多层复合型电磁屏蔽涂料的研究

涂层结构及厚度直接影响所制备涂料的屏蔽效能。本文使用不同材料作为填料制备涂料后,同改性镍涂料进行层状复合,对获得涂层的电磁屏蔽性能进行了研究。实验证明复合方法可以提高涂料的电磁屏蔽效能。     

不同金属填料对电磁屏蔽涂料屏蔽效能的影响

复合电磁屏蔽材料是一类用于防护电磁波干扰的新型功能材料,作为屏蔽组分主体的金属填料的电磁特性及其在涂料中的分布状态对于材料的屏蔽效能具有显著的影响,同时由于复合材料的结构特点使这类复合电磁屏蔽材料的屏蔽效能与传统金属板材的屏蔽效能计算理论有着较大的差异.在实验研究的基础上讨论了几种典型的金属粉末填料构成的复合电磁屏蔽材料的屏蔽效能的特点,并分析了其与传统屏蔽效能计算理论的差异和形成的原因,为设计高效复合电磁屏蔽材料提供必要的参考.     

三明治型电磁屏蔽材料的制备与性能

根据Schelkunoff的多层电磁屏蔽理论，分析了双层和3层屏蔽材料的综合屏蔽特征，提出了一种简单有效的三明治型夹层结构材料设计方案，制备出金属箔、涂料两种三明治型层状电磁屏蔽材料，通过理论计算、样品的综合屏蔽性能测试和SEM微观组织观察，讨论了三明治型材料设计方案的正确性与材料的性能。结果表明，三明治型电磁屏蔽材料的屏蔽效能增量（△SE）随电磁波频率的增加而增大，可以实现结构优化；金属箔三明治型电磁屏蔽材料的屏蔽效能增量与理论计算结果相符合；涂料三明治型电磁屏蔽材料的SE值比普通型高，当入射电磁波的频率为1GHz时，三明治型比普通型高18dB。     

聚苯胺性状及其含量对镍粉/聚苯胺涂层屏蔽性能的影响

系统分析了金属粉末/聚苯胺复合电磁屏蔽材料中导电聚苯胺的性状,体积分数对微观结构和电磁屏蔽效能的影响.从二次掺杂的导电聚苯胺的电磁性能讨论了聚苯胺对电磁屏蔽效能的贡献.研究了二次掺杂聚苯胺性状对电磁屏蔽涂层微观结构形貌以及与金属粉末的复合效应对电磁屏蔽效能的贡献.研究的结果表明导电聚苯胺的加入有利于增加电磁屏蔽材料对于高频电磁波的电磁屏蔽效能,但是对低频部分的电磁波的屏蔽效能与纯金属粉末电磁屏蔽材料相比有所降低,这可能是由于聚苯胺加入导致的导电组分分布不均匀所引起的.实验结果表明胶状体聚苯胺和粉末状聚苯胺在电磁屏蔽涂料基体树脂中具有完全不同的形态,分析了对电磁屏蔽效能的影响.     

膨胀石墨/金属网/ABS复合材料电磁屏蔽性能的研究

以膨胀石墨(EG)和金属网(MN)作为电磁屏蔽基元材料与ABS树脂采用共混、挤出、热压等成型工艺制备了电磁屏蔽复合材料,研究了膨胀石墨的含量、处理方式、复合材料的厚度和金属网的目数对电磁屏蔽复合材料屏蔽性能的影响。结果表明,在膨胀石墨/ABS电磁屏蔽复合材料中,其电磁屏蔽效能随着膨胀石墨含量增加及复合材料厚度增加而增大,膨胀石墨经超声处理后,可以提高复合材料的屏蔽效能。在两种单层金属网/ABS电磁屏蔽夹层复合材料中,屏蔽效能并不随着金属网目数增加而增大。在30MHz～1.8GHz频率范围内,200目不锈钢网/ABS复合材料和100目铜网/ABS复合材料的屏蔽性能最好,最大屏蔽效能分别为76.1和70dB。在多相电磁屏蔽复合材料中,膨胀石墨/不锈钢网/ABS复合材料的屏蔽效能比不锈钢网/ABS复合材料高约5dB。     

