Effective Microwave Absorption Research Articles

Microporous Cobalt Ferrite with Bio-Carbon Loosely Decorated to Construct Multi-Functional Composite for Dye Adsorption, Anti-Bacteria and Electromagnetic Protection.

Currently, facing electromagnetic protection requirement under complex aqueous environments, the bacterial reproduction and organic dye corrosion may affect the composition and micro-structures of absorbers to weaken their electromagnetic properties. To address such problems, herein, a series of CoFe2O4@BCNPs (cobalt ferrite @ bio-carbon nanoparticles) composites are synthesized via co-hydrothermal and calcining process. The coupling of magnetic cobalt ferrite and dielectric bio-carbon derived from Apium can endow the composite multiple absorption mechanisms and matched impedance for effective microwave absorption, attaining a bandwidth of 8.12 GHz at 2.36 mm and an intensity of -49.85 dB at 3.0 mm. Due to the ROS (reactive oxygen species) stimulation ability and heavy metal ions of cobalt ferrite, the composite realizes an excellent antibacterial efficiency of 99% against Gram negative bacteria of Escherichia coli. Moreover, the loose porous layer of surface stacked bio-carbon can promote the adsorption of methylene blue for subsequent eliminating, a high removal rate of 90.37% for organic dye can be also achieved. This paper offers a new insight for rational design of composite's component and micro-structure to construct multi-functional microwave absorber for satisfying the electromagnetic protection demand in complicated environments.

Facile synthesis of eco-friendly mango peel-derived porous carbon for optimizing microwave absorption

An environment-friendly and cost-effective method to deal with electromagnetic pollution is fabricating porous carbon from biomass as a raw material with a simple technique. The purpose of this research is to create porous carbon from mango peel biomass for optimizing microwave absorption. The resulting porous carbon (PC) has the potential to be an effective microwave absorber. Scanning Electron Microscopy (SEM) depictions also revealed the porous carbon with homogeneous shapes and uniform size distribution. Complex permittivity studies were performed to evaluate their microwave absorption capabilities, resulting in a high reflection loss of −50.2 dB at a thickness of 2.1 mm and an effective absorption bandwidth (EAB) of 3.39 GHz for the sample carbonized at 800 °C. The exceptional microwave absorption ability of porous carbon (PC) can be attributed to its effective impedance matching and consequent attenuation of microwaves through dielectric loss. This research introduces a novel biomass source, readily available in nature, which can be easily processed to enhance microwave absorption properties.

Tailorable effective microwave absorption bandwidth of chitosan-derived carbon-based aerogel under different compression

Confronted with ever-increasing electromagnetic radiation problems, developing microwave absorbing materials with tunable effective absorption bandwidth (EAB) is in high demand. In this work, chitosan-derived carbon-based aerogel was synthesized by unidirectional freeze-drying and the following high-temperature carbonization process. The dielectric-magnetic coupling effect was facilitated by the construction of the 3D conductive network, along with the decoration of the Co nanoparticles and the doping of heteroatoms within the carbon-based framework. Therefore, the aerogel achieved minimum reflection loss intensity of -44.30 dB at 5.20 GHz when carbonizing the precursor at 800 °C. More significantly, the strain-responsive properties of the aerogel endows it with tailorable electromagnetic response behaviors, thereby controlling the effective absorption bandwidth covering from X band to Ku band. This work paves the way for designing next-generation microwave absorption materials with tunable microwave absorption bandwidth, catering to stringent practical requirements prospectively.

