Advanced PI coils

[Aziz]

Hi all,

I have been quite busy recently.
Anyone got a ground-breaking idea?
You know, the clock is ticking....
Only good ideas will reset the thread dead timer.
Aziz

[deemon]

Hi all,

I have been quite busy recently.
Anyone got a ground-breaking idea?
You know, the clock is ticking....
Only good ideas will reset the thread dead timer.
Aziz

Hi Aziz

My idea isn't ground-breaking , but what if we use an amorphous magnetic core in the search coil ? Can you calculate the field of this coil ( I'll tell you all dimensions ) and compare it with the simple round coil with the same inductance ? When I made my experiments with ferrite core coils , I noticed that sensitivity is rising with a permeability of the core material ... the problem is that I still cannot find a ferrite with permeability more than 4000 , but I know that these new amorphous magnetic materials can have a tremendous 100000 , so why not ? Maybe this coil can beat the simple air coil ?

[Aziz]

Hi Aziz

My idea isn't ground-breaking , but what if we use an amorphous magnetic core in the search coil ? Can you calculate the field of this coil ( I'll tell you all dimensions ) and compare it with the simple round coil with the same inductance ? When I made my experiments with ferrite core coils , I noticed that sensitivity is rising with a permeability of the core material ... the problem is that I still cannot find a ferrite with permeability more than 4000 , but I know that these new amorphous magnetic materials can have a tremendous 100000 , so why not ? Maybe this coil can beat the simple air coil ?

Hi deemon,

this is a good idea for a single frequency induction balanced coil (single frequency VLF detector). Best done as a concentric co-planar IB coil with large TX and relative small RX with bucking coil BX sitting on the same ferrite core. RX and BX can be wound on a ferrite rod (10 - 20 mm diameter should be enough, 30 - 50 mm long).

Why single frequency?
Due to the frequency dependent susceptibility nature of the ferrite core. The magnetization is dependent on the frequency of course and one can optimally induction balance the coil only for one frequency.

It would be interesting to see the SNR performance. Would the small RX with ferrite core induce less EMI noise compared to the air cored RX? Would the GB work? I don't know. Someone has to make such a coil and report it here...

Cheers,
Aziz


PS: I am restricted to air core coils (µr=1). I can't calculate the interaction between coil and susceptible matter. BTW, this is very non-trivial task.

[6666]

Hi Aziz
is it possible to model a separate TX and RX PI coil ?
the Tx would be a round 300 micro henry coil 280mm Dia
with a 300 micro henry figure 8 RX inside the TX coil.

Its the figure 8 coil I am interested in.


Thanks
6666

[Aziz]

Hi Aziz
is it possible to model a separate TX and RX PI coil ?
the Tx would be a round 300 micro henry coil 280mm Dia
with a 300 micro henry figure 8 RX inside the TX coil.
Thanks
6666

Hi 6666,

yes it is possible. I'm not sure, whether the coil has been done in the latest coil comparison analysis. I know, I have done it once in the past.
(let me see ... )

Ok, this coil hasn't been done yet recently. But I would make the analysis comparable to the other coil configurations.
10" round TX, inside the almost fully filled figure-8 DD (not overlapped). TX=300µH, RX+, RX-: each coil part equivalent EMI noise induction of TX.

This coil isn't going deep due to the planar configuration of the figure-8 RX however. On the other side, each coil half is picking up less EMI noise and both RX+ and RX- coils cancel the EMI noise to some degree (figure-8 = AI configuration). So one can crank up the gain to compensate the depth losses.

Just give me 1 - 2 days and I'll do the SNR compensated comparison...

Cheers,
Aziz

[Davor]

Hi Davor,

could you provide a detailed sketch of the coil configuration? I don't understand your coil configuration.
Cheers,
Aziz

I thought of this:

[deemon]

Hi deemon,

this is a good idea for a single frequency induction balanced coil (single frequency VLF detector). Best done as a concentric co-planar IB coil with large TX and relative small RX with bucking coil BX sitting on the same ferrite core. RX and BX can be wound on a ferrite rod (10 - 20 mm diameter should be enough, 30 - 50 mm long).

