Material-structure-function Integrated Design,Fabrication And Characterization Of Thin Meta-structure With Broadband Microwave Absorption And Effective Load Bearing

Microwave absorbing materials(MAM)and structures(MAS)have great significances on electromagnetic compatibility,communication systems,microwave radiation protection and radar stealth for civil and military use.MAS with excellent performance is required not only to achieve broadband absorption and severe absorption,but also to satisfy application demands including small thickness,high mechanical strength,mechanical load bearing and flexibitliy.Aiming at integrated design and fabrication problems of multifunctional stealth structures on effective load bearing and broadband absorption,an efficient optimization algorithm framework is constructed for optimal design of multi-layer MAS.A method focused on integrated design and realization of material-structure-function for three-dimensional lossy meta-structure is developed.A three-dimensional stepped pyramidal meta-structure with excellent tensile-resistance performance and ultra broadband microwave absorption is designed,optimized and fabricated.Integrated design and fabrication of meta-structure comprised by lossy lattice with small thickness,effective load bearing and broadband microwave absorption is achieved.The major research contents are presented as follows:(1)The analytical electrodynamic solution of multi-layer MAS reflectivity under oblique incidence in TE and TM polarization is deduced through structured approach.Optimization methods and platform based on Large Mutation Genetic Algorithms(LMGA)is proposed and constructed,which is used for multi-layer MAS optimal design.Addition of three new algorithm modules is effective to enhance convergence,stability and optimization efficiency of LMGA.The complex MAS merging transmission loss and interface loss is proposed,which achieves broadband microwave absorption in 2-18 GHz with thickness of below 4mm.The database with 203 types of lossy material is constructed for effective optimal design of impedance-gradient MAS.Optimization results show that enhancing complex permeability,decreasing real permittivity and maintaining suitable dielectric loss have crucial impacts on microwave absorption performance.(2)Based on carbonyl iron/multi-wall carbon nanotube/epoxy resin material system,the database with twelve materials of different formulae is constructed.The carbon fiber reinforced complex MAS with insertion of square-patterned frequency selective surface is optimized by LMGA and fabricated by casting techniques,which achieves tensile resistance,bending resistance and broadband microwave absorption.The three-dimensional stepped pyramidal lossy meta-structure fabricated by two-step method achieves-10 dB absorption bandwidth of close to 38 GHz.Targeting lossy meta-structure,effective optimal design and realization method of material-structure-function integration is developed.(3)Carbonyl iron,multi-wall carbon nanotubes and silicone rubber are used to fabricate flexible nanocomposite with high complex permeability and low real permittivity.Twelve formulae of nanocomposite are incorporated into a database,which is applied to optimize and design flexible complex MAS embedded with square-patterned frequency selective surface by LMGA.The proposed flexible complex MAS achieves-10 dB absorption in 6-18 GHz.The onestep method is used to fabricate three-dimensional flexible stepped-pyramidal meta-structure,which realizes ultra broadband absorption less than-10 dB in 2-40 GHz and 75-110 GHz.Besides,the two-step method is applied to fabricate carbon fiber reinforced flexible stepped-pyramidal meta-structure with optimal design.With the absorption layer thickness of 5mm,the proposed structure achieves tensile strength of 24 MPa and excellent broadband absorption in 2-40 GHz,which solves the design and fabrication problems of mechanical and stealth integration.(4)Thin carbon fiber/glass fiber reinforced lossy lattice meta-structure capable of load bearing and broadband microwave absorption is designed and fabricated based on carbonyl iron,multi-wall carbon nanotubes and room-temperature epoxy resin.The mechanical failure and broadband microeave absorption mechanisms of the proposed meta-structure are revealed.The proposed meta-structure achieves-10 dB absorption bandwidth in 3.42-19.73 GHz,equivalent tensile strength of 167.35 MPa and bending strength of 169 MPa with the thickness of only 3.5mm.Integrated design and fabrication method of broadband microwave absorption and effective load bearing with small structural thickness are developed.Thin structure design,bending-tensile resistance design and broadband absorption design coordinat well together,which solves the conflicts of the three demands in design and fabrication.