Design And Microwave Absorption Mechanism Of Hollow Sphere Lattice Composites

Microwave-absorbing materials have attracted widespread attention in recent years as a solution to the problems of radar stealth,electromagnetic interference and electromagnetic pollution.However,due to its high density,thick coating,and narrow absorbing bandwidth,the traditional coated absorbing materials has been difficult to meet the performance requirements of some high-end fields.Therefore,some sandwich structures with low density and wide bandwidth are favored by researchers.Based on the requirements of integrated structural and microwave absorbing composites proposed in the aerospace field,this paper designed and prepared a hollow sphere lattice composite with good microwave absorption performance,established a simulation model for the absorbing performance of hollow sphere lattice composites,systematically analyzed the influencing factors on the microwave absorption performance of the hollow sphere lattice composites,and revealed the microwave absorbing mechanism of hollow sphere composites,which laid a foundation for the design of new structural absorbing materials.In this paper,the SCFs（Short Carbon Fibers）,Fe₃O₄and CIP（Carbonyl Iron Particle）were used as filler,and EP（Epoxy）were used as matrix to compound two kind of absorbent systems,SCFs/Fe₃O₄/EP and CIP/EP.The electromagnetic parameters of the two systems are tested by the coaxial transmission/reflection method.With the electromagnetic parameters of the two absorbent systems as input,a simulation model of hollow sphere lattice composite materials was established based on HFSS（High Frequency Structure Simulator）software.Then using the simulation model,systematically analyzed the influence of the electromagnetic parameters of the absorbent,the height of the composite,the close-packed gap of the hollow sphere,the radius and the wall thickness of the hollow sphere on the RL-f（reflection loss vs frequency）curve of the hollow sphere lattice composite.According to the simulation results,SCFs/EP hollow sphere lattice composite and3C7F/EP（The volume ratio of SCFs and Fe₃O₄were 3:7）hollow sphere lattice composite were prepared by vacuum casting process.The density of the hollow sphere lattice composites is 0.82 g/cm³～0.92 g/cm³,and the compressive strength,tensile strength and bending strength of the hollow sphere lattice composite are 51.3～57.0 MPa,6.7～9.1 MPa and 24.2～45.0 MPa.The minimum RL（reflection loss）of the hollow sphere lattice composites is-14.5d B with an effective absorption bandwidth of 1.8 GHz（13.7～15.5 GHz）.Compared with traditional microwave-absorbing materials,the hollow sphere lattice composites show a 70%weight reduction and a good structural strength.The long wave approximation method was used to divide the hollow sphere lattice composite into multi-layer absorbing material structure composed of thin layers,and then the electromagnetic parameters of each thin layer were equivalently treated based on Strong Fluctuation Theory.Based on the equivalent electromagnetic parameters of each thin layer,the equivalent attenuation coefficient,equivalent impedance matching ratio,RL-f curve and t-f（thickness vs frequency）curve of hollow sphere lattice composites were calculated by programming software,according to the multilayer transmission line theory.The calculated results of RL-f curve were in good agreement with the HFSS simulation and experimental results,which verified the reliability of the theoretical calculation model.Based on the theoretical calculation model,the destructive interference absorption mechanism of hollow sphere lattice composites was analyzed.Based on the RL-f curve of hollow sphere lattice composites,a broadband absorbing composite structure was explored.The composite absorbing structure composed of impedance matching layer,hollow sphere lattice layer and absorbing layer.The material and thickness of impedance matching layer,the material in the gap between hollow spheres,the material and thickness of absorbing layer were optimized respectively.The optimized scheme of the composite absorbing structure is as follows:the impedance matching layer is 50CIP with a thickness of 1.0 mm;the hollow sphere layer is SCFs/EP hollow spheres embedded in 40CIP with a thickness of 4.4 mm;the absorbing layer was 80 CIP with a thickness of 1.0 mm.The total thickness of the composite structure was 6.4 mm,and the effective absorption bandwidth could reach 15.6 GHz.