Polypyrrole-Coated Zein/Epoxy Ultrafine Fiber Mats for Electromagnetic Interference Shielding

To reduce the environmental pollution and meet the needs for wearable electronic devices, new requirements for electromagnetic interference(EMI) shielding materials include flexibility, biodegradability, and biocompatibility. Herein, we reported a polypyrrole-coated zein/epoxy(PPy/ZE) ultrafine fiber mat which was inherently biodegradable and skin-friendly. In addition, it could maintain its ultrafine fibrous structure after coating, which could provide the mat with mechanical compliance, high porosity, and a large specific area for high EMI shielding. With the assistance of the epoxide cross-linking, the breaking stresses of the PPy/ZE fiber mats could achieve 3.3 MPa and 1.4 MPa and the strains were 40.1% and 83.0% in dry and wet states, respectively, which met the needs of various wearable electronic devices. Along with the extension in the PPy treatment duration, more PPy was loaded on the fiber surfaces, which formed more integrated and conductive paths to generate increasing conductivities up to 401.76 S·m^(-1). Moreover, the EMI shielding performance was raised to 26.84 dB. The biobased mats provide a green and efficient choice for EMI shielding materials, which may be a promising strategy to address EMI problems in multiple fields.

Laser-Induced Graphene Conductive Fabric Decorated with Copper Nanoparticles for Electromagnetic Interference Shielding Application

To meet the demands for flexible electromagnetic interference(EMI)shielding materials,a type of conductive fabric is prepared by generating three-dimensional(3D)porous laser-induced graphene(LIG)in situ on the surface of the aramid fabric(AF)and then electroless plating copper.After LIG treatment,the porous AF demonstrates admirable conductivity due to the generation of graphene.The superior surface resistance of the conductive fabric can reach 1.57Ω/sq after copper deposition,and the average EMI shielding effectiveness(SE)can reach 34.3 dB in a frequency range of 8.2 to 12.4 GHz,with the EMW absorption accounting for about 80%.The proposed technology provides a new idea for preparation of flexible EMI shielding materials.

Adding effects of Ni and Mn on electromagnetic interference(EMI) shield of Sn-based architectural materials

It has been proved by the World Health Organization （WHO） that electromagnetic waves would bring threats to public health in the tourism environment. However, most of the recent research about the relationship between building materials and electromagnetic waves was mainly focused on the electromagnetic products. It has also been claimed that the related research can rarely been found. Generally, ecotourism more tends to emphasize on a development of a new product and uni-environment study. However, these studies did not concern much on the application for conformity of healthcare-living materials, particularly to those block high-transparency materials. Hence, this research approaches to conform the application of architectural technique for producing tin-based powder with the add-on of Ni and Mg, in order to discuss the fully anti-electromagnetic wave property of healthcare material. With a low-cost advantage, the application field of architecture defines the ternary powder system, namely Sn-Al-Ni （SAN） and Sn-Al-Mn （SAM）. Additionally, the surface coating method can be implemented to review the influence of particle size, content ratio of Ni and Mn, stack effect, porosity and thickness to electromagnetic interference （EMI） mechanism.

虑及互耦效应的线缆辐射EMI建模

并行布线结构的开关电源线缆是开关电源辐射电磁干扰EMI(electromagnetic interference)的重要干扰源。针对并行线缆间辐射场互耦效应机理不明晰使得辐射电磁干扰预测不准确的问题,提出1种虑及线缆间互耦效应开关电源线缆的辐射电磁干扰模型。通过对描述线缆互耦效应的互阻抗建模,得到描述开关电源线缆辐射特性的辐射EMI输入阻抗模型,进而得到虑及互耦效应开关电源线缆的辐射EMI模型;搭建辐射EMI测试实验平台进行测试。实验结果表明,所提虑及互耦效应的辐射电磁干扰模型能够更为准确地预测开关电源线缆的辐射电磁干扰。

基于电磁干扰对消EMI有源滤波模块设计

针对火控设备因开关电源电磁干扰所引起的辐射超标问题,基于差模与共模结合的混合抑制原理,运用电磁干扰对消技术,制作一款小型化的有源滤波模块。该模块尺寸为25.4 mm×25.4 mm×6.0 mm,满足低剖面及便于电路板集成的需求。经实测,其能够抑制10 kHz~10 MHz频段内电源干扰,满足GJB 151B相关电磁兼容要求。通过实测比较发现,与无源滤波相比,其具有体积小、成本低、滤波性能稳定等优点。

