Defect identification and classification of multi-frequency eddy current test based on spectrum method

Multi-frequency eddy current test (MFECT) is an important NDT technology, and it can be applied to realize multi-parameter detection and interference elimination effectively. Aiming at the problem that conventional single-frequency eddy current test can only identify defects but can´t classify defects effectively, a new MFECT technology which adopts LFM signal exciting and spectrum analysis method was proposed. The probe-coil in an ac bridge was excited by a LFM signal, and output signals of the ac bridge were amplified and sampled to detect defect´s property by spectrum method. These defects could be detected according to spectrum total energy variation. With the purpose of defect classification, a new feature, termed as spectrum barycenter excursion was proposed. Compared with traditional MFECT, it has the merits of small peak factor and low system cost. The agreement between theory and experiment shows that the present method is correct.