End effect modelling in eddy current tube testing with bobbin coils

摘要

A semi-analytical method for modelling electromagnetic fields is applied to eddy current nondestructive evaluation (NDE) to simulate the end effect in tube testing with bobbin coils. The boundary value problem is formulated in terms of the magnetic vector potential and is solved using orthogonal eigenfunctions, the eigenvalues of which are computed as roots of a transcendent complex equation. Closed-form expressions are derived for the impedance change of the coil and the induced eddy currents. The results are in excellent agreement with those obtained by a 2D-finite element package.