Reflection Loss Value Research Articles

Magnetic vortex configuration in Fe3O4 nanorings/nanotubes for aspect ratio and magnetic orientation regulated microwave absorption

Morphological structure can greatly affect the magnetic domain of magnetic materials, which plays a significant role on regulating the magnetic characteristics and electromagnetic properties. Herein, Fe3O4 nanorings/nanotubes with adjustable aspect ratio were fabricated through a hydrothermal route followed by reduction annealing treatment. The magnetic flux distributions in radial and axial direction were characterized by electron holography, suggesting that the Fe3O4 nanorings/nanotubes show magnetic vortex structure. The magnetic vortex-domain structure is favored to break the Snoek’s limit of Fe3O4, improving the high-frequency permeability and boosting the natural resonance band to 1 ∼ 10 GHz. Meanwhile the complex permittivity is highly sensitive to the aspect ratio. The Fe3O4 nanorings/nanotubes perform excellent comprehensive microwave absorption properties, owing to the special magnetic vortex structure, tunable complex permittivity, big complex permeability, large magnetization and high natural resonance. The Fe3O4 nanorings with the smallest aspect ratio show a minimum reflection loss (RL) value of −47.9 dB at 2.6 mm and EAB of 4 GHz at 3 mm. Besides, rotational orientation by an external magnetic field can cause the parallel arrangement of nanorings/nanotubes, which can increase both the complex permittivity and broad the resonance band. Rotational orientation can realize effective absorption efficiency at a broader frequency range with a thinner thickness, further improving the comprehensive microwave absorption. These findings not only suggest that designing particular magnetic-domain structures by morphologies can break the Snoek’s limit of magnetic materials, but also demonstrate that aspect ratio and magnetic field-assisted rotational orientation is promising ways to regulate the electromagnetic parameters, resulting in high-performance microwave absorption.

Gradient Bi-layer coating for reducing energy consumption and improving electromagnetic wave dissipation: Elucidating the role of interfaces and interfacial polarization

The implementation of smart and logical design for absorbers, along with careful selection of components, has proven to be a successful strategy in creating efficient electromagnetic wave (EMW) absorbers. By utilizing novel nanocomposite materials that integrate various loss mechanisms, including enhanced magnetic and dielectric loss, multiple scattering and reflection, and polarization loss, the fabrication of a gradient bi-layer absorber holds great promise for superior EMW absorption. By employing chemical methods, a novel dielectric-magnetic compound comprising of Co2FeAl Heusler Alloy and MWCNTs@NiSe2 was produced. Subsequently, a gradient bi-layer absorber was developed using these components to optimize impedance matching and bolster low-frequency absorption. Abundant hetero-interfaces within this ternary bi-layer nanocomposite absorber give rise to Schottky junctions and heightened interfacial polarization between its layers, components, and matrix. Notably, the utilization of Co2FeAl Heusler Alloy nanoparticles has been shown to lead to the manifestation of magnetic loss phenomena due to their inherent magnetic properties. Through the strategic utilization of the unique layer structure, in conjunction with the incorporation of multiple loss mechanisms, the ternary bi-layer nanocomposite was able to achieve an impressive reflection loss value of -29 dB, despite having a mere 1.4 mm total thickness. Our study offers a fresh framework for creating innovative bilayer gradient absorbers suitable for low frequency applications.

3D printed honeycomb bilayer structures based on polylactic acid as lightweight microwave absorbing materials