Al颗粒夹层CFRP复合材料力学及电磁屏蔽性能EI北大核心

CFRP复合材料具有优异的力学性能,在航空航天装备中有广泛应用,但是因其单层铺层内部的结构各向异性,单向纤维铺层对于垂直极化波的电磁屏蔽效能较弱。为应对日益复杂的电磁环境,保护电子元器件不受干扰,增强复合材料的电磁屏蔽效能显得尤为重要,本工作利用非连续Al颗粒在层间面内紧密排列,构建了一种层间面内含连续Al屏蔽层的CFRP复合材料,并研究了不同Al颗粒含量对复合材料电磁屏蔽效能和力学性能的影响规律。结果表明,随着Al颗粒含量的增加,CFRP复合材料的导电性和电磁屏蔽效能也随之增加,当聚合物中Al颗粒质量分数达到33.3%时,复合材料的面内电导率提高了3个数量级,在垂直于纤维方向上对频率为3~17 GHz的电磁波的电磁屏蔽效能提高了10 dB以上。随着Al颗粒含量的增加,复合材料层间剪切强度与弯曲强度出现先上升后下降的变化规律,当树脂中Al质量分数为33.3%时,复合材料的层间剪切性能提高了5.2%达到80.5 MPa,当树脂中Al质量分数为50%时,复合材料的弯曲强度提高了20%至1441.0 MPa,弯曲模量提高了10.2%达到101.83 GPa。由此可见,Al颗粒夹层CFRP复合材料可以实现力学性能和电磁屏蔽效能的同步提升,是一种具有广泛应用前景的结构-电磁屏蔽一体化复合材料。     

低温热处理对Fe@Ag复合粒子结构及性能的影响

为了降低Fe@Ag复合粒子的电阻率,研究了低温热处理对其微观形貌、电阻率、磁性能及复合粒子作为屏蔽填料制备的电磁屏蔽橡胶的屏蔽效能(SE)的影响.结果表明:随热处理温度的升高,在140℃获得的Fe@Ag复合粒子的银壳层最致密,电阻率最低,饱和磁化强度基本保持不变;以其作为屏蔽填料制备的电磁屏蔽橡胶的SE在-28~-53 dB,比未处理时提高了-10 dB~-15 dB.同时以界面润湿理论和晶体生长理论合理解释了复合粒子壳层形貌演变规律与屏蔽效能提高的原因.为制备具有高导电导磁的屏蔽填料提供了一种简单方便的处理方法.     

镀银织物基SiO2@FCIP涂层复合材料的制备及电磁屏蔽性能

为增强材料对电磁波的屏蔽性能，同时降低电磁波二次反射带来的危害。基于电-磁损耗协同作用机理，将机械球磨与二氧化硅(SiO₂)包覆双重改性的磁损耗材料羰基铁粉(CIP)与镀银织物复合，制备了结合吸收层和反射层的复合型电磁屏蔽织物。利用微观成像仪、X射线衍射仪、傅里叶红外光谱仪对改性CIP进行了物相表征，并通过同轴法和波导法对改性CIP以及复合织物的电磁参数与屏蔽效能进行了测试与分析。结果表明：双重改性后的羰基铁粉电磁波吸收损耗频带宽度增加且最佳反射损耗为-62.7dB;当涂层与基材整体厚度为3mm时，复合材料对电磁波的反射率(R)由0.96降至0.2,吸收率(A)由0.03增至0.82,实现了以吸收为主的屏蔽效果。     

