Development of a Z-shaped patch-type magnetostrictive transducer for efficient transduction of torsional waves

The guided-wave technology becomes a powerful tool for the nondestructive inspection of cylindrical waveguides. Various wave modes such as longitudinal, torsional, and flexural modes can be used for waveguide inspection, but the nondispersive first branch of the torsional wave mode is the most attractive. So we have recently developed a torsional wave generation/measurement method using slender rectangular nickel patches that are bonded 45 degrees to the pipe/tube axial direction. This transducer is that it does not require circumferential pre-magnetization of the nickel patch before actual experimentation; the premagnetization was necessary in existing transducers, and it hinders the magnetostrictive transducer to be used for long-term on-line monitoring. Regardless of its advantages, however, the sensitivity and the signal-to-noise ratio leave room for further improvement. So, we propose a new transducer which uses specially-designed Z-shaped nickel patch instead of the rectangular patch in order to improve the transducer performance. The motivation for the development of a Z-shaped patch-type magnetostrictive transducer is to avoid the cumbersome circumferential pre-magnetization of the ferromagnetic patch and to increase the transduction efficiency of the torsional waves. Several sets of experiments were conducted to verify the transduction efficiency improvement of the proposed transducer. Excitation frequencies used were between 40 kHz and 150 kHz because the highest transduction was observed for the used nickel patches