Multi-scale Structure And Dynamic Regulation Of Electromagnetic Properties Of Carbon-based Microwave Absorbing Materials

The electromagnetic radiation caused by the wide application of various electronic devices and wireless communication technology threatens human health;In addition,electromagnetic interference will affect the normal operation of precision equipment,Electromagnetic leakage also increases the risk of information security;In military,the development of electromagnetic detection technology puts forward higher requirements for the survivability of weapons.The application of microwave absorbing materials(MAMs)is an effective way to solve the above electromagnetic problems and realize the stealth of weapons,so the development of efficient MAMs has become a hot issue in the field of science and technology.Rational microstructure design is beneficial to enhance the microwave absorption performance due to structural effect.However,it is still a challenge to obtain MAMs with good impedance matching and strong attenuation ability simultaneously by manipulating the structure at multi-scale by a simple method.This study takes carbon-based materials as the research substance,nitrogen doping is used to achieve atomic-scale regulation,and the morphology and microstructure can be regulated by controlling the reaction conditions.And the dynamic changes of electromagnetic properties with the nitrogen doping and microstructure were explored.First of all,phenolic formaldehyde resin(RF)and amino phenolic formaldehyde resin(APF)were synthesized by hydrothermal reaction,then the O-doped carbon and N-doped carbon materials were successfully prepared by further pyrolysis.It is found that there are three types of bonding configurations for nitrogen,including pyridinic N,pyrrolic N and graphitic N through XPS analysis.The study of electromagnetic property indicates pyridinic N and pyrrolic N are the key characteristic to improve dipole polarization relaxation and graphitic N plays an important role in enhancing the conductivity loss of carbon materials.The existence of three types of nitrogen can realize the regulation of electromagnetic properties of carbon materials.The introduction of Fe³⁺in the process of polymer synthesis can effectively change the microstructure of the resin.The microstructure of N-doped materials can be regulated by adjusting the amount of Fe³⁺and the proportion of monomers,and then the interaction between electromagnetic waves and N-doped carbon materials can be regulated.Ultimately,the synthesized three-dimensional N-doped carbon(N/C-0.5-2)assembled by nanoparticles exhibited excellent microwave absorption performance.The optimal absorption of N/C-0.5-2 reached-68.1 d B at the frequency of 13.9 GHz with thickness of 2.6 mm,and the effective bandwidth(RL?-10d B)is up to 6.9 GHz.Furthermore,the leaf-like Fe/C composite assembled by iron veins interpenetrated into amorphous carbon lamina was successfully constructed by hydrogen thermal reduction of iron alkoxide precursor.The minimum RL value of the complete leaf-like Fe/C composite(L-500)is up to-59.7 d B,and the effective bandwidths(RL?-10 d B)at1.5 mm and 2.0 mm thickness are 6.0 GHz and 4.5 GHz,covering the whole Ku band and the X band,respectively.The excellent microwave absorption performance of leaf-like Fe/C composites is attributed to its unique leaf-like microstructure and special composition.