Study On Electromagnetic Properties Of Ultralightweight Cement Composite

Building materials are closely related to daily life.The most common one of building materials is cement concrete which is mixed with water,fine aggregate and coarse aggregate.With the development of civil engineering,many new engineering materials are widely used.Ultra Lightweight Cement Composite(ULCC)is one of them which attracts more and more attention with its advantages of light weight and high strength.A lot of research has been done on the mechanical properties of ULCC,but there is still little study on its electromagnetic properties.It is important to know the electromagnetic properties of materials,such as shielding effectiveness and dielectric constant.Many properties of engineering material can be known from dielectric constant.Some researchers predict the strength of cement-based materials on structure in the early age.The relationship between water content and dielectric constant of engineering material has been found by many researchers.Electromagnetic shielding and electromagnetic absorption of concrete materials have important military significance.In this project,we made the circular polarized “Zhongguo” antenna array with vertical beam and studied the electromagnetic properties of ULCC in the darkroom.The design of the circularly polarized “Zhongguo” array antenna break the conventional method to achieve circular polarization using the same patch structure.Different patch structures make the antenna have the ideographic function.A circular polarized “Zhongguo” antenna array with a downward tilting beam that has good performance in matching,gain and axial ratio was designed.By changing the feed position of the L-shaped probes,a downward tilting beam of antenna array was improved,and the circular polarized “Zhongguo” antenna array with vertical beam is proposed.The problem of downward tilting beam was solved and the measured axis ratio bandwidth reaches 720 MHz.In darkroom experiments,the shielding effectiveness of ULCC(with or without steel fiber)was measured by antenna array.Through comparison,it was found that the shielding effectiveness of ULCC with steel fiber was obviously enhanced than the ULCC of no steel fiber.In order to simulate the application scenario of real material,ULCC was immersed in water to make the material reach the water-containing state and the shielding effectiveness of ULCC is tested.The result shows that the shielding effectiveness of ULCC in the water-containing state is also enhanced.The dielectric constant of ULCC was calculated by free space method and compared with the results of vector network analyzer.It was found that the calculated dielectric constant of ULCC without steel fiber could fit the results of vector network analyzer,but the results of ULCC with steel fiber showed deviation.