Dual Field Pi Coils

[WM6]

ROV,


B makes more sense to me so in effect the user has two coils acting independent to give user best of both the big and small size. Is that correct?


Thanks!

Two coil act more like spiral coils, so not realy independent, but as mono coil with intentionaly distributed/shaped EM field in a way that act near like two independent coil used at same time. Mean such coil is sensitive on shallow small target and at the same time on deeper bigger target.

You can experimet with such coil, but for start: you use for inner coil 1/2 of outer coil diameter and for each coil 1/2 of total (mono) coil inductance. Turns of both coil must continue (and to be interconnected) in the same direction (not in oposite - because of mutually negating).

Look at this Aziz post:

http://www.geotech1.com/forums/showp...1&postcount=28

[Rov]

Yes,your thinking is correct.but as a coil builder myself,I dont wish to elaberate on any proprietry technique or properties,as you can understand.Whites and Other have there developed technique for signal Tx and Rx with Dual Field coils.
Suggest to experiment yourself if you have a TDI,an can build a simple DF coil,within spec.is not too hard,and you will see.
Maybe others here can add more to the topic,than I wish to atm.
regards Rov

[Darp]

ROV,

Thanks.

If you can add some detail to that then think I can finally feel understand it. What you have said is in line with my guess

On the send signal if we can refine that a little bit. Do (A) both coils fire at same time (that would tend to cause interference with each other it would seem) or do (B) they alternate, big one fires and receives at big coil, then small one sends and receives?

B makes more sense to me so in effect the user has two coils acting independent to give user best of both the big and small size. Is that correct?


Thanks!

[Rov]

Yes they act as two seperate coils with broader and also more refined depth of field on targets.imagine two distinct cones of magnetic field penetrate the ground and highlight your target.one broader and deeper the other more refined and smaller for closer smaller targets.you miss less targets overall.good design.and a pleasure to use.

[Darp]

What really is a Dual Field Coil?

I have trying to find this out for days. Even people that have home built them do not feel comfortable to say how they work.

I have a TDI with one, its got a 12" outer and 6" inner. Is it acting as two separate coils, alternating a inner send and receive with an outer send and receive to same coil, or is one sending and the other receiving?

Thanks in advance for any info how they work and what their purpose/advantage is.

Cheers

[Rov]

Hi Mel,Ive replied to your message,check your details.I may be able to help you.
Rov

[mel parker]

Dual Field Coils

I have obtained a Whites Dual Field detector without a coil. Where can I get one of your coils? Thanks Mel Parker

[Aziz]

An induction balance co-planar coil is also a dual field coil!!!
An anti-interference coil (figure-8, double D) is a dual field coil too!!!

Aziz

[moodz]

Hey ... not the Corbyn Patent again !

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.

errmmm .... isnt the Corbyn patent a "dual field" coil ?

"1" and "2" are tx coils.

Regards Moodz.

[Tinkerer]

Thanks Tinkerer!

I imagine for our purposes such a coil would be a poor choice for a variety of reasons, especially an increased time delay. But, you certainly got where I was trying to go! Is the upper coil simply canceling out part of the lower coil's field, or is it actually being deflected? I know a bifilar coil with counter wound coils would have a zero net field and be absolutely useless for an MD.

-Stefan

Stefan,

the upper coil repels the magnetic field of the lower coil. The field is deflected. You can make a simple experiment yourself. Take two magnets and approach them. The equal poles will push away, the unequal poles will attract.

If you sprinkle some iron filings or cutup steel wool, over a sheet of paper and mover the two magnets under the sheet of paper, you will see how the repelling of the fields change the shape of the fields around the magnets, concentrate the field in some places and push the field to different places.

You can also Google "Magnetic field visualizations" and find thousands of pages.

Tinkerer

[MagnetMan]

Thanks Tinkerer!

I imagine for our purposes such a coil would be a poor choice for a variety of reasons, especially an increased time delay. But, you certainly got where I was trying to go! Is the upper coil simply canceling out part of the lower coil's field, or is it actually being deflected? I know a bifilar coil with counter wound coils would have a zero net field and be absolutely useless for an MD.

-Stefan

[Tinkerer]

Hi Aziz,

I mentioned the asymmetrical shapes because I was curious whether a field could be produced that was larger on one side of the z-axis than the other. I understand that for a given segment of wire the field is symmetrical, but is it possible to change the shape of the field over a collection of turns? That is, does the shape of the field always follow the contour of the wires that generate it?

-Stefan

Here is a visualization of a magnetic field that is pushed mostly downward. It is a 5.3Mb video file animation.
the top coil carries 1/3 of the current 180 degrees out of phase from the bottom coil. The 2 magnetic fields interact, that is the top field repels the field of the bottom coil.
The the dots in the 2 coils show the direction of the current.
http://s565.photobucket.com/albums/s...eRepel_640.mp4

Tinkerer

[MagnetMan]

Answer to question 2:
The coil geometry defines the shape of the whole magnetic field around the coil. Every small part of the coil segment (filament of wire) produces it's own magnetic field lines. At a point of interest (x,y,z) , all magnetic field lines at x,y,z produced by every filament add up together (vector addition).

Thanks Aziz. I appreciate your posting those links for me. I'm pretty familiar with the basics of magnetism, but didn't know if things got weird with multiple "mini" fields as is the case with a multiple turn coil. Your mentioning vector addition cleared it up for me. Sounds like fields will always follow the general contours of the coils that produce them.

-Stefan

[Aziz]

Hi Stefan,

Hi Aziz,

I mentioned the asymmetrical shapes because I was curious whether a field could be produced that was larger on one side of the z-axis than the other. I understand that for a given segment of wire the field is symmetrical, but is it possible to change the shape of the field over a collection of turns? That is, does the shape of the field always follow the contour of the wires that generate it?

-Stefan

have a look at the following sites:
http://en.wikipedia.org/wiki/Magnetic_field
http://en.wikipedia.org/wiki/Maxwell%27s_equations
http://en.wikipedia.org/wiki/Gauss%27_law_for_magnetism

The Gauss's law states:

<damn, the formula can't be displayed here>

This law does not allow such wishes. No magnetic mono poles exist.

Answer to question 2:
The coil geometry defines the shape of the whole magnetic field around the coil. Every small part of the coil segment (filament of wire) produces it's own magnetic field lines. At a point of interest (x,y,z) , all magnetic field lines at x,y,z produced by every filament add up together (vector addition).

I am sure, wiki can explain it better.
Aziz

[MagnetMan]

Hi Aziz,

I mentioned the asymmetrical shapes because I was curious whether a field could be produced that was larger on one side of the z-axis than the other. I understand that for a given segment of wire the field is symmetrical, but is it possible to change the shape of the field over a collection of turns? That is, does the shape of the field always follow the contour of the wires that generate it?

-Stefan