Why single frequency?
Due to the frequency dependent susceptibility nature of the ferrite core. The magnetization is dependent on the frequency of course and one can optimally induction balance the coil only for one frequency.

I cannot agree with you here , Aziz . Single frequency = sinusoid wave , isn't it ? But when we use sinus , we'll suffer from another ferrite problem - nonlinearity And this problem is much more painful than that frequency dependency of permeability , that you talking about . During my experiments with mono coil IB I noticed that we easily can balance a ferrite coil in 3-times frequency range ( 5-15 khz , for example ) , but nonlinearity ( with thermal and magnetic instability also ) is the real thing that can spoil our balance

So I came to conclusion that the only method to "cook" ferrite coils it my super-duper "constant-current" technology ... when we maintain the constant current in the coil during all measuring interval , we don't depend on every variations of ferrite permeability , because we are staying on the only one point of the magnetization curve , and can safely receive all the target response . I still working on this technique now , and wanna make new device with the simple air coil .... but if I find the material with very high permeability ( amorph , for example ) - I will try another device such coil too . And this is why I am thinking , how can I calculate the field of this coil ( with the core permeability about 100000 ) - because this material is quite expensive and hard to find here , and it would be bad thing if I find it , but the coil performance disappoint me .

[Aziz]

I thought of this:

Hi Davor,

Ok, I see it now what you have meant.
A fair comparison to the equivalent 10 inch mono coil size wouldn't give any benefits. The coils would be much smaller and they would fail the comparison run blatantly.
Aziz

[Aziz]

I cannot agree with you here , Aziz . Single frequency = sinusoid wave , isn't it ? But when we use sinus , we'll suffer from another ferrite problem - nonlinearity And this problem is much more painful than that frequency dependency of permeability , that you talking about . During my experiments with mono coil IB I noticed that we easily can balance a ferrite coil in 3-times frequency range ( 5-15 khz , for example ) , but nonlinearity ( with thermal and magnetic instability also ) is the real thing that can spoil our balance

So I came to conclusion that the only method to "cook" ferrite coils it my super-duper "constant-current" technology ... when we maintain the constant current in the coil during all measuring interval , we don't depend on every variations of ferrite permeability , because we are staying on the only one point of the magnetization curve , and can safely receive all the target response . I still working on this technique now , and wanna make new device with the simple air coil .... but if I find the material with very high permeability ( amorph , for example ) - I will try another device such coil too . And this is why I am thinking , how can I calculate the field of this coil ( with the core permeability about 100000 ) - because this material is quite expensive and hard to find here , and it would be bad thing if I find it , but the coil performance disappoint me .

Hi deemon,

you don't need a susceptible material of µr=100000. You can try the idea even with µr=100 with common ferrite powder or ferrite rod (or maghemite or magnetite powder).
Just try it, whether it works.
Aziz

[Davor]

Hi Davor,

Ok, I see it now what you have meant.
A fair comparison to the equivalent 10 inch mono coil size wouldn't give any benefits. The coils would be much smaller and they would fail the comparison run blatantly.
Aziz

Maybe so, but they'd be fairly easy to manufacture as the pattern is easily (quadr)uplicated. The other point is that this configuration could be easily reconfigured in 3 different configurations, of which 2 are in IB.
I'd be delighted to see it's performance in this very configuration as this one would be the best imaginable configuration against the far field EMI. It's only odd feature is that it has a sharp minimum in the very centre, hence pinpointing would be extremely sharp, but in the sense of signal absence.

We already discussed a coil in a similar configuration, and it appears that it has a cold spot right in a middle, and my idea was to use it as a submersible rig that would be completely intrinsic, with electronics in a middle.

Could you reconsider testing it :wink: :nudge:

[deemon]

Hi deemon,

you don't need a susceptible material of µr=100000. You can try the idea even with µr=100 with common ferrite powder or ferrite rod (or maghemite or magnetite powder).
Just try it, whether it works.
Aziz

You see , I already tried a thick ferrite rod ( mu=2700 ) in the coil of my PI recuperative device , I just use it in the final variant of this device and it works now , of course . But I noticed that the sensitivity is less than it could be with the usual round air coil with the same electronics . And this is why I wanna use a simple coil in my new device . But the main question is still the same - if I use a kind of high-permeability material , can this new coil beat the old one ?