Modulation of impedance matching of hollow cubic carbon with semi-closed structure for effective microwave absorption

In this paper, a certain degree of semi-closed structure was successfully introduced in hollow cubic carbons (HCCs) by selective dissolution of phenolic resin (PR)/NaCl precursor by acetone. The impedance matching of the HCCs absorber was improved, which in turn lead to the enhancement of the electromagnetic wave absorption capacity. By controlling the selective dissolution time of acetone, HCCs with different degrees of integrity were formed, and the degree and mechanism of the influence of the semi-closed structure of HCCs on the wave absorbing properties were investigated by analyzing the microstructure and physical phase composition of HCCs. From the scanning electron microscope photographs, it can be seen that with the increase of the acetone treatment time of HCCs, the samples gradually appeared a certain degree of semi-closed structure. With the extension of the acetone treatment time to 60 min, the structure of the HCCs was seriously damaged, at which time the impedance matching of the wave-absorbing materials was seriously deteriorated, and the electromagnetic wave absorption performance was also decreased. Among them, the electromagnetic wave absorption performance of HCCs30min is the most outstanding, specifically, when the loading rate is 10 wt%, the maximum absorption peak value of HCCs30min with a thickness of 2.7 mm reaches −41.1 dB, and the corresponding absorption bandwidth is 3.8 GHz (8.9 GHz–12.7 GHz). The experiment confirms that the existence of the degree of structural integrity can affect the impedance matching and wave absorption performance of HCCs.

Collective orientation of CNT coated magnetic microchains for effective microwave absorption in S and C band

The control of undesired electromagnetic radiation in S- and C-band spectra requires novel microwave absorbing materials (MAMs) having high microwave attenuation capability together with optimal impedance matching. CNTs are conformally coated onto the surface of one-dimensional FeCo-based magnetic microchains via electrostatic self-assembly, and then the magnetic inclusions are collectively oriented in matrices by applying an external magnetic field. The proper incorporation of CNTs with magnetic microchains demonstrates a feasible pathway for effectively absorbing microwaves in the S and C band. MAMs consisting of oriented microchains have anisotropic complex permittivity, of which the real part ranges from 6.1 to 30.4 at 2 GHz. When the electric field is parallel to microchains, the 5-mm-thick MAM has an effective absorbing bandwidth (EAB) in the range of 2.3 to 2.9 GHz, and reduces the radar cross section to be lower than ‒15.9 dB m2 from the vertical to the glancing incidence. When the magnetic field is parallel to microchains, the MAM adsorbs C-band microwaves with an EAB of 1.5 GHz, and achieves maximal reflection loss of ‒46.4 dB. The collective orientation of shape-anisotropic magnetic materials, in addition to the composition and microstructure, is a new variable for the design of effective MAMs.

Facile preparation and broadband microwave absorption of multilayered materials based on thin films of reduced graphene oxide

Microwave absorption (MA) materials have received extensive attention for their wide applications in both civil and military areas. However, many MA materials have a large thickness, high filling ratio, and narrow effective microwave absorption bandwidth (Reflection Loss, RL ≤ −10 dB) (EAB), and are prepared by complex processes. In this work, a reduced graphene oxide (RGO) film is prepared for the first time by an approach involving floating-dipping and chemical reduction. Compared with previous micrometers-thick RGO films, the present 200 nm-thick dense RGO film is critical for improving not only the impedance matching but also the capability of the material to attenuate incident microwaves. Based on such a thin RGO film, a multilayered material with a jaaumann structure is constructed with individual RGO layers alternating between low dielectric polyethylene terephthalate (PET) sheets. With the superb impedance matching, multilayer attenuation, and multi-cavity resonance, the present multilayered material can achieve a wide EAB of 13.75 GHz with a minimum reflection loss of −47.69 dB using only 3 layers of RGO films. This study provides a new and simple strategy for the development of layered materials with a thin thickness, low filling ratio, and strong absorption with a wide EAB.

Graphene aerogel encapsulated double carbon shell CoFe@C@C nanocubes for construction of high performance microwave absorbing materials

Recently, Prussian blue analogs (PBAs) have attracted much attention due to their transformation into dielectric/magnetic coupled composites after pyrolysis at high temperatures and their ability to maintain their basic morphology. However, designing efficient microwave-absorbing materials using PBAs is still a challenge. In this work, Co–Fe PBA was prepared by wet chemical method and graphene aerogel-encapsulated double carbon-shell CoFe@C@C nanocubes (CFCCG) were prepared by stirred self-polymerization and hydrothermal method, and heat-treated at different temperatures to obtain composites consisting of core-shell-structured PBA-derived particles encapsulated in a double layer of graphene and polydopamine (PDA). The addition of graphene not only reduces the density of the derived material but also effectively disperses the CoFe@C@C nanocubes to prevent the generated highly conductive carbon layer from adhering to improve the impedance matching, as well as introduces a large number of heterogeneous interfaces to improve the loss capability. Thanks to which the CFCCG7 composites have a reflection loss of −66.33 dB and an effective microwave absorption frequency covering the entire Ku-band. This work provides a new approach for rational design of multilayer carbon structure-coated PBA-based microwave absorbing materials.

