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.     

Shielding Circuits from EMP

It is generally impractical to filter low-frequency electromagnetic pulse (EMP) signals from victim circuits. Twisting signal pair conductors is helpful but often results in insufficient isolation. The remainder must be provided by shielding. Highly permeable ferritic materials have generally been found to provide maximum shielding from low-frequency magnetic fields. It is shown that this may not be the case when the signal source is relatively distant from the shield. With large separation, there appears to be a greatly increased mismatch between the wave impedance at the shield and the intrinsic impedance of the metal. This results in much greater reflection of the impinging wave than occurs for the same signal strength with small source to shield separation. The mismatch is greatest with a highly conductive shield material. All common highly permeable materials have low relative conductivity. High permeability does not improve the shielding effectiveness at low audio frequencies because no significant attenuation occurs as the wave passes through the shield. It is concluded that materials such as copper or aluminum are logical choices for shielding circuits from distant, high-intensity, low-frequency EMP.     

Magnetostatic simulations for design of superconducting magneticshields

A magnetostatic approach to numerical simulations of magnetic field attenuation by superconducting shields is demonstrated on simple geometries. Comparisons to published measurements and analytic calculations show that results are accurate for simulation of a shield in the shape of a cylindrical tube. The capabilities of the method are shown by simulations which close the cylinder with end caps having access ports or gaps. With end caps having cylindrical ports, the simulated attenuation transits smoothly between the analytical results for semi-infinite tubes of the two radii. Radial gaps between solid end caps and the cylinder allow little flux leakage for time-varying fields, but significant leakage for static fields     

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     

垂直入射均匀平面波的多层平板屏蔽效能分析

本文基于电磁场方法,详细导出多层平板屏蔽体对垂直入射均匀平面波的屏蔽效能计算公式。此外,提出计算屏蔽效能时,集肤深度和屏蔽体厚度的约束关系,给出用作计算机机箱的几种常用材料的屏蔽效能计算实例。     

Geometrical Effects on Shielding Effectiveness at Low Frequencies

A frequent approach to computing the magnetic shielding effectiveness of enclosures is to consider the effect of a plane wave impinging on a sheet of infinite extent. This permits an analysis based on a transmissionline characterization. However, when the wavelength is large compared to the dimensions of the enclosure, other analytical approaches provide better results. It has been shown that the current distribution on a box-like object scattering in the Rayleigh region tends to concentrate at the edges and corners of the box. This leads to concentrations of the magnetic field in the vicinity of edges and corners both inside and outside the enclosure. Since the effects of the current concentrations are localized, the magnetic shielding problem can be simplified by assuming a uniform current distribution on the exterior of the enclosure. Under this assumption the socalled ?circuit approach? can be applied. The box-like enclosure is characterized as a series of shorted turns which shield a sensor within the enclosure. Based on the geometry, the mutual and leakage impedances between the source and sensor are used to compute the magnetic shielding effectiveness. This approach yields valid results for shields constructed of either wire mesh or sheet metal. It can also be extended to account for degradation due to bad bonds. A comparison of results, both transient and steady state, of the circuit approach and scattering theory show close agreement for spherical enclosures.     

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.     

Shielding Performance of Metallic Cylinders

Electrical and electronic equipment must often be protected against external interference. Accordingly, metal shields are used against microwave radiation, electromagnetic effects, etc. Conducting materials, impregnated with elastic substances, are also used in many cases. The present paper deals with the performance of such a cylindrical shield, including a reference to shielding effectiveness. It is shown that with the assumed model the shield is pervious along its axis over a spectrum of frequencies.     

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.      

