
'Power Over Wi-Fi' named one of the year's game-changing technologies - tdurden
http://www.washington.edu/news/2015/11/18/popular-science-names-power-over-wi-fi-one-of-the-years-game-changing-technologies/
======
jimrandomh
From the paper: "For instance at a distance of 2 feet the battery charging
system has 100 µW available compared to 10 µW at 10 feet." The Popular Science
and UW Today articles both completely avoid numbers. But the numbers are
vital, and if you do a little fermi math, you'll discover that's not enough to
compete with watch batteries.

(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.)

~~~
imglorp
That's not going to charge your notebook so fast, but that's plenty to power
your thermostat, your tv remotes, your burglar alarm sensors, and some of the
other lesser IoT bits floating around.

~~~
olympus
It's not enough to power a thermostat. µW is microwatts. WiFi radios need
milliwatts. As jimrandomh mentioned, the levels of power here are the same as
what a watch battery can provide for eight years. Watches don't even run off
of a watch battery for eight years.

~~~
jacquesm
It is _more_ than enough to power a thermostat. Just not all the time. The
trick is to wake up from deep sleep often enough to do the job.

------
NikolaeVarius
It's pretty interesting to me that while we simultaneously demand that
companies build everything with power efficiency in mind and embrace
environmental consciousness, we take all this power and use it in increasingly
inefficient ways.

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.

~~~
Dylan16807
In the end, I'm happy with a "five steps forward, one step back" situation
where we spend a bit to fight big inefficiencies and then allow some smaller
ones for convenience's sake.

~~~
TeMPOraL
Right now it's one step forward, five steps back. Or, with this idea, a
hundred steps back. We don't have spare power. Let's talk about it again after
we get the planet off coal.

~~~
Peaker
Isn't charging small watches a negligible amount of energy?

------
gamesbrainiac
I talked to two of my friends who wanted to do some research into this. They
told me, that in the end, power over WiFi was too inefficient, so in
practicality (since they were working with phones), the technology wouldn't
actually charge phones up per se, but rather make them lose charge more
slowly.

~~~
rgarrett88
Yeah, I noticed the article wouldn't mention how much power they actually
captured.

~~~
rm999
I just skimmed the paper, they achieved 10 microwatts at 10 feet. Yes, micro:
this is about a million times less power than a modern smartphone or laptop
charges at.

------
Eduard
We need encryption for Power over Wi-Fi or else my neighbors will steal my
electricity.

~~~
livingparadox
They can't "steal" your electricity. The output from the Wi-Fi is constant,
and range limited. If they are getting any power from your signal, its power
that you'd be casting off outside your house anyways. Net change in power
would be 0.

~~~
lnanek2
Technically, if you have the WiFi password you can have a modern luxury router
beam form more signal to you than otherwise. Although my router has multiple
5GHz radios and one 2.4GHz, so it will just move me over to another radio if
only one person is leeching. More clients does probably keep more radios on,
using more power as well, since otherwise the router can probably sleep more
hardware more often. Sort of like a Bluetooth device being discoverable keeps
the radio on more, then making it connectable makes it keep the radio on more,
etc..

~~~
livingparadox
Did not know this was a thing... Is that a common ability in a router?

~~~
projct
many 802.11ac devices can do beam forming
[http://www.pcworld.com/article/2061907/all-about-
beamforming...](http://www.pcworld.com/article/2061907/all-about-beamforming-
the-faster-wi-fi-you-didnt-know-you-needed.html)

------
olympus
Is it really "game-changing?" You can only use it for low power devices which
could also be powered by a small lithium battery for a year. So preventing me
from having to change a battery once a year is now game changing?

~~~
dmd
In a world where you have 100s of such devices, absolutely.

~~~
jacquesm
And not only that, some devices are very hard to reach once they are
integrated and their mailfunctioning due to failed batteries would be a show-
stopper if the expected lifetime of the device is a multiple of the expected
battery life.

~~~
TeMPOraL
I guess we could beam power to them, using a _strongly directional_ signal.
Boosting Wi-Fi power to charge devices seems like absolutely mind-boggling
waste.

