Advanced PI coils

[Aziz]

Surprise! Surprise!

Ok guys,

another magic is happening here. Fortunately, this spiral coil is prior art and nobody can lock it with evil patents anymore. Pity, but I didn't invent it. And it works pretty well and is even outperforming the mono coil. As I said before, never give it up! How is that now?


Spiral coil:
Beginning from 0.5 unit diameter (=5 inch) and ending at 1.0 unit diameter (=10 inch). 35 loop turns (but I'm using internally in my coil software N=34.7).

Unfortunately, this flat spiral PI coil is picking up approx. 9.7% more EMI noise. So the total coil flux area is 9.7% more compared to the mono coil. On the other hand, it is performing exceptionally well. In the relation comparison below, the 9.7% more noise is divided out (by multiplying the relation by 0.912). So we see the SNR corrected relation and is a good comparison to the mono coil regards to SNR criteria.

Coil Comparison (Calculated Response Ratio to Reference Coil)
© 2012 by Aziz Ögüt. All Rights Reserved. 10-Jan-2013
Reference Coil: 300 µH Round Mono Loop Coil
		10" Spiral PI Coil (0.5 DU .. 1.0 DU)
Target Depth [inch]	Target Depth [cm]	Relation to Reference SNR compensated (9.7 % more EMI noise)
1	2,5	3,007
2	5,1	3,949
3	7,6	3,085
4	10,2	2,433
5	12,7	2,034
6	15,2	1,783
7	17,8	1,618
8	20,3	1,504
9	22,9	1,424
10	25,4	1,365
11	27,9	1,320
12	30,5	1,286
13	33,0	1,259
14	35,6	1,237
15	38,1	1,219
16	40,6	1,205
17	43,2	1,193
18	45,7	1,183
19	48,3	1,174
20	50,8	1,167
21	53,3	1,161
22	55,9	1,155
23	58,4	1,150
24	61,0	1,146
25	63,5	1,142
26	66,0	1,139
27	68,6	1,136
28	71,1	1,133
29	73,7	1,131
30	76,2	1,129

Now look at this magic stuff. I'm really impressed. There is a coil now, which is outperforming the mono coil with ease. One have to tame the shielding capacitance somehow.


Cheers,
Aziz

[Aziz]

The Spiral PI Coil Pics

Wire frame pic:


Magnetic field strength pics:




Cheers,
Aziz

[dfbowers]

Nice work Aziz. I enjoy reading your daily posts very much.

Back in the day of BFO detectors, I built a small spiral coil that outperformed just about anything else I could come up with. They work great on Telsa coils too!

Don.

[Davor]

Wasn't Tesla the one that lodged the patent on a spiral coil?

[techo_bob]

Hey Aziz

How about a centre tapped spiral coil into a full differential amp

would that help !!!

Bob..

[Aziz]

Hi all,

BTW, I have to mention, that the spiral coil response calculations were done at the z-axis and the calculated figures in the first few inches does not contain the maximum target response. Only at the center axis. This is the reason, why you get strange relation figure at 2 inch detection depth. The mono coil response does contain the maximum response on its edge and the spiral coil doesn't yet (would require very time consuming coil calculations). Just ignore the strange relation in the first two response depth.

Some notes on the spiral coil:
It is obvious, that it isn't optimal for highly mineralized ground due to stronger magnetic field strengh on the center region. You will get more ground noise of course (don't confuse with EMI noise). A good compromise would be a round TX (as usual or semi spiral) and a separate spiral RX, which is smaller than TX. So not all magnetic flux of the TX is linked to the RX spiral coil. The RX spiral beginning could even be smaller than 0.5 diameter units of the TX coil.

Let's continue with the WBCT ... to find the ultimate coil technology (UCT).
Anyone want to oppose now?

Cheers,
Aziz

[Aziz]

Hey Aziz

How about a centre tapped spiral coil into a full differential amp

would that help !!!

