Two Parallel Terminated Conductors in External Fields

New equations are derived for voltage and current on two parallel conductors terminated with arbitrary impedances and immersed in external fields. By examining several pertinent static boundary-value problems, it is shown that the source terms of the equations can be split into two parts; one part is directly proportional to the transverse components of the magnetic and electric fields of the incident wave, and the other part is attributable to the unequal size of the two conductors. It is also shown that only one two-dimensional static boundaryvalue problem need be solved for the determination of the coefficients and source terms in the new equations. Detailed calculations are given for two parallel terminated cylinders. Some simple examples are worked out, and the results based on the new equations are contrasted with those derived from the conventional theory.     

The Effect of Neighboring Conductors on the Currents and Fields in Plane Parallel Transmission Lines

In this paper the current distribution is calculated for a microstrip line in the presence of a neighboring strip. The electric field is calculated and the characteristic impedance of the slotted microstrip line is determined. A graph of characteristic impedance is given for odd and even excitations. The calculations are carried out by setting up a singular integral equation which is solved using a finite integral transform. This method has the advantage that the calculations can be generalized in a straightforward manner for the multislotted line.     

Shielding of Electromagnetic Fields of Current Sources by Hemispherican Enclosures

Presented here is a theory of electromagnetic shielding of fields due to current sources by an imperfectly conducting, hemispherican, open shell with its rim in contact with a perfectly conducting ground plane. Expressions for the shielding effectiveness (SE) of the enclosure excited by Hertzian dipole sources have been derived. Numerican values of SE obtained from these expressions have been compared with those for a similarly excited imperfectly conducting spherical shell [9].     

Magnetic Fields of a Dipole in Special Volume Conductor Shapes

Expressions are presented for the magnetic fields produced by current dipoles in four basic volume conductor shapes. These shapes are the semi-infinite volume, the sphere, the prolate spheroid (egg-shape), and the oblate spheroid (discus-shape). The latter three shapes approximate the shape of the human head and can serve as a basis for understanding the measurements of the brain's magnetic fields. The semi-infinite volume is included in order to investigate the effect of the simplest boundary between a conductor and nonconductor. The expressions for the fields are presented in a form which separates the total field into two parts. One part is due to the dipole alone (the dipole field); the other is due to the current generated in the volume conductor by the dipole (the volume current field). Representative plots of the total field and the volume current field are presented for each shape. The results show that for these shapes the component of the total field normal to the surface of the volume conductor is produced completely or in large part by the dipole alone. Therefore, measurement and use of this component will greatly reduce the complexity of determining the sources of electrical activity inside a body from measurements outside the body by removing the necessity of dealing with the volume current field.     

Solution of Some Electrostatic Potential Problems Involving Spherical Conductors: A Dual Series Approach

The solution of several electrostatic potential problems involving open spherical perfectly conducting shells is presented in the context of the dual series equations method. These equations are a consequence of mixed boundary conditions imposed on the electric potential and field. A solution is given for the dual series equations corresponding to two concentric spherical shells, one of which has a circular aperture. The aperture dipole moment, the capacity, and field penetration of some electrostatic devices are also calculated.     

An Optically Coupled System for Quantitative Monitoring of MRI-Induced RF Currents Into Long Conductors

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions.      

Nodal Network Simulation of Transient Temperature Fields from Cooling Sources in Anesthetized Brain

Transient thermal gradients in the brains of anesthetized cats and rabbits due to localized cooling to 5°C with probes of two different shapes were modeled successfully to within 0.5°C by a computer program utilizing a finite difference method and thermal coefficients of water, without addition of a term for metabolic heat or blood flow. Input data to the program required temperature measurements in the brain away from the probe, although in the cylindrical case it was possible to use the probe temperature as the forcing function by assuming that the probe had a larger diameter than was actually the case. The results indicate that for the experimental conditions, metabolic heat and blood flow can be adequately accounted for by means of a rather small adjustment of the thermal diffusivity term in a general diffusion equation, without need of an explicit term for such distributed sources.     

