"In the future, tiny vehicles might travel through your body to image your insides, take samples, and deliver drugs. At Stanford University, my colleague Anatoly Yakovlev and I built a prototype of such a device. It's about the size of Abraham Lincoln's head on a penny. We power and control the prototype wirelessly by sending radio waves to its two-by-two-millimeter antenna from about two inches away. No battery is required, which is key to miniaturization.