Research on the lift-off effect of generating longitudinal guided waves in pipes based on magnetostrictive effect

Non-contact and large lift-off are the advantages of the magnetostrictive guided waves. The lift-off of the excitation coil has direct effect on the generating waves and the receiving signals, because it reduces the alternating magnetic field strength on the pipe surface. The lift-off effect of generating longitudinal mode guided waves in pipes based on magnetostrictive effect is investigated in this paper. The formulation model of generating longitudinal guided waves in pipes based on magnetostrictive effect is obtained from the magnetostrictive theory and the electromagnetic theory. The relation between the alternating magnetic field strength and the lift-off distances of the excitation coil is obtained. And the model is verified by experiment. The results indicate that the detection sensitivity will be decreased with the excitation coil lift-off distance increasing. Furthermore, the model provides the theoretical basis to compensate the lift-off effect of the excitation coil.

► We obtain the formulation model of generating longitudinal guided waves in pipes based on magnetostrictive effect.
► We obtain the lift-off effect of the transmitter.
► We verify the model by experiment.
► The model could be applied to compensate the lift-off effect of the transmitter.