CHARACTERIZATION OF TERFENOL-D FOR MAGNETOSTRICTIVE TRANSDUCERS

Measurements were made of the piezomagnetic d33 coefficient, the free permeability, mu-33T, and the open-circuit elastic compliance coefficient, S33H, of grain-oriented Terfenol-D, Tb0.3 Dy0.7 Fe1.93, 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 electromagnet modified so that one pole piece served as a hydraulically actuated piston. The results indicate that d33, mu-33T, and S33H 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).