Wireless electricity

June 10, 2007 4:04 PM

MIT team experimentally demonstrates wireless power transfer. WiTricity action photos. Previously. Related.
posted by phoque (46 comments total)

I can't wait to have to explain to my kids that "Back in my day, you had to plug in your laptop because the battery only lasted so long. And before that you had to plug it in for the internet too! And before that, computers only sat on your desk, they were too big to take around and put on your lap!"

I can't help but be disappointed that there aren't any wild arcs of electricity between the power source and the lightbulb, but perhaps it's safer without that...
posted by CitrusFreak12 at 4:09 PM on June 10, 2007

I can't wait for the electrosensitivity nuts to get wind of this.
posted by Artw at 4:17 PM on June 10, 2007

For as long as I can remember I have wished for wireless electricity, but I've always talked about it as a bit of a pipe-dream.

I love you MIT!
posted by knapah at 4:24 PM on June 10, 2007

oops, premature due to over-excitement.

If they ever make it work really well it'll be interesting to see how we would be charged for electricity.
posted by knapah at 4:25 PM on June 10, 2007

This will make it far easier to recharge your plasma gun while looking for the yellow keycard.
posted by brain_drain at 4:26 PM on June 10, 2007 [2 favorites]

I had an idea like that for taping high-tension power lines. Inspired by this. I'm not sure if it's based on the same principle, but I think it is.
posted by delmoi at 4:27 PM on June 10, 2007

Yeah, power a laptop with a huge magnetic field.

I can't think of anything that could go wrong.
posted by mzurer at 4:27 PM on June 10, 2007

when are they going to do that internet thru electric sockets thing?
posted by amberglow at 4:31 PM on June 10, 2007

when are they going to do that internet thru electric sockets thing?

Beleive it or not I've seen that done - not with the intenet per-se but with a simple network. This was back in the UK in the 80s, so I'm a bit hazy on what was involved techinally and why it never really took off. I'll have to have a look tyo see if I can find anything on that.
posted by Artw at 4:34 PM on June 10, 2007

Actually in their example they had to use a pretty big transmitter and receiver. Who knows if they'll ever be able to shrink it down small enough to be practical.
posted by delmoi at 4:35 PM on June 10, 2007

Didn't Tesla do this oh, say, 100 years ago?
posted by Balisong at 4:42 PM on June 10, 2007 [4 favorites]

IANAP (I am not a Physicist) but the article appears to say that this system only has 40% efficiency. If that means that half of the energy is lost in transit this system is unfortunately environmentally completely untenable.
posted by simonw at 4:53 PM on June 10, 2007

amberglow, they are trialing that (i think they are calling it PowerLine) in the midwest somewhere.
posted by misterbrandt at 4:54 PM on June 10, 2007

This is going to kill the bees.
posted by WolfDaddy at 4:55 PM on June 10, 2007

Didn't Tesla do this oh, say, 100 years ago?

That was my first thought. My second thought was "who's going to be the new Edison to come along to discredit them, steal their ideas, and become rich and well respected for it?"

Then I remembered that my coworker just named his new kid Edison. Uh oh.
posted by bigtex at 5:05 PM on June 10, 2007 [1 favorite]

“I had an idea like that for tapping high-tension power lines”.

The utilities are pretty sensitive to transmission loss they don't expect and they will track it down.
posted by Ethereal Bligh at 5:06 PM on June 10, 2007

IF HUMANS WERE MEANT TO FLY THEY WOULD HAVE WINGS
posted by disclaimer at 5:15 PM on June 10, 2007

Better pictures

The first shows better the size and simplicity of devices.

The second is fun. They are sitting directly between their vibrating energy machines which were funded by the Institute for Soldier Nanotechnologies.

Which leads me to think ... mild mannered professors and students by day ... wireless light terror fightin' group at night.
posted by phoque at 5:17 PM on June 10, 2007

Yes, this is an old concept. The real problem is if you're shooting high power radio everywhere dont be surprised if your other electronic gizmos start going out or if there's some health issue involved. Secondly, efficiency is a real problem here too. Some of the neat contact pads that are being demo'd have pretty lousy efficiency, this has worse.
posted by damn dirty ape at 5:37 PM on June 10, 2007

IF HUMANS WERE MEANT TO FLY THEY WOULD HAVE WINGS

Dang, you're right, I demand we smash the machines!
posted by mattoxic at 5:38 PM on June 10, 2007

Tesla solved the problem by simply pumping the planet full of potential energy. Then all you would have to do is stick a wire in the ground to have electricity.
Unfortunately, you could do it anywhere on the planet.
His works were stolen and trashed because of these "Socialist" concepts.
What good is it to pump America full of power if those dirty Chinese and Argentinians can have the same access to the power? How do you charge for it? etc.

