Uniform Induced Electromagnetic Features around Longitudinal and Transverse Cracks

Uniform alternating electromagnetic field will be induced in specimen with alternating current excitation. The distribution of induced field will be perturbed by the existence of crack. To study the perturbation feature caused by crack, the specimen containing longitudinal and transverse cracks are detected in the experiment in this paper. The experiment indicates that the longitudinal and transverse cracks can be both detected out in one scan. Furthermore, the simulation of steel and aluminum with longitudinal and transverse cracks are carried out to explain the phenomenon. The result in simulation indicates that while longitudinal and transverse cracks exist in the surface of specimens, the induced alternating magnetic field around the crack would leak out of the specimen, meanwhile, the induced alternating current field around the crack would be disturbed and generated perturbation magnetic field. The magnetic field signal picked above the crack included the leakage magnetic field signal and perturbation magnetic field signal.