Band gap, ferromagnetic resonance and strong microwave absorption of BaFe12-2xZnxSnxO19 compounds and enhanced dielectric loss in BaFe12-2xZnxSnxO19/carbon nano tube composites

The forbidden bandgap energy, magnetic properties, natural ferromagnetic resonance and microwave absorption are studied on the Zn2+ and Sn4+ doped BaFe12-2xZnxSnxO19. The forbidden band gap of BaFe12-2xZnxSnxO19 increases with the increasing doping content x from 1.80 eV up to 1.97 eV. The coercive field, the anisotropy field and the magnetocrystalline constant of BaFe12-2xZnxSnxO19 decreases with the increasing doping. The natural ferromagnetic resonance is observed. The high permeability, accompanied with the ferromagnetic resonance, enables strong microwave absorption. BaFe10.4Zn0.8Sn0.8O19 has a wide effective microwave absorption bandwidth (RL≤-10dB) of 6 GHz with the material thickness below 2.5 mm in 11.4–17.4 GHz. The dielectric loss has little contribution to the excellent microwave absorption of BaFe12-2xZnxSnxO19. The BaFe12-2xZnxSnxO19/carbon nanotube (CNT) composites significantly increase the permittivity. The high dielectric loss and the high magnetic loss further improve the microwave absorption. With a very thin thickness of 1.8 mm, BaFe10.4Zn0.8Sn0.8O19/CNT has a bandwidth of 7.1 + GHz of 10.9–––18 + GHz. With the material thickness thinner than 3 mm, BaFe12-2xZnxSnxO19/CNT composites have very broad effective microwave absorption bandwidth of 11.4+, 10.7 and 10.7 GHz, with x = 0.6, 0.8 and 1.0, respectively. It illustrates that both BaFe10.4Zn0.8Sn0.8O19 and BaFe12-2xZnxSnxO19/CNT composites are very promising microwave absorbers.

Hierarchically three-dimensional ZrO2/Fe3O4/C nanocomposites with Janus structure for high-efficiency electromagnetic wave absorption

Hierarchically three-dimensional (3D) materials present a pivotal challenge and opportunity in achieving effective microwave absorption with synergistic effects. In this work, α-Fe2O3@ZrO2 with core-shell structure were fabricated in-situ on aramid nanofibers by a solvothermal method. Following calcination, 3D ZrO2/Fe3O4/C nanocomposites with Janus structure have been successfully synthesized. By controlling the lattice match and mismatch in both processes, a core-shell structure of α-Fe2O3@ZrO2 and Janus structure of ZrO2/Fe3O4 have been well-define performed. The composite material ZrO2/Fe3O4/C-700 has a minimum reflection loss (RLmin) of −67.4 dB at a thickness of 2.0 mm. The effective absorption bandwidth (EAB) at a thickness of 2.4 mm is 6.0 GHz (11.0–17.0 GHz). This study provides a novel strategy for fabricating high-efficiency electromagnetic wave absorption materials with dual synergistic effects in nanosized scale.

