Description:
Terfenol D, an alloy of iron, terbium, and dysprosium, is a highly magnetostrictive material that can provide significantly more power than lead zirconate titanate (PZT) under field-limited conditions. Field-limiting at resonance, however, requires a mechanical quality factor Qm, less than unity for terfenol D and less than four for PZT. Transducers that are a small fraction of one wavelength in size will have to be elements of a large array in order to achieve the requisite low Qm's. If the Qm is too high, the transducer will be stress-limited, rather than field-limited, and the use of terfenol D is not particularly advantageous. [Work supported by NUSC's IR/IED program and by ONT.]