New power source: wall vibrations

Imagine using a computer that runs on energy generated from your building's wall and window vibrations. Masayuki Miyazaki, a senior researcher at Hitachi Co. Ltd.'s central lab in Tokyo, is trying to do just that.

He recently made a tiny generator that converts building movements into electricity, creating enough energy to run a temperature or light sensor once an hour. Though the output is small right now, only about 10 microwatts, scientists predict the generator's potential could be huge in coming decades - possibly used in battery-free computing systems.

Dr. Miyazaki's work is part of a growing movement by scientists to find, create, or capture alternative sources of energy - even in small amounts much less than one watt. Researchers hope to harvest power from anything from the vibrations of walls and windows to the movements of air and the human body.

While alternative energy sources alone might not produce much electricity, they could help power small devices such as computer chips, wireless sensor networks, or cellphones. The idea is simple. Just as some wristwatches power themselves from the random movements of a person's arm, these devices would capture energy from random movements of other things.

In another approach, Larry Kostiuk at the University of Alberta in Canada, is working on a water-powered battery. Its special trait: creating electricity directly from water on the tiniest scales.

Most people are familiar with hydroelectricity, which uses water falling from a height to drive turbines and generate electricity. Professor Kostiuk's method differs in that water is put under pressure as it moves through microscopic channels within a glass or ceramic-filter tube, allowing electricity to be converted directly from water. The experimental tube, about 2 centimeters in diameter, has about half a million tiny channels or holes through which the water is inserted by a hand-operated syringe.

As water travels over the surface of the channels, it becomes electrically charged when its ions rub up against the solid surface. Scientists placed electrodes at the ends of each channel and then extracted electrical energy as current flows between the electrodes. Right now currents are very low, around 4 microwatts, but millions of channels could be added together to increase the power output enough to create a water-powered battery.

Miyazaki's approach generates electricity from the ambient energy all around us. A building's walls and windows vibrate constantly because of wind, air conditioners, or passing trucks. Since the power is still very small, Miyazaki says he aims to use the power source as an "on-chip battery" for circuits such as those used in computers and other electronic products.

"The application is a field called 'ubiquitous computing.' For example, wireless sensor networks of small chips can be distributed everywhere," he says.

Miyazaki says commercial applications will emerge in several years, although the approach requires more research to make it economically feasible.

Eventually, he plans to put a sensor, wireless transceiver, processor, and power source into one small package that can be used in wireless sensor networks. Such networks are expected to become part of our everyday environment and will be placed in buildings, on roads, and on bridges.

Miyazaki isn't the only one tapping vibrations to create electricity. Shad Roundy, professor of engineering at the Australian National University in Canberra, is pursuing techniques to capture energy from low-level vibrations caused by factors such as building movement. One of his methods is similar to Hitachi's, but he now is leaning toward using a piezoelectric approach, electricity caused by mechanical pressure or strain, which he says can work better.

Professor Roundy's piezoelectric generator is similar to a two-layer diving board with a boulder on the end of it. When the device is shaken, the beam resembling the double diving board bends, creating tension in the top layer and compression in the bottom. The opposite happens if the beam is bent the other way, so power can be drawn in either direction. Roundy says he designed several devices that can be placed on vibrating structures to generate power. The best output so far is about 300 microwatts per cubic centimeter.

This method is "attractive in providing power for very low-power wireless sensors and transmitters, but are not useful for large-scale electrical power generation," he says. Roundy says commercial applications could emerge within a year and may include harnessing energy from a manufacturing floor.

Kostiuk remains cautiously optimistic about the future for such new approaches. "I don't know if it will ever work at an efficiency that makes it relevant for widespread use," he says of his water battery. "But it can take multiple decades for something to see commercial applications."