Electromagnetic Testing - Eddy Current Testing Applications Chapter 5 & 6

A typical curve correlating flaw depth and phase angle is shown in FIG. 5.39.
That is, higher frequency provides greater phase separation than the other
frequencies shown. Analysis shows that the accuracy of flaw depth estimation
by correlating flaw depth and phase angle increases with increasing frequency.
The optimum frequency for evaluating flaw depth by relating it to signal phase
angle has been found to be approximately 2f 90 , and this frequency is
recommended for defect evaluation. (The optimum evaluating frequency, based
on a 90° separation between the through hole and a flaw at 50% of the wall
thickness at the outside surface, is 2.2f 90 ).
Charlie Chong/ Fion Zhang