Analysis of internal wave reflection within a magnetostrictive patch transducer for high-frequency guided torsional...

Recently, megahertz-range torsional waves have been successfully generated and measured by a magnetostrictive patch transducer employing a meander coil. But the waveform of a high-frequency torsional wave generated by magnetostrictive patch transducers becomes greatly distorted with multiple trailing pulses. The hypothesis explaining the cause of the waveform distortion is that the distortion results mainly from the internal wave reflection within the magnetostrictive patch, which is in turn caused by the impedance mismatch between the bare and patch-bonded parts of the pipe. Based on the hypothesis, we developed an analytic model for internal reflection simulation and conducted several experiments using a patch transducer to verify the hypothesis. The comparison of the analytical and experimental results showed that the internal reflection at the edge of the patch was responsible for the distortion of the measured waveform. The present study also confirmed that the standard acoustic impedance matching to avoid sudden discontinuities at the patch edges can effectively reduce the internal reflection and alleviate the waveform distortion problem.