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How to create a projected electric field

  1. Mar 19, 2013 #1
    How to create a "projected" electric field

    First of all, apologies for my naivete, it's been many years since I've studied electromagnetism or electrical engineering in detail, but here goes anyway...

    I am trying to generate a small electric field (about the size of a marble). I am aware of the method of using two oppositely charged plates to create a field between them, but what I'm looking for is something more like a "projected" electric field around a point - or in other words, one that extends outward rather than inward.

    My goal is to create a small electric field that can be detected by a capacitive touchscreen (projected capacitive in this case) from a small distance - for example from about 1 cm.

    I don't know if this is even technically feasible or that I'm approaching it in the right way.. I am open to any and all suggestions.

    Thank you!
  2. jcsd
  3. Mar 19, 2013 #2


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    Last edited by a moderator: May 6, 2017
  4. Mar 19, 2013 #3
    Interesting.. i will give it a try!

    I'd like to use a reliable and consistent power source - like a battery. How might I get a similar effect using an electrical current?
  5. Mar 19, 2013 #4


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    There is a lot to be said for a highish frequency AC source, rather than DC. It is a superior method for many types of measurement because it eliminates DC drift and low frequency noise and hum.
    Why not Google touchscreen technology and see some of the images and designs?
  6. Mar 19, 2013 #5
    Yes, I have, but I'm not trying to create a touchscreen. I'm actually trying to create an object which is detected by the touchscreen as finger input but through a minimal contact point (e.g. a point smaller than a typical finger tip)
  7. Mar 19, 2013 #6
  8. Mar 20, 2013 #7
    Yes, but no. Actually, I've made multiple capacitive styli using various methods and materials and they work like any other capacitive stylus.

    I'm actually trying to create the effect of a stylus touching a capacitive screen, but without having to make physical contact with a large conductive material (like conductive foam or metal).

    I hypothesize (perhaps incorrectly) that if you could create a small electric field near the presence of a projected capacitive screen that it would affect the capacitance and thus trigger a "touch"-like response. That's the idea - a sort of "magic wand" effect.

    It's just a theory... but I'm trying to figure out how to best test it.
  9. Mar 20, 2013 #8
    I don't know any details about the design of capacitive touch screens (field strength used, frequency of the signal, etc.) but you could try and see if a weak electric field has any effect on it. Just take a 9V battery, connect one terminal with a wire to something that's grounded and the other terminal to another insulated wire. Move that wire in front of the screen. The wire produces a field because it becomes charged by the battery.
    Next you could try an ac field. That is also easy to do. Just connect your two wires to the speaker output of your computer instead of the battery. Again, ground one wire and then play sounds of different frequencies.
  10. Mar 21, 2013 #9
    Excellent thank you! I will try this out.
  11. Mar 28, 2013 #10
    So far these techniques are not working, although it is possible that my 9v battery is low or dead. I'll try again, but in the mean time any other ideas?
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