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Metal Detecting Air core Vs Ferrite cores?

Metal Detecting Air core Vs Ferrite cores?

(OP)
Hi, I'm a bit of an electrical noob.
I know the basics of electronics.

Why do small metal detectors (pointers) use the powdered ferrite oxide core, but larger ones use air cores?

I've also heard that there is an option to have a ferrite core that moves in and out, but this may not be suitable for metal detecting applications?

"When it comes to offering the highest resistance, solid ferrite cores are at the top of the list. However, when dealing with HIGH INDUCTANCE they are not always reliable and tend to reach their magnetic saturation level relatively quickly. Ferrite cores will use a different ferrite material based on the application, such as manganese zinc for certain kinds of antenna rods, with various materials offering a different set of advantages. Powdered ferrite cores are available, which are denser and offer greater linearity than solid ferrite cores."

Metal detectors often have Inductance of 300 uH to 500uH.
Is 300uH considered HIGH INDUCTANCE(as stated in above quoted paragraph)?
Is there another reason that large coils don't use a ferrite core (apart from weight)?

Surely the ferrite core could be made thin, as it increases the power of the coil and reduces the necessary windings?

Are eddy's a factor in this?
(I know that eddy's are reduced by using Litz wire.)
And what about Hysteresis?

RE: Metal Detecting Air core Vs Ferrite cores?

If you make the core thin, you're removing material... which reduces the inductance, defeating the purpose of putting the core in there in the first place.

Dan - Owner
http://www.Hi-TecDesigns.com

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