Design of unidirectional torsional guided wave magnetostrictive patch transducer with a single linear coil

Magnetostrictive patch transducers capable of exciting unidirectional ultrasonic guided waves are usually dual-channel structures. Meanwhile, dual-channel excitation devices are required. This results in high development costs and significant technical challenges for guided wave detection systems. To address these issues, this paper proposes a torsional guided wave direction control method employing a single-channel magnetostrictive patch transducer (MPT). This approach utilises the reflection phenomenon of guided waves at the patch edge. By adjusting the relative position between the coil and the patch, the guided wave signal excited by the coil interferes destructively with the guided wave signal reflected from the patch edge, thereby confining wave propagation to a single direction. This paper first analyses the spatial distribution pattern of magnetostrictive stress in MPTs employing linear coils. Subsequently, numerical simulations investigate the reflection behaviour of guided waves at the edges of magnetostrictive patches. Building upon this, a single-channel MPT guided wave direction control method is proposed, exploiting the reflection phenomenon at the patch edges. Experiments demonstrate that the designed transducer can excite unidirectional torsional guided waves. In addition, this paper also studies the improvement of transducer signal-to-noise ratio, and experiments show that the guided wave signal-to-noise ratio is improved by about 70%.