A simple hybrid method for ELF shielding by imperfect finite planar shields

A simple method is described for calculating the shielding performance of a two-dimensional (2-D) thin finite-width shield made of imperfect material in the presence of the magnetic field from line source conductors. First, solutions to two canonical problems with closed-form simple analytic formulas are presented; shielding by reflection from and absorption in thin planar shields of infinite extent and shielding by perfect conductor shields of finite width. Then the method for calculation of magnetic-field shielding by perfect conductor finite-width shields is extended using the simple interpolation method, to thick shields made of imperfect material. Finally, the hybrid solution is developed by adding the two results in quadrature. The result is a simple theory for shielding by finite-width shields made of any real shielding material of arbitrary thickness. Its accuracy has been validated by comparison to finite-element method solutions and existing measurements.     

A sheet impedance approximation for electrically thick materialshields

This paper describes a simple extension of the sheet impedance concept to treat electromagnetic (EM) shields that may be thick in terms of material shield wavelengths. For magnetic shields, a simple relation between the equivalent electric and magnetic currents representing the shield is obtained, and the electric current is found as the solution of a single surface integral equation that is shown to be a simple perturbation of that for a perfect electric conducting (PEC) surface. Finally, it is shown that the computation of the small interior fields of good shields requires the use of the proper PEC interior equivalent problem     

A sheet impedance approximation for electrically thick multilayered shields

This paper describes an extension of the sheet impedance concept to treat inhomogeneous or multilayered shields that may be thick in terms of material shield wavelengths. For shields with magnetic materials, a simple relation between the equivalent electric and magnetic currents representing the shield is obtained. This allows the magnetic current to be treated as a dependent unknown and the electric current to be found as the solution of a single surface integral equation shown to be a perturbation of that for a perfect electric conducting (PEC) surface. By using the proper interior equivalent problem, it is shown that the method produces accurate and stable results for shielding by a rectangular box.     

A computational methodology and results for quasistaticmultilayered magnetic shielding

A methodology for accurate calculations of shielding factors for quasistatic multilayered magnetic shields is described. “Transfer relations” for individual layers with specified magnetic permeabilities and electrical conductivities are spliced together. Specific transfer relations for four layer geometries (planar, cylindrical with transverse fields, cylindrical with axial fields, and spherical) and constraints at source and shielded surfaces for six source-shield configurations involving both externally applied fields and enclosed sources are developed. Limiting cases are extracted for magnetically permeable, nonconducting layers, and for thin, magnetically nonpermeable, conducting layers. Reciprocity conditions are identified for interchanged source and shielded regions in planar, transverse field cylindrical, and spherical geometries. Variations of magnetic field and flux density with position are shown for a specific planar example involving alternating layers of aluminum and steel, with the same total shield thickness occupied by either one or five layer pairs. Simulations with alternating layers of aluminum and steel for the four layer geometries are used to study the effects of material composition, number of layer pairs, and air gaps. An optimal number of layer pairs for a given total shield thickness is identified. Results from simulations where induced currents in the steel layers are neglected are compared with those for simulations with a realistic conductivity value for steel to assess the relative effects of flux shunting and induced current shielding     

Magnetic field attenuation of nonlinear shields

The analysis of shielding performance of planar shields against near field sources is carried out in the time domain to account for the nonlinear behavior of ferromagnetic materials used in low frequency applications. To this end, the Schelkunoff approach for shielding problems has been reformulated in the time domain introducing the transient wave impedances which relates transient electric and magnetic field components and appear in the integrodifferential boundary conditions. The final equation system is solved by means of a numerical procedure based on the finite element method. The obtained results are compared with analytical and measured data in different configurations     

The design of Maxwellian absorbers for numerical boundaryconditions and for practical applications using engineered artificialmaterials

A Maxwellian material interpretation of the Berenger (see J. Computat. Phys., vol.114, p.185-200, 1994) perfectly matched layer (PML) is developed using polarization and magnetization fields. The PML material is found to be a passive lossy electric and magnetic medium with particular conductivity and Debye dispersion characteristics. Although it is recognized that the PML medium is physically unrealizable, this polarization and magnetization field interpretation reveals the necessary characteristics of a perfect electromagnetic absorber. A Maxwellian material that has perfect absorption properties and may be physically realizable is derived with these concepts. This Maxwellian absorber is based upon a time-derivative Lorentz material (TD-LM) model for the dispersive and absorptive electric and magnetic properties of a material. This TD-LM model represents a straightforward generalization of the standard Lorentz material model to include the time derivatives of the fields as driving mechanisms for the polarization and magnetization fields. The numerical implementation of the perfect absorber is given and the resulting reflection coefficients from a perfect electric conductor-backed slab of this material are characterized. It is shown for broad bandwidth pulsed fields that this Maxwellian TD-LM slab, like the non-Maxwellian PML, has absorption characteristics in the 70-110-dB range for large angles of incidence. Strategies are discussed for engineering this dispersive electric and magnetic TD-LM absorber artificially with a substrate that has an array of pairs of appropriately designed small coil-loaded dipole radiating elements embedded in it     

