MHz cut-off frequency and permeability mechanism of iron-based soft magnetic composites

The lack of soft magnetic composites with high power density in MHz frequency range has become an obstacle in the efficient operation of the electrical and electronic equipments.Here,a promising method to increase the cut-off frequency of iron-based soft magnetic composites to hundreds of MHz is reported.The cut-off frequency is increased from 10 MHz to 1 GHz by modulating the height of the ring,the distribution of particles,and the particle size.The mechanism of cut-off frequency and permeability is the coherent rotation of domain modulated by inhomogeneous field due to the eddy current effect.An empirical formula for the cut-off frequency in a magnetic ring composed of iron-based particles is established from experimental data.This work provides an effective approach to fabricate soft magnetic composites with a cut-off frequency in hundreds of MHz.

Frequency-time Domain Shielding Effectiveness of Materials and Their Strong Electromagnetic Field Test

To describe the shielding ability of materials accurately and comprehensively,the frequency-domain and time-domain shielding effectiveness(SE) of material is investigated.The relevance between them was analyzed based on the minimum phase method,and the time-domain SE can be derived from frequency-domain SE.The SE of an energy selective surface(ESS) made of a novel material is investigated,and the relationship between SE and radiation field intensity are analyzed.The results show that not only material,but also the intensity of radiation electric field shows influence on SE in its frequency; for some materials,the dependence of SE on radiation electric field intensity needs to be considered.Therefore,it is necessary to research on the SE of shielding material in high-intensity electromagnetic environment.

Influences of the inner diameter of the solid shielding tube on the characteristics of the radio-frequency cold atmospheric plasma jet

Active control of the local environment of the cold atmospheric plasma(CAP) jet is of great importance in actual applications since the CAP operates in an open atmosphere with the inevitable entrainment of the surrounding cold air. In this paper, the solid shielding effects of the cylindrical quartz tubes with different inner diameters on the characteristics of the CAP jets driven by a radio-frequency(RF) power supply are studied experimentally. The experimental results show that the total length of the shielded plasma jet can be increased significantly by an appropriate combination of the quartz tube inner diameter and that of the plasma generator nozzle exit with other parameters being unchanged. This phenomenon may be qualitatively attributed to the loss of diffusion of the charged particles in the radial direction under different inner diameters of the quartz tubes. Compared with the plasma free jet, the plasma shielding jet is produced with optimized parameters including longer plasma jet length, higher concentrations of chemically reactive species, higher rotational, vibrational, and electron excitation temperatures when the inner diameters of the solid shielding tube and the generator nozzle exit are the same. A maximum plasma jet length of 52.0 cm is obtained in contrast to that of 5.0 cm of the plasma free jet in this study. The experimental results indicate that the solid shielding effect provides a new method for the active control of the local environment of the RF-CAP jet operating in an open atmosphere.

Experimental Data for Study on the Shielding Effect of Electromagnetic Wave

This article presents some new experimental data for study the shielding effect of electromagnetic wave. The frequencies of electromagnetic wave are mainly focused on emission of daily electrical equipments, which are normally called “low frequency electromagnetic waves”. In this work, a water pump with maximum magnetic field intensity of ca. 2300 mG was applied as emission source of the electromagnetic wave. Experimental measurements used various shielding materials with the major constituent iron (Fe) in the form of plate for studying shielding effect of electromagnetic wave. The studied parameters were different thicknesses and gaps of the plate. The results show that pure iron plate has the best effect for shielding the magnetic field and its transmission ratio of magnetic field is proportional to distance between the emission source and the shielding plate. Moreover, the shielding plate close to the emission source received better protection.

Insights into Three-Dimensional Radiofrequency Circuits Connections

The authors state briefly the possibility of various simulators to handle propagation of electromagnetic waves along some interconnections, in 3D RF （Radio Frequency） circuits. The studies are first derived in the time domain： a Finite-Difference Time-Domain method is applied, taking spectra via FFTs （Fast Fourier Transform） as post-processors. Electric and magnetic field distributions, pulse propagations along stripline structures or vias are highlighted. The scattering parameters for various cases are extracted and compared. Some original issue of this work is an insight on crosstalk or shielding phenomena between lines.

High Frequency Transformers for DC/DC Converter Used in Solar PV System

This paper presents and investigates planar and coaxial high frequency power transformers used for DC/DC converters in a three phase photo voltaic （PV） power systems. The winding structure including a Faraday shield between the primary and secondary windings is designed to minimize eddy current losses, skin and proximity effects, and to reduce the leakage inductance, and the inter winding coupling capacitance. Finite Element Method is employed to analyze the magnetic flux and eddy current distributions. The two different kinds of prototype high frequency transformers are designed and tested. The simulation and experiment results are demonstrated and compared with non-shielded transformers. The shielded transformers have achieved the expected results with a relatively small coupling capacitance, compared with the conventional high frequency transformer. This shield decreases the inter-winding coupling capacitance Cps. The topology of this shield has to be such that it acts as a Faraday screen while avoiding eddy current generation.

