孔隙率对三维针刺C/C复合材料电磁屏蔽性能的影响

通过多次重复先驱体浸渍裂解(PIP)工艺过程,改变材料的孔隙率和体密度,制备不同孔隙率的三维针刺碳/碳(C/C)复合材料,并研究了在8.2~12.4GHz频率范围内(X波段)不同孔隙率C/C复合材料的电磁屏蔽效能。结果表明:适当降低孔隙率有利于提高C/C复合材料的总电磁屏蔽效能和电磁吸收屏蔽效能,当开气孔率为33.4%时,C/C复合材料具有最大的电磁屏蔽效能(40dB),且电磁吸收屏蔽效能(30dB)远大于电磁反射屏蔽效能(12dB),是极具潜力的高吸收低反射电磁屏蔽材料。     

A comparative study of EMI shielding properties of carbon nanofiber and multi-walled carbon nanotube filled polymer composites

Electromagnetic interference shielding properties of carbon nanofiber- and multi-walled carbon nanotube-filled polystyrene composites were investigated in the frequency range of 8.2-12.4 GHz (X-band). It was observed that the shielding effectiveness of composites was frequency independent, and increased with the increase of carbon nanofiber or nanotube loading. At the same filler loading, multi-walled carbon nanotube-filled polystyrene composites exhibited higher shielding effectiveness compared to those filled with carbon nanofibers. In particular, carbon nanotubes were more effective than nanofibers in providing high EMI shielding at low filler loadings. The experimental data showed that the shielding effectiveness of the composite containing 7 wt% carbon nanotubes could reach more than 26 dB, implying that such a composite can be used as a potential electromagnetic interference shielding material. The dominant shielding mechanism of carbon nanotube-filled polystyrene composites was also discussed.     

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.     

Electromagnetic interference shielding behavior of poly(trimethylene terephthalate)/multi-walled carbon nanotube composites

Poly(trimethylene terephthalate) [PTT]/multiwalled carbon nanotube [MWCNT] composites having varying amounts of MWCNTs were fabricated with an aim to investigate the potential of such composites as an effective light weight electromagnetic interference (EMI) shielding material in the frequency range of 12.4-18 GHz (Ku-band). PTT/MWCNT composite with shielding effectiveness (SE) of 36-42 dB was obtained at 10% (w/w) MWCNT loading. Shielding mechanism was studied by resolving the total SE into absorption (SE_A) and reflection loss (SE_R). PTT/MWCNT composite showed absorption dominated shielding; thus it can be used as microwave, radar absorbing and stealth material. The effect of MWCNT loadings on electrical conductivity (σ) and dielectric properties of PTT and the correlation among conductivity, tan δ, absorption loss and reflection loss were also studied.     

Electrical conductivity and shielding effectiveness of poly(trimethylene terephthalate)/multiwalled carbon nanotube composites

Poly(trimethylene terephthalate) (PTT)/multiwalled carbon nanotube (MWCNT) composites have been fabricated to evaluate the potential of PTT composites as electromagnetic interference (EMI) shielding material. The room temperature electrical conductivity, complex permittivity, and shielding effectiveness (SE) of PTT/MWCNT composites were studied in the frequency range of 8.2–12.4 GHz (X-band). The dc conductivity (σ) of composites increased with increasing MWCNT loading and a typical percolation behavior was observed at 0.48 vol% MWCNT loading. The highest EMI SE of PTT/MWCNT composites was ~23 decibel (dB) at 4.76 vol% MWCNT loading which suggest that these composites can be used as light weight EMI shielding materials. The correlation among the SE, complex permittivity, and electrical conductivity was also studied. The EMI shielding mechanism of PTT/MWCNT composites was studied by resolving the total EMI SE into absorption and reflection loss.     