Abstract3D printed honeycomb structures constituted by neat polylactic acid (PLA) and conductive PLA (PLAc) with different cell sizes and thicknesses were manufactured through 3D printing technology based on material extrusion (MEX). These structures were arranged into bi‐layer honeycomb structures (BHS) for evaluation of the microwave absorbing properties at the X‐band (8.2–12.4 GHz) and Ku‐band (12.4–18 GHz) frequency ranges. The effects of cell size, sample thickness, layer thickness ratio and the nature of the top layer on the electromagnetic attenuation performance of BHS samples were investigated in terms of reflection loss (RL). The components geometric characteristics and the arrangement of the layers exerted great influence on the RL values and effective absorption bandwidth (EAB). Overall the bilayer structures with 5 mm total thickness presented the best EM response in terms of EAB and minimum RL, where the component with the larger cell size (7.7 mm), PLAc (1 mm) as the top layer and PLA (4 mm) as the bottom layer exhibited the best results with RL values of −41 dB and EAB of 9.5 GHz. The BHS system with 7.7 mm cell size was more efficient in Ku band frequency range, whereas that with 3.5 mm cell size gave better response in the X‐band frequency range. Therefore, RL values and EAB can be adjustable by modifying the building strategy of the printed parts, such as thickness of the sample, cell size and thickness distribution of the conductive and non‐conductive layers. The findings in this work show the importance of the building strategy to fabricate components with controllable BHS and improved properties for microwave absorption application.

Enhancing the eco-friendly use of manganese sulfate residue via recognition and reconstruction of metastable structure

Long-term accumulation of manganese sulfate residue can lead to the release of soluble manganese ions, which in turn can contaminate the surrounding environment. However, effectively guiding the treatment of soluble manganese in manganese sulfate residue is challenging due to limited understanding of its metastable structure. In this study, the metastable phase of manganese sulfate residue was analyzed by transmission electron microscope (TEM), cross-reaction X-ray energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The results reveal that the metastable phase within manganese sulfate residue consists of amorphous hydroxide and calcium sulfate. Furthermore, the amorphous hydroxide colloid is coated by calcium sulfate. The reconstruction of the metastable structural phase in manganese sulfate residue was achieved by adding BaCO3. The toxic leaching of the residue after phase reconstruction was assessed. The results show that the lowest leaching concentration of Mn and Ba were 0.6737 mg L−1 and 1.778 mg L−1, respectively. The leaching amounts of Mn and Ba were within the allowable range of GB 8978–1996 and GB 5085.3–2007, respectively. This suggests that the addition of BaCO3 can achieve harmless of manganese sulfate residue. Finally, the reconstructed residue is used to prepare the unfired brick with wave-absorbing. The obtained results show that the compressive strength of the brick is 17.00 MPa, meeting the standard of MU15. Additionally, the minimum reflection loss value of the brick is −10.51 dB, showing that the material has promising ability in absorbing wave.

Controllable synthesis of CeFeO3/Fe+2Fe2+3O4/C composites with improved microwave absorption performances

Magnetic-dielectric component modulation and heterogeneous interface engineering have been acknowledged as a highly potent strategy for the effective development of lightweight and broad-spectrum electromagnetic wave (EMW) absorbers. In this investigation, a series of carbon-based Ce/Fe-MOF derivatives were successfully synthesized via the carbonization process of Ce/Fe-MOF precursors. The EMW absorption characteristics of these derivatives were investigated by manipulating the metal ion ratio and the pyrolysis temperature. Notably, the Ce/Fe-MOF-700 composite, derived from the calcination of Ce/Fe-MOF with a molar ratio of Ce/Fe of 1:2 at 700 °C, demonstrated an impressive minimum reflection loss value of −44.6 dB at 1.38 mm. Furthermore, it exhibited an efficient absorbing bandwidth (EAB) of 6.88 GHz at a thinner coating thickness ranging from 1.38 to 1.8 mm. This remarkable ability of these materials to attenuate EMW can be ascribed to the heightened conductivity dissipation, polarization dissipation, magnetic dissipation, and enhanced impedance matching achieved by these materials. The findings of this study provide a novel point of reference for the design of lightweight and broad-spectrum EMW absorbing materials.