Assessment of High-Frequency Performance Limits of Graphene Field-Effect Transistors

High frequency performance limits of graphene field-effect transistors （FETs） down to a channel length of 20 nm have been examined by using self-consistent quantum simulations. The results indicate that although Klein band-to-band tunneling is significant for sub-100 nm graphene FETs, it is possible to achieve a good transconductance and ballistic on-off ratio larger than 3 even at a channel length of 20 nm. At a channel length of 20 nm, the intrinsic cut-off frequency remains at a few THz for various gate insulator thickness values, but a thin gate insulator is necessary for a good transconductance and smaller degradation of cut-off frequency in the presence of parasitic capacitance. The intrinsic cut-off frequency is close to the LC characteristic frequency set by graphene kinetic inductance （L） and quantum capacitance （C）, which is about 100 GHz-um divided by the gate length.

Effect of gate engineering in submicron GaAs MESFET for microwave frequency applications

We present an approach of GaAs MESFET incorporating the gate engineering effect to improve immunity against the short channel effects in order to enhance the scaling capability and the device performance for microwave frequency applications. In this context, a physics-based model for I–V characteristics and various microwave characteristics such as transconductance, cut-off frequency and maximum frequency of oscillation of submicron triple material gate（TM） GaAs MESFET are developed. The reduced short channel effects have also been discussed in combined designs i.e. TM, DM and SM in order to show the impact of our approach on the GaAs MESFETs-based device design. The proposed analytical models have been verified by their good agreement with 2D numerical simulations. The models developed in this paper will be useful for submicron and microwave analysis for circuit design.

低频宽脉冲电场作用下钢筋笼结构的时域峰值屏蔽效能

针对低频宽脉冲电场的高能量电磁环境,研究了防护工程中钢筋笼结构的时域耦合响应和峰值屏蔽效能规律,为地面核爆辐射区域敏感电子设备的正常运行提供有效参考。采用多组不同上升沿的宽脉冲模拟激励源,结合频域矩量法和Fourier逆变换,给出了有效且计算耗时较短的宽脉冲时域耦合计算方案,并对10种不同结构的钢筋笼在不同脉冲辐射下的瞬态耦合响应进行了计算。分析了时域峰值屏蔽效能的规律,并给出了实验测量结果进行验证,为难以开展的钢筋笼屏蔽实验提供了有效和简单的计算方案,同时,给出了部分钢筋笼的电场时域峰值屏蔽效能。结果表明,相比增加钢筋直径和钢筋笼大小,增加钢筋笼的层数和减小钢筋网孔的尺寸可以更加有效地防止低频宽脉冲电场耦合进入钢筋笼内部;另外,钢筋笼内部的时域响应较为均匀,达到了区域性的有效电场电磁防护。

串联反褶积在提高下组煤层成像效果上的应用

由于煤系地层具有多煤层叠置的赋存特点,在煤炭地震勘探资料处理过程中,往往遇到由于上组煤层对下组煤层的屏蔽作用进而影响下组煤层反射波成像效果的问题。因此,如何在煤炭地震资料处理中提高下组煤层的成像效果成为当前普遍关心的问题。随着煤层的深度加大,原始资料中的低频成分对反射波成像质量的贡献也越大,资料处理过程中低频成分利用越多,下组煤层成像效果就越好,因此在处理过程中应尽量保留地震资料的低频成分。本次研究在应用地表一致性反褶积的基础上,串联使用预测反褶积方法并结合剩余静校正的运用,充分拓展资料低频段频带宽度,从而达到提高下组煤层成像效果的目的。

典型船用变频电缆电磁屏蔽效能试验方法研究及验证分析

随着船舶综合电力系统的广泛应用,船舶综合电力系统功能的复杂性带来了严重的电磁兼容问题,其中传输大功率的变频电缆对其邻近的仪表、控制系统等产生的辐射干扰尤为明显。对不同的电缆电磁屏蔽效能试验方法进行了研究及对比分析,采用短路-短路三同轴法对6种不同屏蔽结构的典型船用变频电缆样品的电磁屏蔽效能进行了试验。结果表明,在电缆的材料和规格基本相同的情况下,不同的屏蔽结构对船用变频电缆的屏蔽性能会产生较大的影响。

低频强磁场屏蔽效能的测试方法与测试设备研制

为了合理评估屏蔽体对低频强磁场的屏蔽效果,为工程中屏蔽室质量验收提供必要的检测手段,根据小环天线法测量电磁屏蔽室屏蔽效能的原理,提出了低频强磁场屏蔽效能测试系统的整体结构和设计方案,研制了以PIC16F73单片机为核心的低频大电流源,设计和制作了磁场发射、接收环天线,构建了低频强磁场屏蔽效能测试设备;采用研制的测试设备对屏蔽室进行了屏蔽效能实测。测试结果与理论值符合较好,表明测试设备能够满足实际测量的需要,同时验证了计算结果的可信性。

