PI coil using iron core

[gadgetmaker]

If you want to reduce capacitiance of the coil can iron core material be used to increase inductance for a given amount of turns? I have also read that transcranial magnetic stimulators are all going to iron core coils for there increased penetration depth and lower heating properties. Also a open toroid wound core was found to be useful??

I know weight is a very important consideration in hand held units but has anyone done any experiments? Thanks in advance for any input. Karl

[Max]

If you want to reduce capacitiance of the coil can iron core material be used to increase inductance for a given amount of turns? I have also read that transcranial magnetic stimulators are all going to iron core coils for there increased penetration depth and lower heating properties. Also a open toroid wound core was found to be useful??

I know weight is a very important consideration in hand held units but has anyone done any experiments? Thanks in advance for any input. Karl

Hi,
I never tested this but have some considerations... about inductance and energy.

The energy stored in coil will be E= 1/2 * L * i^2

If you use an iron core , even open toroid, you'll increase much inductance of coil cause your coil is not air core (so magnetic circuit have magnetic permeability of air... that's similar to perm. of vacuum) but iron cored: permeability is much higher -> inductance will be much higher than in air core coil.

So your energy storage will increase with inductance...

Now suppose you have to sample for small gold items at e.g. 15us : do you think your increased energy will expire at switchoff like in the air core case ?

NO. You'll need much more time before you could sample for useful signal... probably much more after the famous 15us.

Then there is another problem... in a toroidal config with wounded around coil your magnetic circuit will be inside toroid shape... then not as in the air core coil case...but normal to its field.

Even considering of using a cilindrical iron core or do-nut type (toroid) but with flat (usual) coil around ... you'll get the increased L to complicate things...losing small delay sampling.

Then there is another problem: transient magnetization of core, that will increase inertia of your detection system.

So, one way or another this approach couldn't work in a PI MD at lower delay... that's often the most important for a TH.

In some other cases could be good... e.g. civil engineering... to locate iron or steel big things underground: that's why you don't need to sample with that detectors at very small time interval of few us... but can do at 50 or 100us without losing sens.

Best regards,
Max

[gadgetmaker]

Max,

Thanks for your help. I was refering to a open toriod of lets say 120 degrees.

I am trying to build a detector to find disturbed soil; basically looking for a reduction in magnetic field generated by the ground. I was sent years ago an article from Eric Foster about alignement of magnetic particles in disturbed and undisturbed ground.

One thing I must find out is the difference in signal content between disturbed and undisturbed soil. Eric said he had noticed this affect when his detector would go quiet over ground were a post hole was dug.

It seems I may need to sample very soon in the damped wave to see changes from the effects of the ground??

All the best,

Karl

[Max]

Max,

Thanks for your help. I was refering to a open toriod of lets say 120 degrees.

I am trying to build a detector to find disturbed soil; basically looking for a reduction in magnetic field generated by the ground. I was sent years ago an article from Eric Foster about alignement of magnetic particles in disturbed and undisturbed ground.

One thing I must find out is the difference in signal content between disturbed and undisturbed soil. Eric said he had noticed this affect when his detector would go quiet over ground were a post hole was dug.

It seems I may need to sample very soon in the damped wave to see changes from the effects of the ground??

All the best,

Karl

Hi,
uhm ... I really don't know about that. I know that sometimes in disturbed soil there are small ceramics fragments... e.g. happens in south america frequently... don't know about e.g. UK, think not the same for european sites.

Disturbed soil have different magnetic orientations of crystals respect to undisturbed around... that's why it's also possible find hot-spots with magnetometers that way: magnetic field vary there respect to the average of the sorrounding area.

I don't know how to measure that effect on a PI... cause a small variation could be due to various things... also e.g. a small hot-rock there. Difficault to understand how could be possible make a difference between that effect and others due to hot-rocks or ceramics for example.

But maybe Eric found a way... who knows ?

Best regards,
Max