Potential Driven Volume Diffusion in Nanoporous AgBi at Room Temperature

Volume diffusion is crucial for crystal growth and interface manipulation in electron devices and catalysts. Its kinetics only becomes vigorous at high temperature, in which case grain boundary diffusion and surface diffusion dominate usually. In this study, volume diffusion of Bi atoms in nanoporous AgBi can be driven by electrochemical potential at room temperature due to ligament expansion. Bi diffusion induces conformal covering of amorphous Bi₂O₃ shell onto the spatially interconnected skeletons without ligament coarsening. Growth kinetics of amorphous shell demonstrates that the potential dependence of Bi volume diffusion activation energy corresponds to 0.932 eV V⁻¹. Compared with temperature dependence, potential supply is confirmed to be more feasible to modulate volume diffusion rate and shell thickness, and Bi enrichment increases 3.4 times when potential raises from −0.85 to −1.05 V. Potential driven volume diffusion at room temperature reported here knobs one door to manipulate local composition of functional nanostructures and nano-devices at atomic scale.     

色噪声背景下相干信源DOA估计的空间差分平滑算法

文中提出了一种色噪声背景下相干信源波达方向(DOA)估计的新算法-空间差分平滑(SDS)算法.SDS算法利用均匀线阵协方差矩阵的Toeplitz分解特性,差分平滑运算,将非相干信源与相关(或相干)信源分开分辨,从而重复利用阵列接收数据,可分辨更多信源.SDS算法可对消空间色噪声,适用于更广泛的未知噪声背景及低信噪比环境.相比常规谱估计算法,SDS算法具有更强的信源过载能力及阵元节省能力,利用少数阵元进行迭代空间平滑运算,还可明显减小SDS算法的计算量.计算机仿真结果证明了SDS算法理论的正确性和有效性.     

Quantitative Evaluation of Statistical Variability Sources in a 45-nm Technological Node LP N-MOSFET

A quantitative evaluation of the contributions of different sources of statistical variability, including the contribution from the polysilicon gate, is provided for a low-power bulk N-MOSFET corresponding to the 45-nm technology generation. This is based on a joint study including both experimental measurements and ldquoatomisticrdquo simulations on the same fully calibrated device. The position of the Fermi-level pinning in the polysilicon bandgap that takes place along grain boundaries was evaluated, and polysilicon-gate-granularity contribution was compared to the contributions of other variability sources. The simulation results indicate that random discrete dopants are still the dominant intrinsic source of statistical variability, while the role of polysilicon-gate granularity is highly dependent on Fermi-level pinning position and, consequently, on the structure of the polysilicon-gate material and its deposition and annealing conditions.     

Electromagnetic Modeling of the Jacket in Cable-in-Conduit Conductors

Most magnets designed for thermonuclear fusion experiments rely on the cable-in-conduit conductor technology. These cables are made of several hundreds or thousands of multifilamentary superconducting strands. The strands are refrigerated by a flow of liquid helium in forced convection through a conduit, usually made of aluminum or stainless steel. The complexity of the manufacturing techniques makes it very difficult to perform direct voltage measurements inside the jacket of these cables. Voltage taps are usually placed on the jacket outer surface, deriving relevant information about the inner cable electrical characteristics. In the present study, an electromagnetic model is presented that allows us to take into account the presence of the jacket and its interactions with the superconducting cable. Some unexpected qualitative behaviors of the voltage signals detected on the jacket, whose interpretation is currently under debate in the scientific community, are reproduced by the model.     

Structural Parameter Optimization of Multilayer Conductors in HTS Cable

In this paper, the design optimization of the structural parameters of multilayer conductors in high temperature superconducting （HTS） cable is reviewed. Various optimization methods, such as the particle swarm optimization （PSO）, the genetic algorithm （GA）, and a robust optimization method based on design for six sigma （DFSS）, have been applied to realize uniform current distribution among the multilayer HTS conductors. The continuous and discrete variables, such as the winding angle, radius, and winding direction of each layer, are chosen as the design parameters. Under the constraints of the mechanical properties and critical current, PSO is proven to be a more powerful tool than GA for structural parameter optimization, and DFSS can not only achieve a uniform current distribution, but also improve significantly the reliability and robustness of the HTS cable quality.     

Distributed Latent Heat of Phase Transitions in Low-Dimensional Conductors

Journal of Communications Technology and Electronics - Abstract—It is shown that if the temperature of the second-order phase transition is lowered due to fluctuations, then the dominant...     

