| Electromagnetic(EM)wave absorbing materials represent the EM functional substances which can effectively absorb the EM waves projected on the absorber surface and convert the EM energy into heat or other energy forms to make it attenuated,or reduce the reflected and transmitted waves effectively by interference cancellation.In the contemporary society,with the application and promotion of stealth technology in the military field and the severe health damage caused by EM pollution,the needs for efficient EM wave absorbing materials is becoming increasingly urgent.Thus,EM wave absorbing materials have an important strategic position in both military and civil.Admirable EM wave absorbing materials should be provided with the four characteristics of thin thickness,light weight,wide absorption bandwidth,and strong absorption intensity,namely "thin,wide,light,strong" to meet the requirements under various application conditions.Therefore,the exploration and design for high-performance EM have undoubtedly aroused the attention of many researchers.In the application of traditional electromagnetic wave absorbing materials,Due to the single loss mechanism,some obvious disadvantages emerged in traditional EM wave absorbing materials.But when combined into composite materials,they can take fully advantage of the superiorities and avoid shortages to prepare high-performance absorption materials to satisfy the requirements.Among various composite materials,magnetic nano-metals possess excellent development prospects due to the high permeability and high Snoke's limit.In this paper,we studied the preparation process,chemical composition,microstructure and EM properties fortwo types of composite materials,revealed the positive effects of magnetic nanomaterials in determining the attenuation ability and impedance matching characteristics,and clarified the influence mechanisms on the enhancement of EM wave absorption performance.The main findings were as follows:1.Co nanoparticles loaded ball-flower-shaped TiO2 composites were successfully prepared.And the effects of the Co particle addition and filling mass ratios on the morphology,structures and EM wave absorption properties were deeply studied.The microstructure characterization showed that the ball-flower-shaped TiO2 substrate was successfully prepared,and the Co nanoparticles were evenly loaded on the surface through the impregnation method.Subsequently,the prepared Co nanoparticles loaded ball-flower-shaped TiO2 was mixed with paraffin at a mass ratio of 30%and 50%to test the EM properties,and compared with the unloaded ball-flower-shaped TiO2.The acquired EM wave absorption performance consequences indicated that the sample with 50%filling mass exhibited the best performance.The minimum reflection loss(RL)for this sample was 6.8 GHz with the thickness of 3.1 mm.The effective absorption bandwidth(RL?-10dB)was 13.2 GHz(3.9-17.1 GHz)within the adjustable matching thickness range of 1.1-5.0 mm.The excellent EM wave absorption performance came from the enhanced permeability of Co nanoparticles.By this means,while the magnetic loss was improved,the impedance matching characteristic of ball-flower-shaped TiO2 was significantly optimized,which achieved the synergy between magnetic and dielectric materials.2.Bimetallic-organic-framework-derived CoNi/C nanocomposite were designed and prepared to further improved the EM absorption performance of magnetic nano-metals by compounding with carbon.The effects of carbonization temperature on the phase structure,morphology and microwave absorption properties of the MOFs derivatives were profoundly studied.The microstructure characterization results showed that in the obtained composite,the porous carbon matrix was uniformly loaded with CoNi alloy nanoparticles with the size of 20 nm.The EM wave absorption performance evaluation indicated that the CoNi/C composite obtained at 650? was more superior than those prepared at 500,800,or 950?.With the filling mass in paraffin of 30%,this sample achieved the minimum reflection loss(RL)of-74.7 dB in 15.6 GHz with the thickness of 1.8 mm.The effective absorption bandwidth(RL?-10dB)is 15.1 GHz(2.9-18 GHz)within the adjustable matching thickness range of 0.3-5.0 mm.This study illuminated that the combination of porous carbon and CoNi nanoparticles contributed to obtain excellent electromagnetic wave absorption performances.This is because the CoNi/C nanocomposite material could achieve optimized impedance matching characteristics,establish double loss mechanisms,and strengthen the interface loss between metal nanoparticles and porous carbon. |
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