Negative permittivity and permeability behaviour of SrFe12O19/rGO metacomposite for microwave absorption in 2–18 GHz range

Double-negative performance has played a significant role in electronic applications owing to its both permeability and permittivity negative values. Microwave absorption material has a substantial role in electromagnetic shielding, radar absorption, stealth applications, etc. Herein, a novel double-negative metacomposite, SrFe12O19/rGO, was designed by a simple one-pot hydrothermal method, and the microwave absorption properties of the material were studied in the microwave region from 2 to 18 GHz using VNA analysis. The structural and morphological studies were analysed using XRD, FT-IR, and SEM instrumentation techniques and the magnetic property of the material was studied using VSM analysis. Both studies confirmed the hard magnetic nature of the material. The particle sizes of SrFe12O19 and SrFe12O19/rGO measured from XRD are 55.60 nm and 41.55 nm, respectively. Hexagonal plate-like morphology were observed from FESEM images. The coercivity of SrFe12O19/rGO increased, and the magnetocrystalline anisotropy was changed due to the decrease in particle size. The magnetic saturation value decreases due to the presence of non-magnetic rGO. The resultant SrFe12O19/rGO metacomposite shows negative permittivity and permeability values. The minimum reflection loss values observed for pure and rGO-decorated strontium ferrites are −28.49 dB at 7.76 GHz and −23.78 at 11.04 GHz, respectively. In addition to experimental results, simulation studies were also performed to study the reflection loss with matching thickness using a quarter wavelength mechanism. The results show that this composite can be employed as a left-handed metamaterial that finds applications in absorption, antennas, sensors, wireless power transfer systems, etc. The left-handed metamaterial can shift the frequency region from a lower to a higher frequency region. The rGO decorated metacomposite is a promising material for microwave absorption at higher frequency regions.

Self-assembly of graphene hollow microspheres anchored with FeNi3/NiFe2O4 nanocrystal for highly efficient electromagnetic wave absorption

The graphene-based electromagnetic wave absorption materials have attracted extensive attention due to their lightweight, strong absorption, broadband, and thin thickness. In this work, graphene hollow microspheres anchored with FeNi-coupled nanocrystal (GHMs@FeNi3/NiFe2O4) were synthesized using water-in-oil (W/O) emulsification and high-temperature calcination. The GHMs@FeNi3/NiFe2O4 microspheres have a homogeneous spherical morphology and a pronounced hollow structure, and the FeNi-coupled nanocrystals are homogeneously embedded in a spongy shell assembled by rGO nanosheets. Owing to the optimized impedance matching and enhanced attenuation, the GHMs@FeNi3/NiFe2O4 composites exhibit outstanding microwave absorption ability, particularly in the Ku band. The minimum reflection loss (RLmin) value can reach −58.96 dB at 14.43 GHz with a matching thickness of 2.25 mm, and the effective absorption bandwidth (lower than −10 dB) is up to 6.29 GHz (11.71–18 GHz) covering the whole Ku band. We believe that our work provides an idea for the design of high-performance absorbing composite materials.

Ni-based PCS-derived adsorbent with superior electromagnetic absorption capacity and reduced radar cross section

Low-cost and high-efficiency electromagnetic wave absorption materials had extremely broad application prospects in the realms of military and civilian domains. A series of Ni-based PCS-derived adsorbents made from precursor infiltration pyrolysis at different pyrolysis temperatures were investigated in this research. The results showed that after being pyrolyzed at 1200 °C, the Ni-based PCS-derived adsorbent possessed the lowest reflection loss value of −59.52 dB, while it reached a peak effective absorption bandwidth of 2.84 GHz with 1000 °C treatment, of which the calculated electromagnetic absorption efficiency was meanwhile the best. Besides, the simulation results showed that the adsorbent after being pyrolyzed at 1000 °C could minimize the radar cross section of the target, of which the strongest radar cross section reduction value was 21.34 dB·m2, significantly enhancing its stealth performance. Therefore, the Ni-based PCS-derived adsorbent possessed great electromagnetic wave absorption performances under conditions of high-temperature pyrolysis, which provided a reference for future electromagnetic wave absorption material design.

Regulation Dipole Moments of N-Doped Graphene Coordinated with FePc Toward Highly Efficient Microwave Absorption Performance in C Band.

