In a magnetostrictive actuator, electrical current flows through a solenoid coil of wire to form a magnetic field surrounding a rod of terfenol-d. Within the rod, varying the field rotates local magnetic domains to vary mechanical force and expansion.

This simplified diagram shows key characteristics. Magnetic field is the horizontal axis, expansion is the vertical axis.

• The rod contracts due to compressive preload force.
  
  
  • Six different constant force compressive preloads are shown.
    
    
• The preloaded, compressed rod expands due to a magnetic field of either polarity.

Each curve expands the same amount. Then, more field is required to expand against higher preload compression. Re-stated, the same output force requires less terfenol-d at higher preload compression.


Magnetic Bias

The diagram below is the same as the one above except magnetic bias is added. Magnetic bias enables an unbiased electrical input to the actuator to result in an unbiased mechanical output. Actuator size and cost increase with magnetic bias field.