| As an information carrier,electromagnetic waves also have adverse effects on human health and precision instruments,and there is a risk of military,political and economic information leakage.Cement-based materials are widely used in military facilities and civil buildings,so it is of great value to develop cement-based materials with good wave absorption and mechanical properties.Therefore,in this thesis,porous materials,foam and vibration delamination are introduced to design the structure,and finally cement-based microwave absorbing materials with excellent performance are prepared.The dense structure of cement material makes most of the incident electromagnetic waves reflected back into the free space,so the improvement of impedance matching is the premise to improve the absorption performance.In this thesis,expanded perlite,polypropylene foam and foam are mixed into cement-based materials,and the slurry is stratified by using a vibration table to prepare cement-based materials with double-layer or gradual structure(thickness of 30mm).The main research contents of this thesis are as follows:(1)By mixing expanded perlite and polypropylene foam into cement-based materials,the influence of the distribution and content of porous materials,composite mixing combination,surface layer morphology,and material thickness on the reflectivity or mechanical strength was obtained.When the content of polypropylene foam is 30vol%and the vibration duration is 180 seconds,the bandwidth of the prepared sample cementbased microwave absorbing material is 14.28 GHz,which is lower than-10 d B within 2-18 Ghz,and the flexural and compressive strength is about 4.5MPa and 29.97 MPa.(2)The cement-based material with gradual structure was prepared by foaming plant protein and shaking table.The effects of pore distribution and content,material thickness and stacking combination on the wave absorption properties or mechanical properties were investigated.When the introduction of foam is 60vol%,the bandwidth of foam cement-based material is 15.32 GHz,which is lower than-10 d B in 2-18 GHz.In addition,the electromagnetic parameters of single-layer foam cement-based materials were measured by the free space method and the influence of thickness on the reflection loss was discussed.The results showed that when the volume fraction of foam was high,the reflection loss at low frequencies could continue reducing with the increase of thickness.(3)The preconditions for the absorption efficiency of Fe Si Al were explored.In this thesis,the influence of Fe Si Al absorbent content on the absorption performance is investigated by means of composite doped media and stacking.When the cement-based material contains 30vol% expanded perlite and 30vol% foam,the introduction of Fe Si Al can significantly improve the wave absorption performance,and the optimal content is2vol%.When the upper layer material is a gradient cement-based material containing60vol% foam,the reflectivity decreases with the increase of Fe Si Al content in the lower layer material,and the double-layer material is lower than-10 d B in 2～18GHz.The cement-based material finally prepared in this thesis has excellent wave absorption performance and mechanical properties,and is easy to prepare and low cost,which lays a good foundation for the further research of the absorbent filled cement-based wave absorption material. |