CAN总线在电缆蠕变测控系统中的应用与研究

以架空电缆蠕变量测量系统为应用背景,提出采用CAN总线作为通讯方式和具有多节点的分布式结构的测量系统。重点阐述了CAN总线硬件设计和软件编程等问题。与传统的集中控制相比,该系统具有结构简单、适应性强、易扩充等特点。     

多导体散射中广义谐振的模式分析

在电磁兼容分析中,多导体开放系统中存在的广义谐振现象是一个值得注意的问题.本文利用矩量法分析了多导体散射问题,发现了广义谐振现象,并提出广义谐振腔模型,对广义谐振进行了模式分析,很好地解释了这类散射结构的谐振特性.     

克尔微腔光频梳理论分析模型及多波长光源应用探讨

基于高品质因子微谐振腔的参量四波混频实现光学频率梳是一种新的频率梳实现方法,拓展了传统固体及非线性光纤飞秒激光器等光频梳的应用范围,在精密频率标定、天文光谱校准、任意波形产生、光学存储和孤子传输、片上通信用光源等方面具有较高的优势。本文简要总结、评述了几种主要的光频梳动力学分析模型及数值方法,以及这些不同方法的内在联系。基于描述光频梳动态行为的非线性Lugiato-Lefever方程分析了可能存在的动力学过程,并据此对不同特点光频梳进行了分类。通过设计反馈结构理论上研究了正常色散微腔和反常色散微腔的光梳特点,探讨了作为片上光互连用多波长光源应满足的条件及可能的实现途径。     

New Considerations About Stability Margins of NbTi Cable in Conduit Conductors

The design of NbTi cable in conduit conductors (CICCs) according to the criterion of the limiting current often leads to high copper content, with a Cu/nonCu ratio inside the multifilamentary composites in the range of 6 to 8. This high copper content makes NbTi multifilamentary composites difficult and expensive to manufacture, especially if the required filament diameter is in the range of 5-10 mum. Moreover, a detailed analysis of the cable in conduit stability for expected disturbances or heat deposition on a long length of conductor shows that copper plays, in practice, no role in the case where current is uniformly distributed. An analytical approach is given to demonstrate this statement and propose a cheaper and reliable method to identify the drivers of the stability margins. Certainly copper is needed in large amounts for protection, but this copper can be segregated in dedicated strands. Typical copper content of 60% to 70% in the strands is sufficient for intrinsic dynamic stability and to stabilize the CICC against short mechanical disturbances in the range of 1 ms for the time constant affecting short lengths of CICC (10 mm). Stability issues in NbTi CICCs might also be linked to current distribution effects where contact resistance between strands plays a leading role.     

Electromagnetic Field Analysis of YBCO Coated Conductors in Multi-Layer HTS Cables

Electromagnetic field analyses of YBCO coated conductors in mono-layer and multi-layer high$ T_ c$superconducting (HTS) cables with practical configurations were carried out to calculate their AC losses. Numerical models employing one-dimensional FEM and two-dimensional FEM were used in the analyses. The error of the 1D-model was assessed by comparing the loss calculated by the 1D-model and that calculated by the 2D-model. The gap between the conductors in each layer, the relative position of conductors in the inner layer and in the outer layer, and the number of layers were varied to study their influence on the AC loss. The numerically calculated AC losses were compared with the analytical values.     

加厚型厚膜铜、银导体在功率电路中的应用

国外一些厂家近年来相继研制开发出各种适合那些对于印制，热导率，电特性，丝焊的焊接特性均有苛刻要求的功率电路用加厚型厚膜铜，银导体。按照功率电路的热控制要求，烧结后的导体膜厚度应大于150μm，而且一般的需要印制在大块面积上，在某些设计中，专供粘焊裸芯片用的组装焊盘的厚度还要求局部性的增大。新的加厚型厚膜技术能在一块基板上同时做到使信号控制部分的导体更薄，电路密度更高和使组装功率器件用的焊盘更厚以便于散热。本文介绍适合功率电路应用的加厚铜，银导体在性能优化方面的研究情况，例如各类加厚型厚膜导体材料的特性，工艺和主要工艺参数。     

Reception of Nonhomogeneous Signal Fields in the Presence of Homogeneous Noise Fields

The reception of a nonhomogeneous signal field embedded in a homogeneous noise field, using a simple two-element subtractive array, is studied. For element spacing which is small compared to both the distance to the source and to the center-frequency-wavelength, the signal-to-noise improvement over a single element is shown to be independent of element spacing d, relatively independent of bandwidth and the noise spatial distribution, and to depend only on the distance to the signal source in wavelengths and on the signal ground-wave attenuation rate.