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The notion of using solar cells placed under the skin to continuously recharge implanted electronic medical devices is a viable one. Swiss researchers have done the math, and found that a 3.6 square centimeter solar cell is all that is needed to generate enough power during winter and summer to power a typical pacemaker. The study is the first to provide real-life data about the potential of using solar cells to power devices such as pacemakers and deep brain stimulators. According to lead author Lukas Bereuter of Bern University Hospital and the University of Bern in Switzerland, wearing power-generating solar cells under the skin will one day save patients the discomfort of having to continuously undergo procedures to change the batteries of such life-saving devices. The findings are set out in Springer's journal Annals of Biomedical Engineering.
Most electronic implants are currently battery powered, and their size is governed by the battery volume required for an extended lifespan. When the power in such batteries runs out, these must either be recharged or changed. In most cases this means that patients have to undergo implant replacement procedures, which is not only costly and stressful but also holds the risk of medical complications. Having to use primary batteries also influences the size of a device.
[...] To investigate the real-life feasibility of such rechargeable energy generators, Bereuter and his colleagues developed specially designed solar measurement devices that can measure the output power being generated. The cells were only 3.6 square centimeters in size, making them small enough to be implanted if needed. For the test, each of the ten devices was covered by optical filters to simulate how properties of the skin would influence how well the sun penetrates the skin. These were worn on the arm of 32 volunteers in Switzerland for one week during summer, autumn and winter.
No matter what season, the tiny cells were always found to generate much more than the 5 to 10 microwatts of power that a typical cardiac pacemaker uses. The participant with the lowest power output still obtained 12 microwatts on average.
Journal Reference:
L. Bereuter, S. Williner, F. Pianezzi, B. Bissig, S. Buecheler, J. Burger, R. Vogel, A. Zurbuchen, A. Haeberlin. Energy Harvesting by Subcutaneous Solar Cells: A Long-Term Study on Achievable Energy Output. Annals of Biomedical Engineering, 2017; DOI: 10.1007/s10439-016-1774-4
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(Score: 2) by jmorris on Wednesday January 04 2017, @05:48PM
Generating small amounts of electricity isn't hard. But this application of solar suffers from the same problem all applications of solar power do. It is not constant so you must store it. Meaning you still need a battery and a rechargeable battery must be replaced just like a primary cell does. Pacemaker batteries can already have a ten plus year lifespan, few rechargeable cells can manage such a service life.
Medical devices need a source of power based on the energy found in a human body naturally, once that can supply power as long as the human it is inside of remains alive.
(Score: 2) by Immerman on Wednesday January 04 2017, @07:00PM
If you're assuming regular charging, especially if it can get enough charge from common artificial light (like so many PV calculators), then you might well be able to use a durable supercapacitor instead, and thus extend the service life almost indefinitely. I wonder how many days (weeks? months?) worth of power an acceptably sized supercapacitor could store?
(Score: 2) by VLM on Wednesday January 04 2017, @07:26PM
I wonder how many days (weeks? months?) worth of power an acceptably sized supercapacitor could store?
Two weeks or less. Kinda depressing. I fooled around with some PIC10 series microcontrollers some years (decades?) ago and supercaps and the disconnected from circuit leakage currents mean that at zero current draw the voltage across a cap will drop to unusable in, eh, maybe 3 weeks. This is partially my screwing around and partially off data sheets, the data sheets were pretty accurate. It doesn't matter what the size is, just like lead acid, its the chemistry resulting in a certain current leakage rate vs storage capacity means it don't matter how big or small its dead in, eh, 20-something days.
BTW you think you're building stuff with leakage currents far below uA, that is non-trivial. Not impossible, just saying its at or beyond state of the art for do it at home. When you're checking wire resistance with a megger to make sure you're not throwing a high value resistor across your power supply... yeah. And anything involving high impedances is a magnet for static blowing it to bits. Its all doable, even at home, but a PITA.
The next problem is the data sheet info WRT derating for temperature imply the things will last 100K hours or so at non-fever body temperatures (insert massive handwaving) and that sounds awesome until you realize its just a decade of continuous use. May as well use a lithium battery.
The failure mode is their weird as hell electrolytes evaporate out over time. And or some electrochemistry handwavy BS that boils down to corrosion. Not very fast, but good luck containing a liquid inside anything forever. At least 10-15 years ago there were no solid chemistry supercaps which means no encapsulation in solid brick of plastic (which was my app) or inside a sealed pacemaker.
You can build stuff that lasts forever in space craft and stuff but all solid state... no electrolytics or supercaps (90s/00s anyway) allowed and a bunch of other interesting rules which I can't remember right now. No carbon comp resistors (LOL kids these days likely never seen one), metal film all the way. Something about reverse biased tantalum's blow up 1000x quicker than forward biased tantalum caps but they all blow up in the end (or maybe thats just slander against tantalum mfgrs)
Super caps are perfect for things like real time clock backups in an alarm clock or whatever.
I'd be pleased to hear things have progressed and in the late 00s that scheme works, but it didn't work around the turn of the century.
(Score: 2) by Immerman on Wednesday January 04 2017, @08:38PM
Well, a few weeks should be plenty, assuming you can generate much more power than required most days. And I don't know that leakage current is really an issue, so long as you can include a large enough capacitor to store the energy needed after factoring in leakage losses. I mean, basically everything stored beyond a single day's worth of power is safety margin in case something keeps you from getting your regular charge.
Supercaps also have the advantage of fast charging - so that solar panel could be replaced or augmented with an induction coil so that you can just rest an induction charger against the patch for a few minutes and get a full charge.