Low Frequency domain analysis of alternating magnetic flux leakage method

Alternating Magnetic Flux Leakage method was used to investigate the relation between the leaked magnetic field and crack dimension by changing the frequency of the magnetic field induced in the specimen. In this way, the alternating magnetic field with frequency in range of 1-100 Hz was induced into a defective ferromagnetic steel plate and the magnetic field over the surface was measured. Then, two sensors in differential modes were used to extract the effect of frequency on the relative Magnetic Flux Leakage signal. The results indicated that the frequency of minimum of the relative Magnetic Flux Leakage increases linearly by increasing the crack depth. The experimental results were verified by numerical finite element simulation method.