The development of composites with highly efficient microwave absorption (MA) performance deeply depends on polarization loss, which can be induced by charge redistribution. Considering the fact that polarization centers can be easily obtained in graphene, herein, iron phthalocyanine (FePc) is used as polarization site to coordinate with nitrogen-doped graphene (FePc/N-rGO) to optimize MA performance comprehensively. The factors influencing MA properties focus on the interaction between FePc and N-rGO, and the change of dipole moments. The density functional theory (DFT) results demonstrated that FePc has strong interaction with N defect sites in graphene. The charge loss for FePc and charge accumulation for N-rGO occurred, leading to great increase of dipole moment, and the increased dipole moment can be acted as a descriptor to evaluate the enhanced polarization loss. Due to high charge redistribution capacity of N defect sites and FePc polarization centers, the FePc/N-rGO showed excellent MA properties in C band, and the minimum reflection loss value can reach -49.3dB at 5.4GHz with thickness of 3.8mm. In addition, the fabric loaded with FePc/N-rGO showed good heat dissipation property. This work opens the door to the development of MA performance bound to polarization site with dipole moment.

Tailoring permittivity and permeability of M-type hexagonal ferrite and 2D Ti3C2Tx MXene composites for broadband microwave stealth performance

In this study, owing to the significant advantages of heterogeneous interface engineering for customizing the electromagnetic parameters and microwave absorption properties, high magnetic lossy cobalt/zinc-doped hexagonal ferrite flakes were successfully anchored on two dimensional Ti3C2Tx with varying mass ratios. Inorganic Ti3C2Tx MXene was synthesized through the hydrofluoric acid etching process, and doped hexagonal ferrite was prepared by a solid-state sintering route leading to electrostatic bonding with Ti3C2Tx particles. Scanning electron microscopy revealed that the MXene surface strongly adhered to the ferrite particles. By adjusting the ratio of ferrite to Ti3C2Tx, it is feasible to optimize electromagnetic parameters, as required. Specifically, doped ferrite@4% Ti3C2Tx MXene composite exhibited remarkable absorption performance; the maximum reflection loss (RL) was −49 dB at 15.2 GHz with a thickness of 1.9 mm. The effective bandwidth corresponding to the RL values below −10 dB is 8.3 GHz (from 9.7 GHz to 18 GHz) at a single thickness of 2 mm, and below −15 dB is 6.4 GHz (from 10.7 GHz to 17 GHz), outlining the prospect for application as an electromagnetic wave absorber. Radar cross-section (RCS) simulation was performed with microwave incident angles ranging from 0 to 360°. The results demonstrate a reduction in RCS of up to −47.8 dBsm at a 60° incident angle. This study develops a new approach for constructing multi-component heterostructure composites with tailored electromagnetic parameters as a superior and modulated radar stealth material.

3D multifunctional porous pine carbon aerogels coupled with highly dispersed CoFe nanoparticles for robust electromagnetic wave response

Functional carbonaceous materials with controllable morphology, low apparent density, large surface area, and high porosity starting from natural precursors using environmentally friendly processes are an appealing topic in the electromagnetic wave (EMW) field. In this work, renewable pine woods with ordered pore channels are selected to load highly dispersed CoFe alloy nanoparticles formed by in-situ pyrolysis reaction between Fe3O4 nanospheres and ZIF-67 nanoparticles. The constructed three-dimensional (3D) porous CWA-CoFe-NC aerogel inherits the characteristics of highly dispersed small CoFe alloy nanoparticles, porous carbon aerogel with rectangular honeycomb-like structure, and abundant N heteroatoms. Therefore, CWA-CoFe-NC aerogel achieves an excellent EMW absorption performance with reflection loss (RL) values of −61.6 and −58.2 dB at matching thicknesses of 3.7 and 1.2 mm, respectively. Benefiting from the reasonable design of the composite structure and composition, 3D porous aerogel also enables great potential for multifunctional applications. Particularly, good lightweight and mechanical properties are realized in the CWA-CoFe-NC aerogels due to their ordered pore channels and abundant rectangular pores. Furthermore, good flame retardant performance can ensure the serviceability of the target device in high/low-temperature environments. In addition, CWA-CoFe-NC aerogels show good thermal stability and thermal management characteristics. This work provides a novel and effective method for the preparation of lightweight, high-performance, and multifunctional EMW absorbers.

