Submicron nickel filaments made by electroplating carbon filaments as a new filler material for electromagnetic interference shielding

Short nickel filaments of diam 0.4 μm and containing 94 vol% Ni and 6 vol% C were fabricated by electroplating with nickel 0.1 μm diam catalytically grown carbon filaments. The use of these filaments in polyether sulfone in amounts of 3, 7,13, and 19 vol% gave composites with electromagnetic interference shielding effectiveness at 1–2 GHz of 42,87,84, and 92 dB, respectively, compared to a value of 90 dB for solid copper. Less shielding was attained when 0.1 μm diam carbon filaments or 2 or 20 μm diam nickel fibers were used instead.     

金属网栅电磁屏蔽窗口薄膜的设计与制备

通过光刻掩膜技术、电阻热蒸发沉积技术制备电磁屏蔽窗口金属网栅薄膜,研究金属网栅的红外透射率和电磁屏蔽效能。为了能有效地屏蔽电磁波,使用CST Studio Suite电磁仿真软件设计不同周期、线宽的金属网栅,采用光刻掩膜技术、电阻热蒸发技术在双面抛光单晶硅基片上完成线宽为30μm,周期分别为350μm、450μm、550μm、650μm、750μm的金属网栅薄膜的制备。采用真空型傅立叶红外光谱仪和矢量网络分析仪分别对不同结构参数金属网栅薄膜的光谱特性和电磁屏蔽效能进行测试。结果:实现在双面抛光单晶硅基底上制备的网栅在12~18 GHz频段内,网栅的电磁屏蔽效能均达到12 dB以上。在3~5μm波段的透射率损失仅为8%。为了得到既具有高透光率,又具有强电磁屏蔽效能金属网栅薄膜需要合理设计金属网栅的线宽和周期。制备过程中网栅的光学-电学特性不仅受周期和线宽影响,掩膜板的加工精度、金属网栅的加工缺陷等也会造成不同程度的影响。     

Structuration of the low temperature co-fired ceramics (LTCC) using novel sacrificial graphite paste with PVA-propylene glycol-glycerol-water vehicle

A novel formulation for thick-film graphite sacrificial pastes is studied in this paper. It is composed of coarse graphite powder (grain size: 25 μm), dispersed in a vehicle consisting of polyvinyl alcohol (PVA) dissolved in a propylene glycol (PG)-glycerol (G)-water mix, which is not aggressive to thin LTCC sheets. The presented sacrificial paste has been successfully applied for fabrication of thin (<50 μm) membranes and microchannels in low temperature co-fired ceramics (LTCC) substrate. The properties of the graphite-based paste have been examined using thermo-gravimetric analysis (TGA), differential thermo-gravimetric (DTG) and differential thermal analysis (DTA). The obtained membranes and microchannels have been investigated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and optical profile measurements gauge.     

Shielding Effectiveness Data on Commercial Thermoplastic Materials

Ten different commercially available conductive thermoplastic materials have been tested for near- and far-field shielding effectiveness (SE). Far-field SE was tested using a modified standard measurement technique to provide results comparable with the company-provided data. Further, housings of different thermoplastic materials were constructed and equipped with an electromagnetic interference (EMI) source to model a realistic near-field SE situation. The SE data up to 1 GHz is presented. Conductive thermoplastic materials with fillings of stainless steel fibers and nickel-coated carbon fibers were the two materials that offer the best far-field shielding performance. For the near-field shielding, two materials with filling of stainless steel fibers were the best performing ones. A thermoplastic with polycarbonate (PC) base and stainless steel content of 1.5 vol% showed the best combined far- and near-field shielding results     

Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness

The processing of nickel filaments of 0.4 Μm diameter gives polyethersulfone-matrix composites with high electromagnetic interference shielding effectiveness, high reflection coefficient and low surface impedance at 1-2 GHz. With 7 vol.% nickel filaments, the composite exhibited shielding effectiveness 87 dB (compared to 90 dB for solid copper), surface impedance 1.2 Ω (same as for solid copper), tensile strength 52 MPa, modulus 5 GPa, ductility 1.0%, and density 1.87 g/cm³.     

Cement-based controlled electrical resistivity materials

Low-cost controlled electrical resistivity materials based on Portland cement and exhibiting low values of the relative dielectric constant have been attained. The materials are cement paste containing short electrically-conducting fibers. With steel fibers (0.1 vol.%), the resistivity and relative dielectric constant (10 kHz) are 8 × 10⁴ cm and 20, respectively. With carbon fibers (1.0 vol.%) and silica fume, these quantities are 8×10²Ω-cm and 49, respectively.     

