Torsional mode magnetostrictive patch transducer array employing a modified planar solenoid array coil for pipe inspection

Abstract

In recent investigations, the application of the transducers used in plates has been extended to pipe inspection with circumferential arrays because of the similar particle displacement patterns of some modes between plate and pipe, such as SH and torsional modes. Motivated by the configuration of magnetostrictive patch transducer (MPT), in which a planar solenoid array (PSA) coil was adopted to generate SH waves in plates, we proposed a MPTs array employing a modified planar solenoid array (MPSA) coil, i.e. MPSA coil-MPTs array, for generating and receiving the torsional mode in pipes. The configuration of the MPSA coil modified from PSA coil is suitable to be arranged on the pipe surface and can generate high-power waves. In the suggested configuration of MPT, because the direction of the actuating dynamic magnetic field produced by the MPSA coil is orthogonal to the direction of the static magnetic field produced by the permanent magnets in the magnetostrictive patch, the shear deformation induced by the magnetostriction in the patch will be delivered to the pipe, thus generating the torsional mode. First, it was experimentally verified that the fundamental torsional mode, T(0,1), could be effectively generated and received in pipes with the developed MPSA coil-MPTs array. Then, we studied the relationship between the frequency response characteristic of the developed MPSA coil-MPTs array and the interval defined by the distance of adjacent solenoids in the MPSA coil. Simultaneously, the circumferential crack defects in pipe were successfully identified. Finally, the performance of the MPSA coil-MPTs array was compared with that of previous meander coil-MPTs array. The comparison results demonstrated that the developed MPSA coil-MPTs array could enhance the power of the torsional mode.