Interference problem of the circuit

[Carl-NC]

The shape of the coils is not so important, but a WT gate is usually 2.5m tall so the coils would, at least, need to be elliptical. Most WTs use the figure-8 arrangement which makes each coil even more elongated, so they are usually wound as long rectangles. This makes mounting them easier. But elliptical works, too. The important thing is not to leave a gap between the coils, a gap will create a dead zone. Preferably even overlap them a bit.

[Carl-NC]

A further note: if your goal is to simply demonstrate a multiple zone metal detector, then what you are doing will achieve that. Maybe for your project that is good enough. It will have limitations and faults, and I am just trying to explain what those are, and how they are normally dealt with.

[DJSUOL]

Thanks. In my system, if I put the coils near to each other, I think the interference between adjacent coils will be large and it will influence the stability of the system. If I do not leave the gap, how can I eliminate the interference? Is the figure-8 design to be the only solution?

[Carl-NC]

I don't recall that I've ever tried to put multiple TX coils next to each other, I suppose if they are not exactly timed the same there could be weird effects. I use 1 big TX coil to avoid learning what might otherwise go wrong. The RX coils should OK next to each other providing they are properly damped. If they are not damped, then they can interact and ring.

Most likely you will not be able to solve all the problems needed to make a really good WT. It took me almost 2 years to figure out all the details on my first WT design. What you have probably demonstrates what you need to demonstrate, if I understand what you are trying to do.

[dbanner]

And what of my idea of placing coils overhead and beneath the feet of walk through, are there any known commercial designs with such an arrangement? Multiple field coils placed one within the other, for increased sensitivity to small items.
One question, if Rx coil is perpendicular to tx coil, in other words Rx in vertical plane, tx in horizontal plane, would such an arrangement work?
So having a single coil above, below, and on both sides, four coils in total. The polarity of the coils appropriately applied.
Food for thought.

[Carl-NC]

And what of my idea of placing coils overhead and beneath the feet of walk through, are there any known commercial designs with such an arrangement? Multiple field coils placed one within the other, for increased sensitivity to small items.
One question, if Rx coil is perpendicular to tx coil, in other words Rx in vertical plane, tx in horizontal plane, would such an arrangement work?
So having a single coil above, below, and on both sides, four coils in total. The polarity of the coils appropriately applied.
Food for thought.

Walk-over foot coils have been done, don't recall who. Head coils, I haven't seen. My designs use ankle-boost coils, which are small coils at the very bottom with independent sensitivity control to account for rebar in the floor. This is common practice. Usually when you want more sensitivity, you shrink the RX coil size and make more zones. Perpendicular TX/RX might work, but it makes design & assembly more complicated. I don't see a good return offhand.

The oldest walk-thru design I know of is from 1924. It was a single-coil design and you walked through the coil. Used the energy-theft method, same as how the current Garrett pinpointer works.

[DJSUOL]

During the test, I found different materials have different degree response. Could someone tell me about it or introduce me some resources to learn it?

[waltr]

Lot here about this. Typically it is the conductivity of the metal plus the size and shape that determines an objects TC (Time constant) which produces a different exponential decay (same as RC or L/R TC).

Look for and read the Target testing threads by Green & 666.