Broadband electromagnetic shielding and dielectric properties of polyaniline-stannous oxide composites

Conducting polyaniline-stannous oxide (PAni-SnO) composites were synthesized by the in situ polymerization of aniline in the presence of SnO. The composites formed were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As there is a greater need for materials with electromagnetic interference (EMI) shielding properties over a large operating frequency band, the present study highlights the dielectric and EMI shielding response of PAni-SnO composites in the microwave frequency range from 8 to 18 GHz (X and Ku bands). All the computations were based on microwave scattering parameters measured by transmission line waveguide technique. The EMI shielding effectiveness (EMI SE), return loss, microwave absorption and dielectric properties of the PAni-SnO composites were evaluated for various wt% of SnO (10, 20, 30, 40 and 50 wt%) in PAni. In X-band, the composites exhibits EMI SE in the range ?18 to ?23 dB, with microwave absorbance of 70–83 % and in the Ku-band, the composites exhibits EMI SE values of ?17.5 to ?22.5 dB with 67–85 % absorbance. Our investigations reveal that the PAni-SnO composites are potential candidates for EMI shielding applications for both the X and Ku bands.     

Superior mechanical and electrical properties of multiwall carbon nanotube reinforced acrylonitrile butadiene styrene high performance composites

In-house synthesized multiwall carbon nanotubes (MWCNTs) have been dispersed in acrylonitrile butadiene styrene (ABS) using a micro twin-screw extruder with back flow channel. The electrical and mechanical properties of MWCNTs in ABS with different wt% have been studied. Incorporation of only 3 wt. % MWCNTs in ABS leads to significant enhancement in the tensile strength (up to 69.4 MPa) which was equivalent to 29% increase over pure ABS. The effect of MWCNTs on the structural behaviour of ABS under tensile loading showed a ductile to brittle transition with increase concentration of MWCNTs. The results of enhanced mechanical properties were well supported by micro Raman spectroscopic and scanning electron microscopic studies. In addition to the mechanical properties, electrical conductivity of these composites increased from 10⁻¹² to 10⁻⁵ Scm⁻¹ showing an improvement of ∼7 orders of magnitude. Due to significant improvement in the electrical conductivity, EMI shielding effectiveness of the composites is achieved up to −39 dB for 10 wt. % loaded MWCNTs/ABS indicating the usefulness of this material for EMI shielding in the Ku-band. The mechanism of improvement in EMI shielding effectiveness is discussed by resolving their contribution in absorption and reflection loss. This material can be used as high-strength EMI shielding material.     

Electromagnetic interference shielding of composites consisting of a polyester matrix and carbon nanotube-coated fiber reinforcement

We investigated the electromagnetic interference shielding effectiveness (EMI SE) of composites consisting of an unsaturated polyester matrix containing woven glass or carbon fibers that had been coated with multiwalled carbon nanotubes (MWCNTs). Composite panels consisting of fiber fabrics with various combinations of fabric type and stacking sequence were fabricated. Their EMI SE was measured in the frequency range of 30 MHz–1.5 GHz. The underlying physics governing the EMI shielding mechanisms of the materials, namely, absorption, reflection, and multiple reflections, was investigated and used in analytical models to predict the EMI SE. Simulation and experimental results showed that the contributions of reflection and absorption to EMI shielding is enhanced by sufficient impedance mismatching, while multiple reflections have a negative effect. For a given amount of MWCNTs in the glass-fiber–reinforced composite, coating the outermost, instead of intermediate, glass fiber plies with MWCNTs was found to maximize the conductivity and SE.     

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.     

Novel carbon nanotube-polystyrene foam composites for electromagnetic interference shielding

A novel carbon nanotube-polystyrene foam composite has been fabricated successfully. The electromagnetic interference (EMI) shielding effectiveness measurements indicated that such foam composites can be used as very effective, lightweight shielding materials. The correlation between the shielding effectiveness and electrical conductivity and the EMI shielding mechanism of such foam composites are also discussed.     

微纳米材料在电磁屏蔽方面的应用研究进展

信息技术的迅速发展和电子设备的大量使用,在环境中产生了如电子噪声、电磁波(EM)、电磁干扰(EMI)、射频干扰等电子污染。综述了EMI屏蔽微纳米材料相关方面的研究进展,简要分析了EMI屏蔽的基本机理和比较了纳米EMI屏蔽复合材料的制备方法,同时对比了金属和碳纳米填料EMI屏蔽复合材料,得到金属纳米EMI屏蔽复合材料,虽具有良好效果,但是存在质量大、成本高和耐腐蚀性弱等缺点。因碳系纳米材料具有质量轻,耐腐蚀性,优异的电学、电介质、热学、机械和磁性等独特特性,可替代金属作为EMI屏蔽填料,且EMI屏蔽效果优良。如多层纳米管(MWCNT)和石墨烯/聚苯胺(GN/PANI)纳米复合材料,并且两者材料的混杂可以协同改善复合材料的屏蔽效果。     

