Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.

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Non-Destructive Techniques Based on Eddy Current Testing

This paper reviews and summarizes Maglev train technologies from an electrical engineering point of view and assimilates the results of works over the past three decades carried out all over the world. Many researches and developments concerning the Maglev train have been accomplished; however, they are not always easy to understand. The purpose of this paper is to make the Maglev train technologies clear at a glance. Included are general understandings, technologies, and worldwide practical projects. Further research needs are also addressed.

Review of maglev train technologies

This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

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Induction coil sensors—a review

A comprehensive review of advancements in eddy current (EC) modeling is presented. This paper contains three main sections: a general treatise of EC theory, the thin skin EC forward modeling, and the EC inverse problem. (1) The general treatise of eddy current theory begins with an exposition of the reciprocity formulas for evaluating probe impedance changes, which are derivable from first principles. Two versions of the reciprocity formulas, one with a surface integral and the other with a volume integral, are given. Any particular type of defect, as well as both one-port and two-port probes, can be treated. Second, a brief account of analytical and numerical methods for calculating the field distributions is presented. Third, theory of probe/material interactions with various defect types is described. (2) The paper then proceeds to the forward modeling section, which contains a detailed treatment of the eddy current forward problem for surface breaking cracks and EDM notches in the thin skin approximation. (3) The inverse problem section begins with a general review of commonly used inversion methods, exemplified by selected references from the literature, followed by more detailed examinations of EC inversions for surface breaking cracks and slots. The last part of this section is devoted to the inverse problem for layered structures. Although being a review in nature, the paper contains a number of new accounts for time-domain eddy current interactions. In particular, a modification is proposed to the reciprocity formula in order to take a better account of pulsed eddy current signals.

Review of Advances in Quantitative Eddy Current Nondestructive Evaluation

Energy storage systems (ESSs) play a very important role in recent years. Flywheel is one of the oldest storage energy devices and it has several benefits. Flywheel Energy Storage System (FESS) can be applied from very small micro-satellites to huge power networks. A comprehensive review of FESS for hybrid vehicle, railway, wind power system, hybrid power generation system, power network, marine, space and other applications are presented in this paper. There are three main devices in FESS, including machine, bearing, and Power Electronic Interface (PEI). Furthermore, advantages and disadvantages all of them have been presented. In addition a brief review of new and conventional power electronic converters used in FESS, have been discussed. Finally, practical ways to develop this technology in the future are presented.

A comprehensive review of Flywheel Energy Storage System technology

This paper describes a new method for the magnetic force analysis of a high T/sub c/ superconductor based on the flux flow and creep model. The introduction of the artificial conductivity, which is used in the conventional method, is not needed. The CPU time requirement of the calculations is considerably lower than that in the case of the conventional method. Thereby the vibration of a levitated permanent magnet was numerically analyzed by taking into account the flux flow and creep. >

Magnetic field and force analysis of high T/sub c/ superconductor with flux flow and creep

A new three-dimensional (3-D) finite element scheme for eddy-current nondestructive evaluation (NDE) problems is described that calculates directly the perturbation of the electromagnetic field due to defects in metallic specimens. The computational costs of such problems are usually very high using available finite element schemes, and the new scheme is supposed to lower these costs. The basic concept, the direct calculation of the field distortion due to the flaw, is provided for rather general defects, but the detailed finite element scheme is discussed for zero-conductivity flaws. The source terms of the formulation are determined from the unperturbed field, and the impedance change due to a defect can be calculated as an integral over the flaw. A finite element scheme for solving problems with crack-type defects is also presented as a limiting case of the formulation for zero-conductivity flaws. Solutions of a benchmark problem from the testing electromagnetic analysis methods (TEAM) workshop series (problem number 15/2) and of tube problems with artificial slots are presented and compared to experimental data.

An effective 3-D finite element scheme for computing electromagnetic field distortions due to defects in eddy-current nondestructive evaluation

Benchmark models of eddy current testing for steam generator tube: Experiment and numerical analysis

This paper describes a new scheme for the fast evaluation of eddy current testing (ECT) signals by using databases and formulation of the A−φ method. As the calculation of flaw signals is localized around the flaw region, substantial computational work can be reduced comparing with the conventional FEM–BEM code even for a conductor with complex geometry. Unlike the approach proposed by Badics et al. (Rapid flaw reconstruction scheme for 3-d inverse in eddy current NDE. In Studies in Applied Electromagnetics and Mechanics, Vol. 12, eds T. Takagi et al., IOS Press, 1997, pp. 303–309), the new scheme can predict ECT signals due to a large and complex-shaped crack rapidly because of its higher order interpolation and the newly introduced special element, say, an element with different media. The efficiency of the new method is verified by comparing its numerical results with the measured impedance for several bench-mark problems. The fast and accurate features make this new forward approach especially feasible in the reconstruction of flaw shapes by combining with the conventional optimization method.

Rapid prediction of eddy current testing signals using A−φ method and database

A plasma lens for 18-MeV round-shaped electron beams was experimentally studied; the lens is based on self-focusing due to shielding of the space charge of a particle beam by a quiescent plasma. A differential pumping technique was applied to separate the plasma chamber from the linac acceleration duct. It is shown that overdense plasmas successfully focus the electron beams. Another finding is that the plasmas appear to reduce the transverse emittance.

Kenzo Miya

Papers

Magnetic field and force analysis of high T/sub c/ superconductor with flux flow and creep

An effective 3-D finite element scheme for computing electromagnetic field distortions due to defects in eddy-current nondestructive evaluation

Benchmark models of eddy current testing for steam generator tube: Experiment and numerical analysis

Rapid prediction of eddy current testing signals using A−φ method and database

Direct observation of plasma-lens effect