Lightning compared to piezo electric element

  1. I'm building (or rather, debugging) a lightning detector that detects the electromagnetic charge emitted by a lightning bolt.

    I need a good way to generate a little lightning as a test signal and I'm currently using a the piezo electric part of an electric lighter which generates a small spark.

    The piezo electric element generates about 20 to 25 kV and produces a spark that is about 3 mm long. If I hold it two meters from my antenna, at what distance does an average lightning bolt need to be to produce the same amount of energy in my antenna?

    Of course a lot of estimations and averages will need to be used, but roughly?
  2. jcsd
  3. sophiecentaur

    sophiecentaur 14,730
    Science Advisor
    Gold Member

    You need to sort out your terms of reference, I think. A lightning strike 'emits' an EM pulse and not a "charge". You can save yourself a lot of time and effort by learning more basics before launching out on haphazard measurements, imo.
  4. Pulse is probably the word yes.

    I know it is a difficult question to answer but someone might know how to make such an estimation, I hope.
  5. The relationship will be proportional, assuming the air becomes conductive at the same electric field strength. This is about 3 million V/m, or 30,000 V/mm. Your 20-25kV was probably able to generate a current over a larger 3 mm due to geometric considerations (the field is concentrated near sharp edges of a conductor).

    To find the voltage for 2m, just multiply 25[kV] by 2[m]/3[mm]
  6. sophiecentaur

    sophiecentaur 14,730
    Science Advisor
    Gold Member

    Calibration can be difficult but what you need is a wideband detector with a peak sensing circuit. Something along the lines of a peak programme audio circuit. Having calibrated it with low level signals, you just put a large attenuator at its input to measure high levels.
    [Edit: a log amp would be useful for showing a wide range of signal values (dB scale).]
    Last edited: Sep 12, 2013
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