Field analysis of penetrable conductive shields by thefinite-difference time-domain method with impedance network boundaryconditions (INBCs)

Impedance network boundary conditions (INBCs) are implemented in the finite-difference time-domain (FDTD) method to analyze the electromagnetic field around penetrable shield structures. The shield region is eliminated from the computational domain and the INBCs are applied on the new boundary surfaces, i.e., shield surfaces, to take into account the field discontinuity produced by the shield. The INBCs represent an important extension of the well-known surface impedance boundary conditions (SIBCs) since the INBCs model accurately the coupling of the electromagnetic fields through penetrable shields and lead to a significant reduction of the number of the FDTD unknowns. The INBC expressions are given analytically in both frequency and time domains, and the INBC implementation in a FDTD code is discussed. The proposed INBC-FDTD method is numerically efficient because the resulting convolution integrals are recursively solved. Furthermore, approximate time-constant INBCs are proposed which are valid for many practical applications. The analysis of transient electromagnetic fields around penetrable conductive shields in simple test configurations are presented and compared with the analytical solutions     

Low-Frequency Shielding of a Circular Loop Electromagnetic Field Source

The problem of low-frequency shielding of a loop axially perpendicular to a plane shield of infinite extent is analyzed by 1) the thin shield work of S. Levy, 2) solution of the vector wave equation, and 3) application of the transmission theory of shielding of Schelkunoff. Experimental data are obtained and compared with results of parts 1) and 3) in the frequency range 100 Hz to 50 kHz. The first analytical technique is not general, and the limits of applicability of the results are discussed. In the second solution, which is general, expressions are derived for the total electric and magnetic fields on both sides of and within the shield. The resulting expression for shielding effectiveness is not solved because of its complexity. The results of the third theory are adapted to the problem. The shielding effectiveness expression S = R + A + B is computer evaluated for the six shields considered (1/16-inch and 1/8-inch thick aluminum, copper, and steel). Although some approximations are made, this analytical method is the most useful in predicting the insertion loss of the shield, since the theory includes those parameters neglected in the first analytical technique.     

Rapid Assembly of Large Scale Transparent Circuit Arrays Using PDMS Nanofilm Shaped Coffee Ring

Rapid and precise assembly of functional nanoparticles into well‐defined structures in large scale is motivated by broad fields. In this study, large‐scale transparent conductive circuit arrays are rapidly self‐assembled by simply pipetting a gold nanoparticles suspension onto a PDMS nanofilm patterned substrate with distinct hydrophilic/hydrophobic areas. The solution firstly self‐confines into predefined hydrophilic geometries, followed by assembly of nanoparticles into well‐defined circuits with 1D patterns by coffee ring effect. Submicrometer height and submicrometer‐ to micrometer‐width circuit arrays with various shapes are precisely generated by varying the PDMS nanofilm patterns. Thousands of circuits with different geometries are self‐assembled simultaneously within 1 min. The conductive circuits show good optical transparency up to 95%. After being transferred into PDMS elastomer sheet by encapsulating, the circuits remain highly conductive during bending and stretching. With the advantages of high‐throughput, equipment‐free, scalability, and precise control, this technique will open an avenue for fabricating large‐scale functional materials for applications in electronics, optoelectronics, and healthcare devices.     

Design of multilayered cylindrical shields using a geneticalgorithm

The design of infinitely long multilayered cylindrical shields with circular cross-section are considered and a method based on the genetic approach is proposed. An analytical method for the calculation of the shielding effectiveness of a cylindrical shield, consisting of homogeneous layers is presented for the case of an obliquely incident plane wave. By making use of this method, a genetic algorithm is implemented for the design of multilayered cylindrical shields in order to achieve a prespecified shielding effectiveness for a given band of frequencies or a range of angles of incidence     

High-Performance Slow-Wave Transmission Lines With Optimized Slot-Type Floating Shields

