In the last few weeks there is a big hype about a new BV100 beta-voltage cell spread in the Internet, designed buy the conveniently named Chinese Betavolt company. Well, China puts a lot of effort in promoting its initiatives no matter significant, or a total hoax.
The tech is probably based on Russian research of late 2000s
V. Bormashov et al. ttps://www.sciencedirect.com/science/article/abs/pii/S0925963517307495
May we discuss, does this thing have any right for future life?
- First of all, what I want to know, may it ever be approved by FDA, or any other medical safety controller? Ok, BV-cells were known for a long time, and even used in pacemakers... before safe Li batteries were developed; those patients afaik left us long ago with cancer complications.
- How useful is it beyond use in Casio watches?
What we find from their promo (copied exactly word to word at various resources in different languages, like here https://www.livescience.com/technology/engineering/betavolt-bv100-radioactive-battery-can-last-50-years-coming-in-2025)
3V, 0.1mW, 50 years of rated life. 1.5cm x 1.5 cm x 0.5 cm.
Lets guess, that the 100mW is a hard limit defined by the beta-flux and the volume of the semiconductor. The image shows a stack of 3 cells, actually, so the cell voltage is just a little above 1V.
Again, V. Bormashov gives a more understandable picture where the diamond beta-sinks are indeed Schottky diodes.
Diamond has a bandgap of 5.5eV, which still puzzles me. In Bormashov paper the stack is connected in parallel, which increases the current proportionally to volume, withour rasing the surface much. This scheme is prone to loss of performance due to interconnect resistance, so 4 V from a battery is quite expectable.
However, in the Chinese image the cells are stacked strainght with insulating layers, i.e. in series. But the voltage is just 3 V.
Are they lying? Are they really using a poach-style design, typical for Chinese Li-Pol batteries, with awful drop on interconnect resistance which brings the voltage down to 3-point-something volts?
Why Diamond? Because of radioactivity damage resistance. These things are not safe.
But may diamond produce a considerable amount of Gamma, or X-ray emission when bombarded by the beta-particles? Early pacemaker batteries were particularly dangerous because of this.
Lets seem diamon'ds electron capture intensity is much lower than that of grapphite, so it is... a transparrent material. I am not sure about absolute or practical nubers, just know this comparison https://muller.research.engineering.cornell.edu/spectra/graphite-and-diamond-c-k-edge-spectra/ . б
Just for reference, the only Ka1 line of C is 277 eV, and the bond energy of diamond is around 293eV. Nickel-63 emits beta particles (Emax = 66.7 keV, Eavg = 18 keV)
So are there any better materials?
The fuel is Ni-63, pretty nice because of safe decay to common copper. I have no idea how is it synthesized, but probalby from Fe-63... and where do they get Fe-63?
Regarding the Ni-63 production method, i guess this is a good reference : https://patents.google.com/patent/RU2629014C2/en
Indeed, with 0.1mW or so power one limited to watches or similar thindgs traditionally powered by small batteries. E.g CR2032 has capacity about 230mAh --> 0.69Wh --> 6900hours or almost a year at 0.1mW.
However I guess some e.g. implantable sensors may need to stay powered by tens of years without battery change. E.g pascemaker. On another hand, Cochlear Implants, perhaps the second most popular implant these days needs tens of mW.
The X-ray generation in light Z-material by rather low energies betas is quite small, also most of those X-rays are very 'soft' = low energy so easy to shield by some higher that foil wrapping.
Ah. Activation method. I wonder, what is the yeild, may it really reach industrial volumes. (ох уж эти русские патенты с опечатками)
I checked diagrams, https://thoracickey.com/pacing-and-defibrillation-clinically-relevant-basics-for-practice/
It looks like the most optimal pacing pulse requires a little more than 5mW peak. I guess, 5 mW device may not be called safe, so lets give it a tripple rating of 15mW. No auto-defibrilating function considered.
But today pacemakers also include feedback sensors which may require biasing and some amplifier drain current. And the most power-hungry is RF up-down link for monitoring and tweaking, which should boost the _peak_ power rating above 60mW by my expectations.
- Some really nice high efficiency high voltage boost circuit will be required to charge capacitors between the beats, cannot even guess the ambient power required for such.
- Was it ever researched?
I agree with soft X-ray. A particular instrument for examining thin and transparrent media. However, I have no Idea how much really needed to screen it. When we worked with 5keV, there was no lack of shielding material even for heavy hard radiation. C_Ka1=277 eV is 4.48 nm. Checked google, looks like two orders shorter than the boundary of DNA absorbtion.
So, what was I thinking yesterday when made the post:
Of course the efficiency of conversion with diamond may be quite low, so most of X-ray may be generated in Ni/Cu, and the beta-particle shielding material, as it was in the early atomic pacemakers of 60s~.
hearing implants, yes, I did not consider them. Then there are cardiac and breathing nerve repeaters restoring the lost functions after surgeries.
I think even if you need high voltage pulses you can make them quite effectivly with low power. E.g. pulsed DC/DC storing in HV cap.
The RF also can be made into low duty, normal sleep/ wake up by low power RF enveloped detector.
What can make use of tiny (1uW or so) power is retroreflective modulation RF passive tag, e.g. Conference Paper Millimetro: mmWave retro-reflective tags for accurate, long ...
As I found in papers, the required energy of the pulse does not change much (strictly speaking, there is a minimum used in pacemakers, which makes it look like not changing). It is either high and short, or long and low... well not too long. So in overall it hits the power of the sourse.
As I said, I consider the storage bank, which will require a quite efficient and reliable voltage pump, LDo and capacitors. It may work out, but I did not see much interest in this direction, because the chemical battery is like a salami - you may cut it thin or thick, but the length is the same. Nuclear battery is like a weak spring of water. To collect the energy efficiently and timely, it would require higher voltage and better voltage control; not leaving the power envelope by any means (and the betacell power may drop by 76% in its lifetime). I am not sure that the battery energy is enough for that.
The tag and the reliable up/down datalink are a bit different things. It may work or may not. Most tags operate in open air in the _close_nearfield_ only. But of course we are considering it.
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