MREMS: Micro-Radioisotopic-Electro-Mechanical Systems

This feature article of IEEE spectrum does a good job mentionning the issue of radioactive microbatteries that could power future MEMS.

My own preference is for Polonium-210 which has the ability to release about 120 W per grams. This is huge. Unfortunately, as said in the article:

At the diminutive dimensions of MEMS devices, the ratio between an object's surface and its volume gets very high. This relatively large surface makes it difficult to sufficiently reduce heat losses and maintain the temperatures necessary for RTGs to work. So we had to find other ways of converting nuclear into electric energy.

For a sphere, surface area decreases as the square of the radius whereas its volumes decreases as the cube of the radius. Hence, as the size decreases, the surface area become more important for the volume: i.e. major heat loss is expected from this sphere. Realizing this, Tom Blanchard from Wisconsin-Madison decided to look at this through the building a micro heat barrier. Hopefully, we will be able to keep high temperatures in that sphere so that thermoelectric generators can be used. It is also wrong to think that NASA has been looking at only Plutonium as an RTG sources. Back in the 1960's Strontium was looked into as a source of power for autonmous buoy at sea. Even polonium was looked at but the mission scenario requiring this type of sources with a half life of 138 days were non-existent. I recall the preliminary design needing a lot of shielding and being heavy. But then again, if the only issue is about having polonium not surrounded by a thermally conductive material, what about using aerogel instead ?