Revelation of the Microwave Absorption Properties of Nano‐Sized Doubly Substituted Hexagonal Ferrites

AbstractThe main theme of this work is to synthesize and investigate different properties of Pr3+‐Cu2+ substituted X‐type hexaferrite Sr2‐xPrxCo2Fe28‐yCuyO46 with concentration (x = 0, 0.02, 0.06, 0.1 and y = 0, 0.1, 0.3, 0.5) by adopting the sol–gel method. The XRD patterns show the single phase for all the samples. The Pr3+‐Cu2+ substitution in pure X‐type hexaferrites changes the structural parameters. The increment in dielectric properties with Pr3+‐Cu2+ substitution is observed and the patterns show anomalous dielectric behavior. The FTIR analysis also confirms the single phase for the prepared materials. The magnetic properties of the material are enhanced with additives. The difference in saturation magnetization, coercivity, and remanence is observed on the basis of allocated cations onto the different lattice sites. The linear increase in saturation magnetization, remanence, and coercivity make them useful as permanent magnets. The thermal analysis is carried out to know the sintering temperature at which the single X‐type phase can be attained. The material exhibits the minimum value of reflection loss (microwave absorption) at higher frequencies that make this material useful to act as microwave absorbing material (MAM) for super high frequency (SHF) devices.

Combustion synthesized boron carbide powders by different organic carbon sources and microwave absorbing properties

AbstractBoron carbide powders were synthesized by combustion synthesis using organics chitosan, dextrin, cellulose, starch, and polyvinyl chloride (PVC) as carbon sources. The microwave absorbing properties of boron carbide powders synthesized by different carbon sources were investigated. The results showed that the powders synthesized using organic compounds containing Cl and N atoms as carbon sources have better absorbing properties. The peak value of reflection loss of boron carbide powder prepared with chitosan as carbon source is −46.41 dB at 2.1 mm thickness, with an effective absorption range of 9.21–12.30 GHz and an effective absorption bandwidth of 3.09 GHz. The small and uniform boron carbide grains and residual carbon with multiple morphologies enhance the interface polarization and electronic polarization in the material, which leads to multiple reflections and losses of the microwave. Additionally, the lattice defects and surface holes caused by Cl, N, and other atoms in chitosan and PVC increase the energy storage sites of the material, which makes the materials obtain excellent microwave absorbing properties. Boron carbides fabricated from an organic carbon source provide a potential for the preparation of high‐temperature resistant absorber.

Construction of iron oxide@C@Fe heterointerfaces by oxygen atmosphere heat treatment for enhanced microwave absorption performance

Carbon and iron-based materials are the two most extensively implemented microwave absorption materials. In this paper, carbon/iron-based wave absorption composite materials with tremendous dielectric and magnetic loss were successfully synthesized by carbonizing iron (Ⅲ) acetylacetonate (Fe(acc)3). The heterointerfaces were constructed by oxidation heat treatment to further regulate the dielectric loss and optimize the impedance matching of the composite, and improve the microwave absorption performance. Eventually, ultra-thin lightweight composite materials were prepared. When the thickness of the absorbing coating was only 1.01 mm, the minimum reflection loss (RLmin) value of the composite was −15.8 dB with 50 % filling. In addition, the effective absorption bandwidth (EAB) (RL ≤ -10 dB) was highly up to 8.8 GHz (9.2––18 GHz).

