Minelab 8000

[Aziz]

Look, this is what I mean. A portable Ground Loop IB coil. Yes, it is induction balanced. The RX bucking coil can be placed at the same TX coil height.
The main RX coil is below. The large TX coil is red.

A balanced frame is required to work with big search coil.
Any IB coil instability can be handled by the software (it will give pure X-response).
Just imagine with large TX coil and high power Class E TX. The deep nuggets will be pulled out of the ground.

[Carl-NC]

Look, this is what I mean.

That's called a "top hat" coil, p378 in ITMD3.


For anti-interference you make the RX coils identical. For IB they are not.

[Aziz]

That's called a "top hat" coil, p378 in ITMD3.


For anti-interference you make the RX coils identical. For IB they are not.

Yep.
But the Top Hat (a) coil is upside down for our portable handheld "ground loop" IB coil system. RX- is the main RX coil referred to figure a in your example.
With high power TX, there won't be remarkable ground noise problems as the TX coil is placed well above the RX coil. This is required as the terrain won't allow sweeping such a large coil above the ground level. We are sweeping the TX coil at the grass/shrub/bush height level. A better pin-pointing and locating the target is possible.
The magnetic fields in the RX region won't be refracted and they will penetrate even very hot iron ore ground.
Fine induction balancing is possible by varying the RX coil distance to the TX coil. Rough IB by setting up the number of turns count appropriate for the bucking RX coil.

We would require more TX power. But this is feasible.

[Carl-NC]

But the Top Hat (a) coil is upside down for our portable handheld "ground loop" IB coil system. RX- is the main RX coil referred to figure a in your example.

True, but it can be used either way, depending on whether you want the TX coil closer to or farther from the ground. Either RX coil can also be the primary. In the book it is presented as a test coil to be used on the bench, where EMI is the problem.

[pito]

or like this one

[Carl-NC]

the null is a realistic 32 db.

32dB isn't very good. VLF manufacturers usually shoot for 50-60dB, which requires a "hand tweaking" loop of wire. What is the null limitation in your AI Designer? I assume all coils are an integer number of turns, but that you can vary spacing to achieve way better than 32dB. In any case, nice use of AI!

[Aziz]

True, but it can be used either way, depending on whether you want the TX coil closer to or farther from the ground. Either RX coil can also be the primary. In the book it is presented as a test coil to be used on the bench, where EMI is the problem.

But the RX bucking coil at the center of the big TX coil would have less windings for nulling. Approx. 2.9 times less turns count. Anyway, it should still work.

[Carl-NC]

Yes, correct.

[moodz]

32dB isn't very good. VLF manufacturers usually shoot for 50-60dB, which requires a "hand tweaking" loop of wire. What is the null limitation in your AI Designer? I assume all coils are an integer number of turns, but that you can vary spacing to achieve way better than 32dB. In any case, nice use of AI!

Yes .. thats only about a 40x reduction. This was because I was just putting in some proximate coil radius sizes for TX, RX and Z spacing
...now the tool includes a "gimmick" or trim coil which it calculates and the optimiser has a wider range of control over all parameters except tx coil size.

Now achieves 80 db with theoretical infinity ( impossible in practice ) if you add calculated trim coil.

[moodz]

Added a 3D visualisation tab and DAC fine nulling ( bucking coil does the heavy lifting ).

Below is a "research grade" coil with -140 db nulling using a 12 bit DAC from the cpu ( purple coil ).

The nulling was calculated with a mechanical tolerance at .05mm ( which just happens to be the tolerance of most 3D printers )

The coils are gapped and optimised ... ( the patent did not mention this ) The tool does this optimisation.
As Aziz says there is no free lunch ....
to achieve this performance ( low noise, high nulling, maximum SNR ) a coil that is around 70 cm wide will have a stack height of 94 mm including a rigid 5mm casing allowance top and bottom.

[moodz]

...and while were at it. SPIRAL WOUND COILS = FAKE NEWS

Yes this may be surprising but it was worked out in 1947 by a guy called Medhurst who showed that spiral wound coils on radios were no more than "bling" used by radio manufacturers to sell more radios because they looked "high tech".
This is because the early radios had all their guts on the outside of the case ( valves and coils and brass doohickys ).

In fact spiral wound coils have more self capacitance than say your solenoid wound coil.

So all those ppl who bought into spiral wound coils ... bought into a fad. ( AKA marketing ).

[Aziz]

...and while were at it. SPIRAL WOUND COILS = FAKE NEWS

Yes this may be surprising but it was worked out in 1947 by a guy called Medhurst who showed that spiral wound coils on radios were no more than "bling" used by radio manufacturers to sell more radios because they looked "high tech".
This is because the early radios had all their guts on the outside of the case ( valves and coils and brass doohickys ).

In fact spiral wound coils have more self capacitance than say your solenoid wound coil.

So all those ppl who bought into spiral wound coils ... bought into a fad. ( AKA marketing ).

This is indeed quite interesting.

We have enough z-space for solenoids. + gapping winding to winding.

[moodz]

..now added a tab to the tool to generate the coil former for the optimised coil ... so it can be 3D printed .. with easy to wind but precise construction in mind.

This AI is crazy ... smart.



3D rendering ... it needs work ..but its getting there

[Aziz]

Hi all,

I have got the approximate dimensions of the figure-7 (Z18 ) coil by making a simple measurement with an image editing application using figure-7 in the patent.
I have rebuilt the coil arrangement in the coil software modelling.
I wonder, the RX nulling coil is quite large and has still many windings to null out (N = 11). The main RX has total (N = 2 x 8 ) 16 turns. This will lead to detection hole zone for particular targets.
The coil software predicts inductances of 300 µH for TX and RX total. And the RX bucking coil sits in the right place for induction balance.
This model will be sufficient accurate enough, to look for detection holes (sensitivity map creation).

This is the coil arrangement model:

Aziz

[moodz]

these types of concentric coils can suffer from target holes close to the coil surface ... eg within 5 cm. Basically the are in the nulling zone.

Nevertheless ... we must progress the uber bucking coil.

140 db optimally nulled bucking profile from 3d print files :