考虑结电容和跨导非线性的辐射频段EMI分析模型

宽禁带WBG(wide band gap)半导体电力电子器件由于其开关频率高、开关速度快、寄生参数大等特点从噪声源头引发了越来越严峻的电磁干扰问题。然而,传统的噪声源研究主要集中在30 MHz传导频段以内,如何评估噪声源在30~300 MHz较高频率范围内的辐射频段产生的影响仍存在不确定性,因此提出1种改进的WBG器件电磁干扰分析模型,与传统的非对称梯形波电磁干扰模型相比,首次详细考虑了WBG器件的结电容和跨导体的非线性特性,评估了非线性参数对辐射频段噪声的影响,并进一步提出该模型在辐射频段噪声源抑制中的应用。仿真结果验证了所提计算方法的准确性,基于SiC器件的硬件测试结果与理论分析相吻合。

具有软启动功能的EMI直流滤波器设计

宽禁带半导体器件的应用使电动汽车的电机驱动系统更加小型化和轻量化,但也引发了更为严重的电磁干扰,使得驱动系统的可靠性面临严峻挑战。为此,以24 V/2 A的EMI直流滤波器为例,通过噪声源、滤波器原理及阻抗影响的分析,依据插入损耗指标进行滤波器参数设计。同时,考虑到整车启动时刻的启动冲击,加入软启动电路,进一步提高电动汽车驱动系统可靠性。实验测试验证了滤波器的电磁干扰抑制效果和软启动性能,证明了滤波器设计的可行性和有效性。

Flexible and Waterproof 2D/1D/0D Construction of MXene-Based Nanocomposites for Electromagnetic Wave Absorption,EMI Shielding,and Photothermal Conversion

High-performance electromagnetic wave absorption and electromagnetic interference(EMI)shielding materials with multifunctional characters have attracted extensive scientific and technological interest,but they remain a huge challenge.Here,we reported an electrostatic assembly approach for fabricating 2D/1D/0D construction of Ti_(3)C_(2)Tx/carbon nanotubes/Co nanoparticles(Ti_(3)C_(2)Tx/CNTs/Co)nanocomposites with an excellent electromagnetic wave absorption,EMI shielding efficiency,flexibility,hydrophobicity,and photother-mal conversion performance.As expected,a strong reflection loss of-85.8 dB and an ultrathin thickness of 1.4 mm were achieved.Mean-while,the high EMI shielding efficiency reached 110.1 dB.The excel-lent electromagnetic wave absorption and shielding performances were originated from the charge carriers,electric/magnetic dipole polariza-tion,interfacial polarization,natural resonance,and multiple internal reflections.Moreover,a thin layer of polydimethylsiloxane rendered the hydrophilic hierarchical Ti_(3)C_(2)Tx/CNTs/Co hydrophobic,which can prevent the degradation/oxidation of the MXene in high humidity condition.Interestingly,the Ti_(3)C_(2)Tx/CNTs/Co film exhibited a remark-able photothermal conversion performance with high thermal cycle stability and tenability.Thus,the multifunctional Ti_(3)C_(2)Tx/CNTs/Co nanocomposites possessing a unique blend of outstanding electromagnetic wave absorption and EMI shielding,light-driven heating perfor-mance,and flexible water-resistant features were highly promising for the next-generation intelligent electromagnetic attenuation system.

基于分数阶混沌的反激变换器辐射EMI主动抑制

快速通断的开关信号是造成开关电源电磁干扰EMI(electromagnetic interference)的主要原因。目前,关于混沌抑制EMI技术的研究主要集中在利用整数阶混沌抑制传导EMI。在此基础上,本文对分数阶混沌在辐射EMI上的抑制以及最优阶次的选取问题展开研究。首先,通过分数阶Lorenz的频谱特性及Lyapunov指数谱分析,优选出1.8阶Lorenz信号为最佳扩频序列;其次,基于变开关频率抑制EMI技术的基本原理,在STM32单片机中分别实现了定频、整数阶、2.7阶、1.8阶Lorenz混沌扩频PWM信号,在一台5 W反激变换器中进行近场辐射实验,证明了1.8阶Lorenz信号对近场磁场辐射抑制作用最强;最后,测得分数阶Lorenz混沌与定频PWM控制下,样机的整机效率相差2%左右,验证了分数阶混沌PWM在辐射EMI抑制性能上的优越性。

Annealing effects of Sn-Al and Sn-Cu nano thin films on mechanism of electromagnetic interference shielding

The sputtered Sn-Al and Sn-Cu thin films were used to investigate the effects of the crystallization mechanism and film thickness on the electromagnetic interference （EMI） characteristics. In addition, the annealed microstructure, electrical conductivities and EMI characteristics of the Sn-xAl films and the Sn-xCu films were compared. The results show that the electromagnetic interference （EMI） shielding of Sn-Al film was increased after annealing. For the Sn-Cu films with higher Cu mole concentration, the low frequency EMI shielding could not be improved. After annealing, the Sn-Cu thin film with lower Cu mole concentration possesses excellent EMI shielding at lower frequencies, but has an inverse tendency at higher frequencies.