多层金属纤维混纺织物的电磁屏蔽效能

金属纤维混纺织物由于具有较好的电磁屏蔽性能得到了广泛应用,但其屏蔽效能受纺织工艺等诸多因素影响,难以建立精确的计算模型。在分析介质平板屏蔽体屏蔽效能的基础上提出等效算法,将金属纤维混纺织物等效为均匀介质平板,以计算多层织物材料的电磁屏蔽效能。通过测试单、双层金属纤维混纺织物的电磁屏蔽效能,验证了等效方法的正确性和可行性,可用于指导复合材料的设计。     

电磁屏蔽材料中聚苯胺对屏蔽效能的影响及机理

金属材料与导电聚苯胺复合形成屏蔽组分有效提高了复合电磁屏蔽材料的高频电磁屏蔽效能,从而扩展了屏蔽材料的屏蔽带宽.以金属Ni粉/导电聚苯胺复合屏蔽组分为例,分析了在复合电磁屏蔽材料中聚苯胺的对屏蔽效能的贡献及作用机理.结果表明聚苯胺的加入与基体树脂相溶形成基体导电网络,有效阻碍了高频电磁波的穿透,可能是提高高频效能的主要原因.     

金属导电短纤维提高Ni涂层导电性能研究

探索了金属导电短纤维提高电磁波屏蔽用Ｎｉ涂层导电性能的机制。结果表明，金属导电短纤维能大幅度地提高Ｎｉ涂层的导电性能，经分析是由于增大涂层中导电网络的密度所致。还对复合型涂层的屏蔽效能进行了理论预测。     

Composite electromagnetic interference shielding materials for aerospace applications

Electromagnetic interference (EMI) occurs when electronic devices are subject to electromagnetic radiation from unwanted sources at the same frequency ranges that these devices operate. Metals typically serve as excellent EMI shielding agents, but their heavy weight, high cost and susceptibility to forms of environmental degradation make them an undesired choice for many current electronic devices. Conversely fibre reinforced polymeric (FRP) composite materials are normally light weight, and can be cheaper to produce, but typically lack the inherent EMI shielding capabilities that may be required. This research work addresses the viability FRP composite materials for use as EMI shielding structures, specifically for aerospace applications. It was found that carbon fibre could suffice this purpose, but likely required filler materials to enhance electrical conductivity and shielding effectiveness (SE).     

Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P plated polyester fabric

Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P deposits obtained from an alkaline hypophosphite reducing electroless nickel bath was studied. The effects of plating temperature on the deposition rate, surface morphology, chemical composition and structure of the electroless Ni–P deposits were investigated. Surface resistance and electromagnetic interference (EMI) shielding effectiveness (SE) of Ni–P plated polyester fabric were also evaluated. The results demonstrated electroless Ni–P plated polyester fabric present useful EMI shielding materials.     

Synergetic effect of conducting polymer composites reinforced E-glass fabric for the control of electromagnetic radiations

The use of fibril materials as substrate for reinforcing polymers has wide industrial applications. In this article, we discuss polyaniline and polypyrrole as conducting polymers to provide electronic conductivity in E-glass fabric reinforced conducting composite with varied degree of composition and conductivity using industrially important polymers polymethylmethacrylate and polyvinyl chloride as a host matrix. Aromatic sulphonic acids such as PXSA, OXSA, PSA, PDSA, RDSA, OCPSA and MCSA were used as a dopant. The influence of the aromatic ring substituents in these dopants over the conductivity and processibility due to various interactions has been studied. The study shows that due to bulk nature of conductivity, shielding effectiveness (SE) increases with increase in conductivity and thickness of a composite. The test samples were characterized by conductivity and electromagnetic shielding effectiveness (EMI SE). The electromagnetic shielding effectiveness was measured by co-axial transmission line method in the frequency range of 0.01–1000 MHz. These composites with both side shielded by polypyrrole offered a uniform shielding effectiveness of 69 dB.     

