Noncontact Magnetostrictive Torsional Guided Wave Sensors for Small-Diameter Pipes

The magnetostrictive torsional wave sensors are focused on magnetostrictive patch transducer. These transducers use a material with a high magnetostrictive coefficient on the pipe surface to increase the excitation efficiency for detection. However, this approach loses the noncontact characteristic of the magnetostrictive guided waves. To enable noncontact detection in small-diameter pipes using torsional waves, a magnetostrictive torsional wave sensor with a tile-shaped magnet is designed in this article. By optimizing the structure of the static magnetic field, the circumferential magnetic field of the pipe is enhanced. The amplitude and the signal-to-noise ratio of the guided waves are also improved. The tile-shaped magnet with shoving magnetic structure is used to realize a uniform circumferential magnetic field. A solenoid coil is used to provide the axial dynamic magnetic field to generate the torsional waves that are used to detect the pipes. In this article, the principles of torsional wave sensors are studied first. The static magnetic field results for different structures are then analyzed via simulations. Finally, experiments show that the magnetostrictive torsional wave sensors with the tile-shaped magnets can realize the excitation and detection of torsional waves in pipes, which can be used to detect the locations and sizes of defects in these pipes.