An Equivalent Surface Source Method for Computation of the Magnetic Field Reduction of Metal Shields

A numerical method for computation of the resultant quasi-static magnetic field in the vicinity of parallel wires and metal shields is presented. The primary magnetic field source is time-harmonic currents in wires. This field is modified by conducting magnetic and/or nonmagnetic shields. The material is assumed to be linear under the applied source field. The shielding effectiveness can be estimated by a comparison between the primary and the resultant field. The reaction magnetic field is expressed by a sum of fields caused by equivalent single- and double-layer sources distributed on the shield surface. Integral equations for unknown distributions of these equivalent sources are derived from the Green's second identity implemented inside and outside the shields. These equations are coupled integral equations, and are solved by the moment method. Numerical results of the resultant (shielded) magnetic field obtained with the proposed method are compared with the results of: 1) analytically solvable problems; 2) measurements; and 3) two different numerical methods.      

Shielding effect of hollow chiral sphere

The low-frequency shielding effect of a spherical layer is studied. The layer is made of a chiral material and it is electromagnetically characterized with three material parameters: permittivity, permeability, and chirality. Due to chirality, there is magnetoelectric coupling. The electric and magnetic shielding effects are derived and are shown to be functions of the three material parameters and also the relative thickness of the layer. Illustrations display the effects of the various parameters on the shielding, which is different for the magnetic and electric fields. Among the special effects is that the shielding increases rapidly as the chirality parameter approaches the refractive index of the shell. This makes chiral shells in principle effective shields, and in the future they may offer an alternative to conducting materials for novel shielding applications     

Electromagnetic Transmission through a Filled Slit in a Conducting Plane of Finite Thickness, TE Case

A solution is developed for computing the transmission characteristics of a slit in a conducting screen of finite thickness placed between two different media. The slit may be filled with Iossy material while the two regions on either side of the screen are assumed Iossless. A magnetic line source excitation is used (TE case) which is parallel to the axis of the slit. The equivalence principle is invoked to replace the two slit faces by equivalent magnetic current sheets on perfect electric conductors. Two coupled integral equations containing the magnetic currents as unknowns are then obtained and solved for by the method of moments. Pulses are used for the expansion and testing functions. Quantities computed are equivalent magnetic currents, the transmission coefficient, the gain pattern, and the normalized far field pattern.     

非晶硒对X射线响应特性的理论研究

较为全面地考查了非昌硒对Ｘ射线的灵敏度。引入一个灵敏度模型，在灵敏度与载流子迁移特性、光子能量、非晶硒厚度和场强之间建立了明确的关系。计算结果表明，载流子迁移长度至少应是非晶硒厚度的２倍以上，才能使Ｘ射线激发的电子、空穴有较大的概率到达收集电极（或非晶硒自由表面）（即信号收集效率）；用加大非晶硒厚度的方法增加灵敏度时必须考虑信号收集效率降低的负面影响；场强对灵敏度有重要影响，提高场强可使非晶硒灵敏     

High-frequency power transformer model for circuit simulation

A model for the circuit simulation of transformers used in high-frequency power processing is proposed. Many important transformer effects are combined in a single formulation. An Atherton-Jiles model with improved minor-loop handling ability is employed to simulate the hysteresis effect in the magnetic core. Eddy currents and skin and proximity effects are simulated by dynamically approximating the field and flux distributions in the entire structure. Leakage fluxes, capacitive couplings and the influence of temperature on electric and magnetic materials are also included. The parameters needed for simulation are magnetic material characteristics, available in data sheets, core geometry and winding geometry. The model was implemented (built) in the source code of SPICE3     

A comprehensive analysis of multilayer channel waveguides

Using a simple approach based on the scalar finite element method, propagation characteristics of multilayer channel waveguides are calculated. The effective index, modal field, confinement factor, far-field intensity pattern, and radiation angle of the far-field pattern (full width at half maximum intensity) for multilayer channel waveguides formed with multiple quantum well (MQW) materials and with the MQW materials replaced by a single homogeneous material with the root mean square value of the refractive indexes are compared. Numerical results confirm that the root-mean-square-value approximation, which has been widely used for planar MQW (two-dimensional) waveguides, is useful also for MQW channel (three-dimensional) waveguides with a large number of layers     

The electrodynamic characteristics of a finite-width metal/dielectric/ferroelectric/dielectric/metal layer structure

The electrodynamic characteristics of a finite-width metal/dielectric/ferroelectric/dielectric/metal layer structure are investigated. The eigenmode spectra, field distributions, and dispersion characteristics are calculated with the help of simulation based on the finite element method. It is demonstrated that the properties of the width modes of the layer structure can be controlled through changing the external electric and magnetic fields.     