I drive by the power plant that Tesla melted/blew up every day. Now they just use it for burning seized drugs. And they don't do that very well, either... (wink).
posted by Balisong at 5:49 PM on June 10, 2007

when are they going to do that internet thru electric sockets thing?

It's been technically feasible for a long time, but there are many practical problems. The power grid is a very noisy environment with all manner of junk attached to it, and so is your home. Power lines are unshielded, which would both cause and be affected by RF interference in the part of the spectrum used. The signal can't go through existing transformers, so they'd have to be replaced or new equipment installed at each one to route around it. By the time you spend what it takes to mitigate all these problems, your capital expenditure approaches what it would cost to roll out more appropriate dedicated infrastructure instead.
posted by George_Spiggott at 5:54 PM on June 10, 2007 [1 favorite]

WiTricity is based on using coupled resonant objects. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects.

Q.E.D.
posted by rob511 at 6:05 PM on June 10, 2007

when are they going to do that internet thru electric sockets thing?

you mean like this?
posted by YoBananaBoy at 6:06 PM on June 10, 2007

I'd like to point out that our appendiges can act as antennas. This is essentially why Tesla stopped -- there's no way to safely do it.

Also, nowhere in these articles do I see exactly what they're doing that's particularly different. Is this different from all of the other wireless electricity experiments that've been done before? (this is a serious question -- the articles are ambiguous)
posted by spiderskull at 6:07 PM on June 10, 2007

here's some slides from soljacic's talk at the industrial physics forum last year. one of the things pointed out is how this is different from other work like tesla's, namely radiative vs. non-radiative coupling.

they are short on words and high on pictures (as good presentations should be), but the last slide says "okay, so how come nobody thought of this before?"

a problem as i see it has to do with safety. what happens if you have a metal thingy that happens to be the right size and shape to couple well enough to the field? you touch it and all of a sudden you're plugged in. sure, you know not to put metal things inside the microwave, but what if your whole house is a microwave? this is exactly the opposite principle from what guides safety engineering these days.
posted by sergeant sandwich at 6:28 PM on June 10, 2007

Yes, this is very different from simple magnetic induction, and bears no relation to Teslas work.

To remedy this, the researchers designed an emitter to make use of long-lived resonances with "non-radiative" objects. This keeps the energy close to the antenna until another object with a similar resonance comes within range—no broadcasting into space is necessary. The two resonating objects can sync their frequencies easily, which would then cause energy to "tunnel from one object to another," Professor Soljacic told the BBC. When not transferring energy to another device, "most" unused energy simply gets reabsorbed into the emitter. - Ars Article

This uses quantum tunneling in a novel way that is beyond the feeble intellectual grasp of this EE in training.
posted by phrontist at 6:29 PM on June 10, 2007

Did anyone actually read the article?

At first glance, such a power transfer is reminiscent of relatively commonplace magnetic induction, such as is used in power transformers, which contain coils that transmit power to each other over very short distances. An electric current running in a sending coil induces another current in a receiving coil. The two coils are very close, but they do not touch. However, this behavior changes dramatically when the distance between the coils is increased. As Karalis, a graduate student in electrical engineering and computer science, points out, "Here is where the magic of the resonant coupling comes about. The usual non-resonant magnetic induction would be almost 1 million times less efficient in this particular system."
posted by phrontist at 6:33 PM on June 10, 2007

thanks, George and everyone else.
posted by amberglow at 6:37 PM on June 10, 2007

I'm going to use it to power my new game system - it'll be WiiWiTricity.
posted by pombe at 6:38 PM on June 10, 2007

when are they going to do that internet thru electric sockets thing?

Since 1975! HomePlug, Devolo, Solwise and eConnect all offer networking through your plugs. Never tried it myself, but it's one of those things like fixed wheel bikes or Newtons that seem really attractive thanks to the 'passionate users', which is code for 'nutters'.
posted by jack_mo at 6:55 PM on June 10, 2007

When you're in the dark and you want to see,
You need uh... WiTricity, WiTricity.
Flip that switch and what do you get?
You get uh... WiTricity, WiTricity.
Every room can now be lit
With just uh... WiTricity, WiTricity.

