The difference here is that the 100 dB limit isn't some fundamental law of physics. It's one of the currently accepted standards for safe use of ultrasound. Taking a look through the literature, though, you can find various numbers that say ultrasound several orders of magnitude stronger have had no observable long-term adverse effects. Basically, there's an intensity level that we're pretty sure is harmful, and an intensity level that we're pretty sure is safe, and, as it happens, the intensity level necessary to make uBeam useful is somewhere in between.
Investing in uBeam requires a calculated wager that the threshold for ultrasound safety is a fair bit higher than 100 dB. It's a risky position to take, and I'm not sure how to calculate it, but it's not pure lunacy.
I was wondering about the watts for a different reason...
From Wikipedia:
"Although the long term effects due to ultrasound exposure at diagnostic intensity are still unknown,[24] currently most doctors feel that the benefits to patients outweigh the risks.[25] The ALARA (As Low As Reasonably Achievable) principle has been advocated for an ultrasound examination — that is, keeping the scanning time and power settings as low as possible but consistent with diagnostic imaging — and that by that principle non-medical uses, which by definition are not necessary, are actively discouraged."
All these physics-debunking conversations seem to assume a single source. I naively assumed that UBeam will work sort of like the Gamma Knife (https://en.wikipedia.org/wiki/Radiosurgery#Gamma_Knife), where there are many sources that intersect just at your phone or device. This completely changes all the physics assumptions, and is a good reminder to keep an open mind.
That being said, I'd be highly skeptical of the health risks of this technology, especially given the only benefit is convenience.
A giant 0.1 m^2 tablet charging at 12W (120 W/m^2) needs only a 140 dB field. A watch, which might need 1W but with a cross section of more like .001 m^2 (for 1000 W/m^2), needs a 150 dB field.
If something intercepts the beam at 1m instead of the 3m the device is charging at, the cross section of the beam is about 1/3 by 1/3 the final cross section, which since it has to have the same energy (actually would need more to compensate for attenuation through air) would be nearly a 10dB increase?
Is 160dB of ultrasound (at 40kHz or 110 kHz) safe... for a few seconds? for a few minutes? a few seconds of exposure, daily? To your eardrum? To your eyes?
Higher energies needed if the phone isn't perfectly oriented. Worse case is small edge-on orientation to the transmitter.
Higher energies needed for less than 100% transducer efficiency, and I don't know what kind of engineering magic they've done for the transducer but what percentage of the energy could a thin skin over a device possibly convert? 80%? 50%?
The beam could be 170dB, or more.
I want to believe, but this is too sketchy without more information. Large companies have been conned out of millions by small teams peddling snake oil. I'd first want to see it demonstrated with nothing but the transmitter plugged into a socket (through a power meter), a phone at a known, low battery level, and nothing else with wires or metal in the room. Then I'd like to see a test of the transmitter aimed (from above) at a glass of water with a visible thermometer, to see what it does to water.
If this really works, the only options I see are that a) it works at a massively ineffective power transfer rate or b) it is dangerous if you accidentally get in the focused beam (or c) a combination of the two). Any kind of beamforming which can get a decent power transfer will, naturally, transfer that energy into whatever is where the power is focused. Granted, uBeam claims to stop power transfer if line of sight between beamer and device is blocked, but then you are counting on a safety mechanism which is "default off" in some sense. I personally would want to see more tests than a 5 week pig trial as mentioned in the techcrunch piece [1]. After all, radium used to be seen as a "health medicine" back in the early 1900s - it was only after years we realized that radiation was really, really dangerous. It would be great to ensure that kind of thing would not happen in this case - but this means something like a multi-year trial period, which is not good for a startup.
If it is inefficient, the energy issues we already have in the world make it seem irresponsible (to me at least) to use something that operates even more inefficiently than the current system, which is already causing global problems with respect to energy consumption and generation. Even inductive chargers have efficiency issues, and it seems like converting to ultrasound and back would have some inherent loss, though it is really dependent on the quality of implementation. If they can avoid danger, and only have inefficiency issues, I could see some success here for low-energy requirement devices.
If it is dangerous, well that is pretty obvious. No one wants to slow microwave their dog/child/foot/hand if the beamforming is slightly off.
I just don't see a way for this product (or any number of other related products, or RF energy harnessing generally) to succeed without some (unknown) fundamental breakthrough or incredibly expensive hardware.
I am not a doctor nor an expert in this area, but I would presume that would be a valid risk if the frequency were not tuned specifically to resonate the tumor prior to increasing the amplitude. And then there is the matter of focus / accuracy. Perhaps nih.gov has a study with numbers to show the attainable accuracy and what statistics are given back to the equipment and the doctor to compensate and tune the signal. My understanding is that the inverse is generally true, in that, there is too much heat and the surrounding area is scarred.
