Dual Field Pi Coils

[Aziz]

Interesting coil

Look at the heavy duty coil wire of this patent application:

http://www.freepatentsonline.com/3601691.pdf

It is made of a metal strip wound spiral in the coil housing.

Aziz

[Mechanic]

Hi Rov,

I think it would be worth still looking into the dual field coils. Whites cannot patent all methods of making a dual field. If that could be done minelab would have done it for coils and detectors. I think that as long as the method for building and specifications are different to the whites coils, there should not be a problem.

Is the wire you used silver plated litz?

Cheers Mick

[Rov]

WM6,the few coils made are all in the field in use,by others already.I must wait for their return.but I suspect they will be purchased by the users that have them already,from the brief reports back to me.I could make more,but takes time for me to obtain the coil shells from the US.I have no stock of these left.I appreciate your interest.
Mechanic,wire is silverplated multistrand teflon coated.high temp. spec.made by Belden.I purchased in minimum 300m rolls. the percieved response time over targets is faster an has a crisper feel to it,over other multistrand tin plated wires ive used.an the rise an settle time for the coil on switch on is fast.especially noticeable on the SD/GP series of PI detectors.I will have to Scope an document this carefully to confirm conclusively.On my Pulsemate PI they work well also.
As interest Ive used Aluminium wires also,an this wire offers some interesting characteristics.in solid enamelled,not a multistrand.(which i cant find)
regards Rov

[detectormods]

I have tested a couple of dual field coils and found that you do not get something for nothing. A single wound coil will allow a maximum field at a set distance from the coil for a specific sized object that is optimized for the size coil.

When the coil is split into 2 windings, say one smaller then the distance the initial sized object was detected will reduce, the coil will give an improved response on a smaller object. Multi series coils only shift the balance on size and depth. They may increase ground noise but i would need to carry out some experiments to prove or disprove the theory.

[Rov]

Yes I agree,you dont get something for nothing!Ive noticed the diminished result for overall depth over say an 12inch pure mono wind.with the dual loops you can change the critical winds up or down between the two coils to change the parameter,for marginal increase of sensitivity or depth.depending on which of the windings you change.
eg .simply,up a couple of turns an reduce on turns in the other loop to still match an ideal,overall total coil resistance an inductance an total coil capacitance. so your PI detector will see it an drive it suitably.
I dont know what test bed of PI detectors you use for your results?
I only use my Pulsemate Pi detectors an unmodified standard Minelab Sd/GP Pi machines.with no smoothing or VCO/GPM style mods. I dont have use of a Whites TDI or similar.Pity?
Any conclusive results from my few DF builds on the GPX series are in WA. on active gold prospecting endevours.right now. an the users want to buy these coils.So something must be a + or positive towards their build.
Hope to hear of your coil testing results,detectormods.
think you may well find in the Df configuration some of the concerns for noise over a pure mono is also diminished.alla the figure 8 mono wind config.as you may well know,yourself.
Regards Rov

[detectormods]

Hi Rov,

I carried out some tests using a bed of nasty ironstone hot rocks with a 10" single wind mono of 280uh and again with a 10" and 6" split wound coil. The noise did increase but by only 1.5 db. This indicates that there is some extra proximity effect from the second winding to the ground matrix. This may have a slight adverse effect with very high gain and low noise designs as per the Minelab P.I detectors. In the real World it may not be an issue at all. More tests need to be carried out.

[Aziz]

Hi detectormods,

Hi Rov,

I carried out some tests using a bed of nasty ironstone hot rocks with a 10" single wind mono of 280uh and again with a 10" and 6" split wound coil. The noise did increase but by only 1.5 db. This indicates that there is some extra proximity effect from the second winding to the ground matrix. This may have a slight adverse effect with very high gain and low noise designs as per the Minelab P.I detectors. In the real World it may not be an issue at all. More tests need to be carried out.

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

[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.

[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

[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

[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]

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

[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

[detectormods]

Hi Aziz,

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

[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