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We present a new technique for reducing computation time of numerical solutions to optimal design problems. We incorporate in the optimization procedure a coarse model. Our technique, the two-level response and parameter mapping (RPM) algorithm, is based on space mapping and manifold mapping. Space mapping (SM) performs a mapping between the parameter spaces of the coarse and fine models, while manifold mapping (MM) makes a mapping between the response spaces of the coarse and fine models through the use of response correction. Here, we use and compare the three two-level optimization procedures, SM, MM, and RPM, for the optimization of passive and active shields in induction heating. The results demonstrate accurate and time-efficient optimization of magnetic shields by the RPM algorithm. Index Terms--Induction heating, magnetic shielding, manifold mapping, optimization, response correction, space mapping.

The development of the first practical high Tc SQUID system for the detection of magnetic contaminants in commercial products, which consists of three SQUIDs, cooled by liquid nitrogen, a permalloy magnetic shield, a conveyer, and a magnetization unit is described.

Numerical modeling studies have been carried out for the design of superconducting and high-permeability shields for SQUID-based nondestructive evaluation and biomagnetic measurements. We used finite-element-method software to model magnetic shields with both axial and planar symmetry in axial and transverse uniform noise fields. Improvements in signal-to-noise ratio at the location of the SQUID were calculated for different shield geometries with line current and magnetic dipole sources at various locations near the shield. Index Terms--Biomagnetism, finite-element method, magnetic shielding, nondestructive evaluation, SQUIDs.

This paper discusses the validation of Modal/method of MoMents (MoM) including cases when the apertures are made as big as the wall of the enclosure (equivalent to having one side of the cavity open). The validation is done using field computations involving bodies of arbitrary shape (FEKO), a commercially available code. The results show that Modal/MoM predicts the results close to the analytical results of Robinson et al. Electron. Lett., 32 (17), 1996; Robinson et al., IEEE Trans. Electromagn. Compat., 40 (3), 240-247, 1998 for single-aperture cases and for most double-aperture cases. Also, for the cases of considering oblique incident plane waves, through validation, it has been found that Modal/MoM can predict the shielding effectiveness close to measured results for smaller angles and not for larger angles of incidence due to the edge effects. In this work, the shielding effectiveness is calculated at only one point, the center of the cavity assuming it to be the worst case. This work discovers the limitation of Modal/MoM for certain applications. Index Terms--FEKO, MoM, shielding effectiveness, validation.

This paper describes several practical aspects of shielding provided by openings such as ventilation vents acting as waveguides. Fundamental properties of electromagnetic waves in the interior of a hollow conducting cylindrical tube are presented. Then the guidelines for oscillator's design and harmonic generation by nonlinearities are presented. A consequent wideband setup having low cost and common devices as well as high dynamic range is proposed to perform reliable measurements from 50 MHz to 1.5 GHz. Measurements of circular cylindrical waveguide effectiveness point out the simplicity of the systematic procedure and illustrate the effects of apertures on shielding walls. Shielding loss achieved by these apertures at frequencies below cutoff allows engineers to gain more insight into analysis and design of shields with intentional discontinuities used to exclude and to confine electromagnetic interference. Index Terms--Apertures, cutoff frequencies, interferences, oscillators, shielding walls, waveguides.

A shape optimization technique for quasistatic field problems has been developed. The optimization is based on computing the continuum sensitivity function by solving an adjoint problem. We show how this technique can be used to compute, in a very efficient way, the optimal shape of a conducting (or ferromagnetic) shielding structure, in order to minimize the magnetic field in the region of interest. A two-dimensional example of shielding three-phase underground cables is considered. Index Terms--Continuum gradient, eddy currents, magnetic shielding, optimization methods.

This paper describes a nonlinear analysis of magnetic field based on homogenization. The analysis of a magnetic field is time-consuming when the problem includes magnetic substance with fine structure. Simplification of the fine structure by homogenization makes it possible to analyze them efficiently. The authors have introduced a homogenization method to estimate effective permeability of magnetic composite structure for a static field. This method can be applied not only for linear problems but also nonlinear ones. In this paper, the magnetic shielding effect of layered nonlinear material is analyzed by using the homogenization method, and the applicability of this method is discussed. Index Terms--Effective permeability, homogenization, magnetic shielding, nonlinear analysis.

