Toward more efficient wireless power delivery

Apr 13, 2010 by David L. Chandler
Graphic: Christine Daniloff

In 2007, MIT researchers announced that they had discovered a novel way of transmitting electricity without the use of wires. Now, the researchers have demonstrated that the system?s efficiency at transmitting energy improves significantly when it is used to charge multiple devices at the same time.

The new work, reported in a paper in earlier this year, has also demonstrated a system much closer to one that could be used to typical consumer . In the original proof-of-concept in 2007, both the transmitter and receiver consisted of coils that were about two feet across. These two units were placed more than six feet apart and were used to light a 60-watt bulb — even with people sitting in between. But the new system uses a slightly larger transmitter, with receivers that are only about a foot across - moving closer to a size that could eventually be built into a PC or a television set. The transmitting coil could be built into a wall or ceiling, the researchers say, and the transfer of power has been shown to work over distances comparable to the size of an ordinary room.

André Kurs, a doctoral student in MIT’s Department of Physics and the lead author of the recent paper, says this reduction in size of the receiving coil is an ongoing process. With some more work on further reducing the coil’s diameter and thickness, “we could embed it in a portable device,” he says.

The basic underlying principle for transmitting power wirelessly goes back more than a century to the work of Nikola Tesla and other pioneers of , but the MIT team invented a way of making the process far more efficient and practical.

The system works by creating a strong electromagnetic resonance between the sending and receiving coils — similar to the way a tuning fork can start vibrating when exposed to a sound of exactly the right frequency, or the way a radio antenna can be tuned to just the frequency of a single station out of the hundreds that are simultaneously broadcasting their signals. In this case, the magnetic resonance between the two coils is unaffected by objects in between the coils, and by the same token objects between the coils — including people — are not affected by the magnetic fields.

The key to that advance — that is, the ability to transmit useful amounts of power using coils of a reasonable size — was found in 2005 by MIT assistant professor of physics Marin Soljačić, who developed the idea along with Kurs, students Aristeidis Karalis SM ’03 ScD ’08 (now a postdoctoral researcher) and Robert Moffatt ’09, and physics professors Peter Fisher and John Joannopoulos.

Although predicted by theory, the increase in efficiency when powering two devices at the same time had not been previously demonstrated in experiments. The team that carried out the recent work — Kurs, Moffat and Soljačić — found that when powering two devices at once, which individually could achieve less than 20 percent efficiency in power transfer, the combined efficiency climbed to more than 30 percent. The two receiving coils resonate with each other as well as with the transmitting coil, and help to reinforce the strength of the magnetic field. Kurs says that the efficiency should continue to rise as more devices are added, climbing toward a theoretical limit of 100 percent. The research has been funded by the NSF, the Army Research Office, DARPA, and a grant from 3M.

The amount of power transmitted in the latest experiment was on the order of 100 watts, but Kurs says that is only limited by the amplifier used for the transmitting coil, and can easily be increased. “It could be several hundred watts, or a kilowatt,” he says — enough to power several typical household devices at once, such as lamps, computers or television sets. “You could feed power to a medium-sized room, and power a dozen devices,” he says.

The researchers set up a company in 2007, called WiTricity, to develop the invention and eventually bring it to market. Most of the Watertown-based company’s principals and board of advisors are MIT professors, students, or alumnae. The company originally estimated it would take several years to develop a commercial product, and have “been making good progress. I think it’s reasonably close,” says Kurs, who works at the company while completing his doctorate. No further breakthroughs are required, the researchers say, just continued engineering work to find the optimum design of the coils and the electrical control systems.

In addition to working on reducing the size of the receiving coils, the researchers are also trying to improve the system for tuning the devices to achieve maximum efficiency. In the laboratory tests, they spent considerable time manually tuning each part of the system, but for a practical consumer product this process will have to be fully automated. “It does get a little harder to tune multiple devices,” Kurs says.

A number of other companies have independently jumped on the bandwagon and begun to develop similar wireless power systems, including large companies like microchip maker Intel and electronics giant Sony. “Quite a few companies have reproduced the original results,” Kurs says.

And Tesla, whom the researchers acknowledge in the footnotes to their papers, would no doubt be pleased by the progress. “He did have the notion,” Kurs says, “but in practice it’s a hard thing to make work. You need a good model of how your coupling varies with distance and how to minimize the losses in the system, and people didn’t have a good understanding of it at the time.”

