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I How are electric fields detected?

  1. Mar 10, 2016 #1
    How do you detect a very weak electric field? What kind of measurement devices are out there?

    What are the most sensitive devices used for measuring electric fields? I'm looking for something comparable to how SQUIDs or quartz resonators can be used to detect magnetic fields.
     
  2. jcsd
  3. Mar 11, 2016 #2
    have you heard about 'search coil' attached to a sensitive galvanometer?
     
  4. Mar 11, 2016 #3

    tech99

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    One method is to use an antenna (such as a rod) connected to a simple amplifier with extremely high input impedance, such as a CMOS device or a vacuum tube. It is possible, I believe, to see the field gradient above the Earth's surface and to see a variation when clouds or an aircraft pass overhead. Many of these fields are actually very strong. Of course, if it is an alternating field you want to detect, then the techniques of radio communication can be used.
     
    Last edited by a moderator: Mar 11, 2016
  5. Mar 11, 2016 #4

    tech99

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    The search coil method is applicable to magnetic fields not electric fields.
     
  6. Mar 11, 2016 #5

    davenn

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    with anything from a basic antenna, detector diode and a voltmeter
    right through to a complex radio receiver .... and everything in between, take your pick :smile:

    here's a mass of detector circuits on google
    http://www.bing.com/images/search?q=electric+field+detector+circuits&FORM=HDRSC2



    Dave
     
  7. Mar 11, 2016 #6
    Thanks for the link! Do you know what the most sensitive detectors are? What is the strength of the weakest field that we are able to detect? I'm not sure where to look for this info. For instance, I think that SQUIDs are some of our most sensitive B field detectors, and they can sense down to a few femtotesla. What would be the E field analog to this kind of technology?
     
  8. Mar 11, 2016 #7
    More to the point, I am wondering how sensitive electric field measurements can be made for the following reason. If we can measure very weak fluctuations in electric field, then shouldn't it be possible to track the motion of an electron without interacting with it by monitoring the surrounding fields? Does anything like this exist?
     
  9. Mar 11, 2016 #8
    "Monitoring" the field means interaction with the field. And with the electron, if it's the field of the electron.
     
  10. Mar 11, 2016 #9

    davenn

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    Yes ..... from wiki
    and

    it isn't a project you are going to do at home


    Dave
     
  11. Mar 11, 2016 #10
    Which wiki? I want to read it. I know I read something about observing electrons using very short laser pulses to "trap" them. But this is different from what I mean when I say detecting the electron by monitoring the field it produces.

    What I mean is that you could monitor the field without altering the behavior of the electron. Suppose you built the field detector into the walls of the chamber in which the electron is traveling. Then you could get a readout of the electron's position by field measurements along the walls of the chamber, in real time, without having to interfere with the particle's motion. Compare this, for instance, to detection by optical means, or by analyzing a collision, both of which would clearly alter the trajectory of the charge.
     
  12. Mar 11, 2016 #11

    davenn

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    the one on the electron :wink:
     
  13. Mar 11, 2016 #12
    lol I probably should have checked that first. It sounds like what this wiki is talking about is producing electromagnetic fields in order to "trap" or otherwise get information about the electron through interactions. What I am getting at is the idea of using the electric field produced by the electron in order to get information about its position by detecting the field with a highly sensitive passive device. Is there anything like that being done out there?
     
  14. Mar 12, 2016 #13

    tech99

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    If you want to measure the electric field on the macro scale you can get close to a non invasive measurement. For instance, if the the probe amplifier has very high input impedance so it takes negligible energy from the field. But if you want to measure at the scale of individual electrons, the probe itself must involve electron movement, so it will take energy from the electron under study and will disturb it.
     
  15. Mar 12, 2016 #14

    ZapperZ

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    The walls of the chamber will interact with the electron. Look up electron wakefield, a phenomenon well known in particle accelerators.

    Zz.
     
  16. Mar 12, 2016 #15
    I'm not sure I understand the distinction between macro scale measurements and the scale of individual electrons. By macro do you mean the field due to a number of electrons, as opposed to just one?

    What if you could put an electron in a box, let it roam about, and measure the pressure exerted on a a few static surface charge sheets. So when the electron moves toward wall A, for instance, the pressure on sheet A increases, etc. If we could record the changes in pressure, couldn't we then piece together a story about the electron's location without having to interact with it?
     
  17. Mar 12, 2016 #16

    ZapperZ

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    I think you still don't get it.

    By the fact that the electron exerts this "pressure", it IS interacting with the wall!

    Anyone who has taken undergraduate E&M can also tell you about image charge problem when you have a charge and a plane.

    Zz.
     
  18. Mar 12, 2016 #17
    Do you mean that the electron's field would induce a small polarization in the surface charge and thus alter the behavior of the electron? I hadn't thought of that. But at least this would be a much less invasive strategy for getting a read on an electron's position than firing strong light beams at it or slamming it into some kind of sensor. We can agree on that maybe? Moreover, it would change the potential in the box in a definite and calculable way, unlike hitting the electron with a photon for instance. My question is whether or not this kind of (relatively) non-invasive measurement might be possible, or even if it's being done somewhere.

    Scratch the "definite and calculable." I just realized there is some kind of circular reasoning lurking in there.
     
  19. Mar 12, 2016 #18

    ZapperZ

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    Remember, your starting premise here is that you thought you can make a measurement with NO affect on the electron, not "much less invasive". That is what I've been countering.

    We have MANY devices that do "much less invasive" detection. The integrated charge transformer ICT, the beam positioning monitor BPM, etc are all FAMILIAR devices that are used in particle accelerators to detect where these electrons are without significantly altering their path. So this is nothing new.

    Zz.
     
  20. Mar 12, 2016 #19
    That's cool and exactly why I posted the question. So maybe I can try to understand a little better. Do these measurement devices give real-time read-outs of the electron's position while minimally interacting with the electron? How does that not violate uncertainty?

    Sorry if the questions are puerile... just tryin' to learn.
     
  21. Mar 13, 2016 #20
    Please correct me if I'm wrong, but it sounds like the devices you mentioned are used for getting instantaneous position measurements of a particle beam (like "checkpoints" along the path), rather than continuous "real-time" measurements. What kinds of devices can be used to improve the time resolution of the measurement?

    Thanks for your help.
     
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