Nonmagnetic Conductors Research Articles

Electromagnetic Field Formed by Shock Compression of a Conducting Magnetic

The structure of the electromagnetic field in a conducting magnetic compressed in a shock wave is analyzed. It is shown that compression of a magnetic material in an external magnetic field leads to origination of a system of two currents identical in magnitude but opposite in direction. One of them passes ahead of the shock front in the undisturbed substance, and the oppositely directed current passes over the shock‐compressed substance. As the shock wave moves further, the absolute value of current monotonically increases. The parameters determining the global electromagnetic pattern in the shock‐compressed magnetic are found. These parameters can be considered as the generalization of the governing parameters found previously by the authors for a nonmagnetic conductor. The formulated model offers a qualitative explanation for the results of dynamic experiments with an 80NKhS magnetic soft alloy. The voltage record on the specimen surface indicates effective shock‐induced demagnetization of the material.

Skin and proximity effects in nonmagnetic conductors

The skin and proximity effects in cylindrical and nonmagnetic conductors are considered. The cross sections of these conductors can have arbitrary shape. A procedure is presented for computation of current densities over the sections and an expression for the calculation of the impedances matrix is also developed. The equations are written in a generalized form, which is useful in studying systems of several parallel interacting conductors. Using mathematical software, these two effects can be simulated and the behavior of impedances, losses, and coupling when electrical parameters and geometrical configuration are modified can be analyzed.

Spin-Polarized Current in a Nonmagnetic Conductor and the Role of Electron–Electron Scattering

The influence of electron–electron scattering on the efficiency of certain methods for the injection and generation of spin–polarized current states in nonmagnetic conductors is discussed. We consider the effect of electron–electron collisions on the resistance to electric transport developing at the interface between a magnetic conductor (MC) and a nonmagnetic conductor (NMC). An essentially unbounded increase of the interfacial MC/NMC magnetoresistance with temperature is predicted.

Nonmagnetic spinguides and spin transport in semiconductors

The construction of a spinguide—a semiconductor channel with walls consisting of a dilute magnetic semiconductor with very large Zeeman splitting and transmitting electrons only with one type of polarization—is proposed. Such channels can be sources of spin-polarized current in nonmagnetic conductors. They can be used for creating fast switches of the spin-polarization direction of the electric current and for transmitting spin polarization over large distances (even larger than the spin-flip length). The selective transparency of the walls gives rise to new size transport effects.

Magnetostatic spin waves in metallic multilayers

Magnetostatic spin waves in a multilayer film consisting of two magnetic conductive layers separated by a nonmagnetic conductor are analyzed. Two magnetostatic spin wave branches are shown to exist and their dispesion laws are analyzed. Structures of finite width, which are relevant for device applications, are also considered.

A boundary-integral based forward solution for eddy current nondestructive testing

A new method for the solution of the forward problem in eddy current nondestructive evaluation is proposed. Based on a volume integral formulation the material defect is represented by a secondary current dipole distribution. The scattering by the surface of the tested specimen is taken into account by a Boundary Element Method. This combination leads to a fast calculation scheme for arbitrary shaped nonmagnetic isotropic conductors. Numerical simulation results are compared with public available benchmark data.

Deep field penetration into a conducting cylinder

In this paper we investigate the penetration of both E and H waves into a cylinder of arbitrary cross section (characteristic dimension L). The material of the cylinder is a nonmagnetic good conductor, and we examine the limits of deep penetration (small L//spl delta/, where /spl delta/ is the penetration depth) and small quality factor Q=(/spl omega//spl epsiv//sub 0///spl sigma/). These two asymptotic conditions imply a low-frequency situation, for which we derive formulas for the induced currents and associated Joule and radiation losses.

Penetration of a low-frequency E-wave into a conducting circular cylinder

We study the progressive penetration of current in a good conductor as the penetration depth a increases. More specifically, we perform this task for the canonical problem of a circular cylinder immersed in a low-frequency incident E-wave. The material of the cylinder is a nonmagnetic good conductor, and we examine the evolution of quantities such as the fields at the surface and the radiative losses. Particular attention is devoted to the limits /spl delta//spl rarr/0 (which corresponds to a perfect conductor) and /spl delta//spl rarr//spl infin/ (which leads to the cylinder becoming transparent).

