Given its quantum mechanical origin, magnetostriction itself is atomically fast. This ultimate speed is affected by the practical requirement to package it into a useful solid rod of terfenol-d.

The rod converts an input magnetic field into a mechanical output. The time rate of change of that mechanical output, its speed, requires a time rate of change of the magnetic field. This in turn depends on the time rate of change of current through the actuator coil.

• The maximum time rate of change of voltage to effect a change in current is determined by the materials and construction of the solenoid coil and by power supply capabilities.
  
  
  • A design can be optimized for speed by, for instance, trading coil turns for current.

Magnetic field changes diffuse into and out of the terfenol-d rod at a speed fixed by its geometry and material constants. Local mechanical changes occur in response to local magnetic field changes.

• Known countermeasures to this delay enable effective ultrasonic actuators.

The speed of an elastic plane wave propagating along the axis of a terfenol-d rod is not less than 1,600 meters per second.