Dual Field Pi Coils

[Aziz]

Hi Stefan,

Hi Aziz,

There is a compromise as when you make the height of the coil much less than the width of the coil the shield capacitance will increase. This is of course more profound on smaller coils and elliptical coils. So it is all a question of compromise to obtain optimum results by reducing the inter winding capacitance and the shield capacitance.

Regards,

Stefan

yes, that's true. One must consider the coil perimeter too. The coil flux area should be maximized and the perimeter should be minimized at the same time. This is a good exercise for someone, who likes math.

But there are applications, on which the parasitic capacitances don't matter. Then a IB spiral coils (TX and RX spiral coil) would have the most sensitive performance then.

Aziz

[Stefan]

Hi Aziz,

There is a compromise as when you make the height of the coil much less than the width of the coil the shield capacitance will increase. This is of course more profound on smaller coils and elliptical coils. So it is all a question of compromise to obtain optimum results by reducing the inter winding capacitance and the shield capacitance.

Regards,

Stefan

[Aziz]

BTW,

I forgot the give an unit to the x-axis on the graphs.
The target distance is given in cm on the x-axis.

Who remembers Gary's spiral coils? There is an overrun to his coils obviously.

PI coil wires should be a Litz wire. They can be very thick. Instead of making a thick coil, it is more advantageous to make a spiral coil instead. Higher coil bundle width instead of coil bundle height.


Aziz

[Aziz]

Hi detectormods,

Hi Aziz,

I do not think there is a lot to be patented these days due to all the new idea's being discussed on the net.

Sometimes it is worth quickly lodging a patent to protect an idea before a large corporation locks it up.

A large company can claim prior art by saying they were working on the very thing that gets put into the public domain.

Keep up the good work with coil simulation, now be a Capitalist and sell it as a design program to the experimenters..

I am off to the Gold fields to do some tests on 4 new designs, it will be interesting to document the results.

I am not interested in making money - it has no meaning to me except of buying some parts to make more findings possible.
I have not the big bucks to lodge a patent. I want to share my findings with all of you. Coil software won't be given away.

But I would like to know, how the proposals behave in the field. I hope, you are willing to share your experiences. Some feedback would help to optimize the coils further.

I would suggest to try the spiral coil 0.66-1 or the 0.75-1. The first few detection cm's can't be used either. To make the design easier, it could still be a rectangular spiral coil.


Aziz

[detectormods]

Hi Aziz,

I do not think there is a lot to be patented these days due to all the new idea's being discussed on the net.

Sometimes it is worth quickly lodging a patent to protect an idea before a large corporation locks it up.

A large company can claim prior art by saying they were working on the very thing that gets put into the public domain.

Keep up the good work with coil simulation, now be a Capitalist and sell it as a design program to the experimenters..

I am off to the Gold fields to do some tests on 4 new designs, it will be interesting to document the results.

[Aziz]

Outperforming the Dual Field Coils

Hi all,

I will show you, which coils are performing better.

I proposed a Tripple Field coil and Spiral coil former. All together in a comparison shows, how they perform.

TF 0.33 0.66 1.0 means (Tripple Field Coil):
Coil1 at 0.33*R, Coil2 at 0.66*R and Coil3 at 1*R, where R=outer radius of coil.

TF 0.5 0.75 1.0:
Coil1 at 0.5*R, Coil2 at 0.75*R, Coil3 at 1*R

The Tripple Field split coils have all the same number of windings.


Spiral 0.33-1 (Spiral Coil):
Spirally wound coil starting at 0.33*R and ending at 1*R. The number of windings are evenly distributed from starting radius to ending radius.

and so on...

Fortunatelly, spiral coils can not be patented anymore. It is in the public domain. Anything new to the prior art is also public domain now. I made this analysis on the GPOZ forum already, dated at 19.Febr.2009! You can see this there if you like.

Cheers,
Aziz

PS: the last picture is a log-scale (not linear as shown).

