Characterization of Terfenol-D for magnetostrictive transducers

Measurements were made of the piezomagnetic d33 coefficient, the free permeability, ̈33T, and the open-circuit elastic compliance coefficient, s3311, of grain-oriented Terfenol-D, Tb0.3 Dy0.7 Fe1.93, produced by a modified Bridgman technique. Prestress levels to 9500 psi (64 MPa) and magnetic bias fields up to 2200 Oe (175 kA/m) were applied with a laboratory electromagnet modified so that one pole piece served as a hydraulically actuated piston. The results indicate that d33, ̈33T, and s3311 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). Terfenol-D is not superior to PZT under high-Q, stress-limited conditions.