Design of a magnetostrictive sensor for structural health monitoring of non-ferromagnetic plates

In this work, a magnetostrictive sensor (MsS) is designed and tested for monitoring damage in a non-ferromagnetic plate. Firstly, the mechanism of the MsS to generate and detect guided shear horizontal (SH) waves in a non-ferromagnetic plate is described. Both theoretical and experimental studies are conducted in order to prove that the sensor can generate the first non-dispersive shear horizontal wave mode (SH0) suitable for monitoring of the structural health. The sensor encompasses a nickel strip, a pair of permanent magnets, C-shaped cores wound by a figure-of-eight coil. The incident wave emitted from the MsS propagates in the plate and is reflected from the plate boundaries. Since the time of the arrival can be determined from the reflected wave signal through signal processing, the velocity of the wave can be extracted. Comparing the calculated velocity with the velocity predicted by the theory, the mode of the wave can be identified with a priori knowledge of plate velocity. To demonstrate the effectiveness of the proposed sensor for structural health monitoring, the location of the damage in an aluminum plate is examined. Finally, optimum design of the sensor is determined using ANSYS program yielding improved sensor performance. The effectiveness of the optimized magnetostrictive sensor is confirmed by experimental results.