Eddy current distribution in conductive plate normalized by standard penetration depth

摘要

Knowledge of the eddy current distribution in a test material is important because it determines the sensitivity level of the testing. However, since there is significant variation in this distribution due to factors such as test frequency,material electromagnetic characteristics, and coil configurations, it is very difficult to estimate the distribution induced by the probe for a certain test condition. Thus the authors propose a new method normalizing all the distance parameters by thestandard penetration depth in order to derive the eddy current distribution by predicting its change from various parameters. In electromagnetic analysis the normalization makes the governing equation quite simple, eliminating various parameters andproviding a predictable solution.The numerical calculations of the analytical solution and the finite element analysis under the new normalization method have provided the following results. Tangential coils induce a much deeper eddy current than the conventional pancake probe,especially when the test material thickness is nearly equal to the standard penetration depth of the current. Thus tangential coils can detect far side surface flaws in the material with higher sensitivity than pancake coil probes.