Nature possesses a boundless amount of harvestable energy that can be harnessed to power wireless sensor networks. Potentially, it can eliminate the need for batteries in tethered electronics and solve many power-supply and dissipation problems in one stroke.
Vibration, strain and inertial forces, heat, wind, light, and magnetic fields can all be tapped for this purpose. Piezoelectric materials, for example, can convert mechanical motion into electric currents and vice versa. Magnetic and inductive coils can tap inertial forces. And, thermovoltaic and photovoltaic cells can harvest the energy given off by heat and light.
To successfully harvest energy, one must overcome formidable economic and reliability challenges. The battery industry is fast approaching performance limits in terms of materials and chemistry, which will pose another hurdle. But while the work on energy harvesting is only in its infancy, recent success in the laboratory shows that there's hope.
Perpetuum Ltd. and Innos Ltd. teamed up to develop embedded MEMS silicon microgenerators for wireless communications. The devices feed off the vibrations in the environment to produce consumable energy (see "Microgenerator Harvests Kinetic Energy For Wireless Devices," Electronic Design, Sept. 15, 2005, p. 28, ED Online 11050). Each 5- by 5- by 1.5-mm device can produce a few hundred microwatts of energy under certain conditions, which can drive sensors, small microprocessors, and RF transmitters for a complete self-powered system.
The University of Texas at Arlington's Materials Science and Engineering Department, meanwhile, has produced small piezoelectric-based generators to power wireless networks. Powered by 5- to 10-mph winds, the devices can produce up to 50 mW. That's enough to support individual nodes in a wireless sensor network.
The MIMOSA consortium has made energy harvesting—or energy " scavenging"—a major goal. So to that end, energy sources like photovoltaic cells, RF waves, and thermocouples are certainly worthy of investigation.