Explore further: New microscope collects dynamic images of the molecules that animate life

More information: www.mit.edu/~soljacic/wireless_power.html

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User comments : 26

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dirk_bruere
4 / 5 (5) Apr 13, 2010
Would you like to sit in a room where there are kW of EM fields bouncing around? call me a lawyer...
wolfkeeper
2.5 / 5 (2) Apr 13, 2010
It's just magnetism, you're not very magnetic.
wolfkeeper
4 / 5 (1) Apr 13, 2010
FWIW Tesla invented the basic tech for this. His 1902 Tesla coil used it to transmit power an inch or two, within the Tesla coil, to give a good air gap and to avoid arcing from the secondary to the primary. It's exactly the same principle. He didn't get such good range, but then again, I don't think he tried that hard either, he had bigger fish to fry.
Yogaman
4.7 / 5 (3) Apr 13, 2010
Ooh, shiny shiny, but...

a. Any inefficiency vs. a wire yields more CO2.

b. What is the cost to replace the $1-5 wired solution?

c. How will I keep my neighbors from stealing my radiated power? Retrofit a Faraday cage in my apartment?

d. "We" may not be very magnetic, but we are at least a little, and many animals are more so. What evidence gives us confidence that 24/7 exposure to these fields is good for us?

e. Intentionally adding kilowatt radiators throughout the countryside is yet another interesting environmental experiment for our species to undertake as we continue to try to cram as many of our kin onto the planet as we can.

f. Burying a high-power antenna inside a wood-frame wall may not be immediately compatible with local fire regulations.

g. And in the summer, I need extra cooling for the heat generated by the radiated-but-not-received power.

h. Quibble: You cannot get 100% efficiency from any amp-xmt-rcv-rectifier system. Period.
Graeme
4.5 / 5 (2) Apr 13, 2010
80% of the power is being lost, by heating other material near the transmitter. Any conductor whether resonant or not will be sapping power. If the transmitter could be made more elaborate so that it can beam the energy at the receiver, could be made more efficient. It would be better to have the receiver light powered, and be very efficient.
KBK
3 / 5 (5) Apr 13, 2010
We have enough radiation on our lives, this is along the lines of pure insanity. Power RF? What planet are these people from? Where do they get these people? Why do they want to literally fry us and our DNA? What agenda do they hide? Who gave them their degrees? Who empowers these idiot proposals? Like unwanted corporate sponsorship and agendas in a US congressional bill, it keeps popping up in the small print, again and again. It's like trying to convince people they want and need war, torture, and death. Cut from the same cloth.

This idea of power RF in our lives is PURE UNADULTERATED POISON. The real point is to find out who exactly keeps pushing the crap. There, and only there-- you will finally find your real culprit and agenda.

No-one can explain or reason away the death and damage for the human body and any organic form --that can and does occur with high RF power saturation.

So why do we constantly keep hearing someone push this garbage?

This is the real question.
DaveGee
4 / 5 (1) Apr 14, 2010
I'm with you guys... don't get me wrong the 'idea' of wireless power trans. screams to me 'oooh really cool stuff!' but until someone finds a way to do it in a more efficient and a PROVEN safe way... The gadget geek in me has to pass.. However like Mulder... I WANNA BELIVE! :D
plasticpower
4.5 / 5 (2) Apr 14, 2010
This would still be useful in automated environments, like some automated robotic warehouses. No need for the robots to recharge as they move around, they always have power this way.
retrosurf
4.7 / 5 (3) Apr 14, 2010
If 100 million homes all wasted 60 watts, it would take an extra 3.8 average nuclear power plants to take up the slack.
Conservation is the basis of all sound, comprehensive energy policies.
broglia
3 / 5 (3) Apr 14, 2010
If 100 million homes all wasted 60 watts

Many homes are using electricity for heating, but anyway, you're right - it's useless luxury - and maybe even dangerous. Radiowave field can induce sparks on the metalic connections of the furniture, thus setting the fire, for example. It could destroy your IPod. And it could become harmfull even for you - I wouldn't reccomend you to sleep in the stream of 200 W+ radiowave field, especially when you're on pacemaker.
Sky_Marshall
3 / 5 (4) Apr 14, 2010
Nikoli Tesla invented this almost 100 years ago, its not new...
Glyndwr
1.5 / 5 (2) Apr 14, 2010
We are not particularly magnetic, I am not saying it has no impact on health in large doses but I think any health worries are being over hyped
Shootist
2.5 / 5 (4) Apr 14, 2010
We have enough radiation on our lives, this is along the lines of pure insanity. Power RF? What planet are these people from? Where do they get these people? Why do they want to literally fry us and our DNA?


I don't know what else to say but, RF does not qualify as ionizing radiation. RF does not "fry" DNA.

