Parameters analysis and application of the differential excitation detection technology

A differential excitation probe based on eddy current testing technology was designed. Sheet specimens of Q235 steel with prefabricated micro-cracks of different widths and of aluminum with prefabricated micro-cracks of different depths were detected through the designed detection system. The characteristics of micro-cracks can be clearly showed after signals processing through the short-time Fourier transform (STFT). By changing the parameter and its value in detecting process, the factors including the excitation frequency and amplitude, the lift-off effect and the scanning direction were discussed, respectively. The results showed that the differential excitation probe was insensitive to dimension and surface state of the tested specimen, while it had a high degree of recognition for micro-crack detection. Therefore, when the differential excitation detection technology was used for inspecting micro-crack of turbine blade in aero-engine, and smoothed pseudo Wigner-Ville distribution was used for signal processing, micro-cracks of 0.3 mm depth and 0.1 mm width could be identified. The experimental results might be useful for further research on engineering test of turbine blades of aero-engine.