Author
B. A. Auld
Bio: B. A. Auld is an academic researcher from Stanford University. The author has contributed to research in topics: Eddy current & Eddy-current testing. The author has an hindex of 4, co-authored 5 publications receiving 416 citations.
Papers
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TL;DR: A comprehensive review of advancements in eddy current (EC) modeling is presented in this article, which contains three main sections: a general treatise of EC theory, the thin skin EC forward modeling, and the EC inverse problem.
Abstract: 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.
313 citations
TL;DR: In this paper, a general theory of eddy current flaw response, appropriate to both standard low frequency and ferromagnetic resonance (FMR) probes, was developed for simple two-dimensional and three-dimensional open and closed surface flaw geometries.
Abstract: A general theory of eddy current flaw response, appropriate to both standard low frequency and ferromagnetic resonance (FMR) probes, is developed for simple two-dimensional and three-dimensional open and closed surface flaw geometries. This analysis, based on the assumption of a uniform interrogating field applied to the flaw by the probe, shows that flaw opening responses increase with the operating frequency of the probe. Experimental results using both types of probe confirm this result for realistic practical geometries, where variations of crack mouth opening displacement under load provide useful information about crack dimensions.
66 citations
TL;DR: In this article, a scalar potential formulation of the δZ formula for the change in impedance of an eddy-current probe caused by a surface-breaking flaw is developed.
Abstract: A scalar potential formulation of the δZ formula for the change in impedance of an eddy-current probe caused by a surface-breaking flaw is developed. The resulting formula is evaluated using a finite-difference method, which permits calculation of δZ for semielliptical flaws. The numerical results are checked by comparing calculations for rectangular-shaped flaws to previous calculations using an analytical solution for this geometry. Theoretical results are then verified by comparison with measurements on semielliptical fatigue cracks and EDM notches in aluminum alloy specimens using air-core eddy-current probes. An inversion method that compares features of the flaw profile, obtained by scanning the eddy-current probe along the length of the flaw, to a theoretical inversion chart (McFetridge chart) is demonstrated using the experimental data.
49 citations
TL;DR: In this article, a model for the interaction between an eddy-current probe system and a localized flaw in a test piece is presented in terms of the electromagnetic fields generated by the probe in the absence of the flaw, which are evaluated on an imaging surface near or on the surface of the test piece.
Abstract: In this paper, a model is presented for the interaction between an eddy-current probe system and a localized flaw in a test piece. The model is expressed in terms of the electromagnetic fields generated by the probe in the absence of the flaw, which are evaluated on an imaging surface near or on the surface of the test piece. Assuming that the quasistatic fields scattered by the flaw are proportional to immittance coefficients that are independent of the probe position, explicit expressions for the point-spread functions of the probe are derived. Knowledge of these functions permits one to optimize probe design and identify appropriate image-processing techniques. In contrast with optical image processing, it is shown that more than one point-spread function may be required to characterize a flaw image produced by an eddy-current probe.
12 citations
01 Jan 1981
TL;DR: An electromagnetic NDE technique for measuring the crack ooening displacement of surface fatigue cracks is described in this article, where a ferromagnetic resonance probe utilizing yttrium-iron-garnet was used to induce eddy currents in an aluminum plate.
Abstract: An electromagnetic NDE technique for measuring the crack ooening displacement of surface fatigue cracks is described A ferromagnetic resonance probe utilizing yttrium-iron-garnet was used to induce eddy currents in an aluminum plate The crack opening disolacement of a semi-elliptical fatigue crack evaluated at the surface was measured optically at several values of bending stress on the specimen A technique is presented which allows the crack depth to be calculated from the measured COD at a given stress The relative phase and magnitude of input vs output signal to and from the resonating YIG sphere was recorded during the interaction of the FMR probe eddy currents and the fatigue crack A method is shown to extract quantitative information from these signals and to correlate this information with the crack opening displacement
2 citations
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TL;DR: In this paper, a robust method that uses eddy current measurements to determine the conductivity and thickness of uniform conductive layers is described, and the method is tested by estimating the conductivities of aluminum and copper layers on various substrate metals and the thickness and conductivity of free standing foils of aluminum.
Abstract: A robust method that uses eddy current measurements to determine the conductivity and thickness of uniform conductive layers is described. The method was tested by estimating the conductivity and thickness of aluminum and copper layers on various substrate metals, and the thickness and conductivity of free‐standing foils of aluminum. The electrical impedance was measured for air‐core and ferrite‐core coils in the presence and absence of the layer for frequencies ranging from 1 kHz to 1 MHz. The thickness and conductivity of the metal layers were inferred by comparing the data taken with air‐core coils to the exact theoretical solution of Dodd and Deeds [J. Appl. Phys. 39, 2829 (1968)] using a least‐squares norm. The inferences were absolute in the sense that no calibration was used. We report experimental tests for eight different thicknesses of aluminum (20–500 μm) in free space and on four different substrates: Ti‐6Al‐4V, 304 stainless steel, copper, and 7075 aluminum, and for five different thicknesses...
201 citations
TL;DR: In this paper, the C-rate dependence of lithium metal plating during low-temperature charging at −20°C is investigated, and it is possible to quantify the amount of ‘dead lithium' and observe the chemical reintercalation of plated lithium metal.
146 citations
TL;DR: In this paper, the Dodd and Deeds models were reformulated for eddy current nondestructive evaluation and series expansions for the electromagnetic field and the impedance of the current coil were used.
114 citations
TL;DR: In this article, closed-form expressions for the impedance of rectangular coils of rectangular cross-section located above a conducting half-space and for the eddy current density induced therein were provided.
Abstract: As for any other eddy current probe coil, the analysis of rectangular ones plays a vital role towards understanding their characteristics and performance. In this paper, closed-form expressions are provided both for the impedance of rectangular coils of rectangular cross-section located above a conducting half-space and for the eddy current density induced therein. The formulation is general and can be easily used for any coil shape.
110 citations
TL;DR: This work develops a unified framework for explaining, analyzing, and extending signal processing methods based on GMANOVA and shows the applicability of this framework to a number of detection and estimation problems in signal processing and communications and provides new and simple ways to derive numerous existing algorithms.
Abstract: Generalized multivariate analysis of variance (GMANOVA) and related reduced-rank regression are general statistical models that comprise versions of regression, canonical correlation, and profile analyses as well as analysis of variance (ANOVA) and covariance in univariate and multivariate settings. It is a powerful and, yet, not very well-known tool. We develop a unified framework for explaining, analyzing, and extending signal processing methods based on GMANOVA. We show the applicability of this framework to a number of detection and estimation problems in signal processing and communications and provide new and simple ways to derive numerous existing algorithms. Many of the methods were originally derived "from scratch", without knowledge of their close relationship with the GMANOVA model. We explicitly show this relationship and present new insights and guidelines for generalizing these methods. Our results could inspire applications of the general framework of GMANOVA to new problems in signal processing. We present such an application to flaw detection in nondestructive evaluation (NDE) of materials. A promising area for future growth is image processing.
100 citations