Porous composites coated with hybrid nano carbon materials perform excellent electromagnetic interference shielding

This work reported preparation of porous composites using a simple dip-coating method, and the fabricated composites containing hybrid carbon nanomaterials performed excellent electromagnetic interference (EMI) shielding properties. A commercial sponge was coated with silver nanoparticles before being dip-coated with graphene (GP)/ink, multi-wall carbon nanotubes (MWCNTs)/ink, or hybrid GP/MWCNTs/ink to form Ag/carbon nanomaterial hybrid composites, and then the composites were subjected to EMI measurements in the frequency range of 0.45–1.5 GHz. For comparison, the sponges without Ag nanoparticle coating were also prepared. Herein, we found an insignificant difference in EMI SE among the porous composites without Ag nanoparticle coating, and the maximum values of approximately 14.4 dB was attained. Interestingly, the hybrid composites with Ag nanoparticle coating exhibited maximum EMI shielding of 24.33 dB. Due to their porous structure, the EMI SE measurements showed that reflection dominates the EMI SE for all the sponge composites studied in this work.     

The effect of multi-wall carbon nanotubes on electromagnetic interference shielding of ceramic composites

Multi-wall carbon nanotubes (MWCNTs)-3?mol% yttria-stabilized zirconia (3Y-TZP) (MWCNTs-3Y-TZP) composite was prepared by spark plasma sintering. The complex permittivities of the composite have been measured in the Ku-band range (12.4-18?GHz) and it is found that both the real and imaginary permittivities of the composite increase with the increasing content of MWCNTs. The effect of the content of MWCNTs on the electromagnetic interference (EMI) shielding effectiveness (SE) of the composite has been evaluated, and it is found that the EMI SE of the composite increases with the increasing content of MWCNTs. An EMI SE value as high as 25-30?dB has been achieved in the Ku-band range for the composite with 9?wt% content of MWCNTs, indicating that the MWCNTs-3Y-TZP composite can be used as an effective EMI shielding material.     

Electromagnetic interference shielding effectiveness of short carbon fibre-filled polychloroprene vulcanized by barium ferrite

Short carbon fibre-filled polychloroprene rubber composites vulcanized by barium ferrite were used for the measurement of electromagnetic interference (EMI) shielding effectiveness, at varying carbon fibre concentrations, aspect ratios and sample thicknesses, in the frequency range of 100 to 2000 MHz. The return loss values of the composites have also been studied at different carbon fibre concentrations and aspect ratios in the frequency range of 1100 to 2000 MHz. It was observed that at a particular frequency with increasing carbon fibre concentration the shielding effectiveness of the composite increases and return loss decreases. It was also observed that composites prepared by a cement mixed method with a high fibre aspect ratio (L/D 100) show a higher shielding effectiveness and lower return loss than composites prepared by a mill mixed method with a low fibre aspect ratio (L/D 25). This indicates that loss due to absorption increases with increase in carbon fibre concentration and aspect ratio. Correlation between shielding effectiveness and volume resistivity of the composites indicates that the shielding effectiveness depends not only upon the volume resistivity of the composite, but also on the aspect ratio and sample thickness.     

Effect of silver incorporation into PVDF-barium titanate composites for EMI shielding applications

Composites of polyvinylidene fluoride (PVDF) with micron and nano sized BaTiO₃ powders were developed for electromagnetic interference (EMI) shielding applications in the X band. PVDF-nano BaTiO₃ composites show better shielding property compared to PVDF-micron sized BaTiO₃ composites. The composite of PVDF with 40 vol% of nano BaTiO₃ showed the best EMI shielding effectiveness and is about 9 dB. The contributions from reflection and absorption to the total EMI shielding effectiveness is same for the PVDF-BaTiO₃ composites. Addition of small amount of silver particles improved the shielding properties of these composites due to the increased conductivity. An EMI shielding effectiveness of about 26 dB is obtained in the measured frequency range for the PVDF-20 vol% nano BaTiO₃-10 vol% Ag composite of thickness 1.2 mm. Novel three phase composite combining the advantages of metal, nano ceramic and polymer is obtained with the potential for effective EMI shielding applications.     

