Eddy current distribution using parameters normalized by standard penetration depth

The authors propose a neu method of representing eddy current distributions using parameters normalized by the standard penetration depth. The normalization makes the distributions general and simple. The distributions derived show that: Eddy current decoys less toward the back surface of the material. Circular pancake coils do not induce eddy current deep in the test material (even if the test frequency is reduced) because the eddy current cancels itself. Tangential coils induce eddy current much deeper in the material than circular pancake coils, especially when the material thickness is comparable to the standard penetration depth. Tangential exciting coils are expected to make sensitive probes for detecting back surface anomalies in the test material.