Electromagnetic shielding of nylon-66 composites applied to laser modules

Electromagnetic shielding of nylon-66 composites applied to laser modules was studied experimentally and theoretically. The effects of conductive carbon fiber length and weight percentage upon the shielding effectiveness (SE) of nylon composites were investigated. The SE of long carbon fiber filled nylon-66 composites was found to be higher than short carbon fiber composites under the same weight percentage of carbon fibers. In addition, higher electromagnetic shielding was obtained for the composite with higher carbon fibers contents at the same length. The SE of conductive carbon fiber filled nylon-66 composites was measured to be 42 dB at a low frequency of 30 MHz and 50 dB at a high frequency of 1 GHz. The SE predicted by theoretical models and measured by experiments were in good agreement for filled nylon-66 composites with different length fiber.     

Effective electromagnetic shielding of plastic packaging in low-cost optical transceiver modules

A low-cost plastic package of the standard 1 /spl times/ 9 type with effective electromagnetic (EM) shielding ability is developed. Optical transceiver modules with transmission rates of 155 Mb/s and 1.25 Gb/s are tested to evaluate the EM shielding against emitted radiation from the plastic packaging. The results show that the packaged optical transceiver modules exhibit shielding effectiveness (SE) of over 20 dB. The EM shielding properties of plastic materials consisting of nylon66 and liquid crystal polymer (LCP) with carbon fiber reinforced are investigated. The effects of weight percentage of fibers, carbon fiber length, and material thickness on the SE of the plastic composites are studied both from the plane-wave and near-field sources approaches. The packaged plastic optical transceiver modules with their good SE are suitable for use in low-cost and low electromagnetic interference (EMI) Gigabit Ethernet lightwave transmission systems.     

A carbon nanotube polymer-based composite with high electromagnetic shielding

A novel, polymer-based carbon nanotube (CNT) composite with high electromagnetic (EM) wave shielding effectiveness (SE) and high mechanical properties was developed. Two types of CNTs with different aspect ratios and morphologies are compared in this study. Amorphous carbon and graphite powder are used as reference materials. The liquid crystal polymer (LCP) and melamine formaldehyde (MF) are used as polymer matrices to study the orientation effect of CNTs in a polymer matrix. The influences of orientation, aspect ratio, mass fraction, and morphology of CNTs upon the shielding effectiveness (SE) of CNT/polymer composites are investigated. The experimental results show that the higher the orientation, the aspect ratio, and the weight percentage of nanomaterials are in the composite, the higher the polymer composites’ SE. The nanomaterials’ morphology, especially CNTs, also affects the SE value of the polymer composite. The highest SE for the CNT/LCP composite obtained is >62 dB. The theoretically calculated SE data are consistent with experimentally obtained data.     

A novel structure of woven continuous-carbon fiber composites with high electromagnetic shielding

A novel structure employing the woven continuous-carbon fiber (CCF) epoxy composite with high electromagnetic (EM) shielding is presented experimentally and theoretically. The influences of weave type, number, and angle of overlapped plates upon the shielding effectiveness (SE) of the woven CCF-epoxy composite are investigated. The minimum SE of the single, double, and triple-plain or balanced-twill woven CCF-composite plates was measured to be as high as 50 dB, 60 dB, and 70 dB, respectively. More than 100 dB in SE was obtained for the triple-overlapped, plain-weave CCF composite at a frequency of 0.9 GHz. The weight percentage of the single CCF-composite plate required for electronic application is 4.8% only, which is less than one quarter of the CF content, and the performance in SE is 10 dB higher in comparison with long, CF-filled, liquid-crystal polymer (LCP) composites. The SE calculated theoretically is consistent with that measured by the experiment.     

Ordered Mesoporous Carbon/Fused Silica Composites

A series of novel, dense, and interesting ordered mesoporous carbon (OMC)/fused silica composites with different carbon contents has been prepared by a controllable but simple sol‐gel method followed by hot‐pressing. In the as‐sintered OMC/fused silica composites the carbon particles still exist in the form of perfectly ordered carbon nanowires. Conductivity measurements on the composites indicate that these novel composites are electrically conductive and have a typical percolation threshold of 3.5–5 vol% OMC. The electromagnetic interference (EMI) shielding efficiency (SE) of an OMC/fused silica composite containing 10 vol% OMC is as high as 40 dB in the X band which is higher than that of a carbon nanotube (CNT)/ fused silica composite with the same carbon content (～30 dB). This indicates that these conductive OMC/fused silica composites are very suitable for an application as EMI shielding materials. Upon increasing the volume content of OMC in the composite the overall contribution as well as the increase rate of the microwave absorption are larger than those of the microwave reflection, which suggest that OMC/fused silica composites may also be promising electromagnetic (EM) wave absorbing materials. Based on the promising properties of these composites this work will hopefully lead to the development of new low‐cost and highly efficient EMI shielding or EM wave absorbing materials.     