A novel slow-wave transmission line with optimized slot-type floating shields in advanced CMOS technology is presented. Periodical slot-type floating shields are inserted beneath the transmission line to provide substrate shielding and to shorten the electromagnetic (EM) propagation wavelength. This is the first study that demonstrates how the wavelength, attenuation loss, and characteristic impedance can be adjusted by changing the strip length (SL), strip spacing (SS), and metal layer position of the slot-type floating shields. Wavelength shortening needs to be achieved with a tradeoff between slow-wave effect and attenuation loss. The slot-type floating shields with different SLs, SSs and metal layer positions are analyzed. It is concluded that minimum SL provides the most optimal result. A design guideline can be established to enable circuit designers to reach the most appropriate slot-type floating shields for optimal circuit performance. Transmission line test structures were fabricated by using 45-nm CMOS process technology. Both measurement and EM waves simulation were performed up to 50 GHz. Transmission lines are frequently used at a length of half- or quarter-wavelength. With a shortened wavelength, a saving in silicon area of more than 67% can be achieved by using optimized slot-type floating shields. Experimental results demonstrated a higher effective relative permittivity value, which is improved by a factor of more than 9, and a better quality factor, which is improved by a factor of more than 6, as compared to conventional transmission lines.      

汽车线束的电磁干扰问题研究

介绍了汽车线束电磁干扰传输线模型以及仿真模型,研究了不同屏蔽层及不同线束布置时接收导线的近端电压和远端电压的频响特性.结果表明:多层屏蔽可以有效地减小线束串扰电压,尤其是改善谐振频率附近的电压波动;发射线位于同一屏蔽层和位于不同屏蔽层时对线束的串扰影响除谐振频率点外并不明显,这为汽车线束电磁兼容设计提供了参考依据.     

多层圆筒屏蔽特性计算中的矩阵法

采用矩阵方法分析多层圆筒屏蔽体对内部场的屏蔽特性。对位于屏蔽空间中心的激励沿径向传播的电磁波进行了研究。考虑了多层圆筒屏蔽体的直径、各个屏蔽材料层的媒质参数以及屏蔽层的厚度。分析了在屏蔽空间内到达多层圆筒屏蔽体的电磁波以及穿过多层圆筒屏蔽体的电磁波。利用麦克斯韦方程在各个圆筒屏蔽层的分界处的边界条件,建立相应的矩阵方程。利用矩阵之间的关系,给出了任意多层圆筒屏蔽体的反射系数、屏蔽系统及屏效的完整形     

Experimental analysis of an MIM capacitor with a concave shield

A novel shielding scheme is developed by inserting a concave shield between a metal-insulator-metal (MIM) capacitor and the silicon substrate. Chip measurements reveal that the concave shield improves the quality factor by 11 % at 11.8 GHz and 14% at 18.8 GHz compared with an unshielded MIM capacitor. It also alleviates the effect on shunt capacitance between the bottom plate of the MIM capacitor and the shield layer. Moreover, because the concave shields simplify substrate modeling, a simple circuit model of the MIM capacitor with concave shield is presented for radio frequency applications.     

The penetration of EM waves through loaded apertures

In many cases, the effectiveness of an electromagnetic shield is determined by apertures that exist in the shield. To minimize the penetration of EM fields through a large aperture, the aperture is sometimes loaded with conductive material. The solution of the loaded aperture problem can be reduced to the calculation of equivalent magnetic surface currents, M&oarr;_s, that exist over the surface of the aperture. In the paper, the relevant integro-differential equations have been solved using the method of moments to determine M&oarr;_s for a small, square aperture loaded with a number of impedance sheets of practical interest. These values of M&oarr;_s have been used to calculate the magnetic and electric insertion losses of these impedance sheets. The numerical results are compared with shielding measurements that have been made on carbon composite materials and wire meshes and grids     

Electromagnetic coupling to and from shielded cables-optimizingfactors

Judging the shielding effectiveness of shielded cables often means in practice that only the transfer impedance is considered. The transfer impedance essentially characterizes the coupling via the magnetic field; the coupling via the electric field, the transfer admittance, is mostly neglected. This may be correct for shields with high optical coverage but for optimized single braided shields (coverage ≈0.8 . . . 0.9), the transfer admittance has to be taken into account. In practice, the cable shields are mostly grounded or open-ended at the line ends. With regard to the shield connections, the electromagnetic coupling to a cable by a plane wave and coupling from a cable are investigated. From the results, optimizing factors for the coupling parameters of shielded cables are deduced. By means of these optimizing factors the coupling to and from a cable can be minimized in certain applications