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I've read that the human body has resonant frequencies somewhere around 50MHz. I also think it would be interesting to look for values in other ranges like 10-100 kHz. I'm wondering how to build a device which can measure these frequencies and track them as they change.

I was thinking about using a circuit designed for a crystal oscillator, and just putting a human where the crystal would be. However, I'm not sure about the various ways in which the analogy could fail. Also, usually circuits for crystals specify a very specific oscillation frequency. I might be looking for a circuit where, for instance, I specify a wide range like 20-40 kHz, and if I connect it to some parallel LC circuits with a resonant frequencies of 15 kHz and 34 kHz and 100 kHz, then it will oscillate at 34 kHz because that is where the impedance is minimized within the specified range.

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    \$\begingroup\$ "and just putting a human where the crystal would be" - you'd need some big pads to get me in there ;-) \$\endgroup\$ – Roger Rowland May 6 '16 at 9:26
  • \$\begingroup\$ How would you recognize a human body resonant frequency meaning, what would a human body look like in the process of resonating? Compare this with (say) a tree or a brick or a doormat - what would be the signs of resonance. If you are expecting some form of aura to develop then you are going to be disappointed. \$\endgroup\$ – Andy aka May 6 '16 at 9:53
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    \$\begingroup\$ There is no single answer to this and NO GOOD ANSWER in the usual sense. The body may exhibit various and varying AC impedance minima but it is a big dynamic squidgy mess of multiple varying impedances. THERE IS NO SINGLE OR SHARP resonant frequency. Anyone claiming so should be walked away from slowly. It is the sort of thing that quack 'science' is based on. \$\endgroup\$ – Russell McMahon May 6 '16 at 10:01
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    \$\begingroup\$ The 50 MHz figure comes from the idea that the height of an average adult (about 1.6-1.7m) is a quarter wavelength at roughly 50 MHz, so the thought is that a standing human body might act as an antenna at this frequency. But there's no real physical phenomenon to support this concept. \$\endgroup\$ – Dave Tweed May 6 '16 at 11:39
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    \$\begingroup\$ Who says everything has to have a resonant frequency? If you strike a bell, it rings because it has an acoustic resonance. If you make a bell out of wet mud instead of metal, do you think it will still resonate? \$\endgroup\$ – The Photon May 6 '16 at 15:58

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