At the same time, one does not want to stand too near the business end of a high powered transmitter. RF will rapidly cook your flesh.

You need to read, "Fallen Angels" by Niven and Pournelle.
interceptor
5 / 5 (1) Apr 14, 2010
why not just tune the recieving coils into the natural magnetic resonence of the earth and get free power.
Slotin
4 / 5 (2) Apr 14, 2010
.. RF does not "fry" DNA...

RF is able to split water to hydrogen & hydrogen peroxide. Hydrogen peroxide radicals could induce cancer.
http://en.wikiped..._Kanzius

Long spaghetti-like molecules of DNA are especially sensitive to low frequency radiation because of resonance

http://www.techno...v/24331/
http://www.telegr...ren.html

So, never say never, when you haven't all data...
Royale
2 / 5 (1) Apr 14, 2010
SHOOTIST!

I see Niven in your comment. And that, my friend, is exciting. I'll read "Fallen Angels" (going now to add it to my nook). You read "Destiny's Road". We can call it even.

And yes, I'd be afraid to stand in the middle of this thing. It's a great idea, but not in an environmentally conscious world. Right?
theguy
3 / 5 (1) Apr 14, 2010
this is old.
they use wireless electricity in electric toothbrush and some electric cars.
but it has a short range.
broglia
3.5 / 5 (2) Apr 15, 2010
Technically, wirelless electricity is used in every transformer - but the wireless power is the stuff of different category. We should microwave few rabbits first before introducing this technology to the market - I don't consider it safe at all.
NeuroPulse
3.5 / 5 (2) Apr 16, 2010
Would you like to sit in a room where there are kW of EM fields bouncing around? call me a lawyer...


Strong electric and magnetic fields have been found to cause hallucinations such as seeing ghosts, angels, demons, and alien abduction. Living very close to a power plant can cause this. It has been reproduced in the lab using transcranial magentic stimulation. Stimulating one hemisphere causes one to sense a benevolent presence, and the other a malevolent presence.
http://en.wikiped...mulation
http://en.wikiped...d_helmet
Nartoon
not rated yet Apr 17, 2010
What happens during a lightning storm?

Putting even a 1 foot coil around ever ceiling light/lamp is insane.
twango
not rated yet Apr 17, 2010
So much wasted energy and why? Wall warts are bad enough.

It'd make a helluva lot more sense to design a universal power daisy-chaining scheme to eliminate cordage by simply plugging components into their neighbors. Combine that with a universal data connector in the same scheme to eliminate most messy wiring. *One* source, *one* chain.
Forestgnome
1 / 5 (1) Apr 17, 2010

You need to read, "Fallen Angels" by Niven and Pournelle.


Good book! Very relative in today's environment.
Forestgnome
3 / 5 (2) Apr 17, 2010
FWIW Tesla invented the basic tech for this. His 1902 Tesla coil used it to transmit power an inch or two, within the Tesla coil, to give a good air gap and to avoid arcing from the secondary to the primary. It's exactly the same principle. He didn't get such good range, but then again, I don't think he tried that hard either, he had bigger fish to fry.

Didn't get such good range? You need to read more about Tesla.
retrosurf
not rated yet Apr 18, 2010
why not just tune the recieving coils into the natural magnetic resonence of the earth and get free power.


Schumann resonances manifest themselves as pico-Tesla variations in the earth's field

Let's say you have an antenna loop that stretches from the ground to space, approximately square in cross section, say 50x50 miles. That's 7 billion square meters, and the field varies by a nano-weber 8 times a second.

A single turn of wire will yield about half a volt from Schumann resonance (.4340 volts), at about .0008 amps. Each additional turn in your 50x50 mile antenna will get you another .43 volts!

To get the same energy that is in a single AA battery, about 3 watt-hours, you would have to receive energy from your big antenna for 7500 hours.

That's 10 months. And I bet your antenna would cost at least a billion dollars. That's pretty expensive free energy.

I might have made some mistakes in the math, and I would be glad to hear about them. But

rgw
not rated yet Apr 19, 2010
Would you like to sit in a room where there are kW of EM fields bouncing around? call me a lawyer...

You're a lawyer.
Alizee
Apr 21, 2010
This comment has been removed by a moderator.
DrSmallberries
not rated yet Apr 22, 2010
so, MIT is finally where Tesla was 100 years ago, great. open your eyes, folks. the next order-of-magnitude science advances will occur only after a *dogmatic* paradigm shift, not a technological one -- one that sweeps away all the mimetic-limit overhead that's keeping Big Brother not only close-minded, but woefully in charge.

-dr.S