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Friday, June 08, 2007 A Wirelessly Powered LightbulbResearchers at MIT have created a revolutionary device that could remotely charge batteries and power household appliances. By Kate Greene
Researchers at MIT have shown that it's possible to wirelessly power a 60-watt lightbulb sitting about two meters away from a power source. Using a remarkably simple setup--basically consisting of two metal coils--they have demonstrated, for the first time, that it is feasible to efficiently send that much power over such a distance. The experiment paves the way for wirelessly charging batteries in laptops, mobile phones, and music players, as well as cutting the electric cords on household appliances, says Marin Soljačić, professor of physics at MIT, who led the team with physics professor John Joannopoulos. The research, published in the June 7 edition of Science Express (the online publication of Science magazine), is the experimental demonstration of a theory outlined last November by the MIT team. (See "Charging Batteries without Wires.") "We had strong confidence in the theory," says Soljačić. "And experiment indeed confirmed that this worked as predicted." The setup is straightforward, explains Andre Kurs, an MIT graduate student and the lead author of the paper. Two copper helices, with diameters of 60 centimeters, are separated from each other by a distance of about two meters. One is connected to a power source--effectively plugged into a wall--and the other is connected to a lightbulb waiting to be turned on. When the power from the wall is turned on, electricity from the first metal coil creates a magnetic field around that coil. The coil attached to the lightbulb picks up the magnetic field, which in turn creates a current within the second coil, turning on the bulb. This type of energy transfer is similar to a well-known phenomenon called magnetic inductive coupling, used in power transformers. However, the MIT scheme is somewhat different because it's based on something called resonant coupling. Transformer coils can only transfer power when they are centimeters apart--any farther, and the magnetic fields don't affect each other in the same way. In order for the MIT researchers to achieve the range of two meters, explains Soljačić, they used coils that resonate at a frequency of 10 megahertz. When the electrical current flows through the first coil, it produces a 10-megahertz magnetic field; since the second coil resonates at this same frequency, it's able to pick up on the field, even from relatively far away. If the second coil resonated at a different frequency, the energy from the first coil would have been ignored. The researchers' approach, says Soljačić, also makes the energy transfer efficient. If they were to emit power from an antenna in the same way that information is wirelessly transmitted, most of the power would be wasted as it radiates away in all directions. Indeed, with the method used to transfer information, it would be difficult to send enough energy to be useful for powering gadgets. In contrast, the researchers use what's known as nonradiative energy that is bound up near the coils. In this first demonstration, they showed that the scheme can transfer power with an efficiency of 45 percent. |
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TR10: Wireless Power
02/19/2008
Comments
devassocx on 06/08/2007 at 1:21 AM
22
Evanescent wave coupling from an article
found in wikipedia. Maybe there are some
detail differences that I don't see.
http://en.wikipedia.org/wiki/Wireless_energy_transfer
oeseikel on 06/08/2007 at 10:15 AM
2
Oliver
zkent on 07/19/2007 at 2:18 PM
1
barrycoleman on 06/08/2007 at 12:03 PM
1
salammoniac on 06/08/2007 at 2:32 AM
2
First off, it runs at 10 MHz, which is forbidden by FCC rules because it is a reserved time standard frequency used by NIST. Should have used the unlicensed 13.56 MHz ISM band instead. You can talk about near fields and evanescent waves all you want. This thing is still a magnetic dipole, and it still radiates some energy, too much at this power level. Did anyone tune a shortwave receiver to 10 MHz and walk around the experiment with it? Or would that be too obvious?
45% efficiency is nothing to crow about. It's lousy, requiring 133 watts to drive a 60 watt bulb. On top of that, I bet that number is coil in to coil out efficiency, not wall socket to light bulb. A simple power cord will be at least 99% efficient, socket to bulb, more if you use a fatter cord. That's why we use wires, dummy.
Having this thing running all the time is the electromagnetic equivalent of turning on the fire sprinklers, so that whenever you are thirsty, all you have to do is hold out your cup.
