Pacemakers and implanted defibrillators are both, uh, implanted inside your body. Typically they stick them in the front side of your left shoulder. They run the leads into a vein (or artery) and anchor them into the wall of the heart.
They can implant basically under the fat layer or under the pectoral muscle. Beneath the fat layer is easier both from a surgery and recovery standpoint, but less secure.
The downside of that is that it's possible for the device to flip over. They usually try to avoid securing the device to anything because that can lead to discomfort or pain if the device wants to move around, but they can if they have to.
And yes, they do have to repeat surgery to replace the device when the battery gets low. The leads AIUI are usually a lifetime part (hopefully for all the right reasons). For defibrillators, battery life will be maximized if the device doesn't have to deliver shocks and can stick to just pacing. It turns out if they implant a defibrillator, you get a pacemaker for free.
But that's not true... A pacemaker goes inside your body. It's replaced during a surgery every 15-20 years and has enough battery lifetime to last that long.
There used to be nuclear-powered pacemakers that could last many lifetimes but nowadays the doctors say it's better to replace the whole thing every once in a while, so the nuclear option is overkill.
> 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.
But then this one could be lithium iodide too. A replacement eye can also be replaced more easily.
Anyway, your statement about the pacemaker sitting outside the body with probes going inside is not correct; maybe it once was, but that was decades ago.
Pacemakers are typically lithium iodide which do not have the same risk of uncontrolled burning (that's the nickel variety).
But also, the pacemaker sits outside the body with probes going inside. You'd not want another surgery just to change a battery.