Fabrication of N-Doped Reduced Graphite Oxide/MnCo2O4 Nanocomposites for Enhanced Microwave Absorption Performance

Electromagnetic textile absorber applied to 4G and 5G bands

Absorber materials are developed to reduce electromagnetic radiation and ensure the compatibility of the operation of electronic equipment in environments subject to interference. This work presents the development of a low-cost textile electromagnetic absorber for 4G and 5G technologies, operating at frequencies of 2.5 GHz and 3.5 GHz. The proposed electromagnetic absorber utilizes a 1 mm-thick Denim substrate, with a graphite composite used in the agricultural and commercial polyvinyl acetate glue industry, with the relationship of 25 wt%. The measurements were carried out in a Vector Network Analyzer, model E5071C Agilent Technologies, with the characterization of the Denim substrate, the glue, and the identification of the best parameters for the construction of the absorber. In the project, three low-cost textile absorbers prototypes were fabricated, with G1 = 0.25 mm, G2 = 0.35 mm, and G3 = 0.5 mm of thickness layers of the composite deposited on a Denim fabric. The results indicate that the absorber prototypes G2 presents great results in the frequency range of 4G and 5G band, with a maximum absorption of 26.6 dB in 3.94 GHz, with a structure 98.83% thinner than the commercial absorber LF-75. The variation in absorption performance may be attributed to the different mechanisms by which the absorbers operate: the commercial absorber LF-75 primarily interacts with the magnetic field, whereas the textile prototype predominantly affects the electric field.

Gene-Implanting by a Porphyrin Derivative to Establish Quasi-antennas into the Carbon Microspheres toward Superior Microwave Absorbing/Shielding Performance

Carbon microspheres (CMSs) are recognized as highly effective microwave absorbers due to their exceptional wave absorption properties. In this study, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, a metamaterial, was chemically bonded to CMSs─considered a conjugated carbon structure─using a 1,3-dibromopropane linker to explore the synergistic properties and microwave absorption capabilities of the synthesized composite. The synthesized structures were characterized by using X-ray diffraction, FE-SEM, Fourier transform infrared, diffuse reflectance spectroscopy, and VNA analyses. Remarkably, the gene-modified microwave absorber demonstrated a maximum reflection loss of -105.58 dB at 22.93 GHz, with an ultrathin thickness of only 0.50 mm. When the architected samples were blended with poly(methyl methacrylate), a practical polymer, they exhibited a broad efficient bandwidth across the entire K-band, coupled with moderate shielding effectiveness, making them ideal for mitigating electromagnetic pollution in everyday life. This study offers inspiration for researchers to fabricate and design new enhanced microwave absorbers for a range of applications.

Fabrication of Multifunctional Silylated GO/FeSiAl Epoxy Composites: A Heat Conducting Microwave Absorber for 5G Base Station Packaging

A multifunctional microwave absorber with high thermal conductivity for 5G base station packaging comprising silylated GO/FeSiAl epoxy composites were fabricated by a simple solvent-handling method, and its microwave absorption properties and thermal conductivity were presented. It could act as an applicable microwave absorber for highly integrated 5G base station packaging with 5G antennas within a range of operating frequency of 2.575-2.645 GHz at a small thickness (2 mm), as evident from reflection loss with a maximum of -48.28 dB and an effective range of 3.6 GHz. Such a prominent microwave absorbing performance results from interfacial polarization resonance attributed to a nicely formed GO/FeSiAl interface through silylation. It also exhibits a significant enhanced thermal conductivity of 1.6 W/(mK) by constructing successive thermal channels.

Fabrication of the Fe-Doped Corona Schiff Base for Enhanced Microwave Absorption Performance

A corolla-shaped Schiff base polymer was synthesized from terephthalaldehyde (TPAD), glutaraldehyde (GA), and p-phenylenediamine (PPD) by block copolymerization, and Schiff base iron complexes were formed by doping with FeCl3. The microscopic morphology, crystal structure, and elemental valence state were characterized by field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Comparing the change of conductivity before and after Fe3+ doping, it was found that the conductivity did not break away from the category of insulator, and the doped sample is a paramagnetic material. Morphological changes were observed by adjusting the ratio of GA to TPAD, and it was found that the corolla-like structure was most complete when the ratio of GA to TPAD was 2:1, and its Schiff base iron complex absorbed waves better. At a thickness of 3 mm, the absorption effect can reach below -10 dB at 12.44-15.16 GHz, and the maximum absorption value is -45.07 dB at a thickness of 3.8 mm; it is an organic absorbing agent with excellent impedance matching and absorbing properties.

