Micro Electro Mechanical Systems (MEMS) include a rapidly expanding research field with potential utilisation varying from sensors in airbags, wrist-worn GPS receivers, and matchbox size digital cameras to more recent optical applications. Depending on the application, these devices often require an onboard power source for remote operation, especially in cases requiring for an extended period.
In the quest to boost micro-scale power generation several groups have turned their efforts to well known enable sources, namely hydrogen and hydrocarbon fuels such as propane, methane, gasoline and diesel.
Some groups are developing micro fuel cells that, like their microscale counterparts, consume hydrogen to produce electricity. Others are developing on-chip combustion engines, which burn fuel like gasoline to drive a minuscule electric generator. But all these approaches have some difficulties regarding low energy densities, elimination of by-products, downscaling and recharging. All these problems can be overcome up to a large extent by the use of nuclear micro batteries.
Radioisotope thermoelectric generators (RTGs) exploited the extraordinary potential of radioactive materials for generating electricity. RTGs are mainly practised for making power in space missions. The process may use in this called “See-beck effect”.
The problem may be faced with RTGs is that RTGs don’t scale down well. So the scientists had to find some other plans of transforming nuclear energy into electric energy. They have succeeded in developing atomic batteries.
2. NUCLEAR BATTERIES
Nuclear batteries use the incredible amount of energy released naturally by tiny bits of radioactive material without any fission or fusion taking place inside the cell. These devices use Radioactive thin films that pack in power at densities thousands of times higher than those of lithium-ion batteries. Due to the high energy density, nuclear batteries are tiny. Considering the small size and shape of the array the scientists who developed that cell fancifully calls 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 a self-reciprocating cantilever. The operations of both are explained below one by one.
2.2 JUNCTION BATTERY
Such a kind of nuclear batteries that directly converts the high-energy particles emitted by a radioactive Elements into an electric current. The device consists of a small quantity of Ni-63 placed near an ordinary silicon p-n junction – a diode.
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 ionised the diode’s atoms, exciting unpaired electrons and holes that will separate in the vicinity of the p-n interface. These separated electrons and holes streamed away from the junction, producing current.
The result was 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 extended half-life period (100 years) makes Ni-63 very attractive for remote long life applications such as the power of spacecraft instrumentation.
When beta particles transmitted in the familiar to Ni-63 travel a maximum of 21 micrometres in silicon before destroying; if the particles were more energetic, they would move longer distances, thus escaping. These entire things make Ni-63 ideally suitable for nuclear batteries.
Since it is not easy to microfabricate solid radioactive materials, a liquid source is used instead of the micromachined p-n junction battery. The diagram of a micromachined p-n junction is shown figure 1.
As shown in figure some bulk-etched channels have been micromachine in this p-n junction. Compared with planar p-n junctions, the three-dimensional structure of our device allows for a substantial increase of the junction area and the macro machined ways can be used to store the liquid source. The concerned p-n junction has 13 micro machine channels, and the total junction area is 15.894 sq.mm (about 55.82% more than the planar p-n junction). It is very important since the current generated by the powered p-n junction is proportional to the junction area.
As shown in figure some bulk-etched channels have been micromachined in this p-n junction. Compared with planar p-n junctions, the three-dimensional structure of our device allows for a substantial increase of the junction area and the macro machined channels can be used to store the liquid source. The concerned p-n junction has 13 micro machine channels, and the total junction area is equal to 15.894 square mm.This is very important since the current produced by the powered p-n junction is equivalent to the junction area.
To identify the performance of the 3-dimension p-n junction in the presence of radioactive aspect’s supply, a pipette is used to place 8l of liquid Ni-63 inside the channels micromachined on prime of the p-n junction. It is then blanketed with a black box to shield it from the sunshine.