Special emphasis is given to the computation of the magnetic shielding function associated to the response of a molecule toward an external magnetic field. The special properties of aromatic molecules induced by a magnetic perturbation are discussed in terms of the magnetic shielding function, the ring current model and the electron delocalization.

New nanolayered coatings are designed and deposited on flexible plastic substrate having the thickness of 100 [micro]m, in order to realize lightweight ultrathin transparent shielding foils. The structure of the coating is optimized considering three figures of merit: the average transmittance in the visible range for normal incidence, the normalized average transmittance for oblique incidence at 550 nm, and the transmittance quality factor. The nanotechnology exploited for the deposition of the transparent metals is the dual ion beam sputtering. Tests of durability, optical transmission, and shielding effectiveness demonstrate that the film has a high adhesion under mechanical solicitation, high resistance against aging, peak transmittance in the visible range higher than 70%, omnidirectional properties in the range 0[degrees]-60[degrees], and shielding effectiveness of 40 dB up to 6 GHz. Index Terms--Nanotechnology, optical coating, shielding, thin film.

This paper deals with new definitions of shielding effectiveness, in particular for high-frequency and transient electromagnetic fields. They are practicable and supposed to better characterize the shielding ability than the commonly used definitions. From the ratio of the time-averaged input power of the unshielded load to that one of the shielded load, in the limiting case of a vanishing load the electromagnetic shielding effectiveness is derived. This is a simple combination of the commonly used and easily measurable electric and magnetic shielding effectiveness. A similar procedure is then employed for the transient case, where in the limiting case of a vanishing load the ratio of the absorbed energies turn into the transient shielding effectiveness. Numerical results are shown for closed as well as for nonclosed cylindrical shields. Index Terms--Electromagnetic shielding, measurement standards, shielding.

In this paper, a hybrid technique combining the finite-difference (FD) method and the method of moments (MoM) in the frequency domain is proposed to predict the shielding effectiveness of rectangular conducting enclosures with apertures under external illumination. The interior and exterior regions of the enclosure are analyzed separately by employing the field equivalence principle. Internal electromagnetic fields are discretized using the (FD) method, while external fields are formulated by the MoM. Enforcement of continuity of the tangential magnetic field over the aperture surface gives the desired equation to solve for electromagnetic fields everywhere. Numerical results for the shielding effectiveness of a rectangular cavity with apertures calculated by the new hybrid technique are presented and validated by comparing with experimental data. Index Terms--Finite difference method, hybrid technique, method of moments (MoM), shielding effectiveness.

A subcell model for thin wires in the finite-difference time-domain (FDTD) method using modified telegraphers equations has been developed by Holland et al. Edelvik has previously presented an extension of their algorithm, which allows for arbitrarily located and oriented wires with respect to the Cartesian grid. This is important to be able to accurately model wires that cannot be aligned to the Cartesian grid, e.g., tilted wires and circular loop wires. Recently, a dual set of equations has been proposed for modeling of thin slots. In this paper, we show that using a similar algorithm as for thin wires we can also handle slots of arbitrary location in Cartesian planes. Previous thin slot models have been susceptible for instabilities. We show that a symmetric coupling between field and slot yields a stable time-continuous field-slot system and that the fully discrete field-slot system is stable under a generalized Courant-Friedrich-Lewy (CFL) condition. The proposed method is demonstrated for scattering from a finite-length slot in an infinite conducting wall and a shielding enclosure including a slot. The results are in good agreement with published experimental data. Index Terms--Finite-difference time-domain (FDTD) methods, numerical stability, shielding, subcell models.

This paper proposes a basic model and an analytical study of the transverse flux machines using permanent-magnet (PM) shields to increase the thrust force. By improving the magnetic field distribution in the electrically excited transverse flux linear motor (TFE-LM), the rare-earth PM shields provide an increase of the thrust force. Analytical equations are developed to predict the thrust force and to guide the design of TFE-LM. The thrust force and the thrust force density of TFE-LM with PM shields are calculated also by a 3D-Finite Network Method program. The presence of PM shields in a TFE-LM having a current linkage of 2 kA and the air-gap length of 1 mm leads to the increase of thrust force by approximately 160%. This result reveals a great potential in reducing the mass of the TFE-LM by inserting PM shields in the teeth. Index Terms--Electrically excited transverse flux linear motors, high power density PM shields.

