Eddy current testing for small depth flaw

This paper presents an analytic method for the magnetic field distributions and the impedance change in eddy current testing when the conductor surface contains a small depth flaw. Neglecting the effect of the flaw flank on the perturbation field and by using of the Taylor series, the perturbation problem can be translated into incidence field problem. Formulas are educed for the calculation of the perturbation field and impedance change. At last, square, round and rhombic flaw have been computed, their impedance change are plotted for comparison.