Magnetic NDE using spectrum analysis of changes in induced voltage at pickup coil and magnetic flux density

Magnetic nondestructive evaluation (NDE) for ferromagnetic steel using spectrum analysis of induced voltage at a pickup coil and magnetic flux density has been studied. A voltage induced at the pickup coil was measured, and the corresponding magnetic flux density was calculated. Then, their frequency spectrums were obtained through a Fourier analysis. For deformed specimen, higher harmonic components decrease as compared with undeformed specimen. The wave distortion factor for the induced voltage and the magnetic flux density were defined and evaluated. Those values decrease with increasing reduction ratio of the specimen; this means the waveforms of induced voltage and magnetic flux density for a less deformed specimen has a large distortion in those waves. Those changes reflect a nonlinearity of the magnetization curves of the specimen. The results in this study indicate a potential of magnetic NDE using spectrum analysis of measurement wave forms.