*3.9.2 Course-changing bullets*

Recently, DARPA invented a.50-caliber bullet that can change course in midflight. As absurd as this innovation may sound to some readers, the bullet uses an optical sensor that is mounted on its nose in conjunction with a control system and moveable tail fins to steer itself toward a laser-illuminated target. Although DARPA

**Figure 12.** *Piezoelectric micro robotics.*

has not revealed much about their Extreme Accuracy Tasked Ordnance (EXACTO) bullet, the most likely means of manipulating the tail fins probably involves piezoelectric actuators.
