles for Effective Microwave Absorption

Constructing Heterogeneous Conductive Network with Core-Shell Ag@Fe3O4 for Dual-Band Effective Microwave Absorption

Constructing Heterogeneous Conductive Network with Core-Shell Ag@Fe3O4 for Dual-Band Effective Microwave Absorption

Prediction of material composition for microwave absorption through mathematical modelling

In this paper, we analyse the suitability of various elements and their composition for microwave absorption. This is done by developing a mathematical model based on transmission line theory, polarizability and dielectric and magnetic response of the material. The inputs to this model are the desired specifications of the absorber like reflection loss, resonance frequency and bandwidth. The corresponding output parameters are the range of the atomic radii and magnetic dipole moment of suitable elements and their effective energy parameters. This mathematical model has been verified for compounds like oxides and ferrites that have been proven posses microwave absorption properties through previous experimental research. This mathematical model has been verified for compounds like oxides and ferrites that have been proven to possess microwave absorption properties through previous experimental research. Through numerical computations, we propose new material compositions with various elements that can be used as effective microwave absorbers.

Dual-band metamaterial absorber with stable absorption performance based on fractal structure

In this paper, two kinds of dual-band metamaterial absorbers (MMAs) with stable absorption performance based on fractal structures are proposed. As the key feature, with the increase in fractal order, the fractal MMAs can reduce the weight while keeping the absorption performance. The multi-band absorption property is analyzed by multiple L-C resonances generated by the fractal structure. By virtue of good impedance matching characteristics and the synergy of the circuit and electromagnetic resonance, effective and stable microwave absorption is readily achieved. Finally, two prototypes are fabricated for demonstration, and the measurement result is consistent well with the simulation one. As expected, the proposed fractal MMAs have the advantage of low-cost, light-weight, and dual-effective absorption bands, and have great potential in the application of multi-band radar stealth.

Configuration of Multifunctional Polyimide/Graphene/Fe3O4 Hybrid Aerogel-Based Phase-Change Composite Films for Electromagnetic and Infrared Bi-Stealth.

Electromagnetic (EM) and infrared (IR) stealth play an important role in the development of military technology and the defense industry. This study focused on developing a new type of multifunctional composite film based on polyimide (PI)/graphene/Fe3O4 hybrid aerogel and polyethylene glycol (PEG) as a phase change material (PCM) for EM and IR bi-stealth applications. The composite films were successfully fabricated by constructing a series of PI-based hybrid aerogels containing different contents of graphene nanosheets and Fe3O4 nanoparticles through prepolymerizaton, film casting, freeze-drying, and thermal imidization, followed by loading molten PEG through vacuum impregnation. The construction of PI/graphene/Fe3O4 hybrid aerogel films provides a robust, flexible, and microwave-absorption-functionalized support material for PEG. The resultant multifunctional composite films not only exhibit high microwave absorption effectiveness across a broad frequency range, but also show a good ability to implement thermal management and temperature regulation under a high latent-heat capacity of over 158 J/g. Most of all, the multifunctional composite films present a wideband absorption capability at 7.0–16.5 GHz and a minimum reflection loss of −38.5 dB. This results in excellent EM and IR bi-stealth performance through the effective wideband microwave absorption of graphene/Fe3O4 component and the thermal buffer of PEG. This study offers a new strategy for the design and development of high-performance and lightweight EM–IR bi-stealth materials to meet the requirement of stealth and camouflage applications in military equipment and defense engineering.

Porous cobalt ferrite microspheres decorated two-dimensional MoS2 as an efficient and wideband microwave absorber