Lightweight TiO2@C/Carbon Fiber Aerogels Prepared from Ti3C2Tx/Cotton for High-Efficiency Microwave Absorption

Carbon fiber aerogel (CFA) derived from cotton wool as a potential microwave absorbing material has received intensive attention owing to the low density, high conductivity, large surface area, and low cost, but its applications are limited by the relatively high complex permittivity. To solve this problem, TiO₂@C (derived from Ti₃C₂T_x) is introduced into CFA to prepare lightweight TiO₂@C/CFA composites based on electromagnetic (EM) parameter optimization and enhanced EM wave attenuation performance. The microwave absorption capacity of TiO₂@C/CFA-2 composite is obviously better than that of CFA. It is confirmed that good impedance matching derived from the combination of TiO₂@C and CFA is the main factor to achieve excellent microwave absorption. Moreover, the improved microwave absorption capabilities are closely related to multiple EM wave absorbing mechanisms including multiple reflections and scattering, dipolar and interfacial polarization, and conductivity loss. TiO₂@C/CFA-2 possesses a maximum reflection loss (RL) of -43.18 dB at a low response frequency of 6.0 GHz. As the matching thickness is less than 2.0 mm, the maximum RL values can still exceed -20 dB, and at the same time, the wide effective absorption bandwidth (EAB) below -10 dB achieves 4.36 GHz at only 1.9 mm thickness. Our work confirms that the lightweight and high-performance TiO₂@C/CFA composites are promising choices and offer a new approach to design and construct carbon-based microwave absorbents derived from biomass.

Hematite nanoparticles decorated nitrogen-doped reduced graphene oxide/graphitic carbon nitride multifunctional heterostructure photocatalyst towards environmental applications

The carcinogenic heavy metals and aromatic organic compounds linger as wastewater pollutants implying great menace to the ecological balance. To solve these environmental pollution problems, the photocatalytic process is an...

Room-Temperature One-Step Synthesis of Silver/Reduced Graphene Oxide Nanocomposites as an Excellent Microwave Absorber

The present study is focused on room-temperature synthesis carried out by reduction of an aqueous silver nitrate (AgNO₃) and AgNO₃/graphene oxide (GO) dispersion using a low-cost commercial Fehling B solution in one step to form silver quantum dots (Ag QDs) and their Ag/reduced graphene oxide (Ag/RGO) nanocomposites and their characterization. The crystallinity, surface chemistry, structural, and morphological studies indicated the formation of crystalline small-sized quasispherical-functionalized Ag particles distributed uniformly on the surface of RGO. The conductivity measurements further showed an improvement in the conductivity of Ag/RGO nanocomposites as compared to neat Ag QDs. Our findings showed that Ag/RGO nanocomposites prepared by using 0.055 wt % of GO exhibited a total enhanced electromagnetic interference (EMI)-shielding efficiency (SE_T) of ∼39.2-42.3 dB (2-8 GHz) with a maximum value of ∼43.8 dB at 7. 5 GHz due to conduction loss, an interconnected conducting network, and a synergistic effect, and it followed an absorption mechanism. Furthermore, this superior absorption-dominated shielding conferred reflection loss (R_L) in the range of -79 to -82.5 dB with a R_L minima of -88 dB at 7.5 GHz, considering an effective absorption bandwidth of ∼6 GHz with 99.9% absorptivity. It is anticipated that Ag/RGO nanocomposites prepared in one step at room temperature could find potential EMI-shielding applications.

Functionalized Graphene/Nickel/Polyaniline Ternary Nanocomposites: Fabrication and Application as Electromagnetic Wave Absorbers

The evolution of high electromagnetic absorption materials is essential in the fast growing electronic industry in overcoming electromagnetic pollution. In view of this, a series of Ni nanoparticle-decorated functionalized graphene sheets (FG/Ni) are synthesized by a solvothermal method using different ratios of FG/Ni precursors. Subsequently, FG/Ni is subjected to in situ polymerization of aniline to form FG/Ni/PANI ternary composites and characterized. The total electromagnetic interference shielding efficiency (SE_T) measurements on FG/Ni/PANI with an optimized FG/Ni ratio (50 mg:600 mg NiCl₂·6H₂O) exhibit enhanced performance, i.e., ∼47-65 dB (2-3.8 GHz) and ∼65-45 dB (3.8-8 GHz), following absorption as the dominant mechanism due to the matching of dielectric loss and magnetic loss. It is anticipated that such excellent performance of robust FG/Ni/PANI ternary composites at a very low thickness (0.5 mm) has great potential in the application of microwave-absorbing materials.