Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Vibrating a loop with current - will it radiate?

  1. Jul 15, 2017 #1
    Hi, I am new here so hopefully this is the right place to ask a question like this. Forgive me if I have trampled a rule. If I have, please let me know what I should do to ask this question.

    If you take a wire with a flowing DC current and vibrate it, can it radiate as a radio transmission? For instance, if you vibrate a conductor carrying a small current, at a frequency of 1MHz, will it radiate a 1MHz transmission that can be received by an antenna?

    This is of course different from a 1MHz oscillating current in the wire, which would clearly radiate a 1MHz E & B Field.

    I have read and read on this but I cannot seem to get a clear answer (at least one that I can glean from my reading). I would very much appreciate your thoughts on this.

    Best Regards,

    Rjay
     
  2. jcsd
  3. Jul 15, 2017 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    In general yes, but the emission will be negligible. There will be some vibration mode that doesn't radiate if you hit it perfectly.

    Nearly everything radiates, but unless you have a suitable design it is negligible.
     
  4. Jul 15, 2017 #3

    berkeman

    User Avatar

    Staff: Mentor

    Welcome to the PF.

    Yes, it will radiate, but not very efficiently. Accelerating charges radiate EM, but the less the acceleration, the less the EM radiation launched.

    Actually, I may need to amend my answer -- electron drift is pretty small at low currents, so mechanical displacement may be much larger at higher frequencies. Let me do some calcs...
     
  5. Jul 15, 2017 #4

    berkeman

    User Avatar

    Staff: Mentor

    Upon further review...

    The mechanical vibrations will be at low audio frequencies, which will not couple well to EM radiation.
    Very interesting question, though...
     
  6. Jul 15, 2017 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    You displace electrons and protons in the same way. The only radiating part is the changing magnetic field, a higher order effect.

    AOMs driven by piezos can vibrate with MHz frequencies easily, you can let a cable vibrate in the same way.
     
  7. Jul 15, 2017 #6

    atyy

    User Avatar
    Science Advisor

  8. Jul 16, 2017 #7

    tech99

    User Avatar
    Gold Member

    My understanding is that radiation arises from the acceleration of charges. Usually this is the acceleration of the free electrons near the surface of a metal. I also understand that a magnetic pole will radiate if it is accelerated, and in your case I assume you will vibrate the loop mechanically at 1 MHz. But I have not seen proof of this and no one has managed to do the experiment so far as I know.
    The difficulty is that if we synthesise the moving magnet by using varying currents in a loop, the radiation effect can also be explained from the acceleration of the electrons.
     
  9. Aug 16, 2017 #8
    atyy, Thank you for these sites. This really helps! - Rjay
     
  10. Aug 16, 2017 #9

    Thank you berkeman.
     
  11. Aug 16, 2017 #10
    Thank you tech 99
     
  12. Aug 16, 2017 #11
    Yes, this is a great way to mechanically move a mirror and change light. I can think of a dozen ways to actuate it but I am struggling with how to detect it. The current is small e.g. pA.
     
  13. Aug 16, 2017 #12
    Hence, the trouble at finding some good literature. Although, I can see from atyy's comments that once I found his links, then there is world of stuff written on this.
     
  14. Aug 16, 2017 #13
    Thank you mfb. -Rjay78
     
  15. Aug 17, 2017 #14

    tech99

    User Avatar
    Gold Member

    In Post No. 8, the first reference relates to a crossed pair of ordinary eg half wave, dipoles, and is not just a rotating magnetic field. As I have mentioned before, we cannot get pure rotating magnet action by using fluctuating currents, as that involves acceleration of charges.
    The second reference relating to pulsars seems to attribute the radiation to charges being accelerated into the centre. So although it possesses powerful magnetism, this is not the source of radiation.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Vibrating a loop with current - will it radiate?
  1. Current Loop ? (Replies: 16)

Loading...