Piezo Actuator
WARNING: This page is about a different car, the 2012 Ford Pickup, 2012 Ford F550 Super Duty, 2012 Ford F450 Super Duty, and 2012 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
The piezo actuator consists of a series of small disks. When the piezo actuator is electrically energized, it causes the disks to deform which results in an expansion. The expansion generates a longitudinal motion which pushes down against the valve piston. The piezo actuator returns to its non-energized state by fuel and spring pressure during engine operation, and by the spring pressure from the fuel injector valve return spring when the engine is shut down.