Investigation and Reduction on Conducted Electromagnetic Interference Noise Mechanism for Complex Power Electronics Systems

针对复杂电子系统产生的传导EMI噪声,该文分别利用电偶极子模型、电路分析方法和散射参数方法提出了3种传导EMI噪声理论模型及其等效电路,包括因串扰引起的传导噪声模型,因接地不良引起的传导噪声模型,以及因PCB线缆阻抗失配引起的传导噪声模型。同时,还设计了一种串扰扼流圈以有效抑制因串扰引起的传导EMI噪声。实验结果表明,采用文中方法,某型商用车载导航和刷卡器能够通过GB 9254标准测试,噪声抑制效果分别可达44.8和29.28 dB V,从而验证了方法的有效性。

基于人工神经网络的差模EMI滤波器插入损耗预测

在电力电子设备中,高速开关经常会导致严重的电磁干扰EMI(electromagnetic interfere),严重影响电力电子系统的可靠性。为解决EMI问题,EMI滤波器是1种常用的解决方案。插入损耗作为噪声衰减能力的评价指标,其模型的准确性直接影响EMI滤波器的参数设计精度。为了提高EMI滤波器插入损耗模型的预测精度,首先准确描述系统行为并预测EMI滤波器滤波性能,提高EMI滤波器设计效率,然后利用反向传播神经网络对单级差模EMI滤波器的插入损耗进行建模。相较于理想模型和高频电路的行为模型,所提神经网络模型预测精度具有更好的实际应用价值,可以快速评估EMI滤波器的实际插入损耗,提高EMI滤波器设计效率,并为EMI滤波器的设计和优化提供指导。

基于SiC MOSFET同步BuckDC-DC变换器的宽频混合EMI滤波器设计

由于SiC MOSFET在高速开关电源中的广泛应用,导致严重的电磁干扰(EMI)问题,因此EMI滤波器的设计成为研究热点。为了满足电磁兼容(EMC)标准,无源EMI滤波器可以有效地降低DC-DC变换器产生的电磁干扰,但是无源磁性器件的体积较大,不利于提高DC-DC变换器的功率密度。该文分析DC-DC变换器的电磁干扰源和噪声源阻抗特性,建立无源和有源EMI滤波器的理论模型,提出宽频混合EMI滤波器的设计方法。最后,通过实验验证宽频混合EMI滤波器对DC-DC变换器EMI的抑制效果。

电驱系统高压无源EMI滤波器建模研究

实际工程中,通常使用无源EMI滤波器来抑制电磁干扰(electromagnetic interference,EMI),准确的滤波器模型对滤波器的性能仿真及优化设计具有重要意义。为此,对磁环的频变特性进行等效,采用全电路方法建立精准的EMI滤波器模型。首先,建立磁环的共模和差模高频等效电路模型,模型参数通过遗传算法获得;基于阻抗计算公式建立了X、Y电容的高频电路模型;然后,利用有限元提取了母排、接地以及PCB走线的寄生参数;根据共、差模等效原则建立0.009~60 MHz频段的全电路模型,该模型与滤波器实际的结构相对应,同时包含共模特性和差模特性;最后,通过插入损耗和端口阻抗验证了模型的有效性。

基于矢量拟合法的交流接触器EMI高频模型

随着交流接触器的智能化,越来越多的交流接触器控制系统采用了电力电子器件。但开关器件的引入会产生大量的电磁干扰,影响控制系统的工作稳定性。交流接触器作为控制系统中电磁干扰流经的重要路径,需要对其高频电路模型进行精确建模。针对不易建立高精度、宽频带的交流接触器电磁干扰(EMI)高频模型问题,提出了一种基于矢量拟合法的交流接触器EMI高频模型和建模方法。首先将交流接触器的阻抗表示成网络函数形式。然后使用矢量网络分析仪测取线圈出线端口的阻抗特性数据,对测得的数据进行矢量拟合,求出极点和留数。之后根据网络函数与电路参数的关系,对拟合出的极点和留数进行电路等效,并在电路仿真软件中搭建交流接触器高频电路模型并进行仿真。仿真实验结果表明该高频电路模型在150 kHz~30 MHz频段范围内有较高的精度。最后将交流接触器EMI高频模型代入交流接触器控制系统EMI模型中进行时域仿真。仿真实验结果显示在150 kHz~30 MHz频率范围内,建立的接触器EMI高频模型可用于接触器控制系统的传导电磁干扰分析。

