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is Ib IB radiometer good one in comparison to Induction balance type, what are the advantages and disadvantages...is there any latest circuit
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I'm no pro, so take this post with a grain of salt. I've still got a lot to learn, but this is what I understand so far:
I'm sure someone will correct me if I'm wrong here, but I think the general term of induction balance metal detectors means (or used to mean) detecting a change in amplitude of two balanced coils when a metal object is interrupting the magnetic field, where IB radiometer usually refers to detection of phase shift (rather than signal amplitude) for the same event.
If this is the difference you're asking about, then there are good advantages to detecting the phase shift rather than the amplitude.
First: Much less need for amplification. Since you're not checking the signal level, but just the difference in phase between two signals, the amplitude isn't so important.
Second: (This depends on how you're processing and displaying the data. This part may not apply if you're just using audio as an indicator of detection) Balance between the two signals (when looking at phase) shouldn't be as important. Their relative shift will still be there even if temperature and other things affect the balance. If you're looking for amplitude, though, an imbalance will make detection much more difficult.
Third: If you're doing digital signal processing, analog-to-digital conversion ban be made much more simple in a phase IB circuit by using a Schmitt Trigger to compare the phases of the TX and RX signals. This technique requires much smaller resolution than checking the amplitudes of signals.
I'm sure there are other benefits (and deficits), but I'll leave that to others. Again, I'm no pro, and I've got a lot of learning to do myself. These are just my observations.
As for a latest circuit, you can find variations of both ideas, but I don't know of any specific new example.
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