Polymer Nanocomposites with Hybrid Fillers as Materials with Controllable Electrodynamic Characteristics for Microwave Devices
The results of investigation of microwave electromagnetic properties in wide frequency range (1–67 GHz) of the hybrid polymer composites based on combined introduction of ferrite and MWCNTs nanoparticles are presented. The surge in 3–5 orders of the conductivity value has been founded in MWCNTs/Fe3O4 (BaFe12O19)/epoxy composites with 2 and 5 wt. % of MWCNTs as compared with MWCNTs/epoxy composites, and these changes are more considerable for lower content of MWCNTs in the epoxy matrix. The addition of 30 wt. % of Fe3O4 (BaFe12O19) nanoparticles to MWCNTs/epoxy composites leads to the significant increase of the complex permittivity values and to the frequency shift of relaxation maximums. The natural ferromagnetic resonance was revealed as the main mechanism of magnetic loss in MWCNTs/Fe3O4/epoxy composites at frequencies up to 10–12 GHz while the eddy current induced mechanism becomes the dominant in magnetic loss at the further frequency increase. The natural ferromagnetic resonance determines the character of magnetic loss in BaFe12O19-filled composites in the whole investigated frequency range.
The integration of nanotubes and ferrite admixture of Fe3O4 or BaFe12O19 in MWCNT/30 wt. % Fe3O4 (or 30 wt. % BaFe12O19) ternary composites provides synergetic effects and complementary behavior (e.g., various polarization relaxations as additional loss mechanisms), which greatly contribute to the microwave absorption properties for both studied ternary composites. The absorption bandwidth reaches 13–17 GHz for thin (0.6–0.8 mm) composite samples with 2 wt. % of nanotubes content. The increase of MWCNTs content and the use of two component fillers lead to decrease of the effective reflection loss in the frequency range above 20 GHz. The maximum reflection loss reaches 49 dB for Fe3O4- and 39 dB for BaFe12O19-filled composites of 1.1–1.2 mm thickness while the absorption bandwidth does not exceed 5 GHz.
KeywordsPolymer composite Nanocarbon Hybrid filler Ferrite, microwave shielding
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