Magnetostrictive pulse-echo device for non-destructive evaluation of cylindrical steel materials using longitudinal guided waves

A magnetostrictive device for the low-frequency (< 500 kHz) ultrasonic testing of elongated ferromagnetic structures is presented. The device consists of two transducers, one transmitter and one detector, and operates in pulse-echo mode. The axisymmetric geometrical arrangement of the device is designed for the generation and detection of longitudinal mechanical waves. From experimental observations, the non-linear behaviour of the magnetostrictive transduction versus the polarizing current intensity and amplitude of the driving current is illustrated for different material samples. Concurrently, according to the non-contact nature of the magnetostrictive transducers, the device is used for the study of guided wave propagation in structures. Hence, operating on the experimental data set with a signal processing technique, good agreement of predicted and experimental group velocities of multimodal longitudinal waves in axisymmetric cylindrical structure is achieved. Finally, a pulse-compression technique is applied to defect detection. (C) 2002 Elsevier Science B.V. All rights reserved.