Before long, sensors may be implanted in our bodies to do things like measure blood-glucose levels in diabetics or retinal pressure in glaucoma patients. But to be practical, they'll have to both be very small--as tiny as a grain of sand--and use long-lasting batteries of similarly small size, a combination not commercially available today.

Now researchers at the University of Michigan have made a processor that takes up just one millimeter square and whose power consumption is so low that emerging thin-film batteries of the same size could power it for 10 years or more, says David Blaauw, a professor of electrical engineering and computer science at Michigan and lead researcher on the project.

But when this processor, dubbed the Phoenix, is coupled with a battery, the whole package would only be a cubic millimeter in volume. At this scale, Blaauw says, it could be feasible to build the chip into a thick contact lens and use it to monitor pressure in the eye, which would be useful for glaucoma detection. It could also be implanted under the skin to sense glucose levels in subcutaneous fluid. More broadly, this low-power approach to processor design could be used in environmental sensors that monitor pollution, or structural health sensors, for instance.