Investigation of the Broadband Microwave Absorption of Citric Acid Coated Fe3O4/PVDF Composite Using Finite Element Method

Abstract

Magnetite (Fe 3 O 4 ) have been thoroughly investigated as microwave absorbing material due to its excellent electromagnetic properties (permittivity and permeability) and favorable saturation magnetization. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). Herein, Fe 3 O 4 nanoparticles prepared by facile co-precipitation method have been coated with citric acid and embedded in a polyvinylidene fluoride (PVDF) matrix. The coated Fe 3 O 4 nanoparticles were characterized by X-ray diffraction spectrometer (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometer (VSM). COMSOL Multiphysics based on the finite element method was used to simulate the rectangular waveguide at X-band and Ku-band frequency range in three-dimensional geometry. The citric acid coated Fe 3 O 4 /PVDF composite with 40 wt.% filler loading displayed good microwave absorption ability over the studied frequency range (8.2-18 GHz). A minimum reflection loss of −47.3 dB occurs at 17.9 GHz with 2.5 mm absorber thickness. The composite of citric acid coated Fe 3 O 4 and PVDF was thus verified as a potential absorptive material with improved MAP. These enhanced absorption coefficients can be ascribed to favorable impedance match and moderate attenuation. Appl. Sci. 2019, 9, 3877 2 of 17 attracted much interest in the field of EM wave absorption. However, Fe 3 O 4 as an absorptive material have some limitations such as the rapid decrease in permeability value at microwave frequency, large density, ease of oxidation and mismatch of impedance which impedes its performance as an ideal MAM [6,7].Recently, several research efforts have been geared towards improving the microwave absorption performance (MAP) of Fe 3 O 4 . For example, Mingxu et al. [8] fabricated hollow Fe 3 O 4 nanoparticles via solvothermal route, with the aim of reducing its density while retaining good magnetic properties for efficient MAP. They established improved EM wave absorption with increasing particle size and change in morphology. Maximum EM absorption with RL value of −55.14 dB at 11.76 GHz was achieved with an absorber thickness of 2.07 mm. Guiquig et al. [9] synthesized nano-Fe 3 O 4 by an innovative wet chemical route, employing hydrazine hydrate as anti-oxidation agent. The synthesized Fe 3 O 4 nanoparticle of average diameter of 77 nm possessed high magnetization saturation and coercivity value of 72.36 emu/g and 95 Oe, respectively. The minimum RL value of −21.2 dB was achieved with 6 mm thickness. Similarly, optimization of the MAP of Fe 3 O 4 via design and fabrication of hierarchical nanostructure have also been explored. Chaomie et al. [10] exploit one-step and template-free synthesis method to prepare octahedral Fe 3 O 4 nanostructure by direct decomposition of an iron organic compound with molten salt. The sample annealed at 800 • C displayed maximum EM absorption of −23.67 dB at 15.24 GHz at a ...

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