Geometrical aspects of magnetic shielding at extremely lowfrequencies

The magnetic shielding effectiveness for closed and open shield structures is studied at extremely low frequencies. Analytical solutions are used for simple geometries, while more complex structures are evaluated using a finite-element method. Both highly conductive and ferromagnetic materials are studied, and their different shielding behavior is shown. Ferromagnetic shields give good results for small and closed shields and they also give a large field attenuation at close range to the source for open shield geometries. Highly conductive materials, on the other hand, are found to be suitable for large shield sizes. The attenuation is, however, reduced in the close vicinity of the source. Comparisons of numerical results with analytical calculations and measurements confirmed the high accuracy of the finite-element model     

弱磁场对N=3的自旋链上量子信息传输的影响

基于单比特量子信息在自旋链上的完美传输理论,研究了2种不随时变化的弱磁场对N=3的自旋链上单比特量子信息完美传输的影响。对包含磁场体系的哈密顿量进行对角化,并考虑演化算子的作用,结果表明：空间均匀且不随时变化的恒定弱磁场不会对信息传输的保真度产生影响;大小关于中心对称方向相反的弱磁场直接影响了实现量子信息完美传输的条件, 磁场越强实现完美传输的时间越短。     

海底有限长极低频线电流在海面附近产生的场

针对海缆故障点的检测与定位, 将海缆看作位于海床以下的有限长线电流源, 从麦克斯韦方程和边界条件出发, 推导了其在大气层-海水层-岩层三层平面分层介质下的电磁场的积分表达式, 采用数值积分对海缆在不同观测点位置产生的磁场进行了分析.由断点附近海面上磁场分布的特征可以估计出海缆的走向及断点的位置.     

介质平面光波导TE0模模场分布的高斯近似

基于介质平面光波导端面无受限衍射场光束的光束传输因子的特点,阐明光波导TE0模模场分布采用高斯分布近似表达的合理性。基于场分布间的匹配效率计算公式,提出采用等效匹配效率方法确定用于高斯近似表达的等效模场半宽度,给出基于光波导芯层半宽度和归一化芯层驻波参量和归一化包层倏逝波参量表达的光波导等效模场半宽度的函数表达式,给出高斯近似分布与光波导本征场分布的匹配效率,阐明采用等效匹配效率方法确定等效模场半宽度的合理性。采用求解方程组的方法,给出基于光波导芯层半宽度和归一化频率表达的光波导等效模场半宽度的拟合函数表达式,并基于拟合引起的误差分析阐明了拟合函数表达式的精确性。     

A new approach to diffraction analysis of conductor grids. II.Perpendicular-polarized incident plane waves

For pt.I see ibid., vol.37, no.1, p.84-88 (1988). Diffraction analysis is given for infinite planar conducting-strip grids illuminated by normally incident (perpendicular-polarized) plane waves, the electric fields of which are perpendicular to the strip axes. Iris-surface electric field integral equations are used which are based on the equivalent waveguide theory, and then the electric field is solved for using the moment method. This is a universal approach applicable to infinite planar grids made of conducting strips of rectangular cross section, uniform or periodic, dense or sparse, single layer or multilayer     

表面波放电狭缝天线辐射电磁场的三维数值分析

针对平板型表面波放电等离子体源,建立了表面波放电狭缝天线辐射电磁波模型,对狭缝天线辐射电磁场分布进行了三维数值计算,并与表面波电磁场进行对比分析,讨论了平板型表面波放电机理。结果表明:整个狭缝天线阵激发的电磁场是每个狭缝天线激发电磁场的线性叠加;狭缝天线阵直接激发的电磁场强度在临近波导壁面处很大,并且随着空间距离的增大迅速衰减;狭缝天线阵直接激发和表面波的电场均远大于各自的磁场,分析电、磁场对带电粒子的力作用时可以忽略磁场力的作用;表面波电磁场远大于狭缝天线阵直接辐射的电磁场,强电磁场范围也远大于狭缝天线阵直接激发的强电磁场范围,等离子体有增强电磁场强度、扩大强电磁场范围的作用。     

Vector-sensor array processing for electromagnetic sourcelocalization

The authors present a new approach for localizing electromagnetic sources using sensors where the output of each is a vector consisting of the complete six electric and magnetic field components. Two types of source transmissions are considered: (1) single signal transmission (SST), and (2) dual signal transmission (DST). The model is given in terms of several parameters, including the wave direction of arrival (DOA) and state of polarization. A compact expression is derived for the Cramer-Rao bound (CRB) on the estimation errors of these parameters for the multi-source multi-vector-sensor model. Quality measures including mean-square angular error (MSAE) and covariance of vector angular error (CVAE) are introduced, and their lower bounds are derived. The advantage of using vector sensors is highlighted by explicit evaluation of the MSAE and CVAE bounds for source localization with a single vector sensor. A simple algorithm for estimating the source DOA with this sensor is presented along with its statistical performance analysis