Abstract: To improve detectability of pulsed eddy current testing (PECT) for surface/subsurface defects by obtaining more information, a novel PEC probe, which consists of a rectangular driver coil and three orthorhombic pickup coils for sensing three-dimensional magnetic field components, is designed. A calculation model for three-dimensional transient eddy-current problem is built by using finite element method (FEM). When a rectangular coil is tangentially placed above the conducting plate, the effect of change of coil dimension on the flow pattern of induced eddy-current inside the plate is investigated. When the ratio of coil length, width and height is 1:0.625:0.625, eddy-current distribution has characteristics as follows: the induced eddy-current flows uniformly toward the same direction and its density is approximately equal in the plate region beneath the coil. Such approximately uniform field distribution is highly sensitive to the shape and dimension of a defect, and it is quite helpful to the realization of independent measurement of three-dimensional magnetic field components. As a result, the traditional one-dimensional measurement mode in the pulsed eddy current technology can be extended to three-dimensional testing, thus effectively increasing useful information. The numerical and experimental results show that defect dimensions can be evaluated quantitatively by analyzing three-dimensional transient signals. Both are in good agreements. Consequently, the high performance of the novel PEC probe is validated.

Key words: Finite element method, Pulsed eddy current testing, Quantitative evaluation, Three-dimensional magnetic field measurement, Uniform induced field