Where do you think it all comes from
This powerful... WiTricity, WiTricity?
By quantum tunnels to here it comes,
They're bringing uh... WiTricity, WiTricity.
posted by octobersurprise at 6:55 PM on June 10, 2007

I suspect that this will just lead to a whole new level of denial of service attacks - imagine being able to go after the electrical supply! You could either try to drain more power than the system could handle, or do something to screw up the resonance.

And if we didn't have enough stories about people "stealing" free WiFi from coffeeshops, this will be even more interesting, depending what kind of range they can pull out of devices like these.
posted by adipocere at 6:57 PM on June 10, 2007

This uses quantum tunneling in a novel way that is beyond the feeble intellectual grasp of this EE in training.

phrontist, the analogy to tunneling comes about because the electric field has an evanescent tail that extends beyond the resonator into free space where its propagation is forbidden; introducing a second resonator that couples to this evanescent field in a way thats basically a form of frustrated total internal reflection.

tunneling in quantum mechanics comes about from the same kind of evanescent-tail coupling, only in QM its the particle wavefunction that extends into space, not an electromagnetic field. really, the FTIR analogy is the better one since there isnt anything quantum mechanical about this at all.
posted by sergeant sandwich at 7:00 PM on June 10, 2007

whoa.

/neo
posted by exlotuseater at 7:37 PM on June 10, 2007

Does this mean I can filch power from my neighbours if I have the right-shaped widget?
posted by meehawl at 7:48 PM on June 10, 2007

This uses quantum tunneling in a novel way that is beyond the feeble intellectual grasp of this EE in training.

This doesn't use any quantum mechanics, someone just used the word "tunneling" in an explanation somewhere.
posted by delmoi at 8:11 PM on June 10, 2007

So just to clear this up, when they say "non-radiative" do they mean "waves decay faster than 1/r^2"?
posted by noble_rot at 9:14 PM on June 10, 2007

I've just been looking this up in my old E&M book..

So the wave equations for an electromagnetic wave are:

∇²E + k_c²E = 0
∇²H + k_c²H = 0

k is known as the wavenumber, and in general it is complex (hence k_c). It is determined by the transmission medium (permittivity, permiability, and conductivity) as well as the wave frequency.

The solutions to those equations are complex exponentials, the imaginary parts being sinusoidal oscillations, and the real parts exponential decays. It is the imaginary part of k which leads to the oscillations, and hence the 'normal' wave propagation. Often, the real part of k is minimized or ignored.

In their scheme, they make k real (or at least the real part is not much smaller than the imaginary part), which makes an evanescent wave.
posted by Chuckles at 10:27 PM on June 10, 2007 [1 favorite]

Physics aside, I stick by my previous comment.
posted by Chuckles at 10:30 PM on June 10, 2007

do they mean "waves decay faster than 1/r^2"?

No, in case it wasn't clear :)

Things decay by 1/r^2 because they are dispersing spherically (the flux is diverging, to be more mathematically correct about it). E-M waves decay by 1/r^2 when they have a spherical radiation pattern in a lossless medium. E-M waves also decay do to the lossyness of the transmission medium (the real part of k in the complex exponential solutions to the two equations I typed up above there).
posted by Chuckles at 10:40 PM on June 10, 2007

Err.. "No", except that exponential decay is faster than 1/r^2.. So, it is true that the waves decay faster than 1/r^2, in a certain sense, but that isn't what they mean exactly. :)
That's 4 in a row.. Time to shut up.
posted by Chuckles at 10:43 PM on June 10, 2007

It's only a matter of time until this is a practical method of powering out gadgets. Although in this particular case, 'practical' may have to be stretched a little to accommodate our lead kilts!
posted by a_s_m at 12:06 AM on June 11, 2007

It's promising that their magnetically coupled resonators don't evect organic critters, but what about harddisks, pacemakers, etc.? You might need a solid state laptop.

I can't imagine this eliminating batteries soon, but your doing great if your cofee table & desk recharge your shit. But how much effort would be saved by merely standardizing powerplugs?
posted by jeffburdges at 1:58 AM on June 11, 2007

Since 1975! HomePlug, Devolo, Solwise and eConnect all offer networking through your plugs. Never tried it myself, but it's one of those things like fixed wheel bikes or Newtons that seem really attractive thanks to the 'passionate users', which is code for 'nutters'.

I'm using that right now! While I may well be a nutter, it's not for that reason. It's a great way to extend Ethernet through an old house. Wireless doesn't work so well in here.
posted by me & my monkey at 6:19 AM on June 11, 2007

Then I remembered that my coworker just named his new kid Edison.

I named one of my cats Edison. He's always getting into trouble and discovering new ways to liberate my bread.
posted by drezdn at 6:58 AM on June 11, 2007