Magnetostrictive 1-3 Composites With Internal Field Biasing

Abstract

1-3 composites comprising an array of square Terfenol-D rods continuous in the direction of actuation and separated by an epoxy matrix have been produced. The benefits of a Terfenol-D 1-3 composite over bulk Terfenol-D and powder composites has been investigated. A higher frequency capability is realized while maintaining a greater coupling coefficient, k/sub 33/, to that of powder composites. 1-3 composites were produced containing between 40% and 70% volume fraction of Terfenol-D. Magnetic biasing was achieved using Nd/sub 2/Fe/sub 14/B powder located within the epoxy matrix at 40% volume fraction. Internal bias fields of 75 and 45 kA/m were measured for the 1-3 composites containing 40% and 70% Terfenol-D, respectively. A coupling coefficient of 0.53 was measured for the composites filled with epoxy alone while the coupling coefficient varied from 0.33 to 0.48 for the biased composites with between 40% and 70% volume fraction of Terfenol-D, respectively. The acoustic impedance was determined using the radial resonance and observed to decrease with decreasing Terfenol-D volume fraction. A 50% volume fraction Terfenol-D 1-3 composite containing microspheres within the epoxy had the lowest measured acoustic impedance of 6.8 Mrayl, making this composite the most suitable for coupling acoustic energy into tissue/water for ultrasound/SONAR applications.