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When looking for information on detectors, I came across a PDF file where somebody analyzed the way different targets responded at different frequencies.
It was noteworthy that ferrous objects have a large phase shift, including if their depth or the coil height is changed.
And non ferrous targets did not shift their phase as their depth or the coil height changed. Though the results were performed in a laboratory, not in the ground.
It was also interesting to see how aluminum had a very minimal phase shift, similar to the no target phase.
An ideal frequency range of 1kHz - 20kHz was identified. Higher frequencies don't discriminate as easily. The coil inductance they used was a whopping 8mH, in order to have the frequencies from 1 - 100kHz just below the coil resonant frequency, aiming for a linear behavior across those frequencies. That makes it easier to try and categorize targets. It was noted that different targets can produce the same signal, which means accurate identification is not always possible.
http://dspace.khazar.org/bitstream/2...e%20search.pdf
It was noteworthy that ferrous objects have a large phase shift, including if their depth or the coil height is changed.
And non ferrous targets did not shift their phase as their depth or the coil height changed. Though the results were performed in a laboratory, not in the ground.
It was also interesting to see how aluminum had a very minimal phase shift, similar to the no target phase.
An ideal frequency range of 1kHz - 20kHz was identified. Higher frequencies don't discriminate as easily. The coil inductance they used was a whopping 8mH, in order to have the frequencies from 1 - 100kHz just below the coil resonant frequency, aiming for a linear behavior across those frequencies. That makes it easier to try and categorize targets. It was noted that different targets can produce the same signal, which means accurate identification is not always possible.
http://dspace.khazar.org/bitstream/2...e%20search.pdf
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