Eddy-current inversion in the thin-skin limit: Determination of depth and opening for a long crack

A method for crack size determination using eddy-current nondestructive evaluation is presented for the case of a plate containing an infinitely long crack of uniform depth and uniform crack opening. The approach is based on the approximate solution to Maxwell’s equations for nonmagnetic conductors in the limit of small skin depth and relies on least-squares polynomial fits to a normalized coil impedance function as a function of skin depth. The method is straightforward to implement and is relatively insensitive to both systematic and random errors. The procedure requires the computation of two functions: a normalizing function, which depends both on the coil parameters and the skin depth, and a crack-depth function which depends only on the coil parameters in addition to the crack depth. The practical performance of the method was tested using a set of simulated cracks in the form of electro-discharge machined slots in aluminum alloy plates. The crack depths and crack opening deduced from the eddy-current measurements agree with the actual crack dimensions to within 10% or better. Recommendations concerning the optimum conditions for crack sizing are also made.

Weakly coupled GMR sandwiches

Thin film structures comprised of two magnetic films sandwiching a nonmagnetic conductor can have magnetoresistance several times larger than conventional anisotropic magnetoresistance materials. If the coupling between magnetizations in the two films is sufficiently small (either parallel or antiparallel), the saturation magnetic field can be sufficiently small for improved read heads. Magnetoresistances, coupling fields, sheet resistivities, current density effects, thermal limits, and magnetostrictions of these structures are described. No fundamental restrictions are found for using these sandwiches in magnetic head applications. >

Fundamental Electromagnetic Characteristics of Magnetically Anisotropic Damper-Wedges.

A magnetically anisotropic conductor was applied to the damper-wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper clad steel wires of 1.6mm diameter, which are aligned in the same radial direction. This means permeability in the direction of the wires, i.e. the thickness direction of the damper-wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good. In order to evaluate the electromagnetic characteristics, a trial damper-wedge, 1.2m in length and with a steel space factor of 40% to total volume, was manufactured and mountained in a stand-still model iron core. Test results were as follows when the magnetically anisotropic damper-wedge was employed.(1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the non-magnetic or magnetic isotropic conductor are used.(2) The damper-wedge had a smaller skin effect for AC current than a conventional copper damper bar. The losses concentration for the damper system was relieved, so that better machine performance under heavy load condition would be obtained.

Fundamental electromagnetic characteristics of magnetically anisotropic damper‐wedges

AbstractA magnetically anisotropic conductor was applied to the damper‐wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper‐clad steel wires of 1.6 mm diameter aligned in the same radial direction. This means permeability in the direction of the wires, i.e., the thickness direction of the damper‐wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good.To evaluate the electromagnetic characteristics, a trial damper‐wedge, 1.2 m in length and with a steel space factor of 40 percent to total volume, was manufactured and maintained in a standstill model iron core. Test results were as follows when the magnetically anisotropic damper‐wedge was employed.(1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the nonmagnetic or magnetic isotropic conductor is used.(2) The damper‐wedge had a smaller skin effect for ac current than a conventional copper damper bar. The losses concentration for the damper system was relieved so that better machine performance under heavy load condition would be obtained.

A Method of Calculating Asymmetrical Constants Based on Lock Test for Single-Sided Linear Induction Motor.

The constants of each phase of linear induction motor(LIM) are different, because of it's structure. It is important that the method of calculating asymmetrical constants is established, because the asymmetrical constants cause the thrust pulsation. In this paper, a new method of calculating asymmetrical constants of LIM is proposed. Moreover, the results of simulation performed by the calculated constants are compared with the experimental results.The test machine of LIM is single-sided, short-primary-type, three-phase and 4-poles. The primary winding wires are double layer winding, concentrated winding and full pitch winding. In this paper, first, the asymmetrical equivalent circuits and voltage equations of LIM are showed on suitable d-q axis. Next, the asymmetrical constants are obtained by the calculations based on d axis equivalent no-load test, q axis equivalent no-load test, three-phase equivalent no-load test, d axis lock test and q axis lock test. Here, the equivalent no-load test is the lock test removed the non-magnetic conductor plate from LIM. Finally, it is showed that the simulations results of thrust containing pulsation and primary currents performed by the calculated constants are satisfactorily agreed with experimental results.

