Preparation And Electromagnetic Properties Of Carbon-based Radar Wave Absorbing Materials

Due to the rapid advancements in information technology and military stealth technology,there is an increasing demand for high-performance electromagnetic wave absorbing materials in shipbuilding and marine engineering.These materials effectively absorb electromagnetic wave energy,reducing the risks of electromagnetic interference or detection.The development of electromagnetic wave absorbing coatings is progressing towards thinner,lighter designs with broader frequency ranges and enhanced absorption capabilities.This thesis addresses the stealth requirements of marine equipment by optimizing the geometric structure of carbon-based absorbing materials and controlling their dielectric constant and magnetic permeability.It leads to the design and synthesis of four innovative carbon-based magnetic composite absorbing materials with potential for industrial applications:Mn_0.5Zn_0.5Fe₂O₄/C,HGBs@Ni_xCo_y/C,Fe-3SM-y AN and MMT/Fe₃O₄/PPy.The absorbing performance of these materials was analyzed,elucidating the synergistic interaction between dielectric and magnetic losses,and optimizing the composition to produce a series of high-efficiency carbon-based magnetic composite absorbing materials.The main results are outlined as follows:（1）Study on the preparation and microwave absorption properties of manganese-zinc ferrite carbon-based magnetic wave-absorbing materials.Polydopamine was coated to the surface of bayberry-like manganese zinc ferrite(Mn_0.5Zn_0.5Fe₂O₄)using an in-situ polymerization method,resulting in a polydopamine-coated manganese zinc ferrite(Mn_0.5Zn_0.5Fe₂O₄@PDA).This material was then pyrolyzed to create a carbon-based magnetic composite absorber,Mn_0.5Zn_0.5Fe₂O₄/C.Experimental results demonstrated that Mn_0.5Zn_0.5Fe₂O₄/C has a uniform spherical core-shell structure,featuring a layer of nitrogen-doped carbon material coated on the surface.The nitrogen-doped carbon material coating enhances the dispersion of the ferrite,preventing aggregation.This leads to increased interfacial polarization and conductive loss,significantly boosting the radar wave absorption properties of the material.At a 50 wt.%filling rate,Mn_0.5Zn_0.5Fe₂O₄/C achieves an effective absorption bandwidth（EAB）of 5.36 GHz and a maximum reflection loss of-17.57 d B.These findings confirm that coating nano ferrite materials with carbon significantly enhances their absorption performance.（2）Study on the preparation and absorbing agent properties of nickel-cobalt bimetallic composite carbon-based glass balls.Hollow glass balls were used as templates to synthesize the composite absorbing material HGBs@Ni_xCo_y/PDA through the catalytic polymerization of dopamine,initiated by Ni²⁺and Co²⁺metal ions.This was followed by high-temperature pyrolysis to produce HGBs@Ni_xCo_y/C,a lightweight composite.Experimental results demonstrated that the HGBs@Ni_xCo_y/C material,which combines dielectric,conductive,magnetic losses,and resonance absorption capabilities,shows enhanced absorption properties when the Ni to Co ratio is adjusted.Optimal absorption was observed with a Ni:Co atomic ratio of 2:3,achieving an Effective Absorption Bandwidth（EAB）of 6.83 GHz（from 10.53 GHz to 17.36 GHz）and a minimum Reflection Loss(RL_min)of-27.26 d B at a 20 wt.%filling rate.This confirms that carbon-based magnetic absorbing materials using hollow glass balls can effectively reduce the amount of material needed,further enhancing their lightweight characteristics.（3）Study on the preparation and microwave absorption properties of iron-carbon composite materials.A resin precursor of iron acrylate-acrylonitrile copolymer was synthesized using free radical polymerization and subsequently pyrolyzed at high temperatures to produce the porous plate-like Fe-3SM-y AN（y=6,9,12）iron-containing carbon-based composite material.Experimental results indicate that the radar absorbing performance of Fe-3SM-y AN materials can be adjusted by varying the proportion of acrylonitrile monomer.The Fe-3SM-9AN absorbing material showed optimal performance with an EAB of 8.07 GHz and a minimum reflection loss of-36.70 d B（11.41 GHz）at a thickness of 2 mm,nearly covering the Ku band.With thicknesses ranging from 1.0 mm to 5.0 mm,its EAB could cover 14.8 GHz（3.2 GHz-18 GHz）,almost completely meeting the stealth protection needs of existing equipment in the C,X,and Ku bands.This shows that using free radical polymerization to create metal-containing precursors is a viable method for preparing high-performance,carbon-based magnetic absorbing materials.（4）Study on the preparation and microwave absorption properties of MMT/Fe₃O₄/PPy composite materials.Using a one-pot method,nanoscale Fe₃O₄ was deposited onto the surface of plate-like montmorillonite（MMT）to create magnetic montmorillonite,MMT/Fe₃O₄.Subsequently,a carbon-based conductive polymer,polypyrrole,was also loaded onto the surface of this magnetic montmorillonite,resulting in the formation of the MMT/Fe₃O₄/PPy composite absorbing material.Experimental results reveal that the MMT/Fe₃O₄/PPy material comprises numerous nanoporous plate-like structures,which enhance its magnetic anisotropy,magnetic loss,and dielectric loss properties.The effective absorption bandwidth（EAB）of MMT/Fe₃O₄/PPy is8.92 GHz（ranging from 6.47 GHz to 15.39 GHz）,with a minimum reflection loss(RL_min)of-41.35 d B at 11.52 GHz.By varying the thickness of the MMT/Fe₃O₄/PPy composite between 1.0mm and 5.0 mm,its EAB can extend up to 14.4 GHz（from 3.6 GHz to 18 GHz）,demonstrating exceptional absorbing performance.This thesis successfully integrates dielectric carbon-based materials with magnetic materials,examining how the composition,structure,and size of materials influence their absorption capabilities.It elucidates the mechanisms of microwave attenuation in carbon-based magnetic absorbers.This thesis serves as a valuable reference for designing carbon-based magnetic composite absorbers and has important practical implications for developing cost-effective,high-efficiency,broad-band carbon-based magnetic composite materials.