Flexible and stretchable polyester@reduced graphene oxide composite fabric for tunable electromagnetic absorption

The widespread application of 5 G wireless communication and flexible electronic devices has put forward new demands for electromagnetic (EM) absorbing materials. In this work, a flexible composite fabric was successfully prepared by using polyester (PET) knitted fabric as an elastic scaffold and subsequently anchoring reduced graphene oxide (rGO) through a simple impregnation-drying coating method. Regulating the concentration of graphene oxide (GO) impregnation solution can effectively control the rGO loading content for adjusting the EM parameters of PET@rGO composite fabric. When the concentration is 2.0 mg/mL, the as-prepared PET@rGO exhibits the optimum reflection loss (RL) value of −24.53 dB at 12.4 GHz and a corresponding effective absorption bandwidth (EAB, RL≤−10 dB) of 3.20 GHz (9.20–12.40 GHz). The impressive absorption property attributed to the synergistic effect of impedance matching and dielectric loss originated from the three-dimensional (3D) conductive network on fabric interlaced structures. More importantly, stretching PET@rGO composite fabrics to different deformations can dynamically adjust the EM absorption properties while maintaining the knitted structure. This work demonstrates an efficient avenue for the rational design of next-generation EM absorbing fabric, showing latent applications in flexible functional electronics.

Hierarchical composite CoFe-K/GC@MnO2@MXene for excellent electromagnetic wave absorption

Electromagnetic wave absorption (EMWA) materials with qualities such as low cost, thin thickness, and high efficiency are of tremendous value in addressing the challenges posed by EMW pollution. Herein, we have successfully synthesized a nanoflower-like composite from the Prussian blue analog KCoFe(CN)6 through a combination of hydrothermal and post-annealing methods. Subsequently, we prepared the hierarchical composite CoFe-K/GC@MnO2@MXene (CMM) by electrostatic self-assembly with few-layered Ti3C2Tx nanosheets. Their chemical compositions, microstructures, and EMWA performances were thoroughly investigated. The CMM composite demonstrated outstanding EMWA performance with an impressive minimum reflection loss (RLmin) value of −53.0 dB at 1.68 mm and an effective absorption bandwidth (EAB) value of 4.0 GHz with an ultrathin-matching thickness of only 1.55 mm. The exceptional EMWA performance of CMM can be attributed to the increased conductive loss, enhanced interfacial polarization, and optimized impedance matching. Simulated radar cross-section (RCS) plots confirm the outstanding RSC reduction achieved by the CMM absorber coating. Furthermore, the EAB can be extended to 12.12 GHz by designing a macro 3D quadrangular frustum pyramid structural model for the absorber. The practical application potential of CMM was also enhanced by its good heat dissipation capability, which was demonstrated in real-time using an infrared thermal imager. This work provides a novel insight into developing efficient and multifunctional EMWA materials for practical applications.

Synthesis of Hierarchical CF@Fe3O4 Fibers Decorated with MoS2 Layers Forming Core-Sheath Microstructure toward Tunable and Efficient Electromagnetic Wave Absorption.

Hierarchical structural design has been verified as a feasible strategy to fabricate effective electromagnetic wave (EMW) absorbers, so we designed hierarchical core-sheath composites with magnetic particles and dielectric layers. In this work, a hierarchical structure of carbon fiber (CF)@Fe3O4@MoS2 (CPDF7-M) was prepared by introducing Fe3O4 and depositing MoS2 layers on the surface of fibers. Due to the synergistic effects from the CF@Fe3O4 increasing the conductive and magnetic loss and the outer MoS2 layers improving the impedance matching, the optimal reflection loss (RL) value was -63.1 dB at 2.7 mm and the effective absorption bandwidth (EAB) was 9.1 GHz covering the X and Ku band. Moreover, the EAB values were adjusted with a specific MoS2 loading at different thicknesses, which provided the necessary reference for the construction of efficient and flexible absorbers in the EMW absorption fields.

Dimensional design of Fe0.9Co0.1 nano-alloys with enhanced low-frequency microwave absorption