Bob..

Hi Bob,

it is really nice, that spiral coils can be made center-tapped using the bifilar coil wire. The only advantage is, that you can drive it at L/4 (=coil half) to push more current and damp and receive at both coil halves. There is no benefit regards to EMI noise induction. When you sample at both coil halves, you have the twice target response and the twice EMI noise induction as well. But you have a much more current drive.

Ground noise is a big issue on Oz ground. And this gets more critical with half coil driving.

Cheers,
Aziz

[Aziz]

Wasn't Tesla the one that lodged the patent on a spiral coil?

Yes, Nikola Tesla was a great person & inventor. He is one of my favourite scientists.

I think its going to be very difficult to convince a patent examiner to give his Ok for a new spiral coil patent.
*LOL*
(Oh yes, I forgot: it's only a question of "Fakelaki"/"Bakshish" (money) today.)
Aziz

[Ferric Toes]

Hi Bob,

But you have a much more current drive.

Current is inductance limited for full coil, so for 1/4 inductance it will be resistance limited (depending on pulse width and total coil circuit resistance). However, if the current doubles in half of the inductance you are back to square one i.e. same as a normal mono.

Because the centre tap at 1/2L is not going to be a 1/2Turns, will this not give an unbalance to the common mode response. I expect a balance point for the CT could be calculated.

Ground noise is a big issue on Oz ground. And this gets more critical with half coil driving.

No reason for this that I can see.

Eric.

[Aziz]

1 Million Dollar Question Quiz

Hi all,

you know, I like quiz games.
Here is a 1 Million $ question quiz for you.

What is better regards to mono PI coil performance and SNR:
1. a more compact coil bundle with less copper and less turns count or
2. a wide & thick coil bundle with more copper and more turns count?

Both coils (1. + 2.) have the same inductivity.
2. coil has more resistance and obviously less interwire capacitance. But filled with a lot of "air". Coil looking like a donut coil.

This is a consequent question towards the UCT due to the last finding. What do you think?

Aziz

PS: Damn it, but I don't have 1 Million $ to pay the winner.

[Ferric Toes]

Wire frame pic:
[ATTACH]22691[/ATTACH]

Spiral pcb coil 1970's style. How the artwork person did this at the time is a mystery. No computer programs then; it was all down to adhesive black tape. This is probably the first PI pcb coil attempted anywhere.

Eric.

[Aziz]

See What Happens

Hi all,

I have distributed the spiral coil over 20 mm thickness. There are 3 layers of spiral coil, each 10 mm co-axial apart. Total N=39 (13 each layer). We have more copper and more turns. This is causing 20.4% more EMI noise induction. So I have to compensate a lot. See what comes out:

Coil Comparison (Calculated Response Ratio to Reference Coil)
© 2012 by Aziz Ögüt. All Rights Reserved. 10-Jan-2013
Reference Coil: 300 µH Round Mono Loop Coil
		10" Spiral PI Coil (0.5 DU .. 1.0 DU)	10" Spiral PI Coil (0.5 DU .. 1.0 DU, 20mm thick, 3 spiral layers)
Target Depth [inch]	Target Depth [cm]	Relation to Reference SNR compensated (9.7 % more EMI noise)	Relation to Reference SNR compensated (20.4 % more EMI noise)
1	2,5	3,007	2,743
2	5,1	3,949	3,355
3	7,6	3,085	2,565
4	10,2	2,433	2,027
5	12,7	2,034	1,716
6	15,2	1,783	1,528
7	17,8	1,618	1,409
8	20,3	1,504	1,331
9	22,9	1,424	1,278
10	25,4	1,365	1,241
11	27,9	1,320	1,215
12	30,5	1,286	1,196
13	33,0	1,259	1,183
14	35,6	1,237	1,173
15	38,1	1,219	1,165
16	40,6	1,205	1,159
17	43,2	1,193	1,155
18	45,7	1,183	1,152
19	48,3	1,174	1,150
20	50,8	1,167	1,149
21	53,3	1,161	1,148
22	55,9	1,155	1,147
23	58,4	1,150	1,147
24	61,0	1,146	1,147
25	63,5	1,142	1,147
26	66,0	1,139	1,147
27	68,6	1,136	1,147
28	71,1	1,133	1,148
29	73,7	1,131	1,148
30	76,2	1,129	1,149

