| An electromagnetic wave absorbing materials with fire retardant polypropylene hollow plates as its shell in which filled with carbon coated EPS is studied in the paper. With many closed cavums, the EPS sphere could be considered as a perfect absorber base for its light-weight, high-intensity, good chemical stability water stability and mechanical property. The fire retardancy of polypropylene hollow plates are improved greatly when fire retardant is filled. The hollow structure reduces the weight of materials so that the requirement of light is met easily.The Rayleigh scattering theory is quoted to analyze how single EPS sphere absorbs electromagnetic wave. From formula of scattering section and absorbing section, the influencing factors of absorbing performance are analyzed such as frequency, size of EPS sphere, content of carbon black. Along with frequency increase, the absorbing performance enhances gradually. There is an optimal filling height for absorber. When below this height, absorb capacity increases as height added. Above it absorb capacity has little change as height added. The content of carbon black has an optimal value also. Only when at this content the absorbing performance can reach its top value, and when the content is more or less than this value, the absorbing performance is all not as good as the top value. The surface area of all EPS sphere increase as their diameters become smaller and the content of carbon black is added, so the change of EPS's diameter is relate to the content of carbon black. The absorbing performance of materials is determineded by above four factors which influence and restrict reciprocally. So in certain condition the optimal combination should be analyzed concretely.The absorber which filled with EPS is considered as a resonant cavity, and the formula of resonant frequency is gotten from resonant cavity theory. From the formula, resonant frequency is decreases as the content of carbon black added and absorbing performance is better as resonant frequency become lower. But the precondition is that content of carbon black could not too large. The resonance theory is not suitable if electromagnetic wave could not propagation through the absorber.The test results show that for flat absorber, the optimal technological parameter is as follows: the filling height is 4cm, content of carbon black is 4% and diameter of EPS sphere is 2mm. When frequency is 8-12GHz, the absorption is above 30dB and average absorption is above 40dB, which reaches its best effect. And to pyramids the diameter is 4mm and 4%carbon black reach the maximum absorption, which average absorption is above SSdB. This pyramid is 500mm height, and the absorption would add when the height increases.Based on impedance matching theory, the carbon black is crescent and distribute as staircase structure in pyramids from the top to the bottom. The problem of impedance matching is solved effectively and the reflection is reduced largely. Two kinds of impedance matching modes are listed and compared. The results show that the absorber rilled with EPS in different diameter has better performance; its absorption is superior to the urethane absorber more than 5dB.
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