Solar-powered Amal

So, I’m reading this article from 2016, particularly these bits:

In the summer of last year, Amal Graafstra had a question: Could a solar cell under his skin get enough light to power other devices he may one day implant in his body? To find out, he bought a $5 solar-powered calculator from Wal-Mart, pulled out the 1-by-4-centimeter solar cell, cut open his arm, placed the cell under his skin and sewed it back up. By comparing the power output from the cell below his skin versus its output above his skin, he could tell that the cell was indeed able to gather light and put out power. It worked, and Graafstra cut out the little cell.
[…]
“I now know for this particular spot in my arm the difference in a solar panel’s performance above the skin and below,” he said.

Two questions spring to mind:

  • How much power did the cell get under your skin versus in the open? Was it even usable if it wasn’t summer solstice at noon?
  • Wouldn’t it have been easier to try it under a patch of pig skin? I’m beginning to think you enjoy cutting yourself open :slight_smile:
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When researching a possible UV Sense implant, I kinda got to the conclusion that UV doesn’t get through skin very well.
Don’t know enough about solar energy stuff, guess the energy doesn’t come from UV… but if it uses visible light I’m not surprised that it works, because the xLED’s are a proof that a good portion of light passes through skin.

But in general, what’s the state of implants with a battery, charged the “usual way” via RFID?
I tried finding something for animals but I guess there’s no need for it.

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UV light probably doesn’t penetrate skin very well, otherwise skin would go all dark and cancery when it’s exposed to it.

As for charging, if it gets charged up regularly, an implant could probably do with a supercap instead of a Li-ion battery, which is a lot safer.

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In a dream world my phone and access control systems would charge it on the fly. :slight_smile:

I still have serious doubts/questions on the viability of super caps in implants. For one you’d have to find ones with insane capacitance to have more than a few seconds of power. Plus, I can’t imagine that using an electrolytic cap would be safe since they often contain literal acid, so that narrows the available types for use and raises the costs. And lastly, how capacitors tend to fail is a sudden spontaneous discharge, I’m not sure how safe that would be from within your body.

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Makes a lot more sense than a lead acid battery. :wink:

But seriously, the chemistry of a Li-Ion battery doesn’t handle trickle charging well so that’s out from the outset. TBH I think a supercap is going to be the only reliable option for long life and ability to withstand trickle charging, but even then it probably limits you pretty severely until we get even higher efficiency solar panels and caps.

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Anyone seen the lithium ceramic batteries, that might be a way forward.

Check out the Livestock Labs Embedivet

https://www.mouser.com/ProductDetail/Maxwell-Technologies/BMOD0001-P005-B02?qs=W0yvOO0ixfEzFv8%2F5TnOWA%3D%3D

Solid state ultracapcitors. Drawbacks are a good high efficiency voltage converter is needed as the V+ drops in straight line during discharge.

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Part of a crazy couple days out in the desert shooting a sizzle reel for a production company about biohackers… incidentally Grindfest 1.0 was borne from this event. I have more footage somewhere, but this is what’s easily accessible.

Very thin silicone coating on there… meant for very temporary exposure during the test, then removed. The incision wasn’t even sealed up during testing.

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Pretty wild. It wasn’t “just” an experiment then. That explains.

So then, were you able to measure the attenuation due to the layer of meat on top of the cell?

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Yeah… tons of attenuation, but that was to be expected… and we set it all up to purposely be the worst of conditions. Got around 50uW from a 100W incandescent flood lamp suspended about 48 inches or so directly above my arm in an otherwise totally dark room. That was through blood pooling on top too.

Infrared light goes deepest through tissue so I started looking for IR panels. Most up-convert low energy photons which makes them inefficient… but there was talk of nanotech coming that would directly convert an IR photon into a free electron… never made it commercially though. So that leaves more visible light spectrum doing the heavy lifting, and I’m a little concerned it might be a racist technology - i.e. not working well at all for darker skinned people.

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Interersting. 50uW may not seem much, but if it charges something constantly, it can add up to usable power.

I keep being amazed by the things you think about that never even cross my mind…

Well then, out of curiosity, here’s a loaded question: assume the technology is there (visible light or IR) and dark people aren’t good candidates for implantation - or even that the technology isn’t available to them at all: would you elect not to sell to it anybody as a result?

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that’s a good question… I think I would sell it, but put extra effort into continued development so any differences in performance, if they existed, would be minimized in every possible way… it’s kinda like the early face ID, biometrics, camera face tracking features, etc. all not working well or at all for dark to very dark complexions… and developers just going “oh well, who cares, too bad for them”… that’s not cool.

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Maybe something like this…

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you actually need to go the opposite direction and add waaaay more surface area… make it huge… must collect more photons.

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“This subcutaneous tracker actually had a human tryout before it even got anywhere near a cow.” https://www.technologyreview.com/2018/05/15/66860/cyborg-cows-are-coming-to-a-farm-near-you/

I see, thanks for sharing! Very interesing chip (and story).

Yeah I know but these are cool for their size and they’re SM.
Pretty much need an rf power feed or micro amp range power consumption…

How about using the something like the Samsung Power Sharing feature to charge it with a phone?

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this has been the hurdle all along… inductive charging is totally possible, even with a phone… but what are you charging? safe energy storage at consumer grade prices requires entirely new battery chemistry or at the very least a new method of construction. Solid state electrolytes are looking interesting as is solid lithium metal batteries… something not possible with liquid electrolytes due to dendrites, shorting, and explosions… but the battery also has to be able to deal with overcharging, over current, and other circuit failures and do so without overheating and zero off-gassing. It’s a tall order.

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But a profitable one. Companies and researchers the world over are trying to crack that nut. Gonna make somebody(s) rich if they can figure it out.

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