Research On Properties Of Radar Wave Absorption Of Cement-based Composite Materials;research On Properties Of Radar Wave Absorption Of Cement-based Composite Materials;research On Properties Of Radar Wave Absorption Of Cement-based Composite Materials

With advances in the radar detection technology, demand for high quality, broadband and low-cost radar absorbing materials has been increasing in the military field. Military bunkers, roads, bridges and so on, are the key military to-be protected objects. It is of great significance to defense protection works that the above-mentioned infrastructures were made stealth using high-strength and low price cement-based radar absorbing composites. Therefore, high strength cement-based absorbing composites are studied regarding with electromagnetic properties, microstructure, theoretic calculation and structural design and so on in this paper.In view of the lower strength of cement-based absorbing composite, high strength cement-based materials excluding coarse aggregate were first prepared in the paper. The basic mix proportion of the high strength cement-based materials were determined based on the dense packing theoretical calculations and mechanical property test, and then the specimen was prepared according to the mix proportion. The conductivity belonging to the semiconductor scope of the specimen was obtained by a four-electrode measurement. In order to master the basic law of reflectivity of the cement-based materials, the influence of different water-binder ratio and thickness on the specimen radar (2~18GHz) reflectivity was investigated respectively. The results show that the change of water-binder ratio has little effect on the reflectivity of radar, but the radar reflectivity reduces as the thickness of specimen increases. To further investigate the absorbing principle of cement-based materials, the absorbing properties of cement-based materials, based on their electromagnetic parameters, were simulated by using radar reflection formula of single-layer absorbing materials and then were compared with the measured values.Using electrical loss absorbing materials (such as ultra-fine steel fiber, graphite) and magnetic loss absorbing materials (such as ferrite) compound with the cement-based materials respectively, the effect of dosage of the absorbing materials and thickness on absorption performance of cement-based composites was investigated respectively. The test results indicate that the electrical loss absorbing materials are beneficial to improve the absorbing properties of the cement matrix in high frequency bands and the magnetic materials are beneficial to improve ones in low frequency bands, but there exist the matching problems of thickness and impedance for the cement-based composites. To further clarify the absorbing mechanism of the cement-based composites, their electromagnetic parameters were optimized through presetting the absorbing value of the cement-based composites in S~Ku(2~18GHz). The results suggest that the larger the absorbing value is, the greater the required imaginary part of dielectric permittivity and magnetic permeability are, and the closer electric loss tangent and magnetic loss tangent are.Through analyzing absorbing mechanism, the materials with cavity structure such as zeolit powder, fly ash floating beads and closed cell perlite (vitrified microsphere),were selected as resonant materials to mix into the cement-based materials and then the law of radar absorption of the composites was studied. On this basis, fly ash floating beads and closed cell perlite were combined, respectively, with graphite and ferrite by mixing and coating ways, and then it was compared of the improvement effect on radar absorbing of cement-based materials of the two approaches. Results show that the way of coating perilte with ferrite increases absorption of the composites in the frequency rang of S~Ku (2~18GHz) and the bandwidth of -8dB of the composites reaches 14GHz. Microstructure studies show that the perlite is the similar spherical-type particle in which continuous glaze surface and special honeycomb structures distribute alternately and contains a large number of cavity. When using the absorbing materials to coat the perlite, the absorbing materials distributed uniformly on its surface and in its cavity, formed the good performance resonant absorber, and broadened the absorbing bandwidth of cement-based materials effectively after being mixed into the cement-based materials.Summarizing the above studies, three-layer structure, which can be combined to form the unitary structure, of cement-based composites including the different functional layers was designed in the paper at last. According to the principle of"Transmission, absorption and scattering", the ultra-fine steel fiber or ferrite cement-based composite was used as the bottom of three-layer structures, the absorbing material types in the surface layer and middle layer were changed, and then the reflectivity of the three-layer structure composite was researched. It shows that the absorbing value of the composite of three-layer structure, namely zeolit powder + cement-based material/perlite coated by graphite + cement-based material/steel + cement-based material, are more than 10dB in the frequency range of X~Ku. Therefore, the composites with three-layer structure have stealth role in the whole frequency range of X~Ku.