Characterization of a small Terfenol-D transducer in mechanically blocked configuration

In numerous applications, smart material transducers are employed to actuate upon virtually immovable structures, that is, structures whose stiffness approaches infinity in comparison with that of the transducer itself. Such mechanically blocked transducer configurations can be found in applications ranging from seismic testing and isolation of civil structures, to clamping mechanisms in linear or rotational inchworm motors. In addition to providing high blocking forces, smart materials for this type of applications must often be small in size and lightweight in order for design constraints to be met. This paper provides a characterization of the force produced by a 0.9 cm (0.35 in) diameter, 2.0 cm (0.79 in) long Terfenol-D operated under mechanically blocked conditions. Experimental results are shown for several mechanical preloads as well as various magnetic field intensities, waveforms, and frequencies. Optimal levels are deduced and discussed and the results are compared to published data for a PZT transducer of similar size operated in mechanically blocked configuration The comparison reveals that the Terfenol-D rod provides higher blocking forces than its PZT counterpart. It is thus feasible to employ small magnetostrictive drivers in applications involving zero or near-zero displacement, particularly those based on hybrid magnetostrictive/piezoelectric designs in which high efficiencies are achieved by driving the two electrically complementary transducer materials at electrical resonance.