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Paper on nuclear battery rated as outstanding at conference

Jae Kwon, assistant professor in electrical and computer engineering, and J. David Robertson, chemistry professor and associate director of the research reactor, in Kwon's lab in Laffere Hall on Monday, July 27, 2009. Kwon and Robertson are collaborating on a project at MU to build a tiny nuclear battery for microscale devices called MEMS.

Story by: Jashin Lin

Very small batteries for very small devices are the subject of Mizzou Engineering professor Jae Kwon’s recent paper submitted to the 15th International Conference on Solid-State Sensors, Actuators and Microsystems (also known this year by its snappier name, Transducers 2009).

The paper was awarded the honor of being selected as “outstanding paper” out of the 599 papers admitted out of 1,306 accepted for review to the June conference in Denver, Colo.

Kwon, assistant professor in electrical and computer engineering, and his team at Mizzou have built a very small nuclear battery intended to power microelectromechanical systems, or MEMS. These microscale devices or systems, usually smaller than a computer chip, currently deploy airbags, sense tire pressure, work in jet printers, measure biological contaminants, and perform whole scientific tests on what’s known as “lab on a chip.” That’s just the tip of the iceberg.

But as with all systems, they need power to function. The problem arises when the battery for a MEMS device can be much larger and heavier than the device itself. The goal becomes, then, to devise an energy source that’s small and light, but outputs more power for a longer time.

“To provide enough power, we need materials with high power density,” Kwon said. “The radioisotope battery provides power density that is six orders of magnitude higher than chemical batteries.”

In addition, Kwon’s radioisotope battery is tiny – the current model is about the size and thickness of a penny. Kwon is collaborating with J. David Robertson, MU chemistry professor, to build and test the battery at the University of Missouri research reactor (MURR).

Nuclear batteries for MEMS devices are not new, but what’s different about Kwon’s is its small size. It has another unique characteristic – it uses a liquid semiconductor rather than a solid-state semiconductor like in previously built nuclear batteries.

“The hard part of using radioactive decay is that when you harvest the energy, part of that energy goes towards creating defects that damage a solid-state semiconductor,” Robertson, associate director of the research reactor, said. “Our hypothesis is that with a liquid-state semiconductor, the same damage won’t happen. So we created a battery without that part degrading over time.”

Using a liquid rather than a solid semiconductor was the particular topic covered in Kwon and Robertson’s paper submitted to Transducers 2009. If the “outstanding paper” award is any indication, it stirred some enthusiasm in the audience at the conference.

“There were a lot of questions coming up from the audience,” Kwon said. “Many asked technical questions. Some were from the industry – they asked about cost. So there was not only academic interest, but also business or marketing-related interest.”

A long-lived power source not much larger than a MEMS device could be a hot property in the MEMS manufacturing industry. But Kwon says that there is “a long way to go” before his battery is ready for commercial marketing.

“Not necessarily in terms of a long time, but we have a lot of work before it is ready for industry. At this moment, we’re still at the fundamental research level,” he said.

Kwon, Robertson and their team are currently focused on increasing the power output and shrinking the size of the battery even further – among other things, they are exploring using other materials besides the sulfur-35 isotope they are currently using. They’ve also filed for a provisional patent.

“In the future, the battery can be thinner than the thickness of a human hair,” Kwon said.



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