Research On Dielectric/magnetic Loss Material Structure Design And Electromagnetic Wave Absorption Performanc

With the rapid development of information technology,there have been huge changes to people’s lifestyles,but the ensuing electromagnetic pollution has also become the fourth most accepted source of pollution in the world.Electromagnetic pollution and radiation problems will not only cause the failure of precision equipment out of control,but also cause serious and irreversible harm to the human body,greatly threatening the healthy development of human society.Therefore,many researchers have been increasingly concerned about how to prevent electromagnetic pollution problems simply and efficiently.Electromagnetic wave absorbing materials are new functional materials that absorb and consume electromagnetic energy through internal interaction mechanisms,thus effectively attenuating the intensity of electromagnetic radiation.But,the common electromagnetic wave absorbing materials often have high density,high thickness,narrow band width and weak attenuation ability,which are now difficult to meet the increasingly stringent use requirements.In this thesis,we start from the structural design and component optimization,through the reasonable selection and design of dielectric loss materials and magnetic loss materials,improve the impedance matching characteristics of absorbing materials,give them more attenuation loss mechanisms,and achieve a reasonable match between impedance matching and attenuation coefficient,so that they can meet the requirements of"light weight,strong absorption,wide band,thin thickness".The specific research contents and conclusions are as follows.（1）Rational structural design is a prerequisite for obtaining excellent impedance matching properties.In this work,the self-assembly process of nanosheets is completed by a simple solvothermal reaction,and the morphology of the final sample is controllably adjusted by controlling the annealing temperature.Finally,the stacked nanosheets have rich interfacial space,which prolongs the propagation path of the incident electromagnetic waves on the material surface and facilitates more electromagnetic waves to enter the absorbing material,which can greatly optimize the impedance matching characteristics.In addition,the construction of 3D conductive network provides a transmission channel for the directional movement and leap of electrons,a process that enhances the conductive loss and polarization loss capability of the material.In particular,the ZnCo₂O₄ material prepared at 350℃ has a minimum RL value of-43.61 dB at a matched thickness of 2.4 mm,while the effective absorption bandwidth is 7.12 GHz,covering 10.88 to 18.0 GHz.The excellent electromagnetic wave absorption performance is related to the construction of its 3D structure and the synergistic effect between multiple loss mechanisms.（2）Abundant loss absorption mechanisms are essential to improve the electromagnetic wave attenuation capability.In this work,uniformly sized ZnO hollow spheres were prepared using carbon spheres as templates,and then ZnO/ZnCo₂O₄ composites were further prepared by varying the ZnO loading.The 3D structure generated by the self-assembly of a large number of nanosheets greatly optimized the impedance matching properties of the material,allowing the transmission path of incident electromagnetic waves to be enhanced and have more chances to be absorbed by the sample.In addition,the addition of ZnO hollow spheres not only retains the original high dielectric properties,but also introduces the ZnO-ZnCo₂O₄ interface to further enrich the interfacial polarization phenomenon at the heterogeneous interface,which makes the dielectric loss capability of the ZnO/ZnCo₂O₄ composites much higher than the attenuation capability of the incident electromagnetic waves and enables the excellent electromagnetic wave absorption performance.It is worth noting that the ZnO/ZnCo₂O₄ composite shows the best absorption performance when the addition of ZnO hollow spheres reaches 5 mg,with the minimum reflection loss of-55.42 dB at the matched thickness of 1.99 mm and the maximum effective absorption band of 7.44 GHz at the matched thickness of 2.4 mm.（3）The synergistic effect between magnetic and dielectric losses can substantially improve the electromagnetic wave absorption performance.In this work,we obtained one-dimensional heterostructured NiCo@C/ZnO nanorod composites by high-temperature carbon reduction of NiCo-LDHs-coated ZnO nanorod composites.The generation of graphitic carbon introduces a large number of defects,which further compensates for the lack of electromagnetic energy attenuation by polarization relaxation,in addition to the charge differences between multiple heterogeneous interfaces（alloy-C,C-ZnO and alloy-ZnO）that make the interfacial polarization phenomenon more prominent.Furthermore,the introduction of magnetic particles makes up for the shortcomings of insufficient magnetic properties of dielectric materials.Finally,NiCo@C/ZnO nanorod composites can achieve-60.97 dB reflection loss at 2.3 mm thickness and 6.08 GHz absorption bandwidth at 2.0mm thickness,thanks to the complementarity between the excellent dielectric and magnetic losses.