Electromagnetic interference shielding by carbon fibre-filled polychloroprene rubber composites

The electromagnetic interference (EMI) shielding effectiveness of short carbon fibre-filled polychloroprene composites was studied in the frequency ranges 100 to 1000 MHz and 8 to 12 GHz. It was observed that, at a particular frequency, the shielding effectiveness increases with increasing loading of carbon fibre in the composite. Results show that 30 to 40 phr (parts per hundred parts of rubber) loading of fibre makes the rubber composite a potential EMI shielding material for use in the electronics industry.     

Electromagnetic interference (EMI) shielding of single-walled carbon nanotube epoxy composites

Single-walled carbon nanotube (SWNT)-polymer composites have been fabricated to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) of SWNTs. Our results indicate that SWNTs can be used as effective lightweight EMI shielding materials. Composites with greater than 20 dB shielding efficiency were obtained easily. EMI SE was tested in the frequency range of 10 MHz to 1.5 GHz, and the highest EMI shielding efficiency (SE) was obtained for 15 wt % SWNT, reaching 49 dB at 10 MHz and exhibiting 15-20 dB in the 500 MHz to 1.5 GHz range. The EMI SE was found to correlate with the dc conductivity, and this frequency range is found to be dominated by reflection. The effects of SWNT wall defects and aspect ratio on the EMI SE were also studied.     

Highly Stretchable Polymer Composite with Strain-Enhanced Electromagnetic Interference Shielding Effectiveness

Polymer composites with electrically conductive fillers have been developed as mechanically flexible, easily processable electromagnetic interference (EMI) shielding materials. Although there are a few elastomeric composites with nanostructured silvers and carbon nanotubes showing moderate stretchability, their EMI shielding effectiveness (SE) deteriorates consistently with stretching. Here, a highly stretchable polymer composite embedded with a three-dimensional (3D) liquid-metal (LM) network exhibiting substantial increases of EMI SE when stretched is reported, which matches the EMI SE of metallic plates over an exceptionally broad frequency range of 2.65–40 GHz. The electrical conductivities achieved in the 3D LM composite are among the state-of-the-art in stretchable conductors under large mechanical deformations. With skin-like elastic compliance and toughness, the material provides a route to meet the demands for emerging soft and human-friendly electronics.     

Ultrathin,flexible,and high-strength Ni/Cu/metallic glass/Cu/Ni composite with alternate magneto-electric structures for electromagnetic shielding

Electromagnetic interference (EMI) shielding materials with ultrathin,flexible,superior mechanical and thermal management properties are highly desirable for smart and wearable electronics.Here,ultrathin and flexible Ni/Cu/metallic glass/Cu/Ni (Ni/Cu/MG) multilayer composite with alternate magnetic and electrical structures was designed via facial electroless plating of Cu and Ni on an Fe-based metallic glass.The resultant 0.02 mm-thick Ni/Cu/MG composite displays a superior EMI shielding effectiveness (EMISE)of 35 dB and a great EMISE/t of 1750 dB/mm,which is greater than those of composites with monotonous multilayer or homogeneous structures.The improved EMI SE originates from the massive ohmic losses,the enhanced internal reflection/absorption,and the abundant interfacial polarization loss.Particularly,Ni/Cu/MG exhibits a high tensile strength of up to 1.2 GPa and outstanding mechanical stability,enabling the EMI SE remains unchanged after 10,000 times of bending.Moreover,Ni/Cu/MG has excellent Joule heating characteristics and thermal stability,which is very suitable for heating components of wearable hyperthermia devices.     

电磁屏蔽复合材料电磁屏蔽效能探讨

电磁屏蔽材料目前向着薄、轻、宽、高的方向发展,复合材料已逐渐取代单一材料成为电磁屏蔽研究的主要方向.以机械复合材料为基础,研究高导电材料+高导磁2层复合材料与高导电材料+高导电材料+高导磁材料3层复合材料电磁屏蔽效能的差别.研究结果表明,2层复合材料高导电材料一侧增加1层高导电材料对电磁屏蔽性能的提高非常有限.