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Yet another wireless power transmission thread.

  1. Jul 21, 2011 #1
    Hi everyone, this is my first post on the forums :redface:

    OK so I want to design a microwave power transmitter and I need a few opinions before I make any commitments. I haven't made many complex circuits before, but I am going to do my homework if this is viable and break it into chunks.

    Maybe this will be a lot harder to achieve than I think, but bear in mind the system doesn't need to be very efficient.

    I need to beam maybe 50W max across a distance of 15 centimeters. The rectenna would have to be 5cm across but would be more or less static.

    So my initial questions are -
    Are these totally unrealistic specifications? Has anyone actually played with microwave transmission at all? How simple could I make this design?

    Thanks guys ( I did do a search ;) )
     
  2. jcsd
  3. Jul 21, 2011 #2

    berkeman

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    Welcome to the PF.

    Can you outline the safety considerations for such an experiment? What would be the safety concerns, and how are you addressing them?

    Can you outline the FCC regulatory concerns for such an experiment? How are you addressing these legal regulatory concerns?

    Do you have a faculty advisor for this project?
     
  4. Jul 21, 2011 #3
    The primary consideration would be RF shock from touching the antenna, and RF heating. I would be in the range of 10-20Ghz if possible, so the heating effect would be less of a danger though obviously I will take precautions.

    And it would be OFCOM in my case, not the FCC. If I were to use 10Ghz I would be on amateur radio grounds though I would still need a license.

    If i were to operate everything in a faraday cage could I get away from licensing issues ,as well as add a level of safety?

    Nope no advisor, though I'll be attending UCL in a few months for something unrelated. Maybe I can find someone to help me out.
     
  5. Jul 21, 2011 #4

    berkeman

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    That's a good start. Yes, you should be doing this in a faraday cage, with RF absorbing foam in the target area. You need to be sure that you do not let RF interference out of your test area, or you could have issues with your OFCOM agency.

    It definitely would be good to have an experienced local Mentor to help you with this project. What is your end goal for this project?
     
  6. Jul 21, 2011 #5
    Short term goal is to transmit as close to 50W as I can across 15cm.

    After that I want to get the receiving circuit as small as possible to integrate into a quadrotor. I'll do as you advise and everything will be well protected.

    In terms of what I have talked about (ignoring the quadrotor), do you think this is viable? I would love to use a much safer form of wireless transfer but they all seem to need large coils...
     
  7. Jul 21, 2011 #6
    http://www.witricity.com/pages/technology.html [Broken]
    This one uses resonant magnetic coupling. The technology is pretty interesting and some of the applications are very cool.

    One avenue that I would also recommend spending some time is the patent listings for some of these inventions. There is a surprisingly large amount of technical data in some of of the applications.
     
    Last edited by a moderator: May 5, 2017
  8. Jul 21, 2011 #7
    I've seen his TED talk where he uses a coil half the size of a cellphone, which is interesting but I wrote the idea off as too complex. I guess the idea is based on tuned LC circuits?
    Not sure how much more complex the circuit would need to be than that (I chose microwave transmission because it seemed more straightforward, am I wrong?)
    I'll have a look at the patents like you suggested.
     
  9. Jul 21, 2011 #8

    berkeman

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    How do the 15cm distance and the quadrotor concepts relate? Are you going to power a hovering quadrotor from below or something?

    If you want to transfer 50W across 15cm, just use a powerful stream of air...
     
  10. Jul 21, 2011 #9
    Yeah that's right. There will be a pedestal with the transmitter 15cm below and the thing hovering at eye level. It's sort of a high-tech show piece...

    I sort of need the thing to stay as still in the air as possible; I want to hook up a tiny microcontroller to pull it off (that much I can do). I think would be equally as difficult to get the aerodynamics just right.

    Besides it would be pretty fun to get working don't you think?

    edit: You seem doubtful?
     
  11. Jul 21, 2011 #10

    berkeman

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    And how do you propose to make a clear see-through Faraday cage?
     
  12. Jul 21, 2011 #11
    A dark room and lighting the object from the inside would make it pretty visible despite the small hole size needed for the stuff. I would love to give the inductive coupling idea a try as it would free it all up but that seems too hopeful.

    You sound very against this whole thing, level with me berkeman :wink:
     
  13. Jul 21, 2011 #12

    berkeman

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    If you can do it safely and legally, more power to you. We just get a lot of fast-and-loose DIY folks who stop by the PF, and have no idea of the dangers and RF interference issues for some of their project ideas.

    As a HAM radio person, I'm part of the groups that law enforcement calls when they have interference issues with their radios (or have been notified of interference with other licensed systems). We call them T-hunts (transmitter hunts)....

    Stay creative, but please always keep safety in mind. o:)
     
  14. Jul 21, 2011 #13
    No of course, and I think as I am displaying it at a university I would soon be stopped from becoming a liability.

    If I were to cage off a large area, and then put perspex to stop people getting too close - would that be safe enough?

    How directional could I make the antenna?
     
  15. Jul 21, 2011 #14

    berkeman

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    I still like the air-powered idea. Shoot a high-velocity stream of air up vertically out of a hole 12" to 18" wide, and make a wind-powered quadcopter that gets its power from its autorotating rotors. It starts on a "landing stand" over the air duct, and after the airstream starts and the quadcopter is powered-up, it can release itself from the stand, and rise up. Then it can hover, or turn slowly around, and maybe even do a little maneuvering in the airstream. That would be impressive. :biggrin:

    (and a whole lot easier to make safe and legal)
     
  16. Jul 21, 2011 #15
    If your this unsure I guess the university will be doubly so, thanks for letting me down easy though.

    How would it be powered through the airstream I'm not sure I understand?
     
  17. Jul 21, 2011 #16

    berkeman

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    You would have generators at each of the 4 rotor positions. The airstream turns the rotors, which generates some power for your on-board electronics and control servos. You control the pitch of the rotors individually to control your lift and other flight aspects. You can control the speed of the rotors by controlling extra electrical resistance for each of the 4 power circuits.... Sounds like a fun project....
     
  18. Jul 21, 2011 #17
    That does seem like a much more simple way you've convinced me. (No servos needed for a quadrotor by the way.)

    I'm still going to try r.f. transmission on the side though, I promise I will be careful with interference. Except now it won't be in the public space so you have certainly saved some lives.
     
  19. Jul 21, 2011 #18

    berkeman

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    The servos I had in mind were to control the pitch of the rotor blades. I think you'll need that to control the lift of the autorotation, but I certainly don't know much about aerodynamics.
     
  20. Jul 21, 2011 #19
    Two rotors spin the other way to cancel out the angular velocity. Everything is controlled via rotor speed.
     
  21. Jul 22, 2011 #20
    UCL, not Imperial?

    Don't know much about the background to your project, but Augusta-Westland have just announced an expansionist push and may be interested.

    If it's a science fair thing
    WBeaty here is a specialist in such matters.

    Microwave ovens without a turntable transmit greater power than 50 watts by rotating the antenna.

    See also 'Toshiba DeltaWave'

    go well
     
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