Research on spectral response of pulsed eddy current and NDE applications

Using pulsed excitation, pulsed eddy current (PEC) technique generates responses over a wide range of frequencies, containing more information than traditional eddy current inspection in the frequency domain. This paper investigates the spectral response of PEC under varying probe lift-off, material properties (electrical conductivity and magnetic permeability) and directional tensile stress. It is shown that material properties and lift-off exhibit different spectra patterns. Using normalisation in frequency domain, the lift-off effect can be reduced. Spectra for both electrical conductivity and magnetic permeability show a complex pattern. Tensile stress measurement in aluminium 2024 and 5083 is investigated, which show similar spectra pattern to electrical conductivity variation. Applications for corrosion characterisation, displacement measurement and profile inspection can be developed in the future in conjunction with time-domain features.

► The spectral response of PEC under lift-offs, conductivity, permeability and directional stress are investigated.
► The effect due to lift-off is linear and double normalisation in time and frequency domain can remove lift-off effects.
► Using normalisation, the changes on the magnitude pattern by electrical conductivity cannot be eliminated.
► Magnetic permeability affects the the spectral magnitude pattern like electrical conductivity but in a more complex manner.