~~~
jacquesm
For that you'd need to know where they are.

~~~
TeMPOraL
Phased array antenna and some feedback system, so that I can track the device?

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.

~~~
jacquesm
Let's see: where is my 'x' (tools, keys, shoes, glasses etc), data acquisition
(temp in any room in the house for instance), various scada applications that
now require a large amount of wiring (alarm systems for instance) and so on.
It'd be quite the wave of new technology. Imagine, nothing would ever be
'lost' again once you knew it was yours before.

The possibilities for use _and_ abuse are just about endless.

~~~
TeMPOraL
Uh, ok. I see my imagination isn't good today; now that I see them, those
examples are pretty obvious. Though I admit I was thinking about devices that
eat _much_ more power.

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.

------
sannee
Let's see

They claim 10uW at 3 meters.

A random Lithium Thionyl Chloride battery
([http://www.xenoenergy.com/eng/file/Xeno%20Catalog%20XL-050F_...](http://www.xenoenergy.com/eng/file/Xeno%20Catalog%20XL-050F_E.pdf))
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)

------
michaelcampbell
[https://news.ycombinator.com/item?id=10593008](https://news.ycombinator.com/item?id=10593008)

~~~
ohaal
Hm, I'm curious why this wasn't caught by the HN anti-duplicate. Previously
when I've (obliviously) posted an already posted URL, I've been redirected to
the comments of the pre-existing URL. The URLs are literally exactly the same.

~~~
_yy
HN anti-duplicate allows resubmit for URLs which weren't well received at the
first attempt.

------
rubidium
Paper (linked in article) is here:
[https://homes.cs.washington.edu/~gshyam/Papers/powifi.pdf](https://homes.cs.washington.edu/~gshyam/Papers/powifi.pdf)

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.

~~~
jacquesm
It is interesting and could be a game changer for the 'internet-of-things'.
WiFi is everywhere and just to be able to run a device a couple of seconds per
day without having wires attached to it could enable a huge number of
applications.

~~~
violentvinyl
This got me excited about the idea. Like many others my first thought was that
it can't be nearly efficient enough to charge my phone, but I hadn't even
considered all the little low power sensors I could place around the house
that I wouldn't bother with if they all needed to be wired into mains power.
Think window break and door lock sensors, etc.

~~~
TeMPOraL
> _Think window break and door lock sensors, etc._

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.

------
transfire
We already have it. It is called solar power. Please use it.

------
daveed
I think a company at this summer's YC did something similar (using wifi):
[http://techcrunch.com/2015/08/18/hardware-demo-
day/](http://techcrunch.com/2015/08/18/hardware-demo-day/) ctl+f "supply"

------
vincentkriek
First tech needs to focus on small distance wireless power. I need to be able
to easily and reliably charge my phone wirelessly. Plugging in wires is just
straight up old fashioned. Qi is really getting mainstream now but having to
position the phone perfectly is not that great. I know of A4WP with NXP as one
of the main companies developing tech that can charge everything over the pad,
no matter the placement. It also includes stacking. If we can build out this
to also be integrated in laptops, lamps and other "put down" devices, I can
believe this can evolve into something larger doing it over a bigger distance.

~~~
jacquesm
The one thing I can think of is to massively reduce the power consumption of
phones. That would go a long way towards making various wireless charging
methods (including solar, by the way) much more feasible. Todays phones are
very power hungry.

~~~
TeMPOraL
That's because (smart)phones are portable general-purpose computers. I see two
ways of reducing power use.

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.

~~~
jacquesm
I don't agree phones are 'general-purpose computers'. They're just end-points
of very large eco-systems locked down in as many ways as possible.

Here is one thread about that:

[https://lwn.net/Articles/662147/](https://lwn.net/Articles/662147/)

~~~
TeMPOraL
I know. I tend to whine about it on HN every now and then :). But this time I
meant it from an engineering point of view. Smartphones don't run on ASICs but
on general-purpose microcontrollers, they have a general-purpose OS capable of
running arbitrary code. And they run staggering amounts of it.

------
Arnt
Won't this raise the noise floor considerably for any other networks nearby?

------
an4rchy
Finally, something that might actually be available to consumers.