I think the argument is that while the total power over the full 4p is equal to the sum of the input power, the constructive/destructive interference cause there to be higher power output within some solid angle. But my understanding is that the limit are for avoiding interference from other devices, not for human safety, and that any reasonable amount of non-ionizing radiation is incredibly safe for humans. Congestion wouldn't be impacted by the beamforming, because on average any increase in intensity at one angle would be countered by a decrease at some other angle.
I'm no physicist, but I think that while it may be theoretically possible to distribute power wirelessly doing so in practice seems like it will be necessarily dangerous so as to be impractical. To quote a previous comment I made on HN:
To distribute sound over long distances 'wirelessly' you need to make it loud. That typically means cranking up the power. And ultrasound can be harmful at high power [1].
[1]
"Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss. Exposure in excess of 155 dB may produce heating effects that are harmful to the human body..."
https://en.wikipedia.org/wiki/Ultrasound
Agreed. You could substitute ultrasound waves with electromagnetic waves in this same conversation. We use EM waves every day for diagnotics -- at the 740-380nm range because that's visible light. 10x-100x frequency of that is ultraviolet, which is harmful. And as for resonant frequencies, it doesn't seem unreasonable to me that certain frequencies could denature certain proteins or have other effects.
It's just energy, which can - like any other electromagnetic energy source - be harvested by the right resonant mechanism. The chances of a particular frequency band at such low field-strengths having an impact on a structure not expressly designed for it is super small. It would be like the evolutionary equivalent of finding a 'u-beam[1]' ready receiver in something made in the 1920's.
[1] The fraudulent wireless ultrasound charging company.
I wish the article had a reference to the actual power used. It SOUNDS like it's quiet minimal. In which case, it'd be hard to imagine you are dealing with biologically devastating energy.
That said, the unidirectional nature of this approach also means that actual life that could be affected is a lot smaller than what happens with sonar, where the signal is blasted in all directions at a very high power.
I don't want to sound like a neophyte here but I'm afraid of beams that carry that much power. I have no problem at all letting the milliwatt beam of my cell phone go through my head but lets just say I don't my bedside alarm clock powered by this just yet.
Coupled resonance seems safe to stuff that doesn't resonate in between but when I hear beam and watts I still freak.
190 dB ???!? Is that different under water, and how much is left after 10m?
I mean 130-140 dB is the jet engine and the range were exposure without plugs is painful and longer than few seconds causes damage. This is 6 magnitudes higher, how can this be a good idea?
(Sounds like microwave wireless energy transmission: it's great, unless you care for birds which just get roasted if they fly through the beam?!).
My bad, thanks for the correction. I am surprised though – I thought higher frequency waves were more dangerous, but clearly that is not universally so.
I thought it was the backscatter ones that people objected to. The millimeter-wave ones are much less intrusive and there's no concern about health risks.
It would also fry your electronics and be incredibly noticeable and very easy to prove.
Also, 10 000W wouldn't be enough because that power isn't into a single resonant cavity, we'd be talking about pulses with instantaneous power an order of magnitude higher at the very least.
That's not even remotely close to being a source for what you are saying.
You need a source that shows that there is something different about babies, different about the 5G frequencies, and different from the light, infrared, microwave and radio frequencies that are currently being used everywhere.
Instead, you referenced a paper on a military pain ray that uses focused super high power 100Kw 95Ghz waves that says it penetrates 1/64th of an inch. Your microwave is 2.4Ghz, just like your router, but it works at 1kw. There is an enormous gap between saying "what about babies" and what you linked. They have basically nothing to do with each other. I think you realize that, but you keep saying "we don't know", when you really mean "I don't know".
> the burden is usually on the creators to demonstrate its safety
How can anything be deomstrated to someone who ignores what they are being told and repeats "we just don't know" while supporting their predefined beliefs with giants leaps in logic and excessively irrelevant information?
> I was hoping to have an actual discussion here
I don't believe you. You didn't even confront my original question of what frequencies and effects you are specifically worried about. All you have seemed to being up so far is heat from power 100 times what your microwave uses. 100kw is 4,000 times the power of a soldering iron that can melt tin and lead.
For a manufacturer it's not as cut-and-dry. The damage caused is a factor of the level (dB) received combined with the length of exposure. Assumptions will have to be made as to how far away the user will be from the device and how long they can reasonably be expected to be exposed.
For example, if you assume that someone will be under it for 8 hours (an employee during a work day), the OSHA approved exposure is 90dB, which will likely not be annoying enough to serve its purpose.
Investing in uBeam requires a calculated wager that the threshold for ultrasound safety is a fair bit higher than 100 dB. It's a risky position to take, and I'm not sure how to calculate it, but it's not pure lunacy.
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