Sodium alginate derived SiC-carbon composite aerogel for effective microwave absorption

Biomass-derived carbon aerogels are expected to be ideal candidates for electromagnetic wave (EMW) absorption due to their extensive sources, cheap cost, low density and abundant porosity. Herein, using the natural polymer sodium alginate (SA) as the carbon-based precursor and SiC nano-whiskers (SiCw) as the reinforcing material, a series of three-dimensional (3D) SiCw@C composite aerogels doped with different metal ions (Fe, Ni, Al) were designed and studied for lightweight and effective EMW absorption. The emergence of metal ions and three-dimensional conductive carbon networks enriches the loss mechanism of the composites. The results show that the SiCw@C-Al exhibits a considerable minimum reflection loss (RLmin) value at 1.5 mm thickness (-28.7 dB) and a broad effective absorption bandwidth (EAB, RL < -10 dB) of 4.1 GHz. Meanwhile, SiCw@C-Fe has good wave absorption performance at a thickness of 2 mm, RLmin is −49.2 dB, and EAB is 3.6 GHz. By adjusting the matching thickness of the Al3+ and Fe3+ crosslinked composite aerogel from 1.5 mm to 3.5 mm, the integrated EAB can cover the Ku-band, X-band and even C-band. The SA derived 3D SiCw@C composite aerogels open a new path for the design of lightweight and effective EMW absorption materials used in multi-frequency.

Core-shell designed high entropy alloy CoNiFeCuV-C nanoparticles for enhanced microwave absorption

The widespread interest in high entropy alloy nanostructures stems from their potential utilization in a variety of technological and scientific fields. This study presents an innovative approach employing a one-step metal organic chemical vapor deposition to synthesize quinary high entropy alloy (CoNiFeCuV-C) core-shell nanoparticles designed for microwave absorption applications. Superior microwave absorption performance is attained through the optimization of conduction loss via thermal treatment, coupled with the interfacial polarization across the interfaces between CoNiFeCuV cores and C shell. The paraffin composite filled with an optimal 20% content of CoNiFeCuV-C core-shell nanoparticles demonstrates a minimal reflection loss (RLmin) of −51.8 dB at 13.76 GHz, achieving this performance with a thickness of 2.2 mm. Moreover, the absorbing bandwidth spans 7.44 GHz at a thickness of 2.4 mm. The outstanding accomplishments underscore the potential of utilizing CoNiFeCuV-C core-shell nanoparticles as a promising choice for lightweight, effective microwave absorber material.

An effective microwave absorber using multi-layer Design of carbon allotrope based Co2Z hexaferrite-Polymer nanocomposite film for EMI shielding applications

This report shows impressive electromagnetic interference (EMI) shielding efficiency of laminated nanocomposites of PVDF containing binary nanofillers of rGO and Co2Z hexaferrite. These rGO layers in the PVDF matrix in association with magnetic nanofillers have been considered to improve interfacial polarization by accumulating charges at the interfaces of rGO-Co2Z hexaferrite-PVDF system. The crystallographic phase, chemical composition, and successful incorporation of the binary nanofillers into PVDF have been verified using XRD, XPS, RAMAN, and FESEM analysis. The J-E analysis of rGO-Co2Z hexaferrite-PVDF nanocomposite films confirm that the current density of all the nanocomposite films is very less and found in the order of 10-5 A/m2 under the maximum electric field of 70 kV/m. This indicates the emergence of polarization effect in the nanocomposite films when subjected to high external electric field without having electrical breakdown. The significant magnetization of ∼8.9 emu/g for nanocomposite films, at room temperature is beneficial for boosting the EMI shielding effectiveness due to absorption (SEA). The combination of magnetization and electrical polarization in nanocomposite film helps to attain significantly high total shielding effectiveness (SET) in the frequency range of 12–18 GHz. The shielding effectiveness study of both mono-layer and multi-layer nanocomposite films have been investigated. Improvement of SEA has also been achieved by the elevation of the thickness of the nanocomposite film within the range of 0.8 to 1.0 mm, which in turn improves SET to a value of −54.09 dB at 15.70 GHz for multi-layer system of thickness 0.861 mm with >99.999 % of attenuation whereas the mono-layer film of thickness 0.180 mm shows the SET of −47.03 dB at 14.76 GHz with an attenuation of >99.99 %.

