The remote field eddy current (RFEC) technique[1], [2] is widely used as a nondestructive evaluation tool for inspecting metallic pipes and tubing. Essentially, the RFEC phenomenon can be observed when an AC coil is excited inside a conducting tube (see Fig. 1). The RFEC signal can be sensed by a pick-up coil located 2–3 diameters away from the excitation coil. The signal is closely related to the tube wall condition, thickness, permeability, and conductivity. Particularly the signal phase is approximately linearly related to the tube wall thickness.
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