Abstract
Carbonyl-iron/Fe91Si9 composites for thin microwave absorbers were firstly prepared by a simple blending technique. The patterns of carbonyl-iron and Fe91Si9 were characterized by scanning electron microscope (SEM). The complex permittivity, permeability and microwave absorption properties of the composites were studied in the frequency range of 2 - 7GHz by a HP8720B vector network analyzer. Complex permittivity and permeability decrease gradually with increasing weight percentage of Fe91Si9 in the composites, the variation of permittivity was very large but the variation of permeability was very small. The composites exhibited excellent microwave absorption properties with increasing Fe91Si9 content. The reflection loss (RL) values less than –20 dB were obtained in the 3.7 - 6.7 GHz frequency range for the paraffin matrix composites with 80 wt% carbonyl-iron/Fe91Si9 powders (weight ratio of carbonyl-iron to Fe91Si9 was 1:1), with thickness of 4.0 - 2.4 mm, respectively. The optimal RL of –45 dB was observed at 5.2 GHz with a matching thickness (dm) of 3.0 mm. The excellent microwave absorption properties were attributed to a better electromagnetic impedance match and a higher electric resistivity.
Highlights
In recent years, electromagnetic (EM) interference is worsening with the rapid development of wireless communications and circuit devices
The reflection loss (RL) values less than –20 dB were obtained in the 3.7 - 6.7 GHz frequency range for the paraffin matrix composites with 80 wt% carbonyl-iron/Fe91Si9 powders, with thickness of 4.0 - 2.4 mm, respectively
scanning electron microscope (SEM) images of raw commercial Fe91Si9 powders (FSP) and carbonyl-iron powders (CIP) are shown in Figures 1(a) and (b)
Summary
Electromagnetic (EM) interference is worsening with the rapid development of wireless communications and circuit devices. Since the single-component thin EM-wave absorbers cannot own simultaneously a combination of broad-band and strong microwave absorption in gigahertz range [6]. Several groups have reported good microwave absorption properties of α-Fe/Y2O3 [7], Fe/ZnO [8], Ni/polyaniline [9], Co/Al2O3 [10], Ni/C [11], Fe/SiO2 [12], Co/C [13], etc These composites all show better microwave absorption properties than corresponding single-component metallic magnetic absorbers. Carbonyl-iron as a cheap and popular magnetic metallic material has superior electric conductivity and large saturation magnetization but weak frequency dependence of complex permeability due to the eddy current loss induced by electromagnetic wave [16]. The complex permittivity, permeability and microwave absorption properties of the composites were discussed in the frequency range of 2 - 7 GHz
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