A 64 kHz Langevin sandwich transducer fabricated using giant magnetostrictive composites

Abstract

Rare-earth-iron alloy Terfenol-D (Tb/sub 0.30/Dy/sub 0.70/Fe/sub 1.92/) is one of the finest magnetostrictive materials to date because of its giant magnetostrictive strain (/spl sim/1200 ppm) and strain energy density (/spl sim/20 kJ/m/sup 3/) with an expeditious response (/spl sim/1 /spl mu/s) at both room temperature and low fields (<150 kA/m). However, the use of monolithic Terfenol-D in ultrasonic devices is not yet successful due to the presence of eddy current losses that increase rapidly with frequency. Magnetostrictive composites, consisting of one-dimensionally aligned Terfenol-D particles embedded in a three-dimensionally connected passive polymer matrix, are not subject to this problem due to increased electrical resistivity. Additional benefits of using these composites are their mechanical durability, tailorable properties, and cost-effectiveness. While the dynamic magnetomechanical properties of the composites have just been realized, the application of the materials to ultrasonic devices is still very limited. In order to transplant the magnetostrictive composite materials technology to practical ultrasonic devices, we have aimed in the present study to develop a 64 kHz Langevin sandwich transducer based on a tube-shaped Terfenol-D/epoxy magnetostrictive composite with a Terfenol-D volume fraction of 0.45.