Lets see, if the magnetic field follows the waveform, and a sawtooth generates odd and even order harmonics, then we get BBS (now FBS). Looks like lots of inductance, almost got a linear ramp. Seems like some time constant objects could be cancelled, since the current in the object is still building at turn off.
Candy stated this in patent 5,576,624.
quote column 18 line 50
"Some of these particular first order objects would not be detected, that is there would be a "hole" in the response of the detector. However, if the duration of the interrogating pulse is changed, the form of the FRD {ferrite relaxation decay} changes while that of the first order object remains the same, the respective signals are now dissimilar and that part of the received signal due to the first order object is easily discerned."
See how easy it is.
JC