[detectormods]

The 1(Width) :1.68 (Height) is not performing better. It can be approximated with the 1:1 and 1:2 ones either elliptical or rectangular.

Doing an accurate analysis is quite time consuming process and causes a lot of work. So I want to limit the work to the well known form factor coils.

Aziz

Hi Aziz,

In the real World the Golden ratio coils make for a bladed pattern, on constructing various coil shapes there are pro's and con's for every shape.

I found that deviation from a mathematical representation of Phi caused a conical pattern while an adherence to Phi made for a blade pattern.

It interesting to do real experiments in the field.

[Aziz]

Hi Aziz,

Now try 1.68:1 or the ratio + initial width or 2 X Ratio.

The 1(Width) :1.68 (Height) is not performing better. It can be approximated with the 1:1 and 1:2 ones either elliptical or rectangular.

Doing an accurate analysis is quite time consuming process and causes a lot of work. So I want to limit the work to the well known form factor coils.

Aziz

[detectormods]

Hi Aziz,

Now try 1.68:1 or the ratio + initial width or 2 X Ratio.

[Aziz]

Here is a brief overview, how the result is gained. It is based on a simplified EM field calculation using my unique coil software.

Aziz

[Aziz]

Dual Field Coil Comparison

Hello friends,

I want to show you how the Dual Field coil compares to standard type PI coils with equivalent coil flux area and inductivity.

All coils are normalized to 300µH inductivity and coil flux area of 500 cm². So the detection coverage area stays constant to make a reasonable comparison.

How the target response is calculated:

A coil current of 1 A flows through the transmit coil (TX) at 1 MHz. It is generating a primary transmit magnetic field. A small target of 20 mm diameter (1 winding closed loop wire) is placed at the center of the coil arrangement with some distance (height) to the coil. The target is inducing a voltage from primary transmit magnetic field. The targets complex impedance and the induced current is calculated. The target is generating a secondary magnetic field.
The transmit coil is then operated as receive coil (RX) and induces a target response voltage from the secondary magnetic field. The target response voltage is displayed on the y-axis. The x-axis is showing the distance (height) to the coil center position.

Don't look at the absolute value of the target response. It is not relevant for the comparision. But the relation to the other coil types is very interesting.

You can see, that a Dual Field coil outperforms a standard round coil.
We can congratulate to White's for patenting the Dual Field coil.

But I have a better solution, which outperforms the Dual Field coil.

Aziz

[Carl-NC]

Last week I got the filed application but forgot to post the info here. It's on my desk at work, I'll try to remember to post it tomorrow.

[Aziz]

Hi Carl,

we await the proof of the existence of the White's Dual Field Coil Patent.

I personally need the filing date and patent number. We do not want to infringe any protected claims.

Thanks for your effort.

Aziz

[Aziz]

Hi detectormods,

Hi Aziz,

Just a bed of rocks on the ground over inert soil, I know it needs proper testing but i have to get up to the goldfields to do some more tests.
I will doing some tests in the goldfields on the 13th of this month onwards.

thanks for your quick reply.

This is, what I have expected. In the near coil detection zone, the sensitivity increases with such coils and it will produce also more response to such hot rocks on the bed.

When making tests over a test bed, it is interesting to know, whether the test bed has banded (layered) mineral content. The thickness and depth of this hot mineral band could make a test difficult as it can't be really seen. This would result in having more or less ground noise when comparing different coils. Particularly then, if the detection zone of the different coils varies.

Aziz

[detectormods]

Hi detectormods,




did the nasty ironstone hot rocks lie on the bed or in the bed (in the ground). If they did lie in the ground: evenly distributed on different depth or concentrated at some depth layer?

Aziz

Hi Aziz,

Just a bed of rocks on the ground over inert soil, I know it needs proper testing but i have to get up to the goldfields to do some more tests.
I will doing some tests in the goldfields on the 13th of this month onwards.