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Friday, June 08, 2007

A Wirelessly Powered Lightbulb

Continued from page 1

By Kate Greene
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Wireless power transfer is an idea that's more than 100 years old. In the 1890s, physicist and electrical engineer Nikola Tesla proposed beaming electricity through the air. However, soon thereafter, power cables became the commonly accepted means of transporting electricity across distances. But with the widespread adoption of small, portable devices with batteries in need of constant recharging, people's attention is again turning to wireless power. In fact, the startup Powercast, based in Ligonier, PA, has, using a different approach from that of the MIT team, developed a wireless power system that can transmit low wattages across a distance of about a meter. To start, the company is targeting devices with low power consumption, such as sensors, but it's hoping to ramp up to more power-hungry gadgets in the future.

One concern that people might have, says Sir John Pendry, professor of physics at Imperial College in London, is health effects. "There will be safety issues, real or imagined," he says. "After all, the power has to pass through space in some form or other, and pass through any bodies lying in its path. The [MIT] team has minimized this problem by making sure that the power is mainly in the form of a magnetic field, a form of energy to which the body is almost entirely insensitive."

Based on calculations, Soljačić believes that the scheme is safe, even for people with implanted medical devices, such as pacemakers. Although the researchers have not made a detailed study to test how the system interferes with pacemakers, Soljačić says that they don't expect it to interact strongly with objects that don't resonate at the same frequencies used to transfer power.

At this point, the team has applied for a number of patents and is planning to commercialize the technology, although the researchers expect that it could take a few years before devices with such wireless power systems will make it to consumers. In the meantime, the team is exploring different materials and alternate coil geometries to try to extend the range and ramp up the power.
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Tags

efficiency electricity energy light magnetics MIT wireless

Comments

  • this is new?
    devassocx on 06/08/2007 at 1:21 AM
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    this sounds a lot like something called
    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
    Rate this comment: 12345
    • Re: this is new?
      oeseikel on 06/08/2007 at 10:15 AM
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      I have heard farmer's tales of rigging an induction loop under a high voltage transmission line, and bleeding off enough power to energize an electric fence.  However,I have never seen that in action.

      Oliver
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      • Re: this is new?
        zkent on 07/19/2007 at 2:18 PM
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        1
        Yeah the fella you are referring to was sued by the electric company and lost since the loss of power on the company's line was measurable due to the farmer's setup.
        Rate this comment: 12345
    • Re: this is new?
      barrycoleman on 06/08/2007 at 12:03 PM
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      In the Wikipedia entry you'll note "Their theoretical analysis showed ...".  They just proved it.  That's the news here.
      Rate this comment: 12345
  • a thoughtlessly powered lightbulb
    salammoniac on 06/08/2007 at 2:32 AM
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    This project is a dungheap.

    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...
    Rate this comment: 12345
    • Re: a thoughtlessly powered lightbulb
      kitk on 06/08/2007 at 3:02 AM
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      Sure, old Nik Tesla did this--without computers, and he did so with higher efficiency and much greater range. Some years back I pulled it off without a reciever coil, and at about 15-20 feet, and scared the living crap out of myself. Systems like this can put out nasty little surges of vastly higher peak power than whatever is rated--mine burned a hole through insulated aluminum sheet metal. Sure, the new ones might control that, but ANYTHING that receives this power by coupling even a little, even at a microscopic level, can be cooked! I never tried my test a second time, because I knew if the transfer went wrong, I might light up and cook.
        Great lab trick, but like home nuclear reactors, not too wise.
      Rate this comment: 12345
  • A Wirelessly Powered Lightbulb
    mehzang on 06/08/2007 at 3:48 AM
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    Exciting.This could by extension light some villages in Africa that are enclaved since cost would have been tremendously cut down by eliminating poles,transformers,labour,time etc...wonderful!
    Rate this comment: 12345
    • Re: A Wirelessly Powered Lightbulb
      salammoniac on 06/08/2007 at 11:17 AM
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      Sure, and if you believe the hype, all it would take to light the whole world would be something the size of a trash barrel attached to a pole in
      Mexico.  You have attributed powers to this noninvention that defy the laws of physics.
      Rate this comment: 12345
  • not safe for me
    blackfootx2 on 06/08/2007 at 3:54 AM
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    I recently acquired a pacemaker. The instructions that came with it say "NO MRI". Somewhere in the circuits in my device there is sure to be a loop that could resonate to any frequency being used to transmit power - maybe even in the case enclosing the device. This is a fact that Bell Labs learned a long time ago. This proposal scared the heck out of me.
    Rate this comment: 12345
  • I must be missing something...
    K1GIL on 06/08/2007 at 9:10 AM
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    Well, I bow to the "greater minds" at MIT, but exactly what is new and revolutionary about inductively coupling circuits consisting of self-resonant air-wound coils?  I believe I did exactly that as a kid while studying for my novice amateur radio license some 35 years ago (at the time, the underlying theory and practical applications were already 60 years old). That aside, do these students have any comprehension of the adverse effects of stray coupling with unintentional resonant circuits commly found outside of a laboratory environment?  Household wiring and appliances make wonderful resonant circuits and antennas, coupling with and re-radiating RF energy with very unpredictable results.  As one of the previous poster's noted, experimentation at 10Mhz would appear to be improper.  But again, I'll defer to those novel researchers who "discovered" this 100-year old technology.  
    Rate this comment: 12345
    • Re: I must be missing something...
      KN6LX on 06/10/2007 at 8:16 AM
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      Actually, I think that Nickolo Tesla might have been doing this kind of thing (in principle) out in Colorado a long time before either you or I had to pass that radio theory test!  :-)

