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We are trying to design a metal mineral deposit detection system using low frequency radio waves. I am not sure on the physics of why the ultra low frequency electromagnetic radiation can penetrate the earth and sea. We need to be able to scan to a depth of 3 miles from the surface.

Wikipedia classifies ELF (Extremely Low Frequency) radiation as between 3 Hz and 300 Hz, and ULF (Ultra Low Frequency) from 300 Hz to 3 kHz. Both ranges can penetrate the earth, but I don't know which would be better for our application. Which frequency would yield the most precise, accurate and reliable results for this depth?

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ELF will likely be very problematic for you practically; remember that your antenna will have to be on the order of a wavelength to transmit or receive such a signal. Even for a 1/4 wavelength antenna, a 30 Hz antenna is 2500 km long.

ULF has some history of amateur radio use, so at least it is feasible - and there are commercial antennas made by Aaronia AG. Still, it may be difficult to find other commercial products (signal generators, amplifiers, etc). You may want to do a simple estimate of the cost of your proposed system including commercial parts before designing it. As in much of engineering, we must deal with what's possible rather than what is perfect.

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  • $\begingroup$ thx. Fractals can be used de-couple transmission efficiency from wavelength. Otherwise, we would have to carry bulky antennas for our cell phones. If you have any ideas or references for fractals in antenna design, please detail on this question: engineering.stackexchange.com/questions/16303/… much appreciated thank you $\endgroup$ – Ed Kideys Jul 18 '17 at 1:22
  • $\begingroup$ The antennas in cellphones are still on the order of a wavelength. They are not typically fractal but rather aperture antennas: antenna-theory.com/antennas/aperture/ifa.php "Good" fractal antennas do not tend to be much smaller than other types. See this example of a microwave fractal antenna: antenna-theory.com/antennas/fractal.php It is not exactly a compact design. I am not sure where you are getting your info about de-coupling from wavelength - it has not been borne out in practice. I recommend reading that website or looking at Balanis' "Antenna Theory." $\endgroup$ – phyllis diller Jul 18 '17 at 3:16

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