Research On The Structural Design And The Absorbing Properties Of Nature Rubber Based Composite Absorbing Materials

In this paper, a new type of absorbing materials based on nature rubber with different structure were designed and fabricated aiming at the demands to develop novel and effective electromagnetic (EM) wave absorbers for the increasingly severe electromagnetic pollution, and the properties of the products were discussed. The structure and performance of the prepared materials were characterized by Scanning Electron Microscope, Transmission Electron Microscope, X-Ray Diffraction and Vector Network Analyzer etc, and the microwave absorbing mechanism of the composite films was simply discussed.Findings show that N234 CB is a kind of electric loss medium and it has high electric conductivity and dielectric constants. Carbonyl iron belongs to magnetic material, which have a high permeability. It is found by studying on the monolayer composites that the absorbing properties of the samples are improved with the increase in the amount of the absorbent (CB, CI) for the increasing of imaginary part of electromagnetic parameters and the enhancement of loss. But when the amount of the absorbent reaches a certain level, the absorbing properties begin to decline, because the assembled particles lead to the inequality of the absorbent distribution and the decreased resistance matching between the surface of the composite and the air, which makes a large amount of electromagnetic waves reflected back to the open air. In order to explore the influence of different rubber matrix on the absorbing properties, samples with the same absorbent content and thickness based on single nature rubber (NR) and mixed rubber were prepared respectively, the position of the absorbing peak and the effective bandwidth of absorbing sample based on mixed rubber matrix moved towards lower frequency region as compared with the absorbing sample based on single nature rubber, and the peak value increased. In the frequency range of 2-18GHz, the absorbing samples in which the concentration of CB and concentration of CI are 50phr obtained the minimal reflectivity at 15.9GHz (R=-19.2dB),14GHz (R=-20dB) and 11.6GHz (R=-21.2dB), respectively, when the thickness increased from 1.3mm to 2.0mm, the position of the absorbing peak moved towards lower frequency, but the peak value did not change much, when the thickness of sample more than 2mm, the peak value decreased obviously with the corresponding frequency position keep move towards lower frequency region, results showed that there was not a simple linear relationship between thickness and absorbing property, there existed an optimal thickness. On the bases of monolayer composites, bilayer absorbing materials with resistance gradual changing structure (absorbing layer+ matching layer) were prepared. The electromagnetic parameter was controlled by the amount of the absorbent in the matching layer to achieve the resistance matching between the surface of the bilayer material and the air; the absorbing capacity is increased by changing the amount of the absorbent in the absorbing layer. When the concentration of filler in the matching layer was 70phr CB and 70phr CI, and the concentration of filler in the absorbing layer was 110phr CB, the absorbing sample obtained the minimal reflectivity at 4.6GHz (R=-12dB),12.3GHz (R=-10.6dB) and 11.6GHz (R=-21.2dB), and the effective absorption bandwidth below-8dB reached 4.1 GHz (3.9 GHz～5.4GHz,11.2 GHz～13.8GHz).