电磁屏蔽机理及轻质宽频吸波材料的研究进展

Research Progress of Electromagnetic Shielding Mechanism and Lightweight and Broadband Wave-absorbing Materials

随着智能通信系统、无线网络设备、电子探测设备等技术的发展,空间电磁波辐射对仪器设备的影响不断增大,电磁波屏蔽技术在电磁兼容(EMC)、抗电磁干扰(EMI)设计、飞行器隐身等方面有了越来越广泛的应用。目前,以铁氧体、碳化硅、石墨为代表的传统吸波材料普遍存在着吸收频带窄、吸收性能弱等缺点,一般通过掺杂改性的方法来提高其吸波性能,但得到的吸波层厚度较大,吸波效果不够理想,同时增加了设备质量,也无法达到飞行器减重的目的。近年来,以纳米吸波材料、复合型导电聚合物、石墨烯吸波材料以及超材料为代表的新型轻质宽频吸波材料得到了越来越多的关注。电磁波屏蔽机理主要基于电磁波的反射与吸收,大量的研究结果表明,与电磁波能量衰减相关的参量,如吸收频率、吸收厚度和吸收带宽,与吸波材料的成分和微观结构有着密切的联系。为了得到轻质宽频电磁波吸收材料,一方面电磁波应通过介质表面尽可能多地进入到材料内部,这需要材料具有良好的空间阻抗匹配性;另一方面,进入到材料内部的电磁波应尽可能多地衰减,转化成热能或其他形式的能量,这需要吸波材料具有较高的电损耗或磁损耗。铁氧体吸波材料在低频下具有良好的阻抗匹配性,但在高频波段,磁滞效应和涡流效应都随之减弱,可以通过元素掺杂、制备纳米材料或表面处理技术来改善其吸波性能。金属磁性材料由于晶格结构比铁氧体简单,且没有铁氧体中磁性次格子磁矩的相互抵消,理论电磁波吸收值高于铁氧体,纳/微米结构金属磁性材料成为新一代轻质宽频吸波材料。导电聚合物作为吸波材料可以使产品的质量极大降低,通过改性的方法使其具备可调的电导率和介电常数,而添加金属、金属氧化物或碳纤维能够有效提高导电聚合物的阻抗匹配性。碳基电磁波屏蔽材料具有质轻、耐腐蚀和易加工等优点,石墨烯吸波材料通过改进其自然共振、异质结构界面、电磁耦合来增强电磁损耗,成为轻型超薄吸波材料的代表。超材料吸波结构通过对组成单元的结构和排布控制,在较宽频率范围内实现了对电磁波的吸收。轻质宽频吸波材料不仅具有重要的军事应用价值,在民用电磁干扰防护方面也具有广阔的应用前景。本文从不同的电磁屏蔽机理及材料本征特性出发,对不同种类的新型宽频吸波材料进行了综述,研究了不同吸波体的电磁波吸收性能与微观结构的关系,对实现其轻质宽频吸收的作用机理进行了介绍,为制备性能优异的吸波材料提供了理论技术支持,为发展新一代高性能电磁波吸收材料提供了研究思路。

With the development of intelligent communication systems,wireless network devices and electronic detection equipments,the influence of space electromagnetic wave radiation on equipments is increasing,electromagnetic wave shielding technologies have more and more applications in electromagnetic compatibility(EMC),anti-electromagnetic interference(EMI)design,and aircraft stealth.At present,the traditional absorbing materials such as ferrite,silicon carbide and graphite generally have the disadvantages of narrow absorption band and weak absorption performance.Generally,their absorbing properties are improved by doping modifications,but such materials have a large thickness with a no-ideal absorbing ability,which increase the mass of equipments and unable to achieve the purpose of aircraft weight reduction.In recent years,new lightweight and broadband absorbing materials represented by nano absorbing materials,composite conductive polymer,graphene absorbing materials,and metamaterials are getting more and more attention.Electromagnetic wave shielding mechanism is based on the reflection and absorption of electromagnetic waves.A large number of studies have shown that the parameters for electromagnetic wave energy attenuation,such as absorption frequency,absorption thickness and absorption bandwidth,are closely related to the composition and micro-structure of the absorbing material.In order to obtain a lightweight broadband electromagnetic wave absorbing material,on one hand,electromagnetic waves should enter the inside of materials as much as possible through the surface of the medium,which requires the material to have good spatial impedance matching;on the other hand,it should enter the inside of the material as much as possible,meanwhile the electromagnetic waves entering the inside of the material should be attenuated and converted into heat or other forms of energy as much as possible,which requires the absorbing material to have as high electrical loss or magnetic loss as possible.Ferrite materials have good impedance matching at low frequency,but when the frequency of microwave is high,hysteresis effect and eddy current effect are weakened,so we can improve its absorbing properties by element doping,preparing nanomaterials or surface treatment technology.Metallic magnetic materials have simpler lattice structure than ferrite,and there is no mutual offset of magnetic moment of magnetic sub-grids as ferrite,therefore,their theoretical wave absorption value is higher than ferrite,nano/micro structure metal magnetic materials have become a new generation of lightweight and broadband wave-absorbing materials.Conductive polymers as absorbing materials can greatly reduce the mass of the product,because through modification methods its conductivity and dielectric constant can been adjusted,and by adding metal,metal oxide or carbon fiber,the impedance matching of the material can be effectively enhanced.Carbon-based electromagnetic wave shielding materials with the advantages of light weight,corrosion resistance and easy processing are representative of lightweight ultra-thin absorbing materials,which can enhance their electromagnetic loss by improving the natural resonance,the heterostructure interface,and the electromagnetic coupling.The metamaterial absorbing structures can absorb electromagnetic waves in a wide frequency range by regulating the structure and arrangement of the constituent elements.Lightweight broadband absorbing materials have important military applications,and also a broad application prospects in civil electromagnetic interference protection.This review begins with different electromagnetic shielding mechanisms and intrinsic properties of materials,introduces several new types of broadband absorbing materials,studies the relationship between electromagnetic wave absorption properties and microstructures of different absorbers,summarizes the mechanism for achieving broadband and lightweight absorption,provides theoretical technical support for the preparation of absorbing materials with excellent performance as well as research ideas for the development of the new generation of high-performance electromagnetic wave absorbing materials.