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.

~~~
TeMPOraL
> _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?_

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.

------
Eclyps
I am a serious layman when it comes to this type of stuff, but I swear I
remember reading about similar wireless power years ago. I even remember
seeing a video of a lightbulb being illuminated without being attached to
anything. What makes it this year's game-changing tech? Is it the WiFi aspect?

~~~
frgewut
Yes, Tesla demonstrated wireless power in 1891

~~~
_fizz_buzz_
Wireless transmission has been demonstrated by others before Tesla e.g.
Heinrich Hertz. And I mean induction is arguably a form of wireless
transmission which has been verified by Faraday in the 1830s. The problem is
now as it was then that wireless transmission is governed by the inverse
square law and therefore inefficient to the point of being unusable in most
real world application.

------
mtw
What are the health implications of this?

~~~
egwynn
It doesn’t sound like they are talking about boosting the power output from
access points, so I guess this is, WLOG, the same question as asking “what are
the health implications of wi-fi?” I don’t mean to imply that the answer is
‘none,’ but this new development doesn’t seem to change any of the relevant
primary factors (i.e., how much energy the human body absorbs from wi-fi
transmitting antennas).

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?"

~~~
mtw
I wonder if someone experimented in boosting the signal x1000 and see if it
creates side-effects in organic matter (of varying conductivity, for example
skin, brain neurons etc.)

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

------
TrevorJ
Is this fundamentally different than how RFID works? I'm curious if anyone who
knows could chime in.

~~~
jacquesm
A typical RFID chip has nearby a coil that is used to temporarily power up the
chip using regular magnetic coupling using a (relatively) low frequency.

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.

~~~
ccozan
C'mon, is not _fundamentally_ different, since both techniques use EM energy.
And guess what, where is the RF in RFID comes from??

In order to harvest power from EM (RF) you need a nantenna, a micro rectifying
antenna, aka [1].

[1]
[https://en.wikipedia.org/wiki/Rectenna](https://en.wikipedia.org/wiki/Rectenna)

~~~
jacquesm
Wifi does not use _magnetic_ resonant coupling.

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.

~~~
JoeAltmaier
In fact they are the same - one is the derivative of the other. So the RFID
scanner emits a radio wave; the RFID chip magnetically couples to it to
provide a small charge; enough to run the RFID circuitry for a few
milliseconds.

~~~
jacquesm
At the frequencies and distances at which WiFi normally operates the magnetic
component is all but invisible, it's mostly a matter of electric fields.

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).

------
anilgulecha
Wont the efficiency be ridiculously low -- wifi signals are not really
targeted.

~~~
gus_massa
I agree, it's ridiulouly low. From the article:

> _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](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.

------
thefastlane
call me a fuddy-duddy but i want to be convinced that there are no adverse
health affects -- or understand what the risks are, however minute.

after all, one can get cancer (and die from it) from something as 'harmless'
as sunlight.

~~~
gsteinb88
Sunlight is ionizing radiation -- the ultraviolet light is capable of knocking
electrons off their atoms, damaging nearby biological systems. 2.4 GHz radio
waves cannot do this; absorption just causes local heating (in this case,
truly infinitesmal amounts).

I dont know whether that meets the standard of convincing you, but it is
fantastically well established science.

~~~
thefastlane
thanks, i appreciate the response; that's a distinction i didn't know about.

------
ultim8k
Is that Tesla's dream coming true?

~~~
jacquesm
Not really. Tesla's dream was to set up a resonant field around the globe with
a few giant base-stations that one could tap into at will to draw power. For
many reasons that was an absolutely un-workable proposal, the major ones being
that nature put up a roadblock or two on the way to getting that to work on
anything but the smallest scale.

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?'

~~~
ColinDabritz
I love that the context makes "power law" sounds like anti-competitive
regulation, rather than a natural phenomenon.

------
dang
Url changed from [http://phys.org/news/2015-11-power-wi-fi-year-game-
changing-...](http://phys.org/news/2015-11-power-wi-fi-year-game-changing-
technologies.html), which points to this.

------
JustSomeNobody
Can we ban anything that mentions "game-changing" already?

Please? Pretty Please?

