Eddy Current Evaluation Research Articles

Eddy current loss evaluation of magnetic powder core based on electric and magnetic networks

This paper presents a method for calculating eddy current loss in the magnetic powder core based on electric and magnetic networks. First, an electric and magnetic model of single particle of magnetic powder core to calculate intra-particle eddy current loss generated in each particle of the magnetic powder is discussed. Then, eddy current losses of toroidal cores made from three sizes of magnetic powders are determined. Experimental results demonstrate the validity of the proposed method.

圧縮応力下における電磁鋼板古典渦電流損の検討

圧縮応力下における電磁鋼板古典渦電流損の検討

Development of ferromagnetic nanoparticle filled CFRP for amplification of eddy current signal and evaluation of detectability of fiber disconnection

Development of ferromagnetic nanoparticle filled CFRP for amplification of eddy current signal and evaluation of detectability of fiber disconnection

A Magnetodynamic Error Criterion and an Adaptive Meshing Strategy for Eddy Current Evaluation

In order to address their considerable impacts on both the energy efficiency and performance requirements, eddy current modeling and its accuracy are discussed from a thermodynamic approach. An energy-based error criterion for automatic mesh adaption is developed. Coupled with a remeshing strategy that preserves mesh quality, some numerical results are given on an induction machine.

Thickness Assessment of Thermal Barrier Coatings of Aeroengine Blades Via Dual-Frequency Eddy Current Evaluation

A thermal barrier coating (TBC), consisting of the top and bond coatings, is normally deployed over the alloying body of an aeroengine blade in order to protect the blade from hostile environments. Thickness loss of TBC severely undermines the structural integrity of blades, and thus leads to the failure of aeroengines. Before catastrophic accidents occur, it is important to nonintrusively assess the TBC thickness via effective nondestructive evaluation (NDE) techniques. In this letter, the dual-frequency eddy current technique (DFEC) in conjunction with an efficient inverse model is intensively investigated for quantitative evaluation of TBC thickness in micrometers. The thickness of both top and bond coatings are assessed simultaneously. Comparison between the estimated TBC thickness of blade specimens and true values acquired using scanning electron microscope (SEM) indicates that DFEC is applicable for quantitative evaluation of TBC thickness without much loss of accuracy.

Efficient finite element modelling of eddy current probability of detection with transmitter–receiver sensors

Efficient models are needed in eddy current evaluation to enable fast and accurate predictions also in terms of probability of detection (POD). Here, calculations of the transfer impedance in a transmitter–receiver sensor are considered using the finite element method. It is shown that numerical integration around the flaw gives accurate values even if the solution without the flaw is calculated analytically which also is decreasing the computational time. A closed crack model is validated and used in a model based POD study showing limitations with transmitter–receiver sensors. It is finally suggested how to link the modelled POD to design parameters of components.

An Approach for Eddy-Current Calculation in Railguns Based on the Finite-Element Method

This paper presents a global method of evaluating nodal eddy currents based on the known nodal potentials, which is a Galerkin finite-element method formed by employing the Schaubert-Wilton-Glisson basis function as a weighting function. As a result, the accuracy of eddy-current evaluation in the railgun computation could be increased using the nodal finite-element method. The new method takes all the nodal potential values into account to obtain the global nodal current density directly by solving the finite-element equation, which could overcome the drawback of the traditional local element postprocessing method. The computational results show that the new method could greatly enhance the computational accuracy of eddy current, relative to the traditional element postprocessing method. This method could not only be used in the eddy-current evaluation of the railgun but also in other gradient field computations based on known nodal potential values.

Analytical modelling for edge effects and impedance characteristics of the transverse eddy current displacement sensors with rectangular coils

Analytical method for eddy current evaluation is an attractive field of learning the concept of electromagnetic phe- nomena. This paper proposes an analytical approach to a transverse eddy current displacement sensor with a rectangular testing coil. Solving domain in the Cartesian coordinate system is limited to finite extents through imposing artificial boundaries at x and y axis, and solutions to the electromagnetic field are expressed as double series. Complete closed-form expressions based on second order vector potential for the electromagnetic field in each region can be obtained from the continuity conditions at the interfaces by mode matching. Closed-form expressions of the eddy current density as well as coil impedance related to the transverse displacement can thus be derived, and the calculated results show good agreement with the experimental results.

Eddy Current Testing and Evaluation of Far-Side Corrosion Around Rivet in Jet-Engine Intake of Aging Supersonic Aircraft

This study proposes an automated inspection system to inspect far-side corrosion around rivets in the F-5 supersonic aircraft. The system includes a linear integrated Hall sensor array, a C-type exciter, and an automated scanning system. The inspection system was tested on a modified elliptical intake having artificial defects with 10-mm diameter and 0.12–1.11-mm depth. An algorithm was produced to detect the defects. The probability of detection (POD) curve was obtained with hits/misses data using a log–logistics model. Defect with depths of 0.67 and 0.98 mm were detected with 90 % POD and lower 95 % confidence bound.