A method of moments solution for analyzing the electromagnetic shielding properties of rectangular metal enclosures with apertures over a lossy half space which can model the ground is presented. The objects are modeled by rectangular surface patches. The roof-top basic functions are used to expand the unknown electric and magnetic currents on the surfaces of the cavity and the apertures. An effective method based on the generalized pencil-of-function (GPOF) method is developed to calculate the generalized Sommerfeld integral (GSI). With this method, the value of Greens' function can be obtained quickly and accurately. Validation of the method is presented by comparing the calculation results with the results obtained by measurement. Finally, the method is successfully applied to calculating the shielding effectiveness of a relay cell in a substation. Index Terms--Absorbing media, apertures, electromagnetic shielding, numerical analysis.

A three-dimensional edge element procedure is presented to analyze the magnetic field around thin shields embedded in a physically large domain. The shield region is eliminated from the computational domain and coupled boundary conditions named impedance network boundary conditions are imposed on the new boundary surfaces to take into account the field discontinuity produced by the eliminated shield. An experimental setup is built and the measured magnetic fields are compared to the results obtained by the proposed procedure. Index Terms--Coupled boundary conditions, edge elements, finite-element method (FEM), impedance network boundary condition (INBC), physically large domain, shielding.

This paper describes a method to estimate effective permeability of magnetic composite materials for static field. In the present method, the structures of the composite materials are assumed to be periodic, and the unit cell is defined. The effective permeability is determined on the basis of magnetic energy balance in the unit cell. The present method considers magnetic interaction between inclusions of the composite materials, and is more accurate and useful. Therefore, the present method can be more widely applied than conventional models, for example, the Maxwell--Garnett formula and the Bruggeman formula. Validity of the present method is confirmed by numerical analyses. This approach can be applied also to nonlinear magnetic composite materials. Index Terms--Composite material, effective permeability, homogenization, magnetic shielding.

In the last few years, much effort has been made to describe the behavior of shielded cables. Many researchers have attempted to understand how an electromagnetic field couples into a braided coaxial cable. There are some important publications on this topic. Nevertheless, up to now, it has not been possible to predict the coupling through a braid shield, analytically. An electromagnetic field outside a cable induces a disturbance current in the cable shield. The coupling from the current in the shield into the cable can be described by the transfer impedance. How the current flows in the cable shield is an important quantity in this coupling process. Therefore, to understand the coupling mechanism into a cable, it is necessary to understand the behavior of the current flow in such a braided shield. In this paper, the flow of the current in a braided cable shield is discussed. The assumption often made in the literature, that a braided shield behaves like a homogeneous tube with apertures, is shown to be inaccurate. It is also shown that the standard braid of the shield used in this study had the same properties as a braid made with insulated wires. Index Terms--Cable screen, cable shield, current in a braided shield, current-line-input-impedance method, transfer impedance.

Simple approximate methods are developed and described for calculating the extremely low-frequency magnetic-shielding effectiveness for single- and double-layer infinite planar shields. In addition, exact expressions are given and 'nearly exact' expressions are derived. Each expression has been compared to the exact expression in order to determine the range of parameters over which it is valid. Each of the approximate expression can be calculated rapidly and has a simple physical interpretation that leads to physical insight into the shielding process. Index Terms--Extremely low frequency (ELF), magnetic fields, shielding.

In the study conducted, the transport critical current (I(sub c)) is measured for MgB2/Fe round wires, with magnetic field oriented perpendicular to the wire and parallel to it is discussed. Measurements made on a wire with pure MgB2 core and another wire where the MgB2 core is doped with nano-size SiC.

Research was conducted to examine the 13C NMR shieldings for acetylene, allene and some higher cumulenes which were measured at the MPW1PW91/6-311+G(2d,p) level using both the GIAO and IGAIM methods. The tensor components of the shielding for both allene and acetylene as well as the remarkably large difference in the components about the long axes of the molecules were efficiently reproduced by the calculations. The large difference in isotropic shielding may have resulted from the differences in p-orbital coefficients among the occupied orbitals and the virtual orbitals with which they couple in the presence of a magnetic field.