High electromagnetic shielding of plastic package for 2.5-Gb/s optical transceiver modules

A lightweight, low-cost plastic package for a 2.5-Gb/s optical transceiver module, that also has good electromagnetic shielding properties, has been fabricated using woven continuous carbon fiber (CCF) epoxy composite. The shielding effectiveness (SE) of the CCF epoxy composite has been modeled theoretically and measured from 500 MHz to 3 GHz using the ASTM D4935 and a near-field test method. Two types of weaving patterns were studied: a balanced twill structure (BTS) and a parallel structure. The BTS was able to achieve an SE of about 80 dB under plane wave conditions and about 50 dB under near-field conditions because of the numerous conductive between crossing fibers. The SE of the proposed package is at least 20 dB greater than the previous package which used a liquid crystal polymer composite. In addition to better shielding performance, the proposed package costs less because it uses less carbon fiber. The proposed package for an optical transceiver is suitable for use in a low-cost lightwave transmission system     

导电纤维高分子复合材料研究现状与发展趋势

介绍了国内外专家在以不锈钢纤维、铜纤维、碳纤维为填充物的导电高分子复合材料方面的研究成果,比较了这几种复合材料的性能。阐述了限制导电高分子复合材料进一步发展的因素及改进措施。     

螺旋形碳纤维结构吸波材料的制备及性能研究

用基板法以乙炔为碳源，镍板为催化剂，PCI，为助催化剂，通过化学气相沉积制备了螺旋形碳纤维手性吸收剂，并研究了其在2～18GHz的微波电磁特性：具有较高的介电损耗，电磁参数随频率的增大有减小的趋势，有利于实现宽频吸波。以螺旋形碳纤维作为吸收剂制备了Nomex蜂窝夹芯结构吸波材料，复合材料的厚度为9．5mm时，在3．76～18GHz反射率R小于-10dB，反射率小于-10dB的频宽为14．24GHz；最大吸收峰在10．4GHz，反射率R为-21．62dB。探讨了螺旋形碳纤维的吸波机理，螺旋形碳纤维是一种非常有发展前景的手性吸收剂和吸波材料。     

Low-cost and low-electromagnetic-interference packaging of optical transceiver modules

The low-cost and low-electromagnetic-interference (EMI) packaging of optical transceiver modules employing housings of plastic composites are developed and fabricated. Optical transceiver modules fabricated by the plastic composites with transmission rates of 1.25 and 2.5 Gb/s are tested to evaluate the electromagnetic (EM) shielding against emitted radiation from the plastic packaging. The results show that these packaged optical transceiver modules with their high shielding effectiveness (SE) are suitable for use in low-cost and low-EMI Gigabit Ethernet lightwave transmission systems. By comparison of cost, weight, and shielding performance for optical transceiver modules fabricated by the housings of nylon and liquid-crystal polymer with carbon fiber filler composites, woven continuous carbon fiber (WCCF), and nanoscale hollow carbon nanocapulses (HCNCs) epoxy composites, the WCCF composite shows lower cost, lighter weight, and higher EM shielding than the other types of composites. Future studies may develop the low-cost and low-EMI optical transceiver modules using nanoscale HCNCs that have the combination of excellent physical and mechanical properties, light weight, and thinness compared with the conventional fabrication techniques.     

Large Annular Dipoles Bounded between Single-Atom Co and Co Cluster for Clarifying Electromagnetic Wave Absorbing Mechanism

It is very challenging to demonstrate the intrinsic feature and absorption mechanism for electromagnetic (EM) wave absorber since dipole polarization loss is always discussed together with magnetic loss, conductive loss, defects/interfacial polarization, and so on. To address this issue, here, a kind of atomic composites is reported, including single-atom Co and Co cluster with controllable atom dipole to tune the polarization and establish the link between dipole polarization and the EM wave absorption. Using a chemical synthesis route, the atomic composites are fabricated, including Co single-atom (SA) sites and cluster (Cs) on nitrogen-doped graphitic carbon (Co_1+Cs/NGC). Due to the special design, the effect of magnetic loss, conductive loss, and interfacial polarization on EM wave dissipation can be ignored so that it can only highlight dielectric loss caused by dipole polarization. And, by controlling the Co atoms concentration, it can tune the valence state of Co atoms between 0 to +2 to control dipole polarization and relaxation. As a result, the Co_1+Cs/NGC-2 with Co concentration of 6.0 wt% exhibits optimized dipole moments and thus excellent absorption performance (the reflection loss exceeds −54.3 dB, and the effective absorption bandwidth with RL ≤−10 dB reaches 7.0 GHz at 2.0 mm) due to the effective dipole polarization caused by the large annular dipole bounded between Co SA sites and Co Cs. This study proposes a simplified model to clarify EM wave absorption mechanism from atom view.