And patents? Ludicrous... Undercoupled tuned transformers are as old as radio itself, obvious to those skilled in the art, and have long since been used for power transfer. Check old issues of Popular Electronics. I believe there was an article back in the 1960s for a crystal radio that tuned to any strong AM station to get enough power to drive a small amplifier for the weak ones. Sure, it's farfield not nearfield, but the difference is trivial. Tuned nearfield induction has been applied to RFID tags and in many other ways over the years.
Look at the diameter of the coils and their spacing. Want greater distance? No sweat, just scale the coil diameters proportionately. Who wants coils that big for distances that small? And as an EM expert, I know that there is no magic to be uncovered in playing with the coil configuration. Sure, there is some improvement moving from a solenoid to a pancake winding, but nothing to write home about. Wanna see a pancake winding at play? A lot of museum Tesla coils use them for the primary winding, and Tesla coils are (brace yourself) less then unity coupled, resonant inductors.
I'm embarrased for the undergrads who are hyping this thing. It's an experiment that could have been done in a high school electronics class. But, to the young everything is new, and therefore has obviously never been thought of before. Wow, how dumb we have all been to have overlooked this magnetic miracle. Including, apparently, Tesla, Marconi, DeForest...
kitk on 06/08/2007 at 3:02 AM
52
Great lab trick, but like home nuclear reactors, not too wise.
mehzang on 06/08/2007 at 3:48 AM
1
salammoniac on 06/08/2007 at 11:17 AM
2
Mexico. You have attributed powers to this noninvention that defy the laws of physics.
blackfootx2 on 06/08/2007 at 3:54 AM
1
K1GIL on 06/08/2007 at 9:10 AM
1
KN6LX on 06/10/2007 at 8:16 AM
2
The resonant coupling idea sounds strangely similar to a tuned antenna, dont it!
I guess in a world where electronics is defined by FFTs the concept of doing it with hardware does APPEAR to be new. (Any science sufficiently advanced will appear to be magic! Right? :-) )
_ _ . . . . . . _ _
73 de KN6LX
abcarterjr on 06/08/2007 at 1:50 PM
45
trajectory enough to miss the earth?
KN6LX on 06/11/2007 at 8:48 PM
2
Sorry.
majipa on 06/03/2008 at 12:37 AM
1
alpha 07 on 06/09/2007 at 6:10 AM
1
New? This technology was invented by Nikola Tesla more than 100 years ago. Time to recognize his work.
stustanton on 06/09/2007 at 11:45 AM
1
If I were to be a better person than that, I’d point out that there really are surprising and newsworthy results here, that there is a selectivity in tuning suggested by the helix shapes that we know nothing about, that the AC carrier is delivering way more DC power densities than we’d expect, and that Tesla’s nonlinear resonance has never been explained in a way that experts agree upon. Certainly increased understandings of surprising results usually leads to huge leaps in efficacy, so the applications of running light bulbs and charging lap-tops are symbolic baby steps. Consider that the electric automobile operated from wires embedded in the roadway, powering electric motors in cars, if made to work, are 20 times more efficient than gas autos, (fully-loaded, measured from crude-in-the-ground through transportation-at-the-pavement), making a 700 mile-per-gallon automobile equivalent, from coal, using not a drop of foreign oil, not a drop of petroleum chemistry. It’s not problem-free, but it’s problems are suddenly 20 times less in magnitude. Societies change with less than this.
Even these thoughts are primitive.
IMHO, that this has a huge potential is confirmed by the universal negativity of the comments offered.
attoigo on 06/09/2007 at 3:51 PM
2
BuckyOHare on 06/10/2007 at 11:40 AM
3
rttedrow on 06/11/2007 at 5:11 AM
31
ufolj on 06/11/2007 at 7:56 PM
1
At higher power? the loss is so high and it really become useless.
Our PS technology is having difficulties to break that 90% barrier for efficiency.(wasting millions of dollars and lots of energy by every day on that 10%)
So this technology with that 45% efficiency I'm not sure can be good for any practical use.
TMacshane on 08/08/2007 at 3:56 PM
3
hmwogglebugte on 06/12/2007 at 12:47 PM
1
greg1975 on 06/26/2007 at 8:57 AM
1
JonD on 07/26/2007 at 1:59 PM
4
Stop wasting money on experimenting, and spend more time reading through old consumer magazines.
hwalker on 07/27/2007 at 4:36 PM
1