Object Waveforms - Log plot

[Anonymous]

Eric
The differences that I can think of between iron and other common metals is that iron has a somewhat lower conductivity and a very much higher permeability. The time constant of the exponential decay is L/R. The lower conductivity of iron would increase R and decrease the time constant, but the higher permeability greatly increases L. So the net effect is that iron should have a longer time constant than other metals of the same shape and size. The skin effect also depends on conductivity and permeability. The lower conductivity would increase penetration depth, but the higher permeability reduces it. The net effect is that iron has a shallower skin depth and it takes longer for the current to penetrate to the center.
It seems to me that once the current does penetrate to the center, iron should also go to a single time constant decay (unless other iron losses besides I^2 R are significant). And your plots for very thin iron seem to bear this out. Did you just mean that for practical purposes the iron signal is going to get lost in the noise before it straightens out, or did I miss a piece of physics?
Robert

 

[Anonymous]

Dave
It seems to me that a hybrid design with both PI and VLF characteristics could have very good performance. The PI part would have very good sensitivity and could provide information about the best time for the VLF part to evaluate R and X. The VLF part could ID the shallow targets and track the ground conditions. If the ground information from the VLF could be used to predict what the PI should see for a ground signal then the ground could be subtracted out from the PI. Of course it would be more expensive than either a VLF or PI.
Robert

 

[Anonymous]

Another paragraph from Kaczkowski