A hot "idea" for insulating
physics researchers are devising a unique “blanket” that
will enable them to squeeze as much electricity as possible from nuclear-powered
batteries the size of a grain of coarse salt. Such batteries, which
exploit the natural decay of radioisotopes to generate electricity,
could provide virtually indefinite power for micro-technologies like
fly-sized robots for military applications or sensors that monitor a
Other technologies such as fuel cells, chemical batteries or turbine
generators also might work in micro-scale applications, says Professor
Blanchard. “But all of them are short-lived,” he says.
“They either need to be recharged or refueled. Our niche is things
that need to be placed and ignored, and just keep running for years.”
Nuclear microbatteries convert heat or energy to electricity more efficiently
when they’re hot, so it makes sense to insulate them, says Blanchard.
“The better the insulation, the hotter the source gets, so the
more efficient the battery can be,” he says.
However, insulating a millimeter-square battery in a way that minimizes
heat loss is no easy task. Multifoil insulation is an effective macro-level
insulator that combines several thin layers of foil each separated by
a vacuum. “They work because they’re radiating heat from
one layer to another, as opposed to conducting heat through a solid,”
For the microscale, however, multifoil insulation is far too thick.
So, capitalizing on the layered concept, which reduces heat radiation
for a fixed temperature drop, Blanchard and graduate student Rui
Yao decided to sandwich semicircular silicon oxide pillars—poor
conductors—between very thin silicon sheets. “You want as
little conduction through these pillars as possible,” says Blanchard.
They developed elaborate computer models to study the heat radiation
and conduction of their microscale insulaton. Using Wisconsin
Center for Applied Microelectronics clean room facilities, Yao constructed
He now is experimentally verifying what his computer models suggest—that
heat is radiating through the silicon layers without much heat loss.
“The prototypes he built are a little thicker than the ones we
ultimately want to get, but they’re consistent with his models,”
Funded by a three-year, $300,000 Department of Energy grant and inspired
by an earlier collaboration with Sandia National Laboratory researchers,
Blanchard and Yao are still testing and refining the insulation. Implementation
for this promising technology, they say, is a couple of years down the
“It looks like we’ll have an effective insulator that’s
better than any solid—and better, even, than some of the multifoil
insulations that you can buy commercially,” says Blanchard.