Audio Range Dynamic Models and Controllability of Linear Motion Terfenol Actuators

Fourth and sixth order models for the audio range response of a dynamically continuous, linear motion magnetostric tive terfenol actuator are formulated from physical considerations and presented. Values of model parameters are derived from mate rial values (if the values are a priori known) or measured. The actuator involves a continuous rod of terfenol that extends and con tracts, vibrates in modes, and contains internal physical feedback loops due to inverse magnetostrictive effect and back emf. Motions of the right end of the magnetostrictive rod with respect to the left end are described in terms of lumped dynamic models. Methods for extracting a priori unknown dynamic parameters in the pres ence of the internal physical feedback are outlined. For audio range operation, theory and experiment compare well. It is also shown that interactions between the first and second vibration modes of the continuous rod give rise to nonminimum phase zeroes in the sixth order transfer function, which under conditions of feedback could contribute to instability and/or make active vibration control difficult over an extended bandwidth.