Eddy current detection of crack orientation using elliptical excitation

The use of an elliptical excitation for eddy current detection of crack orientation is investigated. It is shown how the impedance change Delta Z varies as the excitation is rotated above a line crack and how this variation can serve in the detection of the orientation. Numerical results are given for the case of through-thickness line cracks in thin conducting plates. Following the approach of the representation of cracks as a distribution of current sources, attention is concentrated in the evaluation of the field quantities produced by the elliptical excitation in the case of the uncracked thin plate system. The Fourier transformation method is used to treat the differential equations and the fast Fourier transform (FFT) algorithm to perform the calculations.<>