> Despite the often longer life-expectancies, nuclear pacemakers quickly became a part of the past when lithium batteries were developed. Not only did the technology improve, allowing for lighter, smaller, and programmable pacemakers, but doctors began to realize that this excessive longevity of nuclear pacemakers was excessive.
Good points. But a low-duty-cycle laser pointer eyeball could be more useful than a low-duty-cycle pacemaker.
You could use the 2μW to charge up a capacitor for 24 hours and then have a minute and a half of 2mW, which is enough for a visible laser pointer reaching a few meters. 2mW light output is quite a bit brighter than that but requires more like 20mW power input.
A 220 μF cap at 48 volts would hold 35 hours of 2μW, and there are ceramic caps that big that would easily fit into your eyeball.
The lightest weights 2.6 g, which is 1/2 the weight of the eyeball, so cuts the power generation to 1μW.
I think it's telling me there's a 10μA leakage current, which I think means the cap will power up to 0.1V before the leakage rate matches the power rate.
Now that you know my level of ignorance, what's your take?
Yeah, that's a wet tantalum cap, those have higher leakage currents. An X7R MLCC like https://www.digikey.com/en/products/detail/united-chemi-con/... will probably have lower leakage, though the datasheet doesn't specify. Digi-Key says it costs US$45, it's 20 mm × 28.5 mm × 10 mm which is 5.7 cc, and probably close to 15 grams.
Leakage current usually increases superlinearly with voltage, though. If the tantalum's DC leakage is 10 μA at 50 volts, it's probably closer to 0.1 μA at 5 volts.
In capacitors with a given dielectric, the maximum energy is proportional to the volume of the dielectric, so although a 47 μF cap charged to 108 volts stores the same energy as a 220 μF cap charged to 50 volts, it also needs the same volume.
(I'm not an EE either; I only play one on HN.)
https://en.wikipedia.org/wiki/Human_eye says an adult human eyeball is about 23.7 mm × 24.2 mm × 23.4 mm, and a spheroid like that is π/6 of the corresponding cuboid, so you only have about 7.03 cc to work with.
So probably you'd have to settle for under 1 cc of capacitor, which (in the case of X7R anyway) means storing more like 15 seconds of 2 mW.
"The History of Nuclear Powered Pacemakers" - http://large.stanford.edu/courses/2015/ph241/degraw2/
> Despite the often longer life-expectancies, nuclear pacemakers quickly became a part of the past when lithium batteries were developed. Not only did the technology improve, allowing for lighter, smaller, and programmable pacemakers, but doctors began to realize that this excessive longevity of nuclear pacemakers was excessive.
https://en.wikipedia.org/wiki/Betavoltaic_device says betavoltaic "devices include a 100 μW tritium-powered device weighing 20 grams".
That's about 5x the weight of a glass eye - https://www.muellersoehne.com/907.html .
Assuming linear scaling, an energy budget of 2μW isn't going to provide much light.