As I understand it , simple round coil "covers" some area and receives all magnetic lines passing through , converting it to electric current according to Faraday's law , but ferrite core , even with less diameter - "sucks" magnetic lines from outer space and pushes it into a coil , so what is the question - how much permeability must I have to make a little diameter ferrite coil work like a much more diameter simple coil ? My experiments shows the obvious thing , that the sensitivity does depend on 3 factors - diameter of the ferrite rod , it length and magnetic permeability of the core material . But I don't know how to calculate it precisely , here is the problem . As for me - I can well understand physics , but quite bad in mathematics

[Mechanic]

HI Aziz,

Try this, standard mono coil on the ground(25") and at the other end of the detector handle about 1M behind the operator another mono coil parallel to the ground about 1.5m from the ground. The coil behind the operator is used to cancel/reduce emi and is just a standard coil, 300uh. The emi coil will be a smaller coil, 18 or 16". and will have the same self resosnace as the main mono coil. The emi is subtracted in the electronics of the front end.

This should reduce emi making the use of the larger mono coil much more pleasant. Unfortunately both coils will not always be parallel, so the reduction will vary a bit, but this should be better than just a standard mono...... Whatcha think? I'm going to give this a bash on the weekend.

Cheers Mick

[Mechanic]

Hi Guys,

Well perhaps I should get my self some shares in "MadLabs Inc."(c)(tm)(r)" I'm not the best with math, but my missus thinks I'm mad, in fact, I think I could be just a bit mad however it works well, very well!

No target subtraction, just emi reduction and it is quite forgiving. I can almost get the 25" mono quiet at my house, it will be a dream while out bush. I might even be able to use a smaller coil for the emi coil to make it all a bit lighter, but even as it is, the detector is still quite usable

Cheers Mick


Possible "MadLabs Inc."(c)(tm)(r) participant

[mickstv]

EMI reduction and counterbalance, I like it.

[Aziz]

Round TX, Double-D figure-8 RX, AI PI Coil Added

Hi all,

I am referring to the post #335 (6666's wish). This is a 10 inch round TX PI coil, having the RX+ and RX- as figure-8 double-d coil (not overlapped) sitting inside the TX coil, as big as possible (3-4 mm edge space to give the coil bundle some space to fit inside the TX coil). RX+ (RX- identical but opposite winding direction) windings turn increased to have the same level of EMI noise induction as the 300 µH 10" round coil (reference coil). So this coil is SNR compensated.

This is the comparison graph at additional gain of x10 (see 10" Round TX, Double-D figure-8 RX - AI PI Coil):





This is the performance relation to the reference coil (no additional gain):

Coil Comparison (Calculated Response Ratio to Reference Coil)
© 2012 by Aziz Ögüt. All Rights Reserved. 25-Jan-2013
Reference Coil: 300 µH Round Mono Loop Coil
		10" Round TX, Double-D figure-8 RX - AI PI Coil
Target Depth [inch]	Target Depth [cm]	Relation to Reference
1	2,5	2,694
2	5,1	2,744
3	7,6	1,905
4	10,2	1,357
5	12,7	1,032
6	15,2	0,827
7	17,8	0,691
8	20,3	0,590
9	22,9	0,518
10	25,4	0,459
11	27,9	0,414
12	30,5	0,377
13	33,0	0,345
14	35,6	0,319
15	38,1	0,297
16	40,6	0,277
17	43,2	0,260
18	45,7	0,245
19	48,3	0,231
20	50,8	0,220
21	53,3	0,209
22	55,9	0,199
23	58,4	0,190
24	61,0	0,182
25	63,5	0,175
26	66,0	0,168
27	68,6	0,161
28	71,1	0,155
29	73,7	0,150
30	76,2	0,145

Cheers,
Aziz