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Wireless power transmission

  1. Oct 17, 2007 #1
    I was wondering if anyone could give me more information about wireless power transmission, in particular, technical information about the physics and current prototypes made. I've looked on the internet, but as yet I haven't had much luck.
  2. jcsd
  3. Oct 17, 2007 #2


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    Staff: Mentor

    The main reason you haven't had any luck is that there isn't much being done on that idea. Every now and then, someone makes an announcement about a new product or idea, but they rarely (if ever) amount to anything. The basic concept is fundamentally flawed.
  4. Oct 17, 2007 #3
    I'm not so sure... I thought I'd seen something recently in the news... but then again, the news isn't always reliable. I'll try to find it.

    The gist was, the creation of an oscillating EM field, which was then "focused" to be strongest in the spot where it was to be recieved, and then turned back into power.

    The problem I have with that idea is it sounds just plain dangerous. I would imagine the closer you get to the transmitter or reciever, the more absorption you personally get... but this article said that this was an old issue that they think they've found a solution for... etc etc... again, could be BS, but it was a reputable news source, not some tabloid so idk.

    This sort of thing, as my understanding goes, has been done and can be done, but it's currently very inefficient (something like 10% of the power used at the transmitter is reclaimed by the reciever) and naturally dangerous because of that 90% going elsewhere. I believe my dad told me a story once about doing something of the sort in lab in one of his electricity principles classes when at university, or something. Anyway, I'm not one to say improvements are impossible...

    Maybe someone with more knowledge can say better. This isn't exactly my field of study. Just an article I saw some months ago that was interesting enough that I remembered it.
    Last edited: Oct 17, 2007
  5. Oct 17, 2007 #4
    Historically, lots of people have been interested in wireless power. But wires have a significant efficiency advantage (noting the current global problems), plus they avoid worry over the side effects of the transmission (eg, whether it interferes with the long term health of people nearby).

    Until recently, I imagined the house of the future brimming with electronic conveniences, such as those automatic hand-basin taps (saving water while you clean your teeth, preventing the tap you touched last with dirty hands from being the thing you touch first with clean hands). Now I think the sink instead ought have just a foot-operated tap (such as have been available for centuries, with all the above advantages plus mechanical simplicity and zero electricity requirement). Wireless power seems like another shiny gadget to solve a problem which might not really exist.
  6. Oct 17, 2007 #5
    Agreed, the tap is unnecessary when there are indeed better and even simpler alternatives. (Though some places, ie Walmart, are better served by their IR detectors, because you would get mischievious kids/teens putting something heavy on the footrest to cause the very thing that prompted the IR detectors to begin with.)

    However, I can think of a trillion reasons why (efficient and safe) wireless power would be great. At my house, I drag a laptop around. We all have cell phones. Being able to place one in a cable-free charging "zone" would be great, or even having my entire house be a charging zone... cool. Everything is wireless these days, but the devices themselves are still limited to how long a discharge cycle takes.
  7. Oct 17, 2007 #6


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    You can find lots of papers in scientific journals.

    See the following for more info(journal Science):
    André Kurs, Aristeidis Karalis, Robert Moffatt, J. D. Joannopoulos, Peter Fisher, and Marin Soljacic
    Science 6 July 2007 317: 83-86;

    They use near-field magnetic resonance. Like others have mentioned before, this method of power transfer has an unacceptable efficiency rate. I encourage to do your own research into the specifics of magnetic resonance if you're really interested. I think the authors in the aforementioned article achieved a 40% efficiency.
  8. Oct 17, 2007 #7
    Near-field magnetoresistance was exactly the topic I read about, and 6-Jul-07 is about the right time as well. I believe their article also mentioned they expected a large improvement in efficiency as they continued to research, as well.
  9. Feb 27, 2009 #8
  10. Feb 27, 2009 #9


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    It's not efficient, but it works. Crystal radio sets can receive all their power from the signal, enough to drive small earphones.
  11. Feb 27, 2009 #10
    You can also tune one crystal radio to a strong signal and use that energy to power an amplifier for another crystal radio.

    Regarding magnetic power transfer: It is now possible to buy kitchen ranges that will heat a magnetic pan (iron, steel) but will not heat the stove top. This may be low efficiency, but is safer that a hot 'burner'. The pan will transfer heat back to the stove by conduction, but not a dangerous amount. Just don't put steel 'siverware' on the stove!

  12. Mar 31, 2009 #11
    really this subject it is verey interesting but I can't to image this idea as transmitter device how to use & opeart,
  13. Mar 31, 2009 #12
    My brother was assigned to a Nike Missile Base on Sandy Hook NJ along time ago, and they would occasionally focus their radar on birds in trees about 1/4 mile away, and make them fly away.

    The Army now has a microwave crowd control raygun. A US company claims it is ready to build a microwave ray gun able to beam sounds directly into people's heads.
  14. Jul 27, 2010 #13
  15. Jul 27, 2010 #14
  16. Jul 27, 2010 #15
    There could be advantages to wireless power even if it is incredibly inefficient...mainly, the fact that disposable batteries are probably even more incredibly inefficient.

    Of course, wireless power would not only be more convenient, but you could pick up more chicks with a wireless-power gadget than without. This would inevitably lead to the technology's abuse and further escalate the mass waste of energy that humans are known for.
  17. Jul 27, 2010 #16
    I don't buy that. "Leaving a washbasin tap running" (for the five minutes until the next person walks in to the washroom) is hardly such an exciting prank really.

    That's a better point.
  18. Jul 28, 2010 #17


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    No it isn't. Wireless power systems are rediculously inefficient - chemical batteries are very efficient.
  19. Jul 28, 2010 #18
    Is that taking into account the energy required to make the disposable battery?
  20. Jul 29, 2010 #19


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    I'm not actually sure, but let me back up. The claim was:
    But it doesn't make much sense to compare with disposable (assuming you mean single-use) batteries since I've never heard of a real or hypothetical wireless power application that was intended to displace single-use batteries. Most electronics these days come with or are optomized for rechargeable batteries and wireless power applications are typically for charging (cell phones, toothbrushes, ipods). I can't think of an application where eliminating single-use batteries and displacing them with wireless power would be desirable because without batteries, you're tied to the power transmitter.
  21. Sep 15, 2010 #20
    What about a structure that requires many sensors perhaps to measure humidity, temperature of the floor. Or perhaps those on a bridge as is becoming popular with civionics?

    How would you propose power these devices cheaply? Bringing wires to each one would be costly and prone to cable faults while battery operated would be quite difficult to replace when they eventually run out. (also assuming data is wirelessly transmitted)

    Wireless power for large 10's of watts applications may not be needed any time soon, but I'm sure there's a demand for low power applications.
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