【作者】 徐铭；

【导师】 马眷荣； 鲍红权；

【作者基本信息】 中国建筑材料科学研究总院 ， 材料学， 2011， 博士

【摘要】 电磁技术是一把双刃剑，电磁技术的利用给人们带来便捷的同时，大功率、高集成化电气设施的广泛运用却引起了诸如电磁干扰、电磁泄密和电磁污染等一系列安全及环境问题。随着电磁波辐射强度的增加以及电气设备的多样性，传统的屏蔽材料及屏蔽方式已经不能满足复杂电磁环境下的屏蔽要求，因此研究并制备出屏蔽效能高、工作频率宽及轻质的“绿色”电磁屏蔽材料成了目前屏蔽材料研究的热点。本文提出将电磁反射层与电磁吸收层相结合，制备轻质高效的吸收、反射一体化电磁屏蔽新型材料，是由于传统的反射式屏蔽材料目前虽然能够达到较高的屏蔽效能，然而这类材料是利用良导电性对电磁波进行反射作用，将能量约束在特定区域内，并未将能量有效转化。这样在减弱一个区域场强的同时势必会增加其他区域的场强，严重时甚至引起谐振，影响运用。而吸收反射一体化电磁屏蔽材料不仅具有屏蔽效能高的特点，还对电磁波具有吸收和拓展频带作用，可以用来克服反射式屏蔽的不足。本文借助了纤维增强树脂的工艺方法，完成了集屏蔽功能性、承载结构性双重功能于一体的功能结构一体化材料的制备，运用四探针电阻仪、扫描电镜、矢量网络分析仪并采用宽频同轴法、微波暗室法及相关力学性能测试手段对样品的电磁性能和力学性进行了测试和分析。文章通过理论模型的模拟和实测的方法，详细研究了材料导电性与屏蔽性的关系，阐述了吸波剂特性、掺量及材料尺寸对微波吸收性能的促进机理，并在此基础上匹配吸收反射一体化电磁屏蔽材料的最佳参数，以提高其对微波的吸收能力和频率覆盖有效性。研究表明，电磁反射层中镀铝玻璃纤维的掺入量和纤维长度对材料导电性能有最直接的影响。导电纤维的掺入量大于15%就已超过渗滤阈值使得材料形成导体，掺入量继续升高为40%到60%能使材料保持较为稳定的屏蔽性能，而在此基础上继续掺入镀铝玻璃纤维则会降低材料的屏蔽性能；同样地，研究发现因平均接触点数和工艺因素的共同作用，能使材料获得最佳屏蔽效能的纤维长度范围为4cm~10cm。此外，文章还研究了热固性树脂制备工艺中对屏蔽性能可能产生影响的相关问题，通过实验确定了热压产生的层状结构有利于屏蔽效能的提高和估算了导电纤维网络结构产生的感抗损耗大小，并指出添加非导电玻璃纤维配合成型工艺以及引入炭黑的隧道导电效应不可行。二次杂波抑制方面，在屏蔽材料中引入抑制杂波的电磁吸收层是本文特色之一。文章通过将W型铁氧体吸收剂与其它吸收剂复合或叠加的方式，研究了材料特性对抑制杂波的影响。实验发现，多相复合材料的吸波性能优于单相材料的吸波性能，并且当铁氧体中掺杂25wt%介电特性的合金粉时有利于减小吸波材料的匹配厚度和提高吸收效能。文章同时研究了多层吸波材料的电磁吸收性能，发现吸波剂和铺层顺序的选择对多层吸波材料的吸波能力影响重大，实验得出将不同种类吸收剂按介电常数由外至内递增的顺序进行叠加，可使材料总匹配厚度减小、吸收率增加和频带展宽。文章详细论述了吸收-反射一体化屏蔽材料的总屏蔽效能与理想状态下杂波抑制效能的关系，理论值和实测值都表明杂波抑制层的引入对总屏蔽效能增益不大，却可以使得材料有效地抑制二次干扰波并拓宽工作频段。文章计算了垂直干扰状态下材料杂波抑制能力，得出在5GHz~18GHz范围内，一体化材料能消除60%以上的干扰波，并且随着频率升高，抑制率更高。最后，文章研究了材料各项基本力学性能。实验通过对材料抗弯和抗拉伸强度的测定，结合镀铝玻璃纤维单丝强度的成因，详细分析了屏蔽材料在受力变形时应力再分配的过程和破坏机理，并指出相对其抗拉伸能力而言，材料更适合用于抗弯曲的场合。更多还原