Research was conducted to develop ab initio pi-electron first-order current density maps and second-order magnetic properties, measured at the SCF/coupled Hartree-Fock level of approximation, for a series of polycyclic aromatic hydrocarbons. The computational results for the magnetic properties were generally in very good agreement with the available experimental data. Results indicate that the current density maps provide accurate descriptions of the actual pi-electron flow induced by an external, uniform magnetic field in the systems.

Research was conducted to examine the evaluation procedures for obtaining the behavior of the magnetic flux density B(sub in) within the single BPSCCO and superimposed cylinders when exposed to external magnetic flux densities B(sub ex) of less than maximum shielded magnetic flux density B(sub s). The system of superimposed cylinders was found to be effective in improving the shielding characteristics.

Research was conducted to reduce the size and improve the shielding effect of the Magnetically Shielded Room (MSR). The cylindrical MSR was one tenth the size of a human body with both ends closed and a hole at the middle point on the side was built. The shielding effect, which was the ratio of the transverse magnetic field inside the MSR to the external field, was evaluated by applying external magnetic fields parallel and perpendicular to the door.

Research was conducted to examine two different concepts for gradiometer formation using high temperature radio frequency superconducting quantum interference devices operated at 77 K in liquid nitrogen. The first concept used thin-film gradiometers at different positions. The second used electronically deformed gradiometers in various configurations. Biomagnetic calculations were conducted in shielded and unshielded environments to illustrate the performance of the systems.

Research was conducted to examine magnetically unshielded operation of a high temperature superconducting (HTS) radio frequency (rf) superconducting quantum interference device (SQUID) magnetometer using a HTS rf SQUID. The magnetometer was used for the detection of ferrous particles in unshielded environment as a preliminary investigation. Also conducted were magnetocardiograms calculations.

The application of superconducting magnetic shields to neuromagnetic superconducting quantum interference devices (SQUID) is proposed. Magnetic fields emitted from human brains with a 64-channel whole-head SQUID magnetometer in he superconducting magnetic shield of high-Tc superconductor were detected. The characteristics of the superconducting magnetic shield and neuromagnetic SQUID measurements are described.

Research was conducted to examine the influence of critical current density J(sub C) and E-J characteristics on the superconducting fault current limiter (SCFCL) operation. A numerical method based on the Finite Element Method that takes into consideration the E-J characteristics was developed to simulate the behavior of the high temperature superconductor cylinder when the external magnetic field changes actively. A comparison of computer simulation results with those of experimental results was performed.

A time-domain analysis of quasi-static magnetic fields around nonperfectly conductive shields is performed by a numerical procedure based on the nodal-based finite element method (FEM). Eliminating the shield region from the computational domain, a new boundary is generated where impedance network boundary conditions (INBCs) are imposed to take into account the field discontinuity produced by the shield. The INBCs are boundary conditions of the third kind which couple the electric and magnetic field tangential components on the shield surfaces. The application of the INBCs in time domain leads to the solution of convolution integrals. By using exponential expressions for the INBCs and discretizing the time by central finite differences, an efficient algorithm is proposed to solve recursively the convolution integrals. Finally, the implementation of the INBCs in a time domain FEM procedure is illustrated. Index Terms - Impedance network boundary conditions (INBCs), shielding, transients, EMC, FEM, convolution integral recursive solution.

The magnetic shielding tensors in free base porphyrin (H2P), magnesium (MgP) and zinc (ZnP) metalloporphyrins were measured using the gauge including atomic orbital method. The nuclear magnetic resonance (NMR) shifts of the three molecules were also calculated to compare them with observed values, and were found to agree well. Results also revealed that only the nitrogen shielding tensors exhibit any sensitivity to nonplanarity.

In this paper an analytical solution for the quasi-stationary eddy current distribution in a hollow sphere is presented using a divergence free vector potential derived from another spatial vector function by applying the curl operator. The field is excited by a dipole of arbitrary orientation and position. The dissipated power is also considered and hints are given for the analytical treatment of multishield problems excited by current loops. Index Terms - Eddy currents, power loss, shielding efficiency.