扇出型封装EMI电磁屏蔽及部分屏蔽处理方案

随着科技的进步,电子产品变得不可或缺。扇出型封装技术以其性能和设计灵活性受到关注,提高了芯片整合度和电性能。但高性能电子设备密度和复杂性增加带来电磁干扰(EMI)问题,影响设备运作和信号传输。因此,研发有效的电磁屏蔽技术至关重要。文章探讨了扇出型封装中的EMI问题,提出了电磁屏蔽设计方案,包括Diefirst方案和RDLfirst方案。文章总结了扇出型封装技术发展趋势,探讨了未来挑战并为EMI电磁屏蔽设计提供建议,期望启发未来研究和创新。

Synchronous deprotonation–protonation for mechanically robust chitin/aramid nanofibers conductive aerogel with excellent pressure sensing, thermal management, and electromagnetic interference shielding

Aerogels with regularly porous structure and uniformly distributed conductive networks have received extensive attention in wearable electronic sensors,electromagnetic shielding,and so on.However,the poor mechanical properties of the emerging nanofibers-based aerogels are limited in practical applications.In this work,we developed a synchronous deprotonation–protonation method in the KOH/dimethyl sulfoxide(DMSO)system at room temperature for achieving chitin cross-linked aramid nanofibers(CANFs)rather than chitin nanofibers(ChNFs)and aramid nanofibers(ANFs)separately by using chitin and aramid pulp as raw materials.After freeze-drying process,the cross-linked chitin/aramid nanofibers(CA)aerogel exhibited the synergetic properties of ChNF and ANF by the dual-nanofiber compensation strategy.The mechanical stress of CA aerogel was 170 kPa at 80%compressive strain,increased by 750%compared with pure ChNF aerogel.Similarly,the compressibility of CA aerogel was somewhat improved compared to ANF aerogel.The enhancement verified that the crosslinking reaction between ANF and ChNF during the synchronous deprotonation process was formed.Afterwards,the conductive aerogels with uniform porous structure(CA-M)were successfully obtained by vacuum impregnating CA aerogels in Ti_(3)C_(2)T_(x) MXene solution,displaying low thermal conductivity(0.01 W/(m·K)),high electromagnetic interference(EMI)shielding effectiveness(SE)(75 dB),flame retardant,and heat insulation.Meanwhile,the as-obtained CA-M aerogels were also applied as a pressure sensor with excellent compression cycle stability and superior human motion monitoring capabilities.As a result,the dual-nanofiber based conductive aerogels have great potentials in flexible/wearable electronics,EMI shielding,flame retardant,and heat insulation.

Orthogonal experiment design of EMI of security monitoring system in coal mines

Security monitoring system of coal mines is indispensable to ensure the safe and efficient production of colliery. Due to the special and narrow underground field of the coal mine, the electromagnetic interference can cause a series of misstatements and false positives on the monitoring system, which will severely hamper the safe production of coal industry. In this paper, first, the frequency characteristics of the interference source on the power line are extracted when equipment runs normally. Then the finite difference time domain method is introduced to analyze the effects of the electromagnetic interference parameters on the security monitoring signal line. And the interference voltage of the two terminal sides on the single line is taken as evaluating indexes. Finally, the electromagnetic interference parameters are optimized by orthogonal experimental design based on the MATLAB simulation on the normal operation of equipment.

Conducted EMI Suppression in Plasma Cutting Power Supply

A systematic approach to the design of the conducted electromagnetic interference （EMI） filter of high-density plasma cutting power supply has been developed. Converter components have been accurately modeled, with parasitic elements extracted to reveal their impacts on the EMI noises. Circuit simulations have been used to analyze and minimize the EMI noises. Conducted EMI noise measurement and filter design of this power supply have been achieved which successfully satisfy the FCC class B limits in the frequency range from 150 kHz to 30 MHz. The analyses and experimental results show that the designed filter guarantees that the required attenuation will be achieved.

基于噪声源阻抗提取的EMI滤波器高效设计方法

针对传统EMI滤波器设计方法存在单次设计不准确、多次设计调试周期长的问题,提出一种基于噪声源阻抗提取的EMI滤波器高效设计新方法。首先通过插入无源二端口网络准确、迅速地获得噪声源阻抗幅值和相位;其次依据阻抗失配原则进行EMI滤波器拓扑选择;然后综合考虑噪声源阻抗、LISN端等效负载阻抗以及EMI滤波器高频分布参数对滤波器插入损耗的影响,令滤波器的理论插入损耗等于传导EMI测试频段范围内所需的插入损耗,得到滤波器各元件准确参数,实现了EMI滤波器精确设计。最后,通过一台LED驱动电源进行实验,结果表明一次设计即可满足预期效果,验证了所提方法的准确性和高效性。