Display screens integrated into contact lenses (image above)? Micromechanical medical devices? Pervasive biosensors? A big challenge in the development of wearable and implantable gadgets is how to power them. Years ago, I wrote about efforts to develop a "glucose fuel cell" and other possible technologies to scavenge power from the human body itself. In the new issue of Smithsonian, Michael Belifore looks at the latest developments in that field, much of which is funded by the Defense Advanced Research Projects Agency (DARPA)'s Starved Electronics program. Belifore is the author of The Department of Mad Scientists: How DARPA Is Remaking Our World, from the Internet to Artificial Limbs. From Smithsonian:
Obviously, our bodies generate heat–thermal energy. They also produce vibrations when we move–kinetic energy. Both forms of energy can be converted into electricity. Anantha Chandrakasan, an MIT electrical engineering professor, who is working on the problem with a former student named Yogesh Ramadass, says the challenge is to harvest adequate amounts of power from the body and then efficiently direct it to the device that needs it."Embedded Technologies: Power From the People" (Smithsonian)
In the case of harnessing vibrations, Chandrakasan and his colleagues use piezoelectric materials, which produce an electric current when subjected to mechanical pressure. For energy scavenging, ordinary vibrations caused by walking or even just nodding your head might stimulate a piezo material to generate electricity, which is then converted into the direct current (DC) used by electronics, stored in solid-state capacitors and discharged when needed. This entire apparatus fits on a chip no larger than a few square millimeters. Small embedded devices could be directly built onto the chip, or the chip could transmit energy wirelessly to nearby devices. The chip could also use thermoelectric materials, which produce an electric current when exposed to two different temperatures–such as body heat and the (usually) cooler air around us.