Advanced PI coils

[Sergey_P]

DDO coil is much better

http://www.md4u.ru/viewtopic.php?f=94&t=8150

[ppodg]

There is only one problem: ground compensation will never be perfect with nonidentical rx coils and will strongly depend upon the height above the ground ; DDO coil is much better, though its central phase reversal (or 'dip' if rectified) feature seems very unpleasant - but, after rectification, good for pinpointing.

[Aziz]

Last proposal:
TX: 1 unit diameter
RX+: 1 unit diameter, N turns count
RX-: 0.5 unit diameter, 4*N turn count
CX: 0.5 unit diameter, decreased turns count compared to 1/sqrt(2) unit diameter

A better depth & pin-pointing performance compared to 1/sqrt(2) unit diameter CC AI IB coil.

The difficulty is to match RX+ and RX- for best EMI rejection.
Aziz

[Aziz]

Hi all,

let's think further now:
RX- being half diameter and four times turn count of RX+

Anyone want to guess or comment on this idea?
(But don't run into the patent office - Ok? HAHAHA)

Cheers,
Aziz

PS:
Oooops!!! F§$k!, I have obviously killed my previous post by editing it. Sorry for this stupid action by me. I will see, whether I can reconstruct it. You know, I'm saving my posts to argue against the patent trolls.

------------ Ok, reconstructed now -----------------
Yep, it definitely deserves a go. The ground effect rejection to some degree is very valuable of course.
I'll try this coil other time.
Ok, I'm happy too.

Aziz
-----------

[Davor]

No worries, I expected that much. I'm most interested in obtaining a coil which will work well on difficult terrains, such as sea shore and red clays. Being a differential coil, this one will cancel ground as well. With suppressed interferences I can compensate losses (to some degree) with additional gain, and it all fits the bill very nicely.

I'm happy.

[Aziz]

Sorry guys!

I'm so sorry guys. But the last coil does not go deep compared to a equivalent concentric co-planar coil (CC).

The equivalent CC-coil:
TX total: 300 µH, 10" diameter,
RX: 100 turns at 1/sqrt(2) size of TX (7.1" diameter),
BX/RX same distance gap

It offers a better pin-pointing feature in the near coil region (no gain compensation required up to ~3 inch distance).
at 10 inch distance: Gain x 6.5 (~ +16 dB) to be equivalent to a concentric co-planar coil.
at 20 inch distance: Gain x 34 (~ +30 dB) to be equivalent to a concentric co-planar coil.
and it gets worse at more detection distances of course.

If you can get a EMI rejection ratio of 40 dB, there is some improvement possible. No doubt, it will work to some detection distance well enough.

Aziz

[Aziz]

Yesss!

I'm not afraid of cranking up the gain now that the interferences will be cancelled at the source. Same goes to the ground response. If compared with any other IB configuration, this one leaves a bigger chunk of space underneath the inner Rx coil, the one with positive metal response, and unlike the solution with a bucking coil, this one has more homogeneous Tx field in a centre region compared to the rim, so this is win-win all over. And with a bigger hole in a middle to look through.

I'm happy

Yes sure. It would be interesting to know, how this coil compares to a equivalent size concentric co-planar coil. So we can see the required additional receiver gain and see the depth performance comparison. I'll make a comparison, when I have more time.

Cranking up the gain isn't a problem since we can use 1nV/sqrt(Hz) amplifiers. The only problem is the different RX specs as the anti-interference condition suffers a bit (different resistance of RX+/RX-, different parasitic capacitances, etc.) . But it shouldn't be as much critical as the AI feature would suffice I think.

Cheers,
Aziz

[Davor]

Yesss!

I'm not afraid of cranking up the gain now that the interferences will be cancelled at the source. Same goes to the ground response. If compared with any other IB configuration, this one leaves a bigger chunk of space underneath the inner Rx coil, the one with positive metal response, and unlike the solution with a bucking coil, this one has more homogeneous Tx field in a centre region compared to the rim, so this is win-win all over. And with a bigger hole in a middle to look through.

I'm happy

[Aziz]

Congratulations

Congratulations guys,

you finally have a fully concentric-coplanar anti-interference coil with compact coil size and a hole in the center region, if you want to look through it. Do you see the benefit of collaboration now?

Rough induction balance can be achieved by varying the distance gap of RX+ to TX or RX- to CX (compensation coil). Notice, that the CX has the same current/winding direction as TX, so it doesn't counteract the TX coil. RX- being always the half flux surface area or 1/sqrt(2) times the size of RX+. Fiddling with additional single turn CX wire loop nearby the CX/RX- arrangement allows a fine balance tune.
But you have to crank up the gain of the receiver. A substantial amount of target response will be cancelled by the RX- coil.

If you take for instance 0.9*TX for the RX+ size (or smaller; RX-/CX accordingly smaller) you don't need much turns count for the CX coil. You can make the RX+, RX-/CX more smaller of course.

I get an approx. turns count relation for the IB condition of 7/16 (CX/TX) for the full size RX+ coil. Or 29 µH / 233 µH, approx. of course as I calculate with simplified single turn coil models for speeding up the calculations.
Don't forget: RX- 2x turns count of RX+ and opposite winding direction.

Here is a cross-section view of the magnetic field strength (1 A, 300 µH TX/CX total):


You can interchange the positions of RX+ and TX (accordingly: RX- and CX). So you don't need to make it exactly same as shown above.


Cheers,
Aziz

[Davor]

Yes, a minimum gap between Tx-es and Rx-es would do for capacitance reasons. Guess 0.8 is far too much for 19uH boost.

[Aziz]

I think I cracked the Davor-Sergey coil - solution is a Tx boosting coil. It would "homogenise" Tx field. So actually ppodg was right, only I did not think of the boosting variant at that time and I unjustly dismissed the idea.

@Aziz, could you be bothered to run a test as in the example above with:
RX+ N=50, RX- N=100
TX: 300 µH at Rx+ radius, Tx boost 19 µH at Rx- radius, 1A coil current, f=10 kHz

Perhaps it would be interesting to see Tx field as well

That would work.
I'll make some configurations.
TX: 1 unit diameter
RX+: 0.8..0.9 unit diameter
RX-: RX+/sqrt(2) unit diameter
BX: same as RX- but with minimal distance gap
Aziz

[Davor]

I think I cracked the Davor-Sergey coil - solution is a Tx boosting coil. It would "homogenise" Tx field. So actually ppodg was right, only I did not think of the boosting variant at that time and I unjustly dismissed the idea.

Another approach: let's add a compensatig/decompensating tx or rx coil...

@Aziz, could you be bothered to run a test as in the example above with:
RX+ N=50, RX- N=100
TX: 300 µH at Rx+ radius, Tx boost 19 µH at Rx- radius, 1A coil current, f=10 kHz

Perhaps it would be interesting to see Tx field as well

[Aziz]

you have a unified theory of the formation of the secondary induction field ?
Very interesting!

No, I have not. (Or should I apply for the Nobel prize? )
KISS-principle, Divide & Conquer, approximation

Following links might help you:

http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_law

http://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

https://en.wikipedia.org/wiki/Amp%E8re's_circuital_law

http://en.wikipedia.org/wiki/Magnetic_flux

http://en.wikipedia.org/wiki/Maxwell's_equations

... see further links there

Heavy but trivial math. BTW, I hate math (that's my other bipolar disorder brain)! *LOL*

Cheers,
Aziz

[Sergey_P]

Maxwell equations, Faraday's Law

you have a unified theory of the formation of the secondary induction field ?
Very interesting!

[Davor]

OK. So my 4 quadrant Rx is back in race.