Research On The Electromagnetic Wave Absorbing Plate

This paper studied the electromagnetic (EM) wave absorbing properties of the expanded polystyrene (EPS) lightweight cement and the manganese dioxide/silica dioxide composite for the first time.A surface treatment was carried out to enhance the hydrophilic property and the uniformity of the EPS beads with the cement grout, and the EPS cements with different thicknesses and filling ratios of EPS beads were prepared. The EM wave absorbing properties were measured using arch reflecting method in anechoic room. The analysis of the change of the dielectric property during the hydration and the inner macrostructure of the EPS cement were carried out to investigate the mechanism of the absorbing properties of the EPS cement, the effects of thickness, filling ratio and EPS beads' diameter on absorbing properties were studied. The results show that the EPS cement plate holds a good wave-absorbing characteristic. The dielectric loss of the chemical and mineral component in the cement and the resonance of the inner macrostructure contribute to the EM wave absorption and attenuation. The match thickness is determined by the filling ratio and the diameter of the EPS bead; the diameter can affect the wave-absorbing property (with the same filling ratio) when the filling ratio>60%. In 2~18GHz, the sample with a filling ratio of 60%, diameter of 2mm and thickness of 20mm holds a working bandwidth of 6GHz, and the sample with a filling ratio of 50%, diameter of 4mm and thickness of 30mm holds a working bandwidth of 7GHz.The XRD and TEM method was performed to analyze the component and the particle pattern of the manganese dioxide respectively; the complex permittivity and complex permeability was measured by the coaxial method in 2~18GHz, and the EM characteristic of the manganese dioxide was investigated. The manganese dioxide/silica dioxide composite was prepared using the polyvinyl alcohol (PVA) solution as adhesive binder. The wave-absorbing properties of the composites (with the manganese dioxide contents of 10%, 20%, 30%, 40% and 50%) were compared in 2~18GHz, and the complex EM parameter and the wave-absorbing property were calculated by computer. It is found that the manganese dioxide was a dielectric absorbent; the manganese dioxide composites performed well as EM wave absorber in low frequencies, and the best wave-absorbing property showed a characteristic of frequency selectivity, the absorption peak shifted to the lower frequency with the manganese dioxide content increasing. In 2~8GHz the composites showed better wave-absorbing property when the manganese dioxide content between 30%~40%, and in 8~18GHz the composites showed better performance when the manganese dioxide contentbetween 20%~30%. The effective permittivity of the manganese dioxide composites can be calculated by the extended formula of the Rayleigh mixing formula when the volume fraction of manganese dioxide between 20-40%.