Single layer Spiral coil

[Tinkerer]

Spiral Bucking coil

Here you see a spiral coil with the graphite shield and a spiral Bucking coil on top.

Tinkerer

[Tinkerer]

TINKERERS_TANDEM COIL

Nope. I suggested coils of the same size side by side, one next to the other. This solution in video is as per Tinkerer's solution.
Go for it, Aziz also speaks fondly about this configuration.

There are many useful coil configurations possible.
The choice depends on the goal.
The most used coil configurations are for most used detector uses.

If you have a specific purpose, you can build a specific coil that is best suited for that purpose.

Below is a field visualization of a TANDEM COIL, where the coil windings are in series and the fields aiding.

Tinkerer

[Davor]

I made this now as you Davor suggested.

Nope. I suggested coils of the same size side by side, one next to the other. This solution in video is as per Tinkerer's solution.
Go for it, Aziz also speaks fondly about this configuration.

[Jeroi]

I made this now as you Davor suggested. It has outer diameter of 20cm and the inner coil diamemter will be about 8cm.

www.youtube.com/watch?v=RsWQ6vytNwk

What do you think of this?

I think of addin 2 coils in series. The inner coil has opposite direction as outer one. Would they produce quite nice magnetic field?

[Funfinder]

You can use a Bucking coil at a small distance above the TX coil, as seen on my Avatar.
The current in the bucking coil is in opposite direction to the current in the TX coil.

This produces some degree of deflection, as you can measure. To measure, try to detect a target at the same distance above the coil and below the coil. You will not a significant difference in target response.

Tinkerer

Is it possible to disign the bucking coil as flat spiral also?
Or perhaps shaped like a basecap without sunshield.

some other thoughts also could be of interest:

- cylindrical coils (like for wireless power transmission) are
directional so they may also improve detection depth

- spiral coils can be created with 3 to 10 thicker ring areas
like usual coils for creating real powerful inductivity

- the design of the spiral coil could have the shape of an
upside down mushroom, UFO or cone to create an intense
field area for smaller stuff closer to ground

[Tinkerer]

Is it possible to use a thin alu-plate as some kind of reflector?

If yes, how much distance should it have to the coil?

You can use a Bucking coil at a small distance above the TX coil, as seen on my Avatar.
The current in the bucking coil is in opposite direction to the current in the TX coil.

This produces some degree of deflection, as you can measure. To measure, try to detect a target at the same distance above the coil and below the coil. You will not a significant difference in target response.

Tinkerer

[Davor]

I wouldn't play with any core because of the added weight. There were some designs employing ferrite rods, but not a complete horseshoe.
You may think of a humbucker as a cross-section of a torus. Because air gap is very large here, don't expect to gain any benefits from any kind of core and feel free to abandon the core idea altogether.
A picture? usually such configuration is referred to as OO and it depicts it well enough. If in one "O" current flows in clockwise direction, in the other it flows in opposite, and they are connected in series. That's it.

[Jeroi]

Actually, you can have a toroid cross section if you use two coils in opposite polarity placed one next to the other. They'll encompass nice portion of the ground beneath them, and will behave as any other coil for MD purposes, but will cancel out any earth field, and far field RF. Just like humbucker pickups do with electric guitars.

What do you mean? Could you produce image about the polaritities and so on. Atm our desing is singel coil type, so can one sipral horseshoe desing work as metal detector as in demos the siparal generates weaker magnetic field outside of coil that can be made bigger placing ferromagnetic material inside the spiral. So with one coil desing, I would wire one horseshoe sipral coil on to construction yard concreat metal pipe and get quite good magnetic field arround the horseshoe?

Can somebody veryfy if this is true?

[Davor]

Exactly

Is it possible to use a thin alu-plate as some kind of reflector?

If yes, how much distance should it have to the coil?

You need far field conditions for reflection, and the size of a reflector must be a wavelength or bigger.

[UFO]

Just like humbucker pickups do with electric guitars.

So it should be good for "Heavy Metal" then.

Rock on.

[Funfinder]

Is it possible to use a thin alu-plate as some kind of reflector?

If yes, how much distance should it have to the coil?

[Davor]

I assume that you cannot make the spiral as toroide so it will not have magnetism outside coil at all.

Actually, you can have a toroid cross section if you use two coils in opposite polarity placed one next to the other. They'll encompass nice portion of the ground beneath them, and will behave as any other coil for MD purposes, but will cancel out any earth field, and far field RF. Just like humbucker pickups do with electric guitars.

[Jeroi]

I am interested in spiral coil also. We are building pulse induction detector and how do this coil type perform in metal detecting. I assume that you cannot make the spiral as toroide so it will not have magnetism outside coil at all. So you wire the sipral coil as a horse shoe so that it generates magnetic field to outside of the coil trying to go from minus to plus side. This field can be made stronger by adding metal inside the spiral loop to make the magntic field outside spiral stronger I believe. Am I assuming right?

What is good calculation equation for inductanse and magnetic field for spiral coil in metric measures?

I have found that there is so many equations arround net and all produce a bit varied results in micro henries so I need a trust worthy equations for them.

[chemelec]

I'm still playing with this coil. After testing it further, I'm inclined to think it performs much like a 4 inch coil I had for my tesoro, not an 7.5 inch coil.

Am I wrong to say that performance depends primarily on the Inner Diameter of a coil, not it's Outer Diameter? If so, it would explain it's similar performance to a smaller coil.

It's a good coil....still, it's got me digging hot rocks. I'm going to have to research a mod for my minelab. I remember reading something about making the SD's ignore them...

Mario, My Observations:

Greatest Sensitivity on SMALL Objects Occurs at the Inner Diameter Point of the coil.
(Like at the Start Turn.)
And Greatest Sensitivity of Larger Objects occurs at the Center of the coil.

I Find this true for all sizes of these Flat wound Radial Coils.

But Bigger coils also become Less Sensitive to SMALL Objects, even at this Start Turn.

HOT ROCKS: You might try winding Two Conventional Round or OVAL coils, overlapping each other and using the Cancelling Circuit configuration.
It Should help, But I have one area near me where EVERY ROCK is like a Big Piece of IRON. (Both the Small Rocks and HUGE SIZE BOLDERS.)
I would really like to know What Exactially is in them to cause this?

Does ANY ONE KNOW?

[mario]

I'm still playing with this coil. After testing it further, I'm inclined to think it performs much like a 4 inch coil I had for my tesoro, not an 7.5 inch coil.

Am I wrong to say that performance depends primarily on the Inner Diameter of a coil, not it's Outer Diameter? If so, it would explain it's similar performance to a smaller coil.

It's a good coil....still, it's got me digging hot rocks. I'm going to have to research a mod for my minelab. I remember reading something about making the SD's ignore them...