Lightweight and high-strength SiC/MWCNTs nanofibrous aerogel derived from RGO/MWCNTs aerogel for microwave absorption

Developing Silicon carbide (SiC) -based materials with the characteristics of “lower filling ratio, thinner matching thickness, lighter material mass, and better microwave absorption performance” is an important focus of current research. In this work, SiC/Multi-walled carbon nanotubes (MWCNTs) nanofibrous aerogel was prepared using a selective in situ derivatization strategy with Reduced Graphene Oxide (RGO)/MWCNTs aerogels as templates. It is found that when the filling ratio is only 15 %, the minimum reflection loss of the aerogel can reach −57.36 dB. When the matching thickness is only 1.5 mm, the effective microwave absorption bandwidth can reach 3.34 GHz. Moreover, the aerogel exhibits good multi-band microwave absorption performance, significantly reducing the radar cross section (RCS) in C-band, X-band, and Ku-band. In addition, the aerogel features low density and high mechanical strength, with a density as low as 0.046 g/cm3, and specific strength and specific modulus of 4.35 kN·m/kg and 12.39 kN·m/kg, respectively. This work not only provides a new synthesis strategy for the preparation of novel silicon carbide/carbon-based materials, but also contributes to the development of light-weight, high-strength and high-performance microwave absorbing materials.

Structural, Magnetic, and Electrical Investigations of PVA/Ni Ferrite/(MoS2)x Nanocomposites.

Transition metal sulfides (TMDs) possess exceptional dielectric properties and a narrow band gap, rendering them highly efficient as electromagnetic absorbing materials. Among these TMDs, the two-dimensional MoS2 nanosheet has received significant attention in research. However, the quest for new absorbers no longer finds satisfaction in solitary absorption mechanisms. This article introduces a successful method for creating PVA/NiFe2O4/(MoS2)x nanocomposites via a straightforward sol-gel technique, wherein porous amorphous NiFe2O4 microspheres are integrated into MoS2 nanosheets. The investigation uncovers that the incorporation of MoS2 results in an enhanced complex permittivity, facilitating the attainment of a desirable permittivity level. The PVA/NiFe2O4/(MoS2)x nanocomposite absorber exhibits an incredibly low reflection loss (RL) of -16.75 dB at a mere thickness of 1 mm, achieved through the cooperative interaction of dielectric and magnetic loss, along with the advantages of the structure and composition. Consequently, the PVA/NiFe2O4/(MoS2)x nanocomposites effectively absorb electromagnetic waves. Therefore, it is posited that MoS2-based composites hold great promise as highly effective microwave absorbers, boasting strong absorption intensity and a wide absorption frequency range, given the exceptional performance of the as-fabricated PVA/NiFe2O4/(MoS2)x nanocomposites.

Transformation of traditional carbon fibers from microwaves reflection to efficient absorption via carbon fiber microstructure modulation

The high conductivity of commercial carbon fibers leads to a noticeable skinning effect and weak microwave impedance matching. This results in insufficient effective absorption bandwidth and less than ideal overall wave absorption performance, mainly reflecting electromagnetic waves. These limitations restrict the application of carbon fibers. In this study, we successfully prepared carbon fiber/epoxy composites with adjustable electrical conductivity by precisely controlling the temperature and time of pre-oxidized polyacrylonitrile (PAN) fibers during the low-temperature carbonization stage. This allowed us to regulate the components and microstructure of conductive carbon fibers. The carbon fiber/epoxy composites demonstrated exceptional microwave absorption performance due to their various loss mechanisms. The impedance matching conditions and microwave attenuation capability were also quantitatively evaluated. For 850-9 samples, an effective bandwidth of approximately 7 GHz (11 GHz–18 GHz) was achieved with a thickness of 2.5 mm. For 900-9 samples, the best reflection loss achieved is −39.9 dB at 5.8 GHz, which corresponds to a thickness of 3 mm. The carbon fibers with different electrical conductivity can be obtained by modulating the microstructure of carbon fibers, which can improve the impedance matching performance of conductive carbon fibers and reduce their reflection of electromagnetic waves to improve the microwave absorption performance, achieving the transformation of traditional carbon fibers from electromagnetic shielding to effective microwave absorption. This simple and efficient preparation method has yielded promising results and offers a new avenue for the advancement of high-performance carbon fiber microwave absorbing materials.