Low-frequency microwave absorbing materials are critical for enabling radar stealth and interference resistance in gigahertz communication devices and electronic equipment. However, long-wavelength electromagnetic waves are not easily attenuated, due to the limitations of current absorbing materials, including low permeability and a lack of electromagnetic wave loss mechanisms at low frequencies. Herein, we design and prepare one- and two-dimensional Fe0.9Co0.1 nanoalloys with high permeability through an organic templating method combined with a constrained transformation strategy. We systematically investigate the impact of the anisotropy of monodisperse Fe0.9Co0.1 nanoalloys on low-frequency microwave absorption performance. The generous specific surface area of Fe0.9Co0.1 nanosheets facilitate multiple reflections and the scattering of electromagnetic waves within the absorber. This phenomenon, coupled with dielectric resonance, culminates in a maximum reflection loss value of − 48.7 dB at 4.2 GHz. More significantly, Fe0.9Co0.1 nanorods exhibit an absorption intensity of − 35.3 dB at a notably lower frequency of 2.5 GHz, outperforming existing materials, in addition to an efficient absorption bandwidth of 4.2 GHz at a thickness of only 0.7 mm. Through a combination of experimental investigations and finite element simulations, we identify that highly anisotropic magnetic nanorods demonstrate a robust magnetic coupling interaction, substantial interface polarization and quasi-antenna effect. These characteristics result in enhanced low-frequency electromagnetic losses. Our findings indicate that the high anisotropy of the Fe0.9Co0.1 nanoalloys significantly improves their microwave absorption performance, thus emphasizing their substantial potential in the development of efficient low-frequency microwave absorbers.

Microstructures, magnetic properties and microwave absorption of ion-implanted bismuth ferrite thin films

This study investigates the properties and performance of bismuth ferrite thin films on Kapton sheets as electromagnetic (EM) wave-absorbing materials. The main techniques employed in this study involved modifying the surface geometry and using electromagnetic wave-absorbing materials as surface coatings. X-ray diffraction analysis revealed a cubic crystal structure of the bismuth ferrite thin films. The bonding analysis showed the presence of Bi–O and Fe–O functional groups at 432.26 and 519.48 cm−1, respectively. Vibrating-sample magnetometry revealed the ferromagnetic behavior of the bismuth ferrite thin film, confirming that saturation magnetization decreased with increasing sputtering time. Moreover, the calcination temperature affected the coercive field; the higher the calcination temperature, the higher the coercivity of the BiFeO3 (BFO) thin film layer. Scanning electron microscopy with energy-dispersive X-ray spectroscopy of the bismuth ferrite thin films revealed the presence of Bi, Fe, and O—evenly and homogeneously distributed on the Kapton surface. After the ion implantation process, the atomic force microscopy test results showed an increased root-mean-square roughness (Rq). The root-mean-square roughness value for Kapton before the process was approximately 7.5 nm, while the root-mean-square roughness values for BFO 10 min and BFO 12.5 min were approximately 18.8 nm and 25.3 nm, respectively. The microwave absorption ability reached a maximum reflection loss value of − 40.4 dB (99.9 %) in the range of 9.98 GHz with a sputtering duration of 10 min. Therefore, these results suggest bismuth ferrite is a potential candidate as an EM wave absorber.

Production of Lignin-Derived Functional Material for Efficient Electromagnetic Wave Absorption with an Ultralow Filler Ratio.

Industrial lignin, a by-product of pulping for papermaking fibers or of second-generation ethanol production, is primarily served as a low-grade combustible energy source. The fabrication of high-value-added functional materials with industrial lignin is still a challenge. Herein, a three-dimensional hierarchical lignin-derived porous carbon (HLPC) was prepared with lignosulfonate as the carbon source and MgCO3 as the template. The uniform mixing of precursor and template agent resulted in the construction of a three-dimensional hierarchical porous structure. HLPC presented excellent electromagnetic wave (EMW) absorption performance. With a low filler content of 7 wt%, HLPC showed a minimum reflection loss (RL) value of -41.8 dB (1.7 mm, 13.8 GHz), and a maximum effective absorption bandwidth (EAB) of 4.53 GHz (1.6 mm). In addition, the enhancement mechanism of HLPC for EMW absorption was also explored through comparing the morphology and electromagnetic parameters of lignin-derived carbon (LC) and lignin-derived porous carbon (LPC). The three-dimensional hierarchical porous structure endowed the carbon with a high pore volume, resulting in an abundant gas-solid interface between air and carbon for interfacial polarization. This structure also provided conductive networks for conduction loss. This work offers a strategy to synthesize biomass-based carbon for high-performance EMW absorption.