Coupling coefficient: a determinant of eddy current probe performance

N DT Abstracts practical selection of coil configurations and excitation parameters as a guide to testing in practical circumstances. The paper will be in two parts covering the eddy current method and the magnetic flux leakage method of non-destructive testing. 45997 Sabbagh, L.D.; Sabbagh, H.A. A computer model of eddy-current probe-crack interaction Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23-28 Jul. 1989. Vol. 9A, pp. 281- 286. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990) A general three-dimensional eddy-current probe model, developed by Sabbegh Associates has been adapted for the calculation of probe-flaw interactions. The theoretical model, uses integral equations with dyadic Greun's function kernels, and is applicable to both probe and flaw calculations at arbitrary skin depths and frequencies. Discrete approximations of the integral equations are solved using a highly efficient algorithm based on recent developments in numerical techniques and their application to the solution of large problems in electromagnetic field-theory. The model was validated internally through self-consistency tests and externally by comparing predictions with experimental data. 45996 Bowler, J.R. Prediction a n d analysis of transient eddy-current probe signals Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23-28 Jul. 1989. Vol. 9A, pp. 287- 293. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990) In principle, transient excitation of eddy-currents would seem to offer great advantages since the probe response contains the equivalent information of a spectrum of frequencies. This paper explores a number of basic transient solutions due to normal air-cored coils and shows how the induced emf in a coil is related to its coupling coefficient. 45986 Jenkins, S~4.; Bowler, J.R. Calculations of the flaw signal generated by a differential eddy, c u r r e n t probe Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23-28 Jul. 1989. Vol. 9A, pp 829- 835. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990) Differential eddy-current probes are attractive because of their insensitivity to tift-off effects. By using two similar coils wound in opposition we have a sensor that detects variations in the magnetic field along a line joining their center. We have developed a three dimensional probe-flaw model to predict eddy-current signals based on a volume integral formulation. Although the benchmark problem examines the probe response due to a surface slot in a finite conducting slab, we have, instead, computed the signals due to a similar flaw in a half- space conductor. We shall highfight an effective method for calculating the differential signal. This aspect of the problem is of particular interest because it has proved to be very difficult to determine this signal using finite element methods. 45985 Hedengren,K~-I.; Ritscher, D.E.; Groshong, B.R. Probe footprint estimation in eddy-current imaging Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23-28 JuL 1989. Vol. 9A, pp 845- 852. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990) As with other imaging systems, the image of an object represents blurring of the structures of the object by the system point spread function (PSF). This paper presents and evaluates three methods of estimating the PSF: (i) directly form a single image of a small hole, (ii) as an image created by analytic modeling of images of a small hole, and (iii) by a frequency domain approach using several images taken of slots of known sizes to create a least-mean-squared PSF. Finally the analytic and the LMS PSF estimates were each used as the kernel for a matched filter designed for defect detection. 45976 Vernon,S.N. Coupling coefficient: a determinant of eddy current probe performance Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 23-28 Jul. 1989. Vol. 9A, pp. 837- 844. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1990) This article examines one of the parameters needed to achieve probe characterization for eddy current nondestructive inspection. Probe

performance is dependent on these parameters, such as the coupling coefficient of the probe. The coupling coefficient, examined here, requires absolute impedance measm~nunts but is independem of the material used. The other three parameters, effective size, frequency range of operation, and unloaded probe impedance are also considered but rejected. (UK) 45451 Berezyuk,B.M.; Khizhnyak, L.V.; Shumkov, Y.M. Computerised analysis of wide.band eddy c u r r e n t transducers V.E. Riecansky, Technical Translations, VR-4473 3pp. (1990) It is shown that it is n ~ ' y and possible to use automated systems of design of radioelectrnnic equipment in developing nondestructive inspection devices. A designed electrical model of an eddy current transducer, a model of the input circuit of the device and their phasefrequency characteristics are discussed. A problem of linearising the scale of the device using a correcting member whose parameters were obtained in the process of parametric synth~is of the frequency characteristics of the model is solved. 45234 Gusak, N.O. Possibility of " t u n i n g out" the gap when inspecting products by means of higher harmonics with a superposed transducer Soviet Journal of Nondestructive Testing, Vol. 25, No. 12, pp. 898-901 (Aug. 1990) A study is made of the possibifity of "tuning out" the gap between a superposed transducer and the product during a nondestructive inspection by the higher-harmonic method. A means of tuning out the gap is described which is based on correcting the exciting current of the superposed transducer during the inspection process. 45229 Usova,Z.A. Using the pulsed method of exciting eddy c u r r e n t transducers for measuring the parameters of components Technical Diagnostics and Nondestructive Testing, Vol. 2, pp. 96-100 (Apr.-Jun. 1990) Component parameters for nonferrnmagnetic materials were inspected using the pulsed method of exciting the eddy cunent transducer (EC13. A circular coil-plate system was selected for the experiment. The complex resistances of the sheet were calculated in order to obtain qualitative results from the behaviour of the system. 45226 Bowler,J.R.; Jenkins, S.A. Validation of three dimensional eddy-current probe-flaw interaction model using analytical results IEEE Transactions on Magnetics, Vol. 26, No. 5, pp. 2085-2088 (Sep. 1990) A volume element calculation has been used to predict the field at the slot in a conductor excited by an eddy current probe. As a part of an on-going program to validate the computer model, we compare predictions of the volume element calculation with analytical results for a test case. In the test problem a constant, uui-dimctional eddy-current distribution is perturbed by a semicircular crack of negligible opening at the surface of a half-space conductor. By taking the low frequency limit, the field at the flaw and the change in probe impedance due to the presence of the flaw, are given explicitly by simple analytical expressions. Numerical results found using the volume element calculation are compared with values found from the analysis. 44915 Karginov, A.4.; Goncharov, B.V. General approximate solution for superposed transducers with windings of arbitrary dimensions Soviet Journal of Nondestructive Testing, Vol. 26, No. 1, pp. 76-81 (Sep. 1990) A general approximate solution is obtained for the problem of a superposed eddy-current transducer with windings of arbitrary dimensions, which is of the same form as the solution for a two-turn transducer. The cross sections of the windings in it are expressed by means of equivalent turns, and the lengths by means of additional "fictitious" gaps. It is shown that for a winding of great length the maximal value of the fictitious gap is approximately equal to the radius of an equivalent turn.

44746 Bowler,J.R.; Sabbagh, L.D.; Sabbagh, H.4. Eddy-current probe impedance due to a surface slot in a conductor IEEE Transactions on Magnetics, Vol. 26, No. 2, pp. 889-892 (Mar. 1990) A computational model has been developed for the simulation of eddycurrent nondestructive testing. The electric field produced by a probe in the absence of the flaw. is determined; then the field induced at the flaw is found. These field calculations are based on volume integral techniques

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