Graphene/silver nanowire aerogel sponge for highly effective electromagnetic energy attenuation

The development of a highly effective microwave absorber with low filler loading remains a huge challenge.

Construction of heterostructured SnS2/SnS@graphene oxide composite with highly effective microwave absorption

The RLmin of SnS2/SnS@GO is −47.83 dB, and the EAB is 7.18 GHz at 2.00 mm.

Biomass-derived Activated Carbon with Nickel Ferrite Nanocomposite for Broadband Microwave Absorption

This study presents a novel approach using a composite material consisting of Biomass-derived Activated Carbon and Nickel Ferrite Nanocomposite as an advanced option for achieving effective microwave absorption over a wide range of frequencies. The use of biomass, which is a sustainable and easily accessible resource, serves as the fundamental basis for this methodology. This approach effectively tackles the need for enhanced electromagnetic interference shielding in communication and radar systems by integrating activated carbon generated from biomass with nickel ferrite nanoparticles. Traditional approaches often encounter challenges related to the limited absorption of bandwidth and environmental considerations. The utilization of Biomass-derived Activated Carbon for Broadband Microwave Absorption (BMAC-BMA) presents a significant advancement, characterized by a noteworthy Absorption Coefficient of 14.25 Np/m, Return Loss of -20.37 dB, specific surface area of 580.25 m²/g, pore size distribution of 2.8 nm, Saturation Magnetization of 1.35 A/m and Reflection Coefficient of 0.1. These characteristic holds promise for driving breakthroughs in technology and communication systems. This study demonstrates the significant impact of using sustainable biomass resources in producing advanced materials for various applications.

Size regulated N-doped carbon encapsulated NiFe alloys/Ni phosphide composites derived from bimetallic Prussian blue analogues for effective microwave absorption

Prussian blue analogues (PBAs) derivatives have emerged as microwave absorbing materials to address electromagnetic pollution in recent years. In this work, bimetallic NiFe-PBA derived multi-interface N-doped carbon (NC) encapsulated NiFe alloys/Ni phosphide composites (NFPC) were prepared by thermal treatment and phosphating process. The PBAs samples with different chemical compositions and particle sizes were synthesized by manipulating the proportions of raw materials. The particle sizes of PBAs significantly impact the morphology, phosphating degree and electromagnetic properties of the NFPC composites. The results indicated that the NFPC composites exhibit excellent microwave absorption performance, with a minimum reflection loss of −41.4 dB at 1.36 mm and the effective absorption bandwidth of 4.4 GHz at 1.34 mm. The corresponding microwave attenuation mechanisms of NFPC composites were further investigated. This study not only presents a comprehensive investigation into the controlled growth of PBAs, but also provides innovative design strategies and valuable insights on utilizing multiple interfacial magnetic alloys/phosphides@NC composites as efficient microwave absorbing materials.

Synthesis and microwave absorption performance of heat-treated RF/SiO2 aerogels

The well-designed composite with satisfactory electromagnetic microwave absorption at high temperatures remains a serious challenge. Herein, we fabricated a resorcinol-formaldehyde/silica dioxide composite aerogel (RF/SiO2) with a three-dimensional network structure using sol-gel, atmospheric pressure drying technique as well as heat-treated processes to achieve enhanced microwave absorption capabilities in the low frequency range. The pristine RF/SiO2 aerogel presented a typical micropores structure with a surface area, porous volume, and density of 146.82 m2/g, 62.40%, and 0.28 cm3/g, respectively. Remarkably, the RF/SiO2 aerogel showed an effective absorption bandwidth of 3.56 GHz and a minimum reflection loss value of −46.10 dB at 2.25 mm after being heat-treated at 1500 °C, while the maximum effective absorption bandwidth was 3.60 GHz at 2.30 mm. The intricate three-dimensional networks possessed remarkable impedance matching, multiple attenuation mechanisms, interfacial polarization, and dielectric loss, which were attributed to the exceptional ability to absorb electromagnetic microwaves. It offered a fresh approach to creating adaptable and effective microwave absorption materials in military defense.