| Human-induced electromagnetic interference sources(such as communication,navigation,household appliances,industrial equipment,etc.)generate electromagnetic waves,which in turn generate electromagnetic interference(EMI)for precision electronic equipment.Electromagnetic radiation can also cause certain harm to human health.The conductive polymer-based electromagnetic shielding material is made of conductive filler and polymer filled composite,and has the advantages of low cost,low density,corrosion resistance,easy forming and controllable electromagnetic shielding performance,it is a new material that can replace traditional metal-based electromagnetic shielding materials.Through extensive research,it has been found that conductive polymer-based electromagnetic shielding materials with excellent electrical conductivity can effectively prevent electromagnetic wave propagation,but electromagnetic shielding materials with high conductivity mainly improve the total electromagnetic shielding effectiveness by improving the reflection efficiency,which results in secondary pollution of electromagnetic waves.Therefore,research on low-reflection electromagnetic shielding composites has become particularly important.In this paper,the electromagnetic shielding material with low reflection characteristics is prepared on the premise of ensuring high-efficiency electromagnetic shielding performance by designing the structure of conductive polymer composites.The main findings are as follows:(1)Reduced graphene oxide(FeCo@rGO)/ultrahigh molecular weight polyethylene(UHMWPE)nanocomposites decorated with iron-cobalt magnetic nanoparticles with good electromagnetic interference(EMI)shielding properties were prepared by ultrasonic coprecipitation and hot press forming.First,FeCo@rGO with adjustable magnetic and electrical properties is deposited on the surface of the UHMWPE particles.Then,the composite grains were hot compressed to form a segregated 3D FeCo@rGO network in UHMWPE the matrix.This well-formed 3D magnetic and conductive FeCo@rGO network with selective distribution can provide the UHMWPE composite with tunable electrical and magnetic properties.Owning to the multiple reflections of microwaves among the FeCo@rGO conductive network and the magnetic loss induced by the FeCo magnetic nanoparticles,the FeCo@rGO/UHMWPE nanocomposites showed a good EMI shielding effectiveness of 21.8dB at X-band with the presence of only 8.97 vol%FeCo@rGO.Simultaneously,the average SER as low as 2.84 dB and the value of R is only 0.48.(2)A highly efficient electromagnetic interference(EMI)shielding waterborne polyurethane(WPU)composite film with low microwave reflectivity is designed by constructing an FeCo alloy decoration reduced graphene oxide(FeCo@rGO)/nano silver(Ag)layered structure.The FeCo@rGO layer formed by natural sedimentation at the bottom of the WPU film acts as a microwave absorption layer,and the ultra-thin Ag layer covered on the top surface serves as a highly efficient shielding layer.This unique layered structure combines the microwave reflecting characteristic of nano Ag and the microwave-absorbing characteristic of FeCo@rGO to achieve strong microwave shielding effectiveness(SE)with low microwave reflection.When FeCo@rGO has a mass fraction of 10 wt%and a silver layer thickness of500nm,the Ag/FeCo@rGO/WPU composite film with a thickness of only 300?m has an electromagnetic shielding performance of 50.5 dB at X-band.Simultaneously,the average SE_R as low as 3.2 dB and the value of R is only 0.49.(3)An aqueous polyurethane(WPU)oriented composite foam doped with graphene decorative iron-cobalt(FeCo@rGO)and silver-coated expanded polymer bead(EBAg)functional particles is prepared by oriented freeze-drying.Using the density difference of functional nanofillers during orientation growth of ice crystal template to induce the formation of ordered gradient network of FeCo@rGO magnetic absorbing layer and EBAg conductive shielding layer in WPU oriented cell structure,realizing extremely low electromagnetic wave reflection characteristics of ultra-efficient electromagnetic shielding composite foam.Thanks to the special electromagnetic attenuation characteristics of“absorption-reflection-reabsorption”produced by the gradient shielding network in the oriented foam structure,the composite exhibits extremely low electromagnetic reflection characteristics while achieving ultra-efficient shielding effectiveness.At very low conductive particle content(0.15 vol%Ag and 0.33 vol%FeCo@rGO),the X-band average electromagnetic shielding performance is as high as 84.8 dB,while the average reflection efficiency(SE_R)is as low as 0.3 dB and the reflectance(R)is only0.08. |
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