As is the same with other magnetic absorbents, the high density of carbonyl iron powder may become the biggest bottleneck that limits its wide application. In this research, different samples that contains different carbonyl iron powder will be prepared and electromagnetic parameter will be measured, besides, coating design that has lowest density will be obtained by using self-compiled optimization design software under single layer and multilayer conditions as well as the design result will be analyzed. Self-compiled optimization design software can be used in optimizing by using absorption bandwidth and areal density as indicator, thus paraffin and carbonyl iron powder can be mixed according to predetermined proportion.
Performance test of carbonyl iron powder
Pattern analysis of carbonyl iron metal powder has been made by electron microscopy room of forecasting and analysis center in Central South University in China, in which X2650 scanning electron microscope will be used and acceleration voltage will be 20kV. Relative dielectric constant and relative permeability of coaxial samples will be measured with coaxial method by using Angilent8720ET network analyzer. It can be seen from the scanning electron micrograph of carbonyl iron powder that carbonyl iron powder will appear to be spherical shape, most of the particles will be ranged between 0.3-2μm as well as it will have smooth surface.
According to the electromagnetic parameter and thickness of absorbing material, this research will have stimulated calculation of reflectivity by using electromagnetic field transmission line theory as well as the optimization design software and complete enumeration method will be used. In the calculation process, the maximum areal density can be preset as well as coatings can be screened according to areal density so as to remove undesirable items, thus it can greatly reduce calculated amount. It can be seen from the optimal design results that the reflectivity of single layer and multilayer absorber coatings in X wave band will be both less than -10dB, the separated layer will have little effect on the decreasing of coating surface density as well as the lowest density of single layer absorbing coating can reach 5.83kg/m2 and the lowest density of multilayer absorbing coating can reach 5.49kg/m2; after comparing the density between two-layer coating and five-layer coating, it can be seen that the increasing of layer number will not obviously reduce areal density; the areal density of two-layer, three-layer and four-layer absorbing coatings will not differ a lot, while the areal density of five-layer absorbing coating will increase slightly; the overall thickness of single layer and multilayer absorbing coating both will be 1.40mm.
Compared with carbon black, carbon fiber and other electrical loss absorbents, the increasing content of carbonyl iron powder in the absorbing materials will not bring large dielectric constant or electrical loss, thus it can maintain impedance matching characteristic with free space, meanwhile, the increasing of carbonyl iron powder content will be beneficial for reducing magnetic loss, therefore, high carbonyl iron powder content will be beneficial for reducing absorbing coating density, but it should not obstruct the processing property of coating.
In conclusion, by using complete enumeration method, it can presuppose upper limit areal density according to requirement, besides, the coating compositions can be screened according to areal density so as to remove undesirable items, thus it can greatly reduce calculated amount. By adjusting carbonyl iron powder absorbent content, it can adjust electromagnetic parameter as well as multilayer absorbing materials can be prepared according to different contents. The reflectivity of single layer and multilayer in X wave band will be both less than -10dB, besides, the separated layer will have little effect on reducing coating surface density. Single layer will be suitable for being used in carbonyl iron powder absorbing coating.
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