[extropy-chat] Nuclear batteries for hand-helds

[Mike Lorrey]

http://www.spectrum.ieee.org/WEBONLY/publicfeature/sep04/0904nuc.html

"Nuclear batteries can pack in energy at densities THOUSANDS OF TIMES
greater than those of lithium-ion batteries"

http://www.spectrum.ieee.org/WEBONLY/publicfeature/sep04/0904nuct1.html

" For these batteries, which we call radioactive piezoelectric
generators, the radioactive source is a 4-square-millimeter thin film
of nickel-63 [see illustration, "Power From Within"]. On top of it, we
cantilever a small rectangular piece of silicon, its free end able to
move up and down. As the electrons fly from the radioactive source,
they travel across the air gap and hit the cantilever, charging it
negatively. The source, which is positively charged, then attracts the
cantilever, bending it down.

A piece of piezoelectric material bonded to the top of the silicon
cantilever bends along with it. The mechanical stress of the bend
unbalances the charge distribution inside the piezoelectric crystal
structure, producing a voltage in electrodes attached to the top and
bottom of the crystal.

After a brief period—whose length depends on the shape and material of
the cantilever and the initial size of the gap—the cantilever comes
close enough to the source to discharge the accumulated electrons by
direct contact. The discharge can also take place through tunneling or
gas breakdown. At that moment, electrons flow back to the source, and
the electrostatic attractive force vanishes. The cantilever then
springs back and oscillates like a diving board after a diver jumps,
and the recurring mechanical deformation of the piezoelectric plate
produces a series of electric pulses.

The charge-discharge cycle of the cantilever repeats continuously, and
the resulting electric pulses can be rectified and smoothed to provide
direct-current electricity. Using this cantilever-based power source,
we recently built a self-powered light sensor [see photo, "It's Got the
Power"]. The device contains a simple processor connected to a
photodiode that detects light variations. "

" For example, with 10 milligrams of polonium-210 (contained in about 1
cubic millimeter), a nuclear microbattery could produce 50 milliwatts
of electric power for more than four months (the half-life of
polonium-210 is 138 days). With that level of power, it would be
possible to run a simple microprocessor and a handful of sensors for
all those months.

And the conversion efficiency won't be stuck at 4 percent forever.
Beginning this past July we started working to boost the efficiency to
20 percent, as part of a new Defense Advanced Research Projects Agency
program called Radio Isotope Micro-power Sources. "

=====
Mike Lorrey
Chairman, Free Town Land Development
"Necessity is the plea for every infringement of human freedom.
It is the argument of tyrants; it is the creed of slaves."
                                         -William Pitt (1759-1806) 
Blog: http://www.xanga.com/home.aspx?user=Sadomikeyism


		
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