Microwave Absorbing Properties Of Cement Based Composites

The building construction with the use of cement-based materials is everywhere in daily life.With the development of science and technology,more and more functional cement-based materials has arisen,which are applied to all professions and trades.Among them,the cement-based electromagnetic-waves(EMW)absorbing materials are the focus in recent years.With the advent of information age,EMW brings convenience but comes with troubles,including EMW pollution,electronic information leakage,even national information security risks.Therefore,the construction of the construction project with EMW absorption function by using cement-based absorbing materials becomes important applications for civil and military.This paper combines the cement-based materials of civil engineering with the structure of the Metamaterial absorber in electromagnetics engineering.Through the research of electromagnetic properties of cement-based materials,it is applied to the design of the metamaterial absorber.The electromagnetic theory was used via simulation and the absorbing system of cement-based metamaterialwas prepared and tested.The specific topics are divided into the following parts:(1)The electromagnetic parameters calculation methods based on the effective medium theory and the generalized sheet transition conditions are discussed again.The equivalence of the two methods is verified with the unity thickness(1mm).(2)The Specimen of ‘Guo Biao’(GB)concrete(C30,C40,C50),fiber cement mortar and common cement mortar were prepared and cured.The electromagnetic parameters(complex permittivity)of cement-based materials with several ratios were measured and analyzed by using the open coaxial probe method.It was found that the complex permittivity of cement-based materials with stable free water content was between 4-7.(3)The electromagnetic parameters of cement-based materials are designed by CST software and the electromagnetic parameters.The top layer of the meta-surface resonance unit selected the FR-4 PCB dielectric board,which could directly carve the top metal layer according to the shape drawn by CAD,so as to avoid inaccuracy in the preparation of cement-based materials.The structure of the designed absorber of cement-based Metamaterial is "metal resonance element layer + FR4 medium layer +cement-based material layer + metal shield layer".Through the analysis of simulation data,it can be found that the increase of real part and imaginary parts of complex dielectric constant will weaken the absorbing performance to a certain extent,and the real part of complex permittivity would cause the movement of the operating frequency of the absorber.(4)The PCB dielectric board of FR4 is carved according to the design shape by LPKF circuit board Carver;the double layer cement-based material board is prepared with "7mm cement mortar + tinfoil +93mm GB concrete",with a length and width of600 mm × 600 mm,which is poured and maintained according to the test requirements;After curing,the FR4 medium board and the double-layer cement-based material board shall be tightly bonded together according to the requirements,leaving no gap as far as possible.The free space method measurement system is built to measure,the reflection coefficient and transmission coefficient are obtained.The absorbing rate of the absorber of cement-based meta-material is calculated.The absorbing performance of the meta-material absorber of cement based mate-material is analyzed.It is found that the absorbing effect of the absorber of cement based super material can be basically achieved more than 90% in the S-band.