Abstract: The modes of guided wave propagation in the circular pipes are analyzed. The model of magnetostrictive force-gen- erated longitudinal guided waves in circular pipes is discussed. The longitudinal guided waves are generated by applica- tion of magnetostrictive force parallel to the axial direction of circular pipes, and the magnetostrictive force not only relates with the characteristics of detected materials, but also depends mainly on the coupling between the set static bias magnetic field and AC (alterative current) magnetic field. The magneto- strictive sensor generation of longitudinal guided waves in circular pipes is designed in accordance to the developed model, and the longitudinal guided waves are acquired in the experiment. The experimental investigation, static bias magnetic field and AC magnetic field-dependence of generation of longitudinal guided waves by the magnetostrictive sensor applying different static bias magnetic field and AC magnetic field to the circular pipes, are carried out, respectively. The results show that there is a similar paracurve relation between static bias magnetic field applied to the circular pipes and the amplitude of longitudinal guided waves, which means the amplitude of longitudinal guided waves increases initially with increasing static bias magnetic field level, and reaches a maximum, and then decreases with further increase in the static bias magnetic field level. When guided waves propagating along the circular pipes, there is a non-linear relation between AC magnetic field applied to the circular pipes and the amplitude of longitudinal guided waves due to guided waves multi-modes and disperse characteristics.

Key words: Circular pipes, Guided wave, Magnetostrictive effect, Non-destructive testing