Defect Characterization Based on Eddy Current Technique: Technical Review

Eddy current testing is widely used for nondestructive evaluation of metallic structures in characterizing numerous types of defects occurring in various locations. It offers remarkable advantages over other nondestructive techniques because of its ease of implementation. This paper presents a technical review of Eddy current technique in various scope of defect detection. The first part presents Eddy current evaluation on various defects location and orientation such as steam generator tubes, stress crack corrosion, and fatigue cracks. The next section analyzes the use of pulsed Eddy current and pulsed Eddy current thermography as an alternative method for monitoring the growth of cracks with the aid of computational techniques for postsignal analysis.

A NDE strategy based on a database for evaluation of the anti-corrosive coating on curved steel bases of various sizes using ECT signals

The anti-corrosive coating in pipeline and oil tanker is taken as a crucial component in petroleum industry and needs a robust NDE tool to evaluate its thickness. For the thick coating on the curved steel bases of various sizes, the eddy current sensor's evaluation capability for thick coating and the influence of the test-piece sizes on the evaluation precision are two key problems had to be solved. Taking into account the dimension effect of the sensor on signals, a wide-range sensor was designed and applied to the coating evaluation. The relationship between coil responses and liftoff was investigated and a NDE strategy based on a polynomial coefficient database was proposed to cope with the influence of test-piece sizes. Its applicability was verified by simulation results.

Manufacturing Stress Corrosion-Cracking Tube Specimens for Eddy Current Technique Evaluation

To detect degradation in steam generator (SG) tubes, periodic inspection using nondestructive examination techniques, such as an eddy current testing, is a common practice. Therefore, it is critical to evaluate and validate the reliability of the eddy current technique for ensuring the structural integrity of the SG tubes. The eddy current technique could be evaluated by comparing the data estimated by the eddy current with the destructive examination data of field cracks, which would be both costly and labor intensive. A viable alternative to pulled tube data is to manufacture crack specimens that closely represent actual field cracks in laboratory environments. A crack manufacturing method that can be conducted at room temperature and atmospheric pressure conditions is proposed. The method was applied to manufacture different types of stress corrosion cracking (SCC) specimens: axial outer-diameter (OD) SCC for straight tubes, circumferential ODSCC and primary water SCC (PWSCC) at hydraulic expansion transition regions, and axial PWSCC at the apex and tangential regions of U-bend tubes. To help the growth of SCC into the tube, corrosive chemicals (sodium tetrathionate) and tensile stress were applied. Eddy current and destructive examination data for SCC specimens were compared with the available field crack data to determine whether those SCC specimens are representative. It was determined that the proposed method could manufacture the representative crack specimens.

A Bayesian Probabilistic Approach to Improved Health Management of Steam Generator Tubes

Steam generator tube integrity is critical for the safety and operability of pressurized water reactors. Any degradation and rupture of tubes can have catastrophic consequences, e.g., release of radioactivity into the atmosphere. Given the risk significance of steam generator tube ruptures, it is necessary to periodically inspect the tubes using nondestructive evaluation methods to detect and characterize unknown existing defects. To make accurate estimates of defect size and density, it is essential that detection uncertainty and measurement errors associated with nondestructive evaluation methods are characterized properly and accounted for in the evaluation. In this paper we propose a Bayesian approach that updates prior knowledge of defect size and density with nondestructive evaluation data, accounting for detection uncertainty and measurement errors. An example application of the proposed approach is then demonstrated for estimating defect size and density in steam generator tubes using eddy current evaluation data. The proposed Bayesian probabilistic approach helps improve health management of steam generator tubes, thereby enhancing the overall safety and operability of pressurized water reactors.

Eddy current evaluation of air–gaps in aeronautical multilayered assemblies using a multi-frequency behavioral model

This paper reports on the estimation of the air–gap thickness between parts in an aeronautical multilayered metallic assembly, by the means of the eddy current method. A behavioral multi-frequency modeling of the interactions between the used cup core sensor and the multilayered structure was developed thanks to the analysis of experimental data, completed with finite element electromagnetic computations. The elaborated model was used to estimate the air–gap thickness (in the range of 0–500 μm) of a multilayered structure featured by a metallic coating of known thickness (1.5 mm) and a distant metallic layer of unknown thickness (in the range 1.5–3.5 mm). The obtained estimation error is smaller than a few percents, either for simulated or experimental data.

PEC: Computation of coil-induced voltage due to a defect-free plate using Stehfest's method for pulsed eddy current evaluation

The pulsed eddy current technique has demonstrated considerable promise as a new tool for the evaluation of conducting plate structures. Recently, much attention has been paid to the Laplace transform-based method for the calculation of transient probe response. However, use of the Laplace transform-based method usually results in solutions in the complex domain that are not exactly invertible. In this paper, Stehfest's algorithm is proposed to numerically convert the coil-induced voltage from the Laplace domain into the time domain. To evaluate the Stehfest's method, prediction of induced voltage for a driver-pick-up probe above an aluminum plate energised by a step current has been compared with analytical results. The comparison shows excellent agreement between numerical and analytical methods, which confirms the applicability of Stehfest's algorithm for the computation of coil-induced voltage.

