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Matthew Traum

The Walls are Crawling with Energy

Those of us who make precision measurements are all too aware that the micro-world is a virtual smorgasbord of perpetual earthquakes. While annoying to scanning electron microscopists, these tremors represent an inexhaustible supply of energy for very small, low-power devices that could soon make a big impact on the way we live. Collecting low-grade ambient energy via microelectromechanical systems (MEMS) is called micro energy scavenging; it is essentially the micro-equivalent of the self-winding watch.

For raw power generation capacity, micro energy scavenging cannot be compared against commercial-scale solar cells or wind turbines, and this technology alone certainly will not free us from the “oil addiction”. Nonetheless, micro energy scavenging is the only way to deploy networks of useful wireless devices without having hard-wire each node into a power line. Wireless sensor networks in-turn enable a degree of information management and energy conservation previously unattainable. Early examples include residential envelope control offerings from the ZigBee and Z-Wave consortiums, groups of companies competing to commercialize various wireless network standards.

For a more technical take, Erick Torres and Prof. Gabriel Rincón-Mora at Georgia Tech’s Analog and Power IC Design Lab posted a nice article that overviews various sources of ambient energy that can be scavenged: light, thermal gradients, and vibrations. The article also highlights issues facing micro energy scavenging, most notably energy conditioning and storage.

Vibration-based energy scavengers will be the first to see commercialization for sensor networks since they function day-and-night. Vibration scavengers include cantilever configurations like those under development at MIT’s Micro & Nano Systems Laboratory as well as membrane configurations like those created at Imperial College in the Control and Power Group and the Optical and Semiconductor Devices Group.

I performed a quick back-of-the-envelope calculation to determine how much energy could be scavenged from inside a typical 1000 square-foot residential home like this one. I obtained 105 watts, provided the walls and ceiling are completely covered with scavenging devices.

I’m not suggesting we paint our walls and ceilings with energy scavengers to power the TV and the lights. However, there is certainly enough energy in the walls to create an intelligent deploy-and-forget network that assures the TV and the lights are not wasting energy when they are not in use.