Treasure hunting metal detectors

[wolram]

How do they discriminate between good (targets ) and rubbish, it seems that the orientation of the (Target) can fool the detector, from using one of these detector for many years , i find that the depth of the (Target) is instrumental in the discrimination, and only after years of (detecting) can can one fine tune the signals received.

[pallidin]

Maybe this site can help(and look for other sites)

http://www.gi.alaska.edu/~jesse/treasure/misc/howdetector.html

"Metal detectors can distinguish metal objects from each other based on the ratio of their inductance to their resistivity. This ratio gives rise to a predictable delay in the receive signal at a given frequency. An electronic circuit called a phase demodulator can measure this delay"