The near detection zone suffers. But is going slightly deeper (not significant). It's not a good idea, to separate the coil bundle in the co-axial direction/region. Better in the radial/concentric direction/region (like a thin/flat spiral).
BTW, one can see the accuracy of the latest relation: approx. +/-0.003

Cheers,
Aziz

[Prospector_Al]

There are some newer papers and dissertations related to human demining with thorough theoretical background. I even found some detailed analysis of ferrous targets. Hopefully it will enable me to tune up the spice target models for Fe.

Hi Eric,
Speaking of Australia, someone told me that when you were there, you measured the Tcs of som big nuggets. Do you have any idea of the Tc of a 30 oz. nugget? I'm interested in developing a Giant Nugget detector, usig the thyratrons I mentioned in a different thread...

Allan

[Aziz]

Flat Spiral 0.75 DU - 1.0 DU

Hi all,

I have added another flat spiral PI coil to the comparision. Spiral beginning at 0.75 diameter unit and ending at 1.0 diameter unit (10"). Turns count N=27-28 (somewhere between for 300 µH, N=27.1 internal, 0.4 mm thin wire this time due to recuded loop area). See, what comes out:

Coil Comparison (Calculated Response Ratio to Reference Coil)
© 2012 by Aziz Ögüt. All Rights Reserved. 11-Jan-2013
Reference Coil: 300 µH Round Mono Loop Coil
		10" Spiral PI Coil (0.5 DU .. 1.0 DU)	10" Spiral PI Coil (0.75 DU .. 1.0 DU)
Target Depth [inch]	Target Depth [cm]	Relation to Reference SNR compensated (9.7 % more EMI noise)	Relation to Reference SNR compensated (13 % more EMI noise)
1	2,5	3,007	1,334
2	5,1	3,949	2,112
3	7,6	3,085	1,962
4	10,2	2,433	1,759
5	12,7	2,034	1,609
6	15,2	1,783	1,501
7	17,8	1,618	1,423
8	20,3	1,504	1,366
9	22,9	1,424	1,323
10	25,4	1,365	1,291
11	27,9	1,320	1,266
12	30,5	1,286	1,246
13	33,0	1,259	1,230
14	35,6	1,237	1,217
15	38,1	1,219	1,207
16	40,6	1,205	1,198
17	43,2	1,193	1,191
18	45,7	1,183	1,184
19	48,3	1,174	1,179
20	50,8	1,167	1,175
21	53,3	1,161	1,171
22	55,9	1,155	1,167
23	58,4	1,150	1,164
24	61,0	1,146	1,162
25	63,5	1,142	1,159
26	66,0	1,139	1,157
27	68,6	1,136	1,155
28	71,1	1,133	1,154
29	73,7	1,131	1,152
30	76,2	1,129	1,151

We can conduct some important rule for a PI coil bundle:
Make it vertically thin and make it radially (horizontal) thick. It doesn't matter, when the coil bundle even gets radially quite thick. It's just an approximation of a spiral coil. You can fill the inner area with additional loops if you like. I don't see much difference. But we usually want to see through the center hole. Just leave some reasonable hole.

Another coil type: Rodin-Starship coil
Not optimal - forget it.


Cheers,
Aziz

[Tepco]

I tried similar coil, .75:1 and .66:1 shape, not optimal, 0.5:1 seems to be best, but not higher. Part in coil center of full spiral serves to no purpose at all, just unnecessarily adding more material and slowing down the coil.