Characterization of Terfenol-D for magnetostrictive transducers

Abstract

Measurements were made of the piezomagnetic d 33 coefficient, the free permeability, μ 33 T , and the open-circuit elastic compliance coefficient, s 33 H , of grain-oriented Terfenol-D, Tb 0.3 Dy 0.7 Fe 1.93 , produced by a modified Bridgman technique. Prestress levels to 9500 psi (65 MPa) and magnetic bias fields up to 2200 Oe (175 kA/m) were applied with a laboratory electromagnetic modified so that one pole piece served as a hydraulically actuated piston. The results indicate that d 33 , μ 33 T , and s 33 H are dependent on stress and magnetic field, so that proper mechanical prestress and magnetic bias conditions are critical to the successful use of Terfenol-D in transducers and actuators. Radiated-power limits for underwater acoustic projectors are estimated and compared with those for projectors having lead zirconate titanate(PZT-4)piezoelectric drivers. Terfenol-D based transducers can be as much as 8 dB superior to PZT-4 under low-Q, field-limited conditions (Q=mechanical quality factor).