In this article, the CoFe2O4/MoS2 composites have been well constructed via a facial hydrothermal method, from which the porous CoFe2O4 microspheres were embedded into MoS2 ultrathin nanosheets. As a typical two-dimensional transition metal sulfide, MoS2 with high electrical conductivity and flexible properties is expected to exhibit high dielectric loss and magnetic loss when combined with magnetic material CoFe2O4. Meanwhile, the unique hierarchical structure of as-synthesized MoS2 nanoflowers is conducive to scattering and reflection of electromagnetic waves, and endows designed composites with competitive microwave absorption properties. Notably, although the saturation magnetization of MoS2/CoFe2O4 composites is significantly decreased compared to pure CoFe2O4 microspheres, the coercivity still maintains a high value of 626.1 Oe. As expected, the results demonstrate that as-fabricated MoS2/CoFe2O4 composites do have superior microwave absorption properties in comparison with CoFe2O4 and MoS2. It is found that the complex permittivity is enhanced with increasing filling ratio from 45 wt% to 60 wt%, which is helpful for obtaining a moderate permittivity value. When the filling ratio is 50 wt%, the MoS2/CoFe2O4 composites exhibit a minimum reflection loss (RLmin) of − 53.1 dB at 12.08 GHz when the thickness is 2.5 mm. An effective absorption bandwidth less than − 10 dB of 6.61 GHz from 11.28 to 17.89 GHz is achieved with a thin thickness of 2.2 mm, almost covering the whole Ku-band. The improvement in microwave absorption properties can be ascribed to the synergistic effect of the magnetic CoFe2O4 and dielectric MoS2. The impedance matching characteristic and interfacial polarization are significantly optimized by inserting CoFe2O4 spheres onto the surface of MoS2 nanosheets. Considering the excellent performance of as-fabricated MoS2/CoFe2O4 composites, it is believed that the MoS2-based composites can be applied as a promising candidate of highly effective microwave absorbers with strong absorption intensity and broad absorption frequency.

Multiwall-carbon nanotubes and carbon microbeads hybrid utilized for microwave absorption: A cost effective approach

Materials for stealth application requires efficient microwave absorption ability. Since in real practice they have to be applied on large platforms so the uniform dispersion with proper coating of these materials are of utmost importance. Quantity of material requires is high so altogether the cost of coating material defines their overall usage. In this regard hybrid composite material of micro with nano form had been explored as newer microwave absorber. The hybrid involved low cost carbon microspheres which were porous at their surface. These microbeads were well dispersed in the epoxy matrix with the help of modified Multiwall Carbon nanotubes (MWCNTs). A minimum amount of 2% modified MWCNTs with 7% microbeads showed efficient microwave absorption in X band region. Thus this novel hybrid material paves path for easy, low cost and bulk production of functional material which could be utilized for effective microwave absorption application.

Physicochemical properties and microwave absorption performance of Co3O4 and banana peel-derived porous activated carbon composite at X-band frequency

Agricultural waste-derived absorbers have drawn extensive attention in electromagnetic wave absorption owing to their unique advantages such as good carbon content and porosity. In this study, porous activated carbon (PAC) was derived from banana peel via chemical activation and carbonization at different temperatures. Then, Co3O4@PAC composites were prepared using the facile hydrothermal method. The thermal stability, phase crystallinity, chemical composition, surface morphology, and porosity of the samples were studied using TGA, XRD, FTIR, XPS, FESEM, and SAP characterization techniques, respectively. Co3O4@PAC700 composite with a cornales flower-like morphology achieved an optimum reflection loss (RL) of −44.50 dB at 2.0 mm thickness. Likewise, Co3O4@PAC600 showed an optimum RL value of −51.50 dB at 11.39 GHz with a matching thickness of 2.5 mm. The magnetic loss, interfacial polarization, porous flower-like structure, and conduction loss contributes adequately towards the superior absorption performance of Co3O4@PAC composites at X-band frequency. The unique flower-like morphology of the composites with good porosity would favour EM wave scattering and multiple reflections of EM wave, thereby resulting in high attenuation of the EM wave. The flower-like morphology prolongs the electromagnetic wave propagation path which would favour gradual attenuation of the electromagnetic wave. This work suggests that the Co3O4@PAC composites can be considered as a promising absorber for EM absorption application. This study provides a new path to designing novel magnetic and dielectric composite for effective microwave absorption.

Onion skin-derived hierarchical carbon/hollow CoFe2O4 composite with effective microwave absorption in multi-band

The absorption of multi-band electromagnetic waves is still a challenging project in the field of microwave absorption. Herein, onion skin-derived hierarchical carbon/hollow CoFe2O4 composite was successfully prepared through an in-situ growth method. The OC-CFO composite exhibits excellent microwave absorption performance with a minimum reflection loss of −53.54 dB at 2.46 mm and a maximum effective bandwidth of 4.92 GHz at 1.7 mm. It is notable that with varied thicknesses, OC-CFO can achieve strong absorption in multi-band. The excellent performance can be attributed to the synergistic effect of the conduction loss, polarization loss, magnetic loss and impedance matching. This work further facilitates the development of biomass-derived carbon materials with multi-band microwave absorption properties.