计算机的电磁辐射分析与防护

针对计算机电磁信息泄漏对信息安全的影响,结合屏幕分辨率为1 280×1 024的液晶显示屏的信号辐射情况,利用计算机进行了仿真,分析了辐射信号的时频特性,并对计算机进行了屏蔽设计与实测。测试结果表明,所设计电子屏蔽箱的辐射发射总体<35 dBμV/m,适当增加防护半径,其辐射发射量可降到20 dBμV/ m以下,低于20 dBμV/m的环境噪声,达到防电磁泄漏的要求。     

Flexible MXene-Based Composite Films for Multi-Spectra Defense in Radar,Infrared and Visible Light Bands

Simultaneously developing protective electronics film for multi-spectra, including the radar, infrared (IR), and visible ranges, for both the military and civilian sectors is extremely challenging. The existing multi-spectra-compatible materials mainly concentrate on either the radar/IR or IR/visible bands, trailing the rapid evolution of advanced devices for monitoring electromagnetic signals. Here, it is designed and fabricated an ultra-thin MXene-based composite film (20 µm) containing black phosphorus (BP) and Ni chains (M-B-M(Ni)) with integrated highly efficient thermal IR stealth, visible light absorption, and electromagnetic wave shielding. M-B-M(Ni) exhibits an extremely low IR emissivity of 0.1, decreasing the radiation temperature difference between the surrounding environment and target device. BP offers a high solar absorptance of 80%, which guarantees energy conversion from visible light to heat. Moreover, the absorption proportion of the electromagnetic shielding effectiveness for M-B-M(Ni) is 16% higher than that of pure MXene films (68.7%), owing to the improved magnetic loss by decoration with magnetic Ni chains. Due to the combined merits of MXene, BP, and Ni chains, M-B-M(Ni) opens an avenue for the construction of advanced multi-spectra compatible materials for versatile applications in thermal IR stealth, electromagnetic wave shielding, and energy transformation.     

Carbon-black thixotropic thermal pastes for improving thermal contacts

This paper addresses thermal interface materials for thermal conduction of excess heat for microelectronic applications. Carbon black (30 nm) thixotropic paste based on polyol ethers is comparable to carbon black fluidic paste based on polyethylene glycol (PEG) in its effectiveness as a thermal paste, and in its dependence on pressure history. Prior pressure (up to 0.69 MPa) application is helpful. The optimum carbon black content is 2.4 vol.% for the thixotropic paste. The thermal contact conductance across copper surfaces is 30 × 10⁴ and 11 × 10⁴ W/m²-°C for surface roughness of 0.05 μm and 15 μm, respectively. The volume electrical resistivity is 3 × 10³ Ω-cm. Boron nitride (BN) (5–11 μm) and graphite (5 μm) thixotropic pastes are less effective than carbon black thixotropic paste by up to 70% and 25%, respectively, in thermal contact conductance, due to low conformability.     

基于有限元方法的波导管结构电磁屏蔽屏蔽效能分析

提出一种在屏蔽箱体孔缝结构的外部增加截止波导管结构的方法,利用截止波导管对高频电磁波的衰减作用来提高屏蔽箱体屏蔽效能。基于有限元法分别对截止波导管的长度、厚度及其形状进行仿真,仿真结果表明:在0.1 GHz~1 GHz频率范围内,随着截止波导管长度及厚度的增加屏蔽箱体屏蔽效能提高15d B以上,圆形和矩形截止波导管对屏蔽效能影响不大。根据实际情况合理选择截止波导管的长度及厚度可以提高微弱信号处理电路的电磁抗干扰能力。     

高频状态下的圆孔屏蔽效能经验公式

电子设备电磁屏蔽效能的好坏直接影响着屏蔽体内电子器件工作的稳定性,而电磁屏蔽体上的孔洞造成的电磁泄漏是一个不容忽视的问题。针对这个问题,对有孔洞的屏蔽体的电磁泄漏进行了仿真计算,定量分析孔洞大小对屏蔽外壳的屏蔽性能的影响。分析结果表明在屏蔽体壁厚保证的情况下,孔洞的直径越小,屏蔽效能越高。当孔洞的半径在10mm以下时,屏蔽效能在30dB以上,满足实际工程要求的屏蔽效能要求。并由此得到屏蔽效能经验公式。     

聚氨酯乳液／纳米石墨微片复合导电涂料的制备及其电磁屏蔽性能

以纳米石墨微片为导电填料,聚氨酯乳液为基体,制备水性导电复合涂料,研究其导电性能和电磁屏蔽性能。结果表明,质量分数为35wt％纳米石墨微片,粘度区间160～180MPa·s,质量分数为2％的OP-10分散剂为最佳配方,最佳施工工艺为超声波分散30min后喷涂,涂层厚度控制在80um左右,在65℃的条件下固化。通过该法制备得到的导电涂料,其涂层表面电阻率降低至7．5Ω·cm^-2,平均的电磁屏蔽效能在27dB左右（300kHz～1．5GHz）。     

ELF and VLF Shielding Effectiveness of High-Permeability Materials

Research was conducted to determine the low-frequency shielding effectiveness of magnetic materials. Both analytical and experimental approaches were used. This work is unique in that it provides a technique for experimental separation of the various terms in the shielding expression. Expressions of shielding effectiveness of flat sheets for very low frequencies are derived, and the results of experiments with the following are given: 1) sheet materials, including AMPB-65,1 HyMu 80, conetic AA, mumetal, copper-plated AMPB-65, and galvannealed steel; 2) AMPB-65 sheets perforated with various size holes and various numbers of 0.125-inch diameter holes; 3) an overlap junction of two AMPB-65 sheets with a) various numbers of fastening screws and b) various depths of overlap; 4) overlap junctions of copper-plated AMPB-65 sheets; 5) AMPB-65 sheets clamped in Lindsay structure; and 6) honeycomb-core stainless steel sandwiches.     