渦電流による非磁性金属箔の厚さ測定

渦電流による非磁性金属箔の厚さ測定

Power efficiency of eddy current shielding of structural steel in transverse magnetic field

The authors analyze the power efficiency of eddy current shielding of structural members from the field produced by nearby cables. A two-dimensional geometry is used for illustration. Power loss in the structure, in the absence of the shield, is compared with the aggregate power loss in the structure and in the shield when the shield is present. Results show that eddy current shielding is power efficient only when the dimension of the shield is smaller than a certain characteristic length. A criterion is proposed to assist the estimation of this characteristic length. It depends on the dimensions, the magnetic permeability, the conductivity of the structure to be shielded, and the operating frequency. In the case of nonmagnetic conductors, the effect of an eddy current shield is to reduce the power loss in the object. The aggregate power loss does not, however, decrease.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Some theorems of the eddy-current theory

In the paper, theorems for the electric vector potentialT and magnetic scalar potentialU are discussed, which occur in the boundary-value problems for eddy currents induced in a conducting block by an external magnetic field. Uniqueness of the solution is examined. An integral representation of the scalar potentialU is derived for a nonmagnetic conductor. It is shown that for a thin metallic shell the integrodifferential equation results from general formulas related to the block.

Low-frequency eddy-current loss estimation in long conductors by using the moment of inertia of cross sections

A simple method is presented to estimate low-frequency eddy-current losses in long nonmagnetic conductors of uniform cross section when subjected to axial or transverse magnetic field. The method involves calculation of the moment of inertia of the conductor cross section. In the case of transverse fields, the relationship obtained agrees with analytical results for cross sections which have a symmetry axis parallel to the incident field. For axial fields the proposed relationship agrees with the analytical expressions for circular and elliptical cross sections and gives results with reasonable accuracy for rectangular cross sections. >

On the use of the impedance boundary conditions in eddy current problems

The paper examines the use of the Impedance Boundary Condition (IBC) for the reduction of the field problem encountered in the computation of eddy currents in non-magnetic and magnetic conductors with small penetration depths to a simpler exterior problem. A brief review of the various IBC's for linear and nonlinear problems and their limits is presented. The formulations of the original field problem and the approximate IBC problem in terms of boundary integral equations are developed for two dimensional and three dimensional linear problems. These formulations are used to analyze the eddy currents in conducting magnetic cylinders with circular or rectangular crosssection when subjected to transverse-magnetic time-harmonic fields. The results are used to identify the conditions under which the IBC formulation gives acceptable results. The computational requirements of the two formulations are compared. Problems associated with edges are discussed.

Asymmetric biasing fields from mismatched current-carrying overlay conductors on magnetoresistive replay sensors

Magnetoresistive thin-film sensors used in magnetic recording applications are often linearized using a transverse biasing field. For single-domain behavior the biasing field is computed as the average planar value throughout the volume of the sensor element. This paper shows how the correct bias field can be calculated in the general case for a nonmagnetic current-carrying overlay bias conductor not having the same dimensions as the sensor and not symmetrically positioned. This allows the effect of mismatching, for example due to faulty fabrication, to be predicted. The theoretical expressions are confirmed by experiment using a Hall probe. Various graphs are presented which show how the theory can be used in practical cases with typical sensor and conductor dimensions.

Numerical computation of the eddy currents on the vacuum vessel of a Tokamak

In this paper the computation of the eddy currents in thin non-magnetic conductors is discussed, with a specific reference to the vacuum vessel of a Tokamak fusion device. In particulars the problem is stated in terms of the surface current density vector and of the scalar electric potential. The resulting mathematical model is described in detail, together with the numerical formulation based on the finite elements method. Results are given with reference to the vacuum vessel of the Intor reactor and of the Ignitor experiment.