Study On Electromagnetic Protection Design And Tensile Properties Of Multilayer Self-Foaming Polyurethane-Based Magnetic Foam

Electromagnetic absorbing materials and structures have important application value in military and civilian fields such as electromagnetic protection,radar stealth,and communication systems.The ideal electromagnetic absorber should not only meet the performance requirements of broadband wave absorption and strong absorption,but also have practical application requirements such as flexible veneer,impact resistance,stretchability,and light weight.Although single magnetic particles(such as iron,cobalt,nickel,etc.)have the advantages of strong magnetic loss and low cost,their shortcomings such as high density,easy corrosion,poor impedance matching,and narrow effective frequency absorption have severely restricted the field of electromagnetic shielding and wave absorption.In addition,it combines one/two-dimensional carbon nanomaterials(such as carbon nanotubes,graphene,etc.),and uses thermoplastic/solid polymer as the matrix to prepare a new type of electromagnetic absorber that takes into account both dielectric and magnetic loss through simple forming and processing.Wave composite materials have received widespread attention.Aiming at the integrated design and preparation of electromagnetic protection/mechanical load-bearing,this paper discusses the electrodynamic theoretical model of the electromagnetic reflectivity of the multilayer structure under the oblique incidence of TM polarized waves;the tadpole-like carbon nanotubes/tetroxide synthesized by the hydrothermal method Tri-iron(CNTs@Fe₃O₄)and coral-like carbon nanotubes/graphene nanosheets/Fe₃O₄(CNTs@GN@Fe₃O₄)nanoparticles are precursors,and a series of multilayer magnetic foams(CNTs@Fe₃O₄/PU or CNTs@GN@Fe₃O₄/PU),systematically studied particle morphology,cell size,multilayer structure,surface-interface,temperature change,etc.on its magnetostatic properties,electrical conductivity,wave absorbing properties and The influence law of tensile mechanical properties.The specific research content is as follows:1.The tadpole-like CNTs@Fe₃O₄ magnetic nanoparticles were synthesized by solvothermal method,and further dispersed in a single-component moisture-cured polyurethane for self-foaming to obtain CNTs@Fe₃O₄/PU composite magnetic foam.The electrical conductivity of 90CNTs@Fe₃O₄/PU composite magnetic foam reached12.86S/cm,which was much higher than that of Fe₃O₄/PU,indicating that CNTs had a significant effect on the improvement of composite material's electrical conductivity.The tensile strength of 90CNTs@Fe₃O₄/PU composite magnetic foam is 3.5MPa,which is 1.48 times that of pure PU,but the doping of CNTs will reduce the foam's resistance to deformation.The RLmin value of 70CNTs@Fe₃O₄/PU at a thickness of2.0mm reaches-42.63d B,and the effective absorption bandwidth is 4.91GHz.Through temperature adjustment,it is found that the magnetic foam has temperature control and can effectively improve the absorbing performance of the material.For example,when 70CNTs@Fe₃O₄/PU is at 313K,its matching thickness of 2.0mm RLmin reaches-55.65d B,which is better than normal temperature.That's 27.9%.2.Three-dimensional CNTs@GN@Fe₃O₄ nanocomposites were synthesized by solvothermal method.When the 50C2G1 sample is 2.28mm thick,the RLmin value can reach-59.44d B,and the effective absorption bandwidth is 6.09GHz(8.36GHz-14.45GHz),which almost perfectly realizes the full coverage absorption of the X-band.The introduction of GN on the one hand makes the resistance of the magnetic foam more sensitive to the deformation of the matrix,on the other hand it increases the mechanical properties of the material.At the same time,increasing the temperature can significantly increase the absorption strength of the magnetic foam and reduce the matching thickness.The RLmin value generated by 70C1G2 at 333K at 14.31GHz is-55.69d B,and the minimum matching thickness is reduced to 1.5mm.3.A series of double/triple structure magnetic foams were prepared by LBL layered pouring method.Through the analysis of foam morphology,electromagnetic parameters,and absorbing properties,it is found that the multilayer structure has an important influence on the electromagnetic absorbing properties of magnetic foams..The research results show that,compared with the single-layer foam with the same filler composition in the second layer,the double-layer structure can effectively increase the microwave absorption intensity.For example,compared with the single-layer 50C1G1 sample,the absorption peak value of D4 is increased by 151%.The three-layer foam exhibits better electromagnetic absorption performance at a thickness of 3.0mm,mainly in that the RLmin values of S2,S3,S4 and S5 are between-52d B?-67d B,and the effective absorption bandwidth is all at 5.0GHz The above and can cover the entire X-band.Compared with single/double-layer foam,the effect of three-layer foam in broadening the effective absorption bandwidth is very obvious.Through the observation of the foam fracture morphology,it is found that there will be a bonding zone with almost no cells between the layers of the foam.Due to the existence of the bonding zone,the mechanical properties of the multilayer foam have been enhanced,such as the fracture required for S4 The stress has reached6.58Mpa,and the minimum elongation at break is also above 67%,which is much greater than that of a single-layer foam.However,due to the influence of the bonding zone,the sensitivity of the three-layer foam's wave-absorbing performance to temperature control is not as obvious as that of the single-layer foam.The main reason is that the cells of the three-layer foam will be subjected to resistance from the upper and lower bonding bands when the cells of the three-layer foam are heated and expanded.The deformation of the holes is hindered,so that the accumulation of fillers in the matrix and the destruction of the conductive network are not obvious.