Investigation On The Electromagnetic Interference Shielding Effectiveness Of Designed MWCNTs/MnO₂ Composite Structure

In this thesis,SiO₂@MnO₂ core-shell structure with SiO₂ as the core and MnO₂ as the shell is successfully prepared by hydrothermal method.Multiple interfaces in the structure can enhance multi-reflection of the incident electromagnetic?EM?waves,while MnO₂ will induce dielectric loss for more wave absorption.Along with multi-walled carbon nanotubes?MWCNTs?,which also belongs to dielectric loss type wave-absorbing materials with high aspect ratio and high conductivity,we design and fabricate two different structural absorbers.One has multilayered structure,where a commercially available aluminum?Al?foil is selected as a reflection layer,and MWCNTs/MnO₂/polydimethylsiloxane?PDMS?composite is used as an absorption layer.The other is graphene aerogel combining with MnO₂ and MWCNTs.In the multilayered structure,MWCNTs and MnO₂ distribute uniformly in the absorption layer.Electromagnetic interference?EMI?shielding effectiveness is enhanced due to the conductive network formed by MWCNTs,the polarization induced by SiO₂@MnO₂ and the multiple scattering between different interfaces in the absorption composites.High conductivity of the reflection layer helps to consume EM waves rapidly.Furthermore,the impedance mismatch between two layers restricts the EM waves within the absorption layer,which benefits multi-reflection.When 3 wt.%MWCNTs and 15 wt.%SiO₂@MnO₂are added to the absorption layer,and the thickness is adjusted to 3 mm,the reflection loss peak of the designed multilayered structure reaches 13.70 d B in X-band?8.2-12.4 GHz?and total shielding effectiveness?SE_T?reaches 88.97 d B.The layered structure can absorb over 90%of the impinging EM waves in X-band,which provides an absorption-dominant EMI shielding.In the MnO₂/MWCNTs/graphene aerogel,the intrinsic three-dimensional porous structure greatly reduces the impedance mismatch between aerogel and air.The conductivity improved by appropriate addition of MWCNTs,together with the dielectric loss induced by polarization of SiO₂@MnO₂ core-shell structure,enhance the microwave absorption performance.Meanwhile,multiple interfaces in the porous aerogel cause multiple scattering.When the graphene,MWCNTs and SiO₂@MnO₂ are adjusted to 1:1:5,SE_T of the aerogel in the X-band is 11.34 d B,and the aerogel can absorb 75%of the incident EM waves on average in X-band.In summary,the as-prepared multilayered structure and aerogel are absorption-controlled attenuators,which are promising microwave absorption materials for the applications in commercial and military fields.