WE-C-213A-03: MRI Annual Equipment Performance Evaluation & Acceptance Testing

The ACR MRI Accreditation program requires that sites applying for MRI accreditation submit an annual MRI system performance evaluation performed by a medical physicist or MR scientist. The medical physicist/MR Scientist follows the ACR MRI Quality Control (QC) Manual in order to perform a complete annual system performance evaluation. This evaluation includes an evaluation of the weekly QC performed by a technologist. This presentation shall review a standard set of tests and procedures that satisfy the ACR compliance testing guidelines. A model program for satisfying the ACR MRI performance standards shall be provided. Steps for setting up the QC Program include determining which tests are appropriate, establishing a mutually agreeable testing frequency, training technologist and other personnel to carry out their portions of the MRI QC program, reviewing artifacts and other problems that result from the test data and documenting corrective actions that are taken. Attention will be paid to specific tests, such as Magnetic Field Homogeneity, in which spectral width, phase-difference and bandwidth difference methods will be discussed and compared. Tests for gradient field linearity (geometric distortion) and radio frequency (RF) coil testing will be presented, including measuring slice thickness accuracy, determining mean and maximum signal-to-noise ratios, ghosting ratios and image intensity uniformity. The relevance, applicability, and performance of each element will be discussed. A brief discussion of suggested, additional elements that would constitute an Acceptance Testing (AT) program for Magnetic Resonance Imaging devices will conclude the presentation. Tasks under consideration will include comparing equipment received with purchase order specifications, checking environmental conditions of the MRI suite, RF room shielding survey, cryogen consumption, magnetic field stability, magnetic fringe field survey, gradient field strength, eddy current evaluation, evaluation of image acquisition and image processing software and optional features. Individual testing procedures and the rationale for their use will be presented and performance evaluation acceptance criteria will be suggested. Upon completion of this presentation, participants will understand how to: • Design Quality Control (QC) Testing and Acceptance Testing (AT) programs for Magnetic Resonance Imaging • Define the role of the Technologist, equipment service personnel and the clinical medical physicist/MR scientist in this programs. • Configure the equipment necessary for MRI QC and AT testing.

Fast analytical modelling for pulsed eddy current evaluation

Numerical simulations of electromagnetic non-destructive evaluation (ENDE) can be time-consuming in comparison to analytical methods which provide fast closed-form solutions to the ENDE problems. In this paper, the Truncated Region Eigenfunction Expansion (TREE) modelling is extended to solve problems of pulsed eddy current (PEC) evaluation from the traditional multifrequency eddy current. The Fourier transform is employed to make the TREE feasible for solutions to PEC problems in both time and frequency domains. Moreover, because PEC employs magnetic field sensors/arrays to quantify magnetic field, the magnetic field signals from solid-state magnetic field sensors have been simulated using the extended TREE. It has been found that the predicted signals using the extended TREE has good agreement with the experimental results. Consequently, the established model can not only offer an effective solution in terms of faster simulation time and higher computational accuracy, but also be used for PEC evaluation in industry and in the inverse process for exploring the structural and electrical information of stratified conductive specimens during real-time monitoring.

Detection of the Cracks using High-Tc SQUID

Eddy current non-distractive evaluation (NDE) is very useful technique for detection of cracks. We use the high-Tc SQUID in this system. First, we respect the result of this measurement by the finite element method. We can detect of the signal from the hole by NDE system with high-Tc SQUID. This result is reasonable to compare with the result of simulation. Finaly, we can detect of the hidden defect under 5mm depth from the sample surface.

Eddy-current evaluation of three-dimensional flaws in flat conductive materialsusing a Bayesian approach

This paper deals with quantitative eddy-current non-destructive evaluation ofvolumetric flaws. The inversion of eddy-current data leads to detection,localization, sizing and shape reconstruction of a flaw. The eddy-current probe isconstituted by a driving coil which is placed at an adapted fixed position and apick-up coil which scans the surface above the flawed region in order to collect thedata. The eddy-current probe response is linked to the local variations of theelectrical conductivity of the inhomogeneous material. A numerical model followsfrom the discretization of the coupled integral equations by using a method ofmoments. To solve the resulting nonlinear inverse problem, an inversionscheme is proposed within a Bayesian estimation framework. Lack ofinformation due to the band-pass behaviour of the forward operator iscompensated by introducing prior knowledge. The advantages of thisapproach result from combining the information contained in the data andthe a priori knowledge on the solution to be estimated. The inversionproblem is transformed into an optimization problem which is dealt withusing a sequence of local minimizations performed via a standard descentalgorithm. In order to illustrate the behaviour and the efficiency of theproposed approach, several reconstructions from simulated data are presented.

Eddy-current evaluation of three-dimensional defects in a metal plate

The retrieval of voluminous defects in a non-magnetic metal plate from maps oftime-harmonic anomalous magnetic fields in air due to a nearby low-frequencysource is considered. The wavefield is modelled from a rigorous full-wave vectordomain integral formulation and the inversion is performed via a binary version ofthe so-called contrast-source, gradient-type technique. The functional analysis isoutlined and the efficiency of the approach is discussed in the light of inversionresults obtained with synthetic data in three typical defect configurations.