Torsional wave transduction using obliquely-bonded magnetostrictive nickel strips in cylinders

Abstract

Magnetostrictive transducers become more widely used for guided-wave based non-destructive evaluation. In comparison with more popular piezoelectric transducers, they are cost-effective and capable of generating high-power without direct wiring. As an effort to advance the magnetostrictive transducer technology, a recent study has reported that torsional elastic waves can be generated and measured quite efficiently if a set of thin nickel strips is bonded at 45 degrees to the cylinder axis. However, the orientation giving the largest torsional wave signal for a given solenoid coil current, and the reason for it, remain to be determined. The objective of this work is to investigate the transduction efficiency depending on the angle of strip bonding relative to the cylinder axis and to explain the observed phenomena. Several sets of experiments were conducted with various orientation angles of the nickel strip in an aluminum pipe. Excitation frequencies used were between 40 kHz and 100 kHz because the highest transduction was observed for the used nickel strips.