Study looks to nuclear energy as micro-scale fuel

A trio of UW–Madison engineers have a new scale in mind for nuclear energy: Rather than huge plants powering entire cities, they envision tiny batteries turning a single microscopic gear.

Extremely small amounts of radioactive material already perform functions in smoke detectors, photocopiers, pacemakers and other devices. But the researchers are studying whether even tinier amounts might provide a power source for the tiny experimental machines being built in laboratories worldwide.

See also: Smaller, taller micromachines show commercial promise (2/20/97)

Nuclear engineering professors James Blanchard and Douglass Henderson, along with electrical engineering professor Amit Lal, are leading the three-year, $450,000 project. The U.S. Department of Energy, which looks at potential new uses for nuclear energy, supports the research.

Known as micro-electromechanical structures, of MEMS devices, they tend to be smaller than a width of human hair, about 60 to 70 microns, Blanchard said. Because of their small size, they can perform extremely precise functions in applications such as medical equipment, environmental management and automobiles.

The most common MEMS device is the tiny sensor that tells auto air bags when to deploy. But MEMS technology is limited by the lack of a reasonable power source that is lightweight and intense enough to run such a small device.

“There’s nothing being studied like this on this scale,” Blanchard said. “The key issue for us is the size of the radiation source.”

Using extremely small amounts of radioactive material in products is not new, Blanchard said. For example, smoke detectors function with the aid of a radioactive substance that electrically charges the air. Some photocopiers use a of radioactive material to eliminate the static charge in sheets of paper.

Exposure to radioactive materials is by nature hazardous and their use is closely regulated. But the amount of material required for these applications is so minuscule it would not pose safety risks or require regulation, he said. The traces of radioactive material are encapsulated so no one is exposed to the radiation.

The idea is to harness the natural decay of radioactive material and convert it into a power source, without use of a reaction such as fission or fusion, Blanchard said. By keeping the material securely contained within the device, he said, the majority would decay before it leaves the product.

“We would capture the energy from that decay, and convert it into a power source that could run a sensor or tiny moving part,” Blanchard said.

The energy could either be in the form of heat or charged particles, both of which could be generated in sufficient amounts to be useful on a tiny scale. Blanchard said alpha and beta particles generate high voltages.

Lal, who builds MEMS devices, said micro-machines could see many more applications once the power issue is solved. The technology has been stalled by a near-absence of power sources that can efficiently fuel something so tiny. “You would be creating a set of applications that have never been possible,” he said.

For example, MEMS batteries could be used as power sources for small hand-held computing devices or micro-laboratories. Sensors could be developed to recognize “signatures” of gases from chemical plants or oil pipelines, to give early warning of leaks. It could also be used in a network of self-powered sensors to guard against chemical warfare. The tiny sensors could also be mixed right into the grease of heavy machinery to detect when maintenance is required.

“The biggest impact could be in making everyday systems more reliable, safer and smarter by integrating these sensor systems,” Lal said.

The project is part of Nuclear Engineering Education Research (NEER) at the Energy Department, which primarily funds university-based projects in fission and other applications of radiation. This is part of a small category of funding that encourages potential alternative uses for nuclear energy.