Quantum mechanics endows terbium and dysprosium with an inherent, indestructible, inseparable coupling between magnetic and mechanical effects. Combining with iron yields an alloy, "terfenol-d," that is a soft ferromagnet -- a permanent magnet will stick to it but terfenol-d itself cannot be either permanently polarized or permanently depolarized. Since its origin is atomic, magnetostriction:

• Is immune to magnetic fields beyond saturation.
  
  
• Cannot be fatigued by high mechanical output.
  
  
• Cannot be permanently destroyed by temperature. If heated but not melted, alloy magnetostriction is restored below its Curie temperature of 357C.

Magnetic field from the energizing wire coil crosses a small gap between alloy and wire. Since they are not in contact, strain differences cannot cause fatigue cracks.

Billions of energization cycles of individual alloy rods inside actuators have been run without detectable degradation.

• Power ultrasonic actuators. Billions of ultrasonic cycles -- fast and durable.
  
  
• The Navy tested a high preload alloy sonar projector to billions of cycles without performance degradation, confirming that the property of interest is indestructible.

Compression Fatigue

Stress Cycle: -250 250 MPa @ 10 Hz
Runout Point >1 10^6 Cycles

Source: Load Capacity of Giant Magnetostrictive Materials

Packaging the quantum mechanical effect into a suitable alloy and then packaging that into a suitable actuator are why it will survive in a harsh environment such as an engine cylinder head and why the words robust, durable, and survivable are applicable. Packaging is a matter of alloy metallurgy and ordinary engineering. Why now and not long ago? Because the previous materials that responded to a magnetic field had very small response. Quantum Control Works, L.C., discovered (and patented) the keys to speed of the alloy, unlocking its usefulness.