【Abstract】 Electromagnetic technology is a double-edged sword, it brings us muchconvenience. However, the popularity of high-power electrical equipment also causessome safety and environment problems such as electromagnetic interference,electromagnetic leaks and electromagnetic pollution. The traditional shieldingmaterial and way of shielding cannot meet the complex requirements in the newelectromagnetic environment especially when the intensity of electromagneticradiation increases. So to research and prepare a new kind of "green" material whichhas a higher shielding effectiveness and can cope with a wider frequency but with alower density becomes a "hot spot" in the material science.In this paper, we integrate the reflection layer and the absorbing layer as one.Comparing with any other material, this kind of material can reach a high shieldingeffectiveness but maintain a low density. As we all know, although traditionalshielding material can reach a high electromagnetic shielding effectiveness at present,the main shielding mechanism is reflection. That is to say, those material are onlyrestricting the energy into the very area, but not convert them into other kind ofenergy. So the result is, it causes a new electromagnetic interference at other place. Insome cases, it can cause resonance, making big trouble to the operation of equipment.However, the integrated material can remedy the defect of traditional material—itnot only absorbs the interfering radiation and broadens the band, but also maintains ahigh shielding effectiveness like traditional material.With the help of fiber reinforced resin process method, the experimentsuccessfully finished the preparation, and this material not only had functionalfeatures, but also had some structured features. Four-point probe, scanning electronmicroscopy and vector network analyzer were used to analyze the material. At thesame time, broadband coaxial, microwave anechoic chamber methods were used totest its electromagnetic properties. The mechanical properties of material were also beanalyzed. With the help of theoretical model and metrical value, the paper researchedthe relationship between conductivity and shielding effectiveness, and described themechanism of wave absorbing when the absorbent feature, content and material sizewere shifting. The paper at last found the best parameters of the integrated material; itcould promote electromagnetic wave absorbing ability as well as the efficiency ofband coverage.The research indicates that, Aluminized glass fiber’s length and adding contentwere important to the conductivity. Material would change into a conductor whenfiber content above15%. It could keep a stable shielding effectiveness when fiber content reached40%to60%. However, excessive fiber content would result in thedeclination of the shielding effectiveness. The paper also found that, because of theco-work of average contact point and technological factors,4cm~10cm fiber lengthcould more possibly gain a higher SE. The paper also gave some explanation on therelationship between technological factors and shielding, it believed that the layerstructure of material had some positive effect on shielding, and calculated theinductive losses. The research confirmed that it was wrong to add insulated glass fiberand black carbon into the material.Bringing absorbing layer into material was a feature of the paper. Through themethod of composite and superposition the W-type ferrite and other absorbent, thepaper researched the relationship between material parameters and absorbing rate.Absorbing rate of multiple phase composite material was better than single phasematerial, and it was helpful to decrease the matching thickness and increase theabsorbing rate when the alloy powder content was25%. This paper also researchedthe absorbing ability of multiple layer material, and found that the choice of absorbentand the sequence of layer were important to the absorbing rate. The research showthat, matching thickness would decrease and absorbing rate would increase when weput the bigger dielectric constant layer in the inside and put the lower dielectricconstant layer on the outside.The paper discussed relationship between shielding effectiveness and clutterrestriction effectiveness in detail. Metrical and calculated value shows that the usageof clutter restriction layer could hardly increase the total shielding effectiveness,however, it could efficiently restrict the clutter and broaden response band. The papercalculated the ability of material restricting clutter in a vertical interference situation,and obtained that, the integrated material could restrict60%clutter from5GHz to18GHz area, and its restriction rate could be higher at the high frequency area.At last, the paper analyzed mechanical properties of material, and its bending andtensile strength were tested. The process of stress redistribution and wreck mechanismwere analyzed with the relationship of Aluminized glass fiber. The paper pointed outthat, comparing with other kind of material, such kind of material could used into theplace which baring bending stress more than tensile stress.更多还原