Study on the transformer equivalent circuit of eddy current nondestructive evaluation

Abstract

The modeling of a practical configuration of nondestructive evaluation (NDE) by eddy currents (EC) generally requires extended analytical or numerical developments. This is a drawback to any understanding of the EC NDE principle and of its basic features. Nevertheless, it is possible to exploit a simple equivalent circuit based on an analogy with the operation of an electrical transformer. In this model the EC sensor constitutes the primary of the transformer whereas the evaluated conductive plate forms the transformer secondary and its electrical load. In this paper, thanks to the transformer analogy, the author obtains a simple analytical expression of the impedance of the EC sensor by using a distributed constant representation of the evaluated plate. This expression allows to exhibit some fundamental features of the EC NDE method.