New Concentric Co-planar Coil with Strong MF.

[Aziz]

I am sorry to say, that some analysis of the coils will be delayed for some time. Due to the fact of dealing successfully with lock-in amps, important things on noise elimination has more priority to me. Anyway, my problem of induced target current modeling exists still and I hadn't time to solve this yet. I have to fill the lack of physics on my side.

Aziz

[Unregistered]

http://www.deeptech-bg.com/pdfroudc/coplanar_150.pdf

This link don't seem to work.
This is the new:
http://www.deeptech-bg.com/round_coils/coplanar.pdf

[Aziz]

Soon, I will analyse the standard concentric coplanar IB coil, because I need a coil for my laptop MD very soon.
I will analyse deeply the inner radius (RX + bucking coil) related to outer radius (TX coil) of the coil. As I am not good in math to derivate the exact formulas analytical, I am going to simulate different configurations of coils to see the optimum level.

Aziz

[Unregistered]

method of the GEOPHEX's GEM-3

Apparatus and METHOD for detecting a weak induced magnetic field by mean of two loops

http://www.google.fr/patents?id=PMIeAAAAEBAJ&dq=5557206

www.geophex.com

[Tinkerer]

Do magnetic fields cancel

Apparatus and METHOD for detecting a weak induced magnetic field by mean of two loops

http://www.google.fr/patents?id=PMIeAAAAEBAJ&dq=5557206

www.geophex.com

[IMG]file:///C:/Users/SAMSON/AppData/Local/Temp/moz-screenshot.jpg[/IMG][IMG]file:///C:/Users/SAMSON/AppData/Local/Temp/moz-screenshot-1.jpg[/IMG]Interesting description.

But.... do magnetic fields cancel each other?

Or is it the currents created by the fields that cancel each other?

Tinkerer

[rumensat]

by the end i have to say all this is known 30 years before.
great specialists in this area say - IB coil have to be 20-26 cm diameter,
tx/rx =1/2 in diameter , Tx=70-100 turns 01.0-0.8 mm, Rx = 250-300 turns 0,25-0,15mm.
with this parameters you will reach maximum results for standard hunting - coins, gold pieces, rings etc.
thats mean 32 cm deep 2cm coin - maximum!

[simonbaker]

Aziz, your field pictures are very valuable! I think you show that pin-pointing a target that is sitting at an angle is tricky, because it peaks to the side of the coil. Do you think the sweep direction has much influence on that?

[DOOLEY]

do magnetic fields cancel

hello , i know this thread is 3 years old when it stopped , but got to reading it this wet sunday morning , and tinkerer's question is a good one , and i also would like a definative answer .

tinkerer's quote / question:

But.... do magnetic fields cancel each other?

Or is it the currents created by the fields that cancel each other?

so , when using coplanar coils if the outer TX coil and the inner "bucking" tx coil are in opposite directions is the magnetic field canceled out / weakened or mearly deformed ??

next question is , standard arrangement is , inner bucking coil is half the diameter or the outer TX coil , with a quarter of the turns,
if the RX coil and bucking coil were bigger , surley this would reduce the effective TX field ?

lets say standard is TX=10 inch
RX and BUCKING=5 inch

if we had a larger rx to get more sensitivity say 8 inch
so now TX=10 inch
and RX and bucking=8 inch

bucking coil turns would have to be increaced yes , and with it now being closer to the TX coil , but would in an opposite direction this would reduce the effective TX magnetic field yes ??

next question , do larger diameter RX coils have more sensitivity ??

if so , would it be possible to have main TX say 12 inch
RX say 10 inch
and a reverse / bucking TX allot smaller in the middle say 3-5 inch

have many questions , full detailed explination about pros and cons and what works and what doesn'e appreciated.cheers

[6666]

Aziz
in post #24 you show a picture of your coil with a graphite shield
can you please tell me how you made the graphite shield
was it a type of paint that you made with graphite powder ?

thanks

[simonbaker]

hello , i know this thread is 3 years old when it stopped , but got to reading it this wet sunday morning , and tinkerer's question is a good one , and i also would like a definative answer .

tinkerer's quote / question:

But.... do magnetic fields cancel each other?

