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Q:Can EM waves naturally create sonic waves?

For example, could a natural antenna (e.g. a seam of conductive metal or the right kind of rock)receive em radiation and through thermal/mechanical or piezoelectric effects re-emit low-volume sound?

Background: In some esoteric internet rabbit holes the Schumann resonance is mentioned as fundamental to some psycho acoustic effects (including 440vs432 conspiracy theories). As a plot point in my next book, I am considering a subterranean chamber of the right dimensions able amplify harmonics of the Schumann resonance which are naturally generated in the correct geology.

Edit 1: Better fit this community's guidelines. Edit 2: Telluric currents

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  • $\begingroup$ Update: I just read up on Telluric Current which are electric currents in the crust. These currents would be modulated by magnetic activity in the ionosphere (e.g. Schumann Resonance) so the question that remains is whether the piezoelectric deformation of rocks from the modulated Telluric Current would be sufficient to create audible sound. No idea how to calculate this... $\endgroup$ Jun 21, 2023 at 17:24
  • $\begingroup$ @JBH thanks for the input, I have edited the question and moved anything of marginal relevance to the background section. Point taken on the Gold antenna. I think that leaves piezoelectric effects, but at this point I have no idea if this is plausible. I did read about an ancient Chinese device for detecting combat tunneling under castle walls: fpri.org/article/2015/04/… (I try to be as 'Hard' as possible with my SciFi so would like this to be possible!) $\endgroup$ Jun 21, 2023 at 17:32
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    $\begingroup$ Thank you for the edit. That's a much better question. Nicely focused. +1 $\endgroup$
    – JBH
    Jun 21, 2023 at 20:20

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Yes, if the air becomes ionised, either by the power of the antenna or through some other means.

All you need then is to modulate your high-frequency carrier with an audio-frequency signal and you've got yourself what's basically a speaker made out of air.

P.s.: This is a real thing by the way.

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  • $\begingroup$ +1 for identifying a Real World application that can be used to model the OP's fictional world rule. $\endgroup$
    – JBH
    Jun 20, 2023 at 14:55
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    $\begingroup$ Many thanks, very interesting, but in my ideal case the energies involved would be too low to ionise the air. $\endgroup$ Jun 21, 2023 at 16:28
  • $\begingroup$ @TobyWeston Are we talking about a receiver antenna here? $\endgroup$
    – biziclop
    Jun 21, 2023 at 17:45
  • $\begingroup$ @biziclop Yes, a receiver antenna, or more crudely any conducting material in which a current can be induced. E.g. perhaps a seam or vein of conductive piezoelectric material (granite?) sandwiched between insulating strata. $\endgroup$ Jun 21, 2023 at 23:40
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    $\begingroup$ In that case piezo-electric effects are probably your best bet. However energy is still energy, so if your field is weak, so will be your audio signal. $\endgroup$
    – biziclop
    Jun 22, 2023 at 11:08

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