Minelab 8000

[Carl-NC]

This is a rocket science now. Nobody has thinked of it till now.

1970, and I own one:

[Aziz]

1970, and I own one:

You need to rotate the coil by 27 degree now.


I am preparing a new coil comparison between a 18 inch round and square coil.

[Aziz]

Hi all,

I've realized that Google's AI has been telling me a lot of nonsense.
We cannot do without the coil software.
The coil models have been made.

The results are very interesting..
I need to find a way how to visualize the results ..
The square coil wins. It has a larger detection area at depth too.
Aziz

[Tinkerer]

Have you taken into account the uniformity of the coil field?
With the round coil the field(lines) is the most uniform and gives the biggest depth.
With the square coil, the field is less uniform. In the 4 corners the field it "pinched". The "pinching" produces more divergence of the field(lines) when coming out of the "pinched" area.
The divergence is greater with a small diameter coil than with a large diameter coil. Because of the divergence, the same field (strength) at the coil level gets more "diluted" at distance.

[Aziz]

Hi Tinkerer,

Have you taken into account the uniformity of the coil field?
With the round coil the field(lines) is the most uniform and gives the biggest depth.
With the square coil, the field is less uniform. In the 4 corners the field it "pinched". The "pinching" produces more divergence of the field(lines) when coming out of the "pinched" area.
The divergence is greater with a small diameter coil than with a large diameter coil. Because of the divergence, the same field (strength) at the coil level gets more "diluted" at distance.

the coil software does take it into account.

We have three regions to look at it:
- Near-field zone (z distance < coil radius R):
We have an intense magnetic field strength inside and nearby the 4 corners of the square coil compared to round coil. Outside the corners less due to increased geometric mean distance to the wires.
If we rotate the square coil by 27 degree and swing the coil left to right and vice versa, these 4 corners cover a good region for the shallow small target detection. So it is compensating the detection sensitivity loss to small targets when using larger coils. These 4 corner regions are big enough to cover the whole swinging coil area.

- Intermediate-field zone (z > R, z < 2*R)
There is a trip point (in my case between 27.5 cm and 30 cm z-distance). This is independent of target size.
Above the trip-point, the square coil always wins.
Below the trip-point, the target response diminishes slightly. So the square coil behaves like a slightly bigger round coil.

- Far-field zone (z > 2*R (or diameter))
It's a winner for big deep gold.
The interesting fact is, that the detection zone is larger compared to round coil (small cone region). So you are covering more detection area for big deep gold.


We have to look at all the regions extensively yet.

This is the coil model (both shown at same position). The super cheat: "same size coil". You swing a "same size coil".


More to come later ..

Cheers,
Aziz

[Aziz]

BTW,

regarding the rotation angle of the square coil:

Rotation angle of 0 degree:
A rotation angle of 0 degree will do it either. The coil mounting is simple. The small shallow target is beeing hit twice the time when swinging the coil at in front and rear position. When swinging in overlapped ground coverage, the shallow target is beeing hit anyway.

Rotation angle of 45 degree:
You have sqrt(2) = 1.41 times more ground coverage. Same applies to the shallow small target. Coil mounting is also easy. Maybe a bit better across the corner.

Rotation angle of 27 degree:
Too difficult for coil mounting. But you have the best target response coverage for small shallow targets.
It isn't practical of course. It looks very strange and crazy.

[Aziz]

Hi all,

this is the target response comparison of the 18 inch round vs square mono coil (see zipped Excel file in the attachment).
I am still using my 20 mm diameter standard target.

My coil bundle is 8 x 8 mm in this example. It is very compact. This is the worst you can ever do.
If you wind a mono coil, you should have 20 x 20 mm or 30 x 30 mm coil bundle thickness. The more, the better.
-> more Ampere-turns count

Note, that the square coil has more space to be well wasted in thicker coil bundle.
Aziz

[Aziz]

Hi all,

now the comparison of magnetic field cross-sections at different z below the coils.
I have reduced the number of palette colors to have discretised magnetic field strenght regions.
And I had to change the scaling range.

File names describe the coil name and z position.

[Aziz]

two more