      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
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  • Wireless DeSpin
    abcarterjr on 06/08/2007 at 1:50 PM
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    Would wireless despinning of an asteroid move its
    trajectory enough to miss the earth?
    Rate this comment: 12345
    • Re: Wireless DeSpin
      KN6LX on 06/11/2007 at 8:48 PM
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      "De-spinning" an asteroid would change its rotational momentum, but would not change the orbital parameters of its center of gravity one iota!

      Sorry.
      Rate this comment: 12345
    • Re: Wireless DeSpin
      majipa on 06/03/2008 at 12:37 AM
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      1
      Yes  yes...  I think we can...neee they can the grads at MIT,  do we seek some funds!!
      Rate this comment: 12345
  • New?
    alpha 07 on 06/09/2007 at 6:10 AM
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    1

    New? This technology was invented by Nikola Tesla more than 100 years ago. Time to recognize his work.
    Rate this comment: 12345
  • why so skeptical?
    stustanton on 06/09/2007 at 11:45 AM
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    I’m told that the normal progression of new science is someting like: 1) What a stupid idea, they’re idiots 2) It will never work, they’re idiots, 3) Someone thought of that long ago, they’re idiots, and finally, 4) I thought of it first.

    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.
    Rate this comment: 12345
    • Re: why so skeptical?
      attoigo on 06/09/2007 at 3:51 PM
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      Thanks for your positive input about wireless power transmission. I agree with you regarding potential use that will add much greater distances to plug in hybrid and all electric vehicles. The first thing that I could imagine was having all of our major highways retrofitted with the coils described here under the roadway emitting available power to all types of automobiles containing the matching receiver passing over them. This would definitely solve the distance issues posed by current battery technology limitations allowing a bridging technique until power storage technology catches up. This can potentially bring about the reality of electric propulsion drivetrains for automobiles and finally make electricity a practical power source for transportation. Is there enough efficiency here in this transfer medium to qualify it as a feasible solution? If so, it is not hard to imagine where this will take us.
      Rate this comment: 12345
  • Tesla?
    BuckyOHare on 06/10/2007 at 11:40 AM
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    I believe this was done, about 100 years ago or so. In the book "Tesla: Master of Lightning" there is a photograph of a lit light bulb inside a series of coiled wires. A caption from a Century Magazine article about Telsa read, "The coil shown in the photograph has its lower end or terminal connected to the ground, and is exactly attuned to the vibrations of a distant electrical oscillator." (June 1900)
    Rate this comment: 12345
  • MIT Tech. Review
    rttedrow on 06/11/2007 at 5:11 AM
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    I once loved this publication but -- as the reviews on this piece show -- the Review has fallen on hard times.  Even a lay person such as myself knows that the tech. for this wirelessly powered lightbulb is not anything like new.  Frequently the pieces published are neither about technology nor new.  Too bad, too bad.
    Rate this comment: 12345
    • Re: MIT Tech. Review
      ufolj on 06/11/2007 at 7:56 PM
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      1
      The way I see this as an EE the efficiency is too poor.
      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.
      Rate this comment: 12345
      • Re: MIT Tech. Review
        TMacshane on 08/08/2007 at 3:56 PM
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        3
        IMHO this would created a definite increase in your electric bill...and for what, to be anal about not wanting some cords around the house?
        Rate this comment: 12345
  • got a better one
    hmwogglebugte on 06/12/2007 at 12:47 PM
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    1
    Agreed, this is very close, if not identical to reinventing the wheel, but I had a bizarre experience when a corporate belch put me in a group developing a microwave powered lightbulb. Although there is nothing wrong with such a thing,(it does exist, for strong UV sources), and the science was seemingly ok, all the other stuff, like dumping hundreds of watts of unshielded gigahertz into peoples living rooms somehow was of no concern. The concept that the shielding would have to be mostly opaque didn't bother management; it was just an engineering detail.  Many millions were spent on this project. 
    Rate this comment: 12345
  • Really?
    greg1975 on 06/26/2007 at 8:57 AM
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    1
    What is it with this society and claiming old ideas as new?  This reminds me of the "new" hard drive technology recently of putting bits vertically through the platter.  Turns out to be 1970s technology.  Nice to see old ideas get used, but claiming them as new?  I don't think so.
    Rate this comment: 12345
  • 1960's Popular Electronics Project
    JonD on 07/26/2007 at 1:59 PM
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    Knock, Knock!  1965 or 1966 monthly project I built to light a bulb via radio-waves, not even needing to be near the source.

    Stop wasting money on experimenting, and spend more time reading through old consumer magazines.
    Rate this comment: 12345
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