The Importance of Multi level Porous Carbon Materials Absorbing Waves in Electronic and Defense Security

The increasingly severe electromagnetic pollution has caused serious harm to human health, electronic security, and national defense security. To solve this problem, people have been committed to researching materials with advantages such as strong absorption, wide screen bandwidth, and lightweight thin layersAbsorber.

Recently, advances in electromagnetic wave absorption theory and material preparation technology have shown that excellent absorption performance is attributed to well-designed microstructures, such as porous, core-shell, and sandwich structures. However, there are still many problems in the microstructure construction of absorbing materials in the current market, such as complex preparation processes and high costs. In addition, the influence of structure on absorption performance still needs to be studied.

Our advanced technology institute has prepared various structures using simple methods and low-cost raw materialsHigh performance absorbing materialsAnd conducted in-depth research on the influence of different structures on the absorption performance.

The main content is detailed as follows:

(1) A series of excellent absorbing properties were prepared by one-step carbonization of natural biomassMulti porous carbon materialDuring the carbonization process, the inherent alkali metal elements of biomass etch the carbon material in situ to produce nanoporous structures, while the micro pore structure of the natural tissue of biomass is partially retained, thus forming a multi-level pore structure. Among all samples, the maximum reflection loss (RL_ (max)) of multi-level pore carbon derived from spinach stems was as high as -62.2dB, and the effective absorption bandwidth (EAB) reached 7.3 GHz. In addition, the multi-level porous carbon materials prepared from spinach stems matured in different seasons as precursors have similar microwave absorption properties, indicating excellent repeatability of the material. Research has found that the superposition effect of multi-scale pores endows multi-level porous carbon materials with excellent absorbing properties.

(2) Fe3O4 @ polypyrrole (PPy) core-shell composite microspheres with excellent absorbing properties were prepared by a simple etching polymerization method. Using prefabricated Fe3O4 microspheres as templates, a large amount of Fe~(3) formed on the surface of the microspheres by hydrochloric acid etching triggers in-situ polymerization of pyrrole monomers, thus forming a core-shell structure. The thickness of PPy shell and the mass fraction of Fe3O4 core can be precisely controlled by adjusting the etching time. When the etching time is only 5 minutes, the RL_ (max) of the sample reaches -41.9dB, and the EAB covers the entire Ku band (12.0-18.0GHz) with a matching thickness of 2.0 mm. This excellent absorbing performance mainly comes from the strong dielectric loss caused by the polypyrrole shell.

(3) Sandwich type carbon/FeOx/graphene ternary composite materials were prepared by a simple method. Soak the melamine sponge in a mixed solution of graphene oxide and Fe (NO3) 3, then dry and carbonize under a nitrogen atmosphere. During the pyrolysis process, the porous structure of the sponge is preserved, and graphene oxide is reduced and loaded onto the carbon skeleton. At the same time, iron nitrate reacts to form iron oxide microparticles or nanoparticles attached to the reduced graphene oxide, thus forming a sandwich structure composite material. The RL_ (max) of the prepared sample reached -51.2dB, with an EAB of 8.7GHz, covering the entire Ku band and most of the X band (8.0-12.0 GHz). Research has shown that the excellent absorption performance of this material comes from the enhanced interface polarization relaxation and electromagnetic wave multiple reflection by the sandwich structure.

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