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Double-layer microwave absorber based on nanocrystalline CoFe2O4 and CoFe2O4/PANI multi-core/shell composites

Xu Y., Shen G., Wu H., Liu B., Fang X., Zhang D., Zhu J.

Materials Science Poland

2017

Vol. 35, No. 1

94--104

Organic-inorganic nano-CoFe2O4/PANI (polyaniline) multi-core/shell composites have been successfully synthesized by chemical oxidative polymerization of aniline. The characterization results showed that the ferrite nanocrystals were efficiently embedded in PANI. The electromagnetic parameters of the composites were measured by a vector network analyser in the frequency range of 2 GHz to 18 GHz. Double-layer absorbers based on the CoFe2O4/PANI composite (matching layer) and calcined CoFe2O4 ferrite (absorbing layer) have been designed. The reflection loss of the microwave absorbers of both single layer and double-layer with a total thickness of 2.0 mm and 2.5 mm was calculated according to transmission-line theory. The results indicated that the minimum reflection loss of the CoFe2O4/PANI composite was −19.0 dB at 16.2 GHz at the thickness of 2.0 mm and −23.6 dB at 13.1 GHz at the thickness of 2.5 mm, respectively. The minimum reflection loss for double-layer absorbers reached −28.8 dB at 16.2 GHz at the total thickness of 2.0 mm, and −31.1 dB at 12.8 GHz at the total thickness of 2.5 mm. The absorption bandwidth under −10 dB was 4.2 GHz (13.8 GHz to 18.0 GHz) and 5.5 GHz (10.3 GHz to 15.8 GHz), respectively. The results show that the reflection loss and absorption bandwidth of the double-layer absorbers are obviously enhanced compared to corresponding single layer absorbers.

Study on absorption and mechanical properties of rubber sheet absorbers

Gong R., He Y., Li X., Liu C., Wang X.

Materials Science Poland

2007

Vol. 25, No. 4

1001--1010

Based on the impedance matching principle and electromagnetic wave propagating law, double-layer absorbers with impedance-matching structure were designed both theoretically and experimentally. Microwave absorbers were prepared by mixing a commercially available rubber with magnetic micropowder (MMP) and/or dielectric materials. The first layer, made up of MMP has large permeability and magnetic loss, while the second layer (matching layer), comprised of MMP and/or dielectric material, has frequency dispersion with the parameters of permittivity and permeability to match the incidence free space over a wide frequency range. Experiments showed that the matching layer plays a key role in the absorption. Electromagnetic parameters and thickness need to be controlled precisely to achieve high absorption. It was reasoned out that with increasing electromagnetic performance of matching layer, matching thickness will decrease. Tests showed that the reflectivity was below -10 dB for samples 1 and 2, and below - 8 dB for samples 3-6 in the frequency range of 8-18 GHz. Finally, mechanical characteristics were also investigated with tensile strength above 10 MPa, indicating that the materials may find practical use in the engineering of microwave absorbers.