复合材料工频电场和工频磁场屏蔽效能实验研究

为了得到复合材料对工频电场和工频磁场的屏蔽效能,根据屏蔽室法测量材料屏蔽效能的原理,分别提出了工频电场和工频磁场屏蔽效能测试系统的实验方案。并且,通过分析调整实验配置对实验结果的影响,提出改进方案,进一步完善了该测试系统。通过实验得到了屏蔽室内部和外部的电场分布情况,实验结果可以用于指导被保护电子器件在屏蔽体内安放位置和屏蔽体的设计。

强电磁脉冲对材料屏蔽效能的影响

为评价材料在强电磁脉冲作用下的屏蔽效能,根据同轴法屏蔽效能测试原理,建立了1套脉冲电场屏蔽效能测试系统,提出了采用脉冲峰值屏蔽效能和脉冲能量屏蔽效能共同评价材料对于电磁脉冲屏蔽效能的方法,并应用该测试系统对2种材料进行了屏蔽效能测试,分析了脉冲峰值和脉宽对材料屏蔽效能的影响。结果表明:随着脉冲峰值的增大,构成材料的金属纤维在强电磁脉冲作用下产生电晕放电使距离近的金属纤维相互导通,从而提高了材料的屏蔽效能;而当脉冲峰值不变,随着脉宽的变化,材料的屏蔽效能并无变化。以上结果表明:脉冲峰值是影响材料屏蔽效能的主要因素。

低频磁场屏蔽材料的复合结构与屏蔽性能研究

针对10～100 kHz的低频磁场设计了几种屏蔽材料的复合结构,研究不同屏蔽材料对低频磁场的屏蔽效能。结果表明:低频磁场的屏蔽效能主要与材料的磁导率和电导率有关,屏蔽效能随磁场频率的增加而增加;对于不同频率的磁场,通过调整屏蔽材料的复合结构,能够以较低的厚度获得较高屏蔽效能。

开缝矩形腔屏蔽特性的研究

该文计算了在矩形腔上开有单缝时，缝长变化对所激励的屏蔽腔中最低模式的幅度和频率特性的影响。同时，采用时域一频域联合分析的方法，对屏蔽腔内观察点时域波形进行了分析，得到了不同频率分量在时域上的变化特性，以及缝长变化对它们的影响。

电磁屏蔽纤维的研究进展与应用

探讨电磁屏蔽纤维的发展现状。在电磁屏蔽理论的基础上,介绍了金属纤维及金属镀层纤维、碳纤维、涂覆金属盐纤维、本征型导电聚合物纤维、碳化硅纤维和有机导电纤维用作电磁屏蔽纤维的现状。认为,电磁屏蔽纤维的研究应更注重于电磁吸收纤维和可纺性更好的纤维。

远海浮式结构物与供应船旁靠系泊特性研究

针对远海浮式结构物与供应船进行旁靠作业时,水动力干扰、两船的相对运动、旁靠系缆系统和护舷系统的受力特征等问题开展研究。建立各船的有限元模型,设计出两船旁靠连接缆系统,选取合适的系泊缆和护舷参数。研究表明:浮式结构物和供应船的横荡、纵荡方向存在一定的同步性或跟随性,幅值相差不大,其它方向的运动并不存在明显的同步特征;供应船的各自由度运动幅值均比浮式结构物偏大;旁靠护舷的受力时历出现了明显的低频效应,说明护舷的受力较大程度上受船体低频慢漂运动的影响;浮式结构物对供应船的水动力干扰较大,当浮式结构物在供应船的上风位置时,表现为屏蔽效应,供应船的运动较小;在其背风位置时,运动加剧,出现多次共振、峰值放大现象,供应船对浮式结构物的水动力性能几乎无影响,因此,供应船从浮式结构物的下风口一侧靠泊作业将更有利于船舶的安全性能。这些研究结论可为实际工程操作提供参考。

极化方向对含圆孔电磁屏蔽织物屏蔽效能的影响

研究电磁波极化方向对含圆孔电磁屏蔽织物屏蔽效能的影响。选择不锈钢电磁屏蔽织物制作含圆孔的样布,在1GHz^18GHz范围内分别测试垂直极化与水平极化方向样布的屏蔽效能。结果表明:无论是垂直极化波还是水平极化波,圆孔对样布屏蔽效能的影响均较大;随圆孔直径增大,屏蔽效能均呈整体降低趋势;圆孔直径大于10cm时,样布屏蔽效能接近零。相同频率下,样布在垂直极化方向和水平极化方向的屏蔽效能差异明显。认为:根据圆孔对电磁屏蔽织物屏蔽效能的影响规律可以设计相关电磁屏蔽产品。

超高压输电线下屏蔽线对工频电场的影响

为降低超高压输电线下工频电场对周围环境及人群的影响,笔者基于模拟电荷法,建立了超高压输电线路下方架设屏蔽线时计算工频电场强度的数学模型,并运用MATLAB软件对某500 kV输电线路下方架设屏蔽线后的工频电场强度进行仿真计算。重点分析了屏蔽线的架设数目、架设高度及排列方式对超高压输电线路下方工频电场强度分布的影响规律。最后从环境保护和屏蔽效果及屏蔽范围的角度,提出了垂直排列的最佳屏蔽线架设方式。