'Power Over Wi-Fi' named one of the year's game-changing technologies
washington.edu
washington.edu
(The first watch battery I found with numbers on it had 240mAh*3V=720mWh, so one such battery could in theory provide 10 µW for 7.2e4 hours or 8 years.)
Seriously, wireless power has existed for over a century, we don't use it because 99% of the power you throw out goes to waste.
Personally, I'd put up with a 50 watt device that only gets a watt to my phone. I'm pretty sure that's doable with a smart transmitter and small receiver.
Don't know about your, but my phone tends to draw ~2.4W when idle with screen on, and I'm pretty sure it stays over 1W even with screen off. That watt would, like 'gamesbrainiac said only make it lose charge more slowly.
And that's just one phone. My household has 4, not counting other mobile devices like tablets and Kindles. Putting a 2% efficient (!) power system to use seems like a crazy and absolutely scary idea. Just multiply that over the number of potential users (~2 billions).
Also, 98% of this energy will have to go somewhere. It probably means heat.
But the only time my phone drains 1 watt with the screen off is when it's doing cellular data transfers with a terrible signal. It has an 8 watt-hour battery and it lasts more than 8 days when I toss it on a shelf to wait for calls.
So if my phone's sitting there using 1/25 of a watt, a 2% efficient maintenance charge only costs 2 watts. And we can do much better than 2%.
And that in turn does not take into account the real efficiencies involved, I would be highly surprised if a device like the one you described had even a 2% efficiency.
See my other reply, I don't need anywhere near 1 watt average for my phone.
When I see a report from MIT of a 1 foot receiving coil running at 20% efficiency at 7 feet, I don't see what's unreasonable about a phone receiver beating 2%. I said at the start I wasn't talking about using undirected transmission.
In practice this effect should be small though (for the case of Wi-Fi power).
What I mentioned is a natural extension of information-theoretic arguments to computational hardness assumptions; they're the same assumptions that allow safe encryption methods in spite of them being 'broken' in an information-theoretic sense (which doesn't consider computer limitations). Without those limitations only variants of the one-time pad are secure and public key crypto (which relies on integer factorization hardness) is impossible.
Some basic readings if you're interested:
https://en.wikipedia.org/wiki/Maxwell%27s_demon#Recent_progr...
https://en.wikipedia.org/wiki/Computational_hardness_assumpt...
I assumed you meant PoE, but just the first paragraph of that document was fkn hilarious. I needed the laugh.
Anyway, you obviously have something particular in mind; could you give an example of a device, for which an omnidirectional wireless solution would make sense, factoring in inefficiencies?
The only similar-sounding problem I'm familiar with are long-lived devices mounted underwater or otherwise mounted inside a structure. I've seen wireless power via inductive coupling being used to power such devices, because both the device and battery pack can be sealed off from the environment during manufacturing, and replacing the latter doesn't require any disassembly.
The possibilities for use and abuse are just about endless.
As for "where is my 'x'", I'm actually surprised this isn't a solved problem yet, but I attribute it to the fact that we're still in the early IoT era, when every company wants to lock us in into their bullshit ecosystem of beacons and beacon apps. Though maybe it's changing, now that (again) China is popping out cheap BLE tags.
They claim 10uW at 3 meters.
A random Lithium Thionyl Chloride battery (http://www.xenoenergy.com/eng/file/Xeno%20Catalog%20XL-050F_...) for about 2$ can deliver 35uW for 10 years in a ridiculously small package. This well outlasts the lifetime/usefulness of anything which could be potentially connected to it. And even if not, changing a battery every 10 years is not exactly a huge problem.
(Disclaimer: I have only skimmed the paper very quickly)
Disregarding the usual HN snark for media terms ("game-changing") and the usual criticism ("been done before", "won't be effective"), this is actually really cool. If we look at all the innovations in the past year, this is a pretty dang neat one.
They mention Tesla in the opening line of their paper. In short, the biggest innovation they came up with was solving the mismatch of Wifi operation and optimal power transmission. Read the paper; it's quite good stuff.
A fun tech I had in my hands once that I haven't seen being use anywhere is turning kinetic energy into power. I've played with a light switch that can generate enough energy from you just pressing them, that they can boot up an internal uC, a radio, and then send a signal. The device had a typical home-automation range of several meters. I've been told that there are versions mounted into window handles, etc.
1) Go back to small, low-power screens and physical keypads for data input.
2) Heavily optimize the stack. You could put less power-hungry parts in a smartphone, but then it wouldn't boot up. Even top phones have trouble keeping up with software bloat, being somewhat-usable when you buy them, and barely-usable after a year or two. And let's not talk about the cheap phones, which have barely enough power to run the OS.
Here is one thread about that:
To everyone else that is talking about it not happening because of inefficiencies etc, wouldn't the fact that we are also working on ways to generate more renewable energy and working on improving efficiency factor into this equation?