The modelling of nonlinear hysteretic magnetic material in the computation of shielding problems with sinusoidal excitation at power frequency is investigated. A complex valued effective reluctivity model is chosen which allows a sinusoidal calculation in spite of the material's nonlinearity. The absolute value and the phase of the reluctivity are determined from the hysteresis curves of the material. The complex Newton-Raphson method is adapted to solve the arising equation system. The results obtained are compared with measurements and with calculation results using a real valued effective reluctivity. Index terms - Effective reluctivity, hysteresis (magnetics), ferromagnetic materials, finite element methods, power cable shielding.

This paper presents our work o n magnetic modeling of degaussing coils. The main reason of bad results on coils effects is a locally insufficient mesh. Instead of using a finer and expensive mesh, we propose an alternative method named 'reduced potential jump' to solve the problem of coils and present comparative results on a simple geometry and on a ship model. Index terms - Finite elements method, Magnetic fields, Magnetic shielding, Marine vehicles.

The shielding effectiveness of a corrugated thick screen is theoretically and experimentally investigated. This screen consists of a half-plane of finite thickness in which corrugations are etched on the smaller side. This structure provides a significant attenuation in the shadow region for both polarizations of the incident field; thus, it can be effectively used for protecting apparatuses from radiating interference as well as for decoupling nearby operating antennas. The shielding properties of the screen are described by a high-frequency formulation that involves closed-form expressions. An experimental setup at X band has been arranged to test the effectiveness of a corrugated screen; the field in the shadow region is compared with that of a screen without corrugations. The experimental results compare very well with those obtained by the high-frequency expressions. Index Terms - Diffraction, high-frequency, shielding.

Research was conducted to characterize a formalism for examining superconducting disk shielding an arbitrary magnetic field. A cylindrical permanent magnet was considered in the study. It was characterized by a levitation force and induced supercurrent density that were computed into closed forms. Results showed that integral transforms can be utilized to study and investigate finite size effects in the screening of magnetostatic fields.

The two-dimensional (2-D) magnetostatic field problem of a homogeneous permeable elliptic cylinder embedded in a confocal layer of another permeable medium and containing an axially directed line current is reformulated as a problem of finding an equivalent current distribution inside the cylinder. Using some integral identities for the potential modes, the image source is identified as a line current at the location of the original current plus a combination of a sheet current and a bilayer distribution of current located on the fundamental strip between the two loci. The expressions for the image currents are tested analytically and illustrated numerically, and their relevance in the study of the impact of the layer permeability to the magnetic shielding efficiency is discussed. Index Terms - Coated elliptic cylinder, image sources, magnetic shielding, magnetostatic fields.

A study was conducted on superconducting inertial guidance gyroscopes inside superconducting magnetic shields. The analysis included solutions of Ampere's law for rotating and nonrotating superconductors and boundary conditions. The results indicate the inability of a superconducting device to distinguish between rotation and an applied magnetic field. Moreover, a superconducting device surrounded by a co-rotating superconducting shield cannot detect rotation.

This paper describes an experimental study of shielding of 60 Hz magnetic fields with nested long cylinders with open ends and short cylinders with capped ends, constructed from multiple layers of steel and aluminum. Measurements of shielding factor were made for a large number of specific configurations of steel and aluminum in shields of up to eight layers, with both externally applied uniform fields and enclosed dipole sources. Measured results are compared with calculated results from a recently developed computational tool for multilayered shielding, with generally excellent agreement.

An optimal design method was proposed for a high-field, highly homogeneous superconducting magnet system with ferromagnetic shielding. The design approach involves a combination of the simulated annealing method for computing optimization problems and the equivalent magnetization current approach for solving magnetic field problems. The design method was successfully applied to a 9-tesla magnet system with hybrid iron and active shielding.

The superposition of a hybrid ferromagnetic cylinder over a Bi-Pb-Sr-Ca-Cu-O cylinder was found to enhance the value of maximum shielded magnetic flux density (MSMFD) in high-critical temperature superconductor cylinders. Several models were employed in determining the value of the MSMFD. Theoretical MSMFD values were found to be consistent with experimental results.