Processing of graphene nanoribbon based hybrid composite for electromagnetic shielding

The advent of graphene heralded by the recent studies on carbon based conducting polymer composites has been a motivation for the use of graphene as an electromagnetic interference (EMI) shielding material. One of the variants of graphene, graphene nanoribbon (GNR) shows remarkably different properties from graphene. The EMI shielding effectiveness of the composite material mainly depends on fillers’ intrinsic conductivity, dielectric constant and aspect ratio. We have synthesized graphene nanoribbon (GNR) – Polyaniline (PANI) – epoxy composite film for effective shielding material in the X-band frequency range of 8.2–12.4 (GHz). We have performed detailed studies of the EMI shielding effect and the performance of the composite and found that the composite shows ∼−40 dB shielding which is sufficient to shield more than 95% of the EM waves in X Band. We checked the shielding effectiveness of the composite film by varying the GNR percentage and the thickness of the film. The strength properties of the synthesized composited were also studied with a aim to have a material having both high strength and EMI shielding properties.     

Segregated poly(vinylidene fluoride)/MWCNTs composites for high-performance electromagnetic interference shielding

Conductive polymer composites (CPCs) that contain a segregated structure have attracted significant attentions because of their promising for fulfilling low filler contents with high electromagnetic interference (EMI) properties. In the present study, segregated poly(vinylidene fluoride) (PVDF)/multi-walled carbon nanotubes (MWCNTs) composites were successfully prepared by mechanical mixing and hot compaction. The PVDF/MWCNTs samples with 7 wt% filler content possess high electrical conductivities and high EMI shielding effectiveness (SE), reaching 0.06 S cm⁻¹ and 30.89 dB (in the X-band frequency region), much higher than lots of reported results for CNT-based composites. And the EMI SE greatly increased across the frequency range as the sample thickness was improved from 0.6 to 3.0 mm. The EMI shielding mechanisms were also investigated and the results demonstrated absorption dominating shielding mechanism in this segregated material. This effective preparation method is simple, low-cost, and environmentally-friendly and has potential industrial applications in the future.     

Effect of carbon nanofiber reinforcement on electromagnetic interference shielding effectiveness of syntactic foam

A novel carbon nanofiber (CNF)-reinforced syntactic foam (CNFRSF) was fabricated. The electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) of CNFRSF with various volume fraction of CNFs (0–2.0 vol%) were evaluated experimentally. The measurement of EMI SE was carried out in a frequency range of 30 MHz to 1.2 GHz. The experimental results showed that the SE of CNFRSF increases with increase of CNFs content and CNF is more effective in providing EMI shielding compared to chopped carbon fiber and long carbon fiber due to the larger aspect ratio. The CNFRSF having 2.0 vol% CNFs has a SE of 25 dB, which is good enough for most practical applications. Compared to CNFs composites, the EMI SE of CNFRSF has been enhanced by the presence of hollow carbon microspheres. The underlying mechanism is discussed in detail.     

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.     

单壁碳纳米管无纺布/环氧树脂复合材料的电磁屏蔽性能

采用一种导电材料预制体-单壁碳纳米管(Single-wall carbon nanotube,SWCNT)无纺布与环氧树脂复合制备了电磁屏蔽复合材料,并对所制复合材料的电磁屏蔽性能进行了表征。结果表明:所制复合材料对电磁波的屏蔽效率随SWCNT无纺布厚度的增加而增加。在较低的SWCNT无纺布填加量下所制复合材料可以实现对低频电磁波较高的屏蔽效率。不同于填加粉体导电材料所制电磁屏蔽复合材料,作为导电材料预制体使用的SWCNT无纺布是一个独立的整体导电薄膜,可以直接引入到基体当中,不存在分散问题。并且通过简单的导电预制体多层叠加的方式即可实现复合材料更高的屏蔽效率。