If nothing, any extra improvement in energy efficiency can be considered the overhead needed for wireless power.
It might start of as a luxury more than a necessity.
One of the most important questions of the early XXI century is whether we'll manage to switch the world from coal to green energy before we cook the planet and without starving big parts of the population for power. One of the talking points is the observation that renewables may not be efficient enough yet and we may not be able to pull it off without going into nuclear ASAP. We have barely enough energy, the third world is rising their living standards to the point they themselves will need a shit ton of power for things like fridges, washing machines and hot showers, and we're thinking of putting all our surplus into ridiculously inefficient things like wireless power?
I think if this idea gets into market now, I'll ask Copernicus to stop this planet and let me get off.
> It might start of as a luxury more than a necessity.
Yes. The kind of luxury like using up $30 000 worth of water in the middle of a drought in California, just because you can. Rightfully pissing everyone else off.
0. http://www.technologyreview.com/news/413957/intels-wireless-...
EDIT: Sort of nevermind? I re-read and see that they are telling the access points to send more data, but not to send them above or beyond the antennas’ already-intended power output. So I guess the analogous question is, “what are the health implications of using your wi-fi a lot?"
Also "already-intended power output". If this available, there is motivation for buyers to hack the device and boost significantly the signal -- whereas there's little motivation to hack existing wifi devices
For the power transfer, both generate an electromagnetic field, which is received by an antenna, then converted to DC by a Detector (eg a rectifier).
So the principle is the same, but the details of the technology differs, as does the frequency, type of antenna, etc.
There are many tutorials out there on the web if you care to do some research.
That same coil is then used as the antenna (at a much higher frequency) to transfer a little bit of data.
So yes, it's fundamentally different, the article describes energy transfer using radio frequency waves alone.
In order to harvest power from EM (RF) you need a nantenna, a micro rectifying antenna, aka [1].
To expand on that, the difference is (in laymans terms) 'radio waves' versus 'magnetic fields'.
The difference being that in WiFi the magnetic field component is not relevant and in NFC technologies such as RFID it is the main component (the hint is whether the main active component is a coil or an antenna).
There is a close relationship between the two fields governed by Maxwells equations.
At lower frequencies the electromagnetic field portion becomes dominant. This is one reason why the 'antenna' inside one of those old fashioned AM receivers is actually a coil with a ferrite core (and conveniently internal to the device), and an FM radio (the A/F have to do with the modulation, not specifically with the frequency but the bands are between 455 and 1600 KHz vs 88-108 MHz) typically uses a rod antenna.
Now you could make an FM radio with a coil for its antenna or an AM radio using a rod but neither would be very efficient.
So it's the small distance and low frequency of RFID technology that drive the choice for magnetic coupling, whereas the high frequency and longer distances of WiFi make the choice for antennas.
AM radio, with its low frequency and enormous power output allows magnetic pick-up at very large distances from the point of origin, this is also why it is not 'line-of-sight' but WiFi is line-of-sight (yes, you can bounce radio waves off objects (such as the moon or the Heavyside layer) but that's another subject entirely).
The higher the frequency of operation the more you'll be looking at properties resembling those of light (which is also a form of electromagnetic radiation).
> In their proof-of-concept experiments, the team demonstrated that the PoWiFi system could wirelessly power a grayscale, low-power Omnivision VGA camera from 17 feet away, allowing it to store enough energy to capture an image every 35 minutes.
I made a back of the envelope calculations for a similar project ( see https://news.ycombinator.com/item?id=10323565 ) This other projet claim that they can harvest ~30µW, this is very little. For example, it can only blink a led a few times per minute, because a normal led use 30mW=30000µW. Read the complete comments for more details.
after all, one can get cancer (and die from it) from something as 'harmless' as sunlight.
I dont know whether that meets the standard of convincing you, but it is fantastically well established science.
Maxwell laid out the maths and Hertz demonstrated the principles many years before Tesla.
They are both needed. They shouldn't be compared.
For one there is this thing called a power-law which required the voltages to be significantly higher than those needed to make a system like this work in a laboratory, the other is the breakdown voltage of the atmosphere, which causes any voltage in excess of this to return to ground, frying whatever it finds in its way (think lightning).
It would have made for a hell of a display piece.
Of course this does not stop Tesla groupies from claiming the government suppressed the design.
On another note: regular radio frequency transmitters put out enough power that so called 'crystal radios' can be powered by the transmitter directly. So in a way 'the system works' but the amounts of power that you can draw from it are minute. Tesla claimed that you could run regular industrial machinery from his technology. There is a funny parallel between the Tesla story and uBeam, the dreams are remarkably similar. 'Wouldn't it be a good thing if wireless power with substantial power transfer existed?'
Please? Pretty Please?