A high temperature superconducting direct current-superconducting quantum interference device was employed in measuring the magnetic noise power spectra in a Bi-Pb-Sr-Ca-Cu-O cylinder. NPS was measured at 5.0x10(super -6) Phi(sub 02)/Hz at 1 kHz excluding the magnetic field functioning as the background noise and 1.0x10(super -5) Phi(sub 02)/Hz at 1 kHz for the magnetic field of 3.0x10(super -4) T. In the region of 0.0 T to 3.0x10(super -4) T, NPS values at 1 kHz rose linearly with magnetic field values.

A study was conducted on the shielding characteristics of high temperature superconducting (HTS) devices. A compact, portable system made up of HTS components was then fabricated based on the results. Cold isostatic processing was employed in forming disks and tubes of different sizes, which were then sintered at reduced oxygen pressures. The devices exhibited low-frequency noise rejection capabilities that may be applied for nondestructive testing and magnetocardiography.

A reverse calculation based on previous magnetic shielding studies was employed in measuring the shielding currents flowing in (Bi,Pb)2SrSCa2Cu3Oy oxide superconducting plates. The approach determined the relationship between the distribution and magnitude of the shielding current and the magnitude of the external field. The shielding current's critical current was consistent with the results of an investigation using the susceptibility method.

The effect on a proportional electromagnetic valve of a strong external magnetic field orthogonal to the valve's axis and the optimal design of a magnetic shield are presented in this paper. The valve is used to control the gas flow in a fusion device, and its throughput should not be influenced by the external field. The valve, the shield and the perturbing field are modeled by using a 3-D finite-element code based on the reduced scalar potential formulation. An optimization procedure is applied to minimize the volume of the shield together with the effect of the perturbing field on the force produced by the valve's magnetic circuit.

This paper presents an integral equation and method of moments (MoM) solution to the problem of TM transmission by a metallic conducting shield at extremely low frequencies (ELF). In order to accurately compute the total fields interior to the shield, equivalent problems are formulated which avoid the numerically difficult problem of computing the total fields as the sum of the incident plus scattered fields. In particular, the total electric field on the interior surface of the shield is obtained by a volume current equivalent problem, and then the total magnetic field interior to the shield is formulated in terms of equivalent magnetic surface currents flowing on the interior surface of the shield replaced by a perfect conductor.

Magnetostatic calculations-based simulation of superconducting magnetic shields gives precise results for two-dimensional axisymmetric shields. A shield in the shape of a cylinder having end caps with access ports or gaps has been simulated, the results of which conform closely to practical measurements. It has been shown that gaps and cracks substantially reduce field attenuation for static fields, while the flux leakage for time-varying fields is not affected significantly.

The continuous development of electric power utilities has led to the increase in the problems concerning fault currents. The use of fault current limiters, which suppress fault currents below a prescribed level, has been examined in many places. The authors have studied a superconducting fault current limiter that is based on the magnetic shielding effect of superconductors. In this paper, we derive a requirement for leading to a flux-jumping inside a ceramic superconductor at liquid nitrogen temperature. Next, two kinds of magnetic-shield type superconducting fault current limiters are designed, and their current-limiting simulations are tried using a computer.

A particle beam can be shielded from external magnetic fields by ferromagnetic shields, up to a certain field strength depending on the saturation characteristics of the used shielding material. The limits of passive shielding, in terms of external flux densities and local orientations of the field, are studied. The alternative solutions, i.e. the cancelation of the external field by either actively powered coils or by using a passive superconducting shield, are also discussed. The active and passive shielding can also be combined. As an example the proposed shielding of the HERA electron beam at the HERA-B experiment site at DESY is described.

The maximum shielded magnetic flux density ([B.sub.s]) was shown to be improved by the superposition of a six-layered ferromagnetic cylinder over a Bi-Pb-Sr-Ca-Cu-O (BPSCCO) cylinder; termed the six-layered superimposed cylinder. The values of [B.sub.s] for the six-layered superimposed cylinder were found to be about 100 times greater than that of a single-BPSCCO cylinder. The values of [B.sub.s] were analyzed by using several different models. It was found that the experimental values orbs agree well with theoretical values. The results confirm that an important criterion was determined for the design of an effective shield for large chambers.