Shielding the sides of a coil.

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How is outside detection prevention and shielding accomplished in a commercial machine(walk-thru)?? Aren't there technical drawings of such machines available?
That would be intersting. Seems to me there is always a perimeter of empty space around such machines(no-go areas). With a properly designed coil array(pot core) and minimal exclusion materials( aliminum backing), it would be able to focus the thing for minimal side leakage.

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have a look at this sort of arrangement.

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Are we trying to inhibit detection on one side, edge detection, either or both? With a metal detector? With a walk thru?

[Carl-NC]

Are we trying to inhibit detection on one side, edge detection, either or both? With a metal detector? With a walk thru?

See post #1.

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A flat ferrite ring with thickish aluminum backplate around the 12 inch circle coil???. The width of the ring might be considerably wider than the coil thickness.?

[Funfinder]

OK - now we even have to deal with different kind of ferrite-materials -
if you wanna make this stuff even more complicated or profilate yourself
as "ferrite-profi", do it *laugh*.

What I was talking is this here:

https://electronics.stackexchange.co...-m-at-10-metre

1 Answer - A ferrite rod does this - see sketch -

Generally, a ferrite concentrates the magnetic field that would otherwise have passed by the receive coil not yielding a signal. In effect it multiplies the cross sectional area of the receive coil several times. The effective flux density seen by the receive coil is significantly increased and it is a good ploy to use one in a receiver of around 1MHz. Ferrites are good for significantly higher frequencies too but their permeabilities reduce to avoid losses and their effectiveness at concentrating lines of flux are therefore also reduced.

Now what you wanna know?
How the permeability affects the MDs EM-field?
With "uni-directional" I meant that the ferrite is not in one direction
like a magnet. btw depending on the circuit the metal-detector
will detect the ferrite, same as it detects hot-rocks which could
cause the contrary effect - make the MD less sensitive.

And sorry, if I don't know every little sh*t in every
little so far useless area of electronics.
I'm interested in MDs and not in AM-radios!
Built your ferrite-shield-detectors if you can and
publish the results of your experiments and then we
look further. And if the ferrite can "shield" the sides of
the coil it also might be able shield the coil cable.

And now this thread has died for me, I don't write here
if the vibes are that "anti" and mocking.

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It might help focus the magnetic lines of flux more towards the intended area, and away from the sides, that is the point. Perhaps even a double ring with a toroidal coil to repel the flux of the main coil. All just conceptual ideas, of course, none of which may work.
I tend to visualize a physical arrangement which is practical and feasable in construction, then try to determine what the geometry says about the electromagnetic characteristics. Many solutions sometimes tend to have a geometric elegance to it. Geometry and physics are like hand and glove.

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How about a second coil which is slightly larger in diameter than the main coil, connected to a weaker synchronised TX pulse, but of opposite polarity. The second field generated repels the main field away from the edges and focuses the main coil field more to the intended area. Maybe even winding the second coil on a toroid core may enhance the effect. The second coil would be encased in a ferrite ring except for the portion facing the first coil.

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Still trying to figure out what a " unidirectional anti-magnetic structure" is all about Maybe my idea fits the bill