Investigation of signal features of pulsed eddy current testing technique by experiments

As a new non-destructive testing (NDT) technology, pulsed eddy current (PEC) is attracting increasing interest from researchers. In order to understand PEC more deeply and systematically, this paper investigates the signal features of PEC by means of a series of experiments that take into account different specifications. Firstly, a PEC experimental testing platform was set up. Then, based on the experimental platform, the detected signals under the sample with or without defects were acquired and analysed, whilst taking into account different excitation frequencies, different duty cycles of the excitation signal and different lift-offs. The experimental results indicate that: (1) the presented PEC experimental testing platform can characterise the defect effectively. It illustrated that the PEC experimental platform set up in this paper can be used in quantitative evaluation of the defect in a sample; (2) the excitation frequency and duty cycle of the excitation signal influence the detected signals and the higher the excitation frequency of the coil, the lower the value of the detected signal, and the closer the duty cycle is to 50%, the stronger the value is. In addition, the response obtained by the coil is equal to the differential signal obtained by the Hall sensor. It can be referred to in choosing the duty cycle of the excitation signal and ways to measure the magnetic field; (3) lift-off has an important effect on the detected signal, especially when the lift-off is very small. This means the measurement noise due to the lift-off variation will be stronger when the probe is close to the sample. Therefore, it is urgent to present a way to remove or decrease the influence of the measurement noise due to the lift-off variation on the measurement accuracy of PEC.