Hybridization of oxidized MWNT and silver powder in polyurethane matrix for electromagnetic interference shielding application

Multiwalled carbon nanotubes (MWNTs) are chemically modified with respect to various different oxidative conditions, including the acid concentration, treatment time, and temperature. The conductivity of polyurethane (PU) composites filled with the MWNTs oxidized under optimal condition is measured as a function of frequency with the content of MWNTs and analyzed using percolation theory. Because the PU composites filled only with the MWNTs cannot satisfy the requirements for materials providing shielding against electromagnetic waves, conductive polymer composites are fabricated by the hybridization of MWNTs with Ag flakes. It is observed that a small amount of the MWNTs remarkably enhances the conductivity and shielding effectiveness of the MWNT/Ag flake/PU composites, by bridging the gap between the flaky Ag clusters. The electromagnetic interference shielding effectiveness of the composites can be controlled from about 60 dB to more than 80 dB at an extremely low loading level of both the MWNTs and the Ag flakes in the frequency range from 10 to 1000 MHz.     

矩量法计算烟幕粒子的红外消光特性

基于矩量法建立了旋转体烟幕粒子的红外消光模型,对圆片、等效球体和等效柱体等形状的石墨粒子进行了消光性能计算,研究了形状、尺寸、厚度等参数对粒子红外消光能力的影响.计算结果表明,小尺寸粒子以吸收消光为主,大尺寸粒子以散射消光为主;圆片形状的粒子具有最佳的红外消光能力,厚度变小时,圆片粒子对红外的消光能力显著升高;半径在1...     

An Empirical Study of ELF and VLF Shield Cans

An empirical ELF and VLF study of 1/16- and 1/32-inch thick shield cans (stainless steel, aluminum, copper, Polyform, annealed Hipernom, and annealed and unannealed coldrolled steel, mumetal, and Co-Netic) was performed to investigate shielding effectiveness versus frequency characteristics with emphasis on the effects of machining (notches, slots, holes, and louvers), dropping, annealing, and welding. The erratic nature of many of the shielding functions is explained by the resonance theory of shielding, and the shielding characteristics of certain shield cans are compared. The paper also presents a brief introduction duction to the automated testing system used during this study to obtain the numerous shielding effectiveness versus frequency curves that were required.     

Plane-wave shielding properties of anisotropic laminated compositecylindrical shells

The plane-wave shielding properties of advanced composite cylindrical shells are analyzed. Based on a rigorous theory that clearly displays the propagating nature of the electromagnetic field in an anisotropic, multi-layered, and lossy cylindrical shell structure. In this study, numerical results are presented for graphite/epoxg fiber-reinforced composite shells. In particular, the parameters that influence the shielding effectiveness, such as material properties, cylinder configuration, fiber orientation, and incident wave polarization, are investigated in detail. For design purposes, an empirical formula is also proposed to estimate the shielding effectiveness in the lower frequency range. Finally, a sharp reduction of shielding performance due to resonance is also examined     

片式电容器用石墨浆料的分散稳定性

以石墨为导电填料,羧甲基纤维素钠(CMC)为分散剂,制备了片式电容器用石墨浆料。用吸光光度法对其进行了稳定性测试,讨论了CMC、聚乙烯醇(PVA)和苯丙乳液用量对浆料稳定性的影响和球磨时间对粒径的影响。结果表明:当CMC干料与石墨的质量比为0.035时,体系稳定性最好。苯丙乳液对体系稳定性影响不大,可作为成膜粘合剂使用。球磨90min为适宜时间,粒径集中在较小的范围,平均粒径6.374μm。     

镍基电磁波屏蔽复合涂料制备及在EMC中的工程应用

针对日益严重的电磁环境污染问题,根据电磁波屏蔽材料对电磁波作用原理,用镍粉和金属纤维作为复合填料,以丙烯酸树脂作粘结剂,按照涂料制备的方法,制备了一种能屏蔽电磁波的复合涂料。将其应用在某有线电视网和电子工作间,进行对比法测试,结果表明:在射频段,该材料将有线电视传输网设备中的干扰场强度降低了40%~50%,在电子工作间上的屏蔽效能达到了30~50dB。     

Erbium-doped fiber splicing and splice loss estimation

Erbium-doped fibers, deployed in erbium-doped fiber amplifiers (EDFA), often have small mode diameters (about 4-6 μm). If these fibers were to be abruptly interfaced with larger mode field diameter (7.5-10.5 μm) dispersion-shifted or conventional fibers, unacceptably large transmission loss penalties would be incurred. However, since the diffusion speed of most erbium fiber designs is higher than other fibers, a special real-time control (RTC) splicing technique is developed based on an image processing and a synamic splice loss estimation procedure in order to assure optimum thermal diffusion of the fiber core dopants, thereby creating a tapered transition region between the mating fibers, resulting in fiber splices that have consistently low losses (<0.1 dB) and high strength (>200 kpsi)