mechanical systems (MEMS) comprise a rapidly expanding research
field with potential applications varying from sensors in air
bags, wrist-warn GPS receivers, and matchbox size digital cameras
to more recent optical applications. Depending on the application,
these devices often require an on board power source for remote
operation, especially in cases requiring for an extended period
of time. In the quest to boost micro scale power generation several
groups have turn their efforts to well known enable sources, namely
hydrogen and hydrocarbon fuels such as propane, methane, gasoline
and diesel. Some groups are develo ping micro fuel cells than,
like their micro scale counter parts, consume hydrogen to produce
electricity. Others are developing on-chip combustion engines,
which actually burn a fuel like gasoline to drive a minuscule
electric generator. But all these approaches have some difficulties
regarding low energy densities, elimination of by products, down
scaling and recharging. All these difficulties can be overcome
up to a large extend by the use of nuclear micro batteries.
Radioisotope thermo electric generators (RTGs) exploited the extraordinary
potential of radioactive materials for generating electricity.
RTGs are particularly used for generating electricity in space
missions. It uses a process known as See-beck effect. The problem
with RTGs is that RTGs don't scale down well. So the scientists
had to find some other ways of converting nuclear energy into
electric energy. They have succeeded by developing nuclear batteries.
use the incredible amount of energy released naturally by tiny
bits of radio active material without any fission or fusion taking
place inside the battery. These devices use thin radioactive films
that pack in energy at densities thousands of times greater than
those of lithium-ion batteries. Because of the high energy density
nuclear batteries are extremely small in size. Considering the
small size and shape of the battery the scientists who developed
that battery fancifully call it as "DAINTIEST DYNAMO".
The word 'dainty' means pretty.
2.1 TYPES OF NUCLEAR BATTERIES
Scientists have developed two types of micro nuclear batteries.
One is junction type battery and the other is self-reciprocating
cantilever. The operations of both are explained below one by
2.2 JUNCTION TYPE BATTERY
of nuclear batteries directly converts the high-energy particles
emitted by a radioactive source into an electric current. The
device consists of a small quantity of Ni-63 placed near an ordinary
silicon p-n junction - a diode, basically.
As the Ni-63 decays it emits beta particles, which are high-energy
electrons that spontaneously fly out of the radioisotope's unstable
nucleus. The emitted beta particles ionized the diode's atoms,
exciting unpaired electrons and holes that are separated at the
vicinity of the p-n interface. These separated electrons and holes
streamed away form the junction, producing current.
It has been found that beta particles with energies below 250KeV
do not cause substantial damage in Si. The maximum and average
energies (66.9KeV and 17.4KeV respectively) of the beta particles
emitted by Ni-63 are well below the threshold energy, where damage
is observing silicon. The long half-life period (100 years) makes
Ni-63 very attractive for remote long life applications such as
power of spacecraft instrumentation. In addition, the emitted
beta particles of Ni-63 travel a maximum of 21 micrometer in silicon
before disintegrating; if the particles were more energetic they
would travel longer distances, thus escaping. These entire things
make Ni-63 ideally suitable in nuclear batteries.
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