Or is it the currents created by the fields that cancel each other?

so , when using coplanar coils if the outer TX coil and the inner "bucking" tx coil are in opposite directions is the magnetic field canceled out / weakened or mearly deformed ??

next question is , standard arrangement is , inner bucking coil is half the diameter or the outer TX coil , with a quarter of the turns,
if the RX coil and bucking coil were bigger , surley this would reduce the effective TX field ?

lets say standard is TX=10 inch
RX and BUCKING=5 inch

if we had a larger rx to get more sensitivity say 8 inch
so now TX=10 inch
and RX and bucking=8 inch

bucking coil turns would have to be increaced yes , and with it now being closer to the TX coil , but would in an opposite direction this would reduce the effective TX magnetic field yes ??

next question , do larger diameter RX coils have more sensitivity ??

if so , would it be possible to have main TX say 12 inch
RX say 10 inch
and a reverse / bucking TX allot smaller in the middle say 3-5 inch

have many questions , full detailed explination about pros and cons and what works and what doesn'e appreciated.cheers

I would hazard that the bucking coil does cancel the magnetic field of the TX coil at zero depth inside its circle. At greater depth, the TX coil dominates more and more in the area under the bucking coil.

It seems intuitively optimal to make the bucking coil the same size as the RX coil to avoid flux that works against the purpose. If the bucking coil is smaller than the RX coil, then a lot of it's flux (outside the circle) cancels the effect of the flux from the inside because the RX coil sees both fluxes on its inside.

Although a larger RX coil would be desirable, it means also a larger bucking coil, and a larger bucking coil would tend to cancel the TX coil more. I don't know how to theoretically show it, but I have a feeling that RX diameter = TX diameter / 2 is a good choice. But if you look at the coil for a Tesoro Vaquero, the RX coil looks awfully small, maybe smaller than TX/2, so maybe going smaller with the RX coil has some advantages.

-SB

[DOOLEY]

hello SB,

i also used the word "cancel" aswell as you on previous posts , we are using "laymans terms" , and it makes sense to us i think , but if i remember right a few folks used the terms deflect or bend , this was a few months ago , you asked the same question as me "do fields cancel" and i don't think we got a deff answer , did we ??

i think cancel , if we wind an electromagnet with same number of turns in one direction and then same number of turns in the other , we end up with power useage and nothing else , so i say cancel .

regarding the half diameter bucking coil , with 1/2 diameter and 1/4 of the turns , we have to loose 25% of the tx field doing this , don't we ??

a while ago , can't remember if it was aziz , tinkerer or moods , i saw a post where rx was the biggest and tx was 1/2 the size in the middle and the bucking coil was on the outside of the rx , even bigger diameter , can't remember if aziz did a field vis for that idea of not , would be interesting to see.

i remember about a year ago , when i first started looking into the whole metal detecting milarky , seeing a cartoon pic of a metal detector with rx and tx with the brief explination of sending a pulse and listening to the return , oh how easy it all sounded , why , i think i'll go off and make one of those i thought !!

i now look back and think of that pic , if only life was that simple.

[Aziz]

Aziz
in post #24 you show a picture of your coil with a graphite shield
can you please tell me how you made the graphite shield
was it a type of paint that you made with graphite powder ?

thanks

Hi six-six-six-six,

yes, I made a paint of fine/pure graphite powder.

Last time, I took a water based glue (Kid's Glue) as this makes it much more easier to handle (easier to make the paint, more dry time, etc.).
The paint contains not much glue (solved in water) but more water in it. It should contain as much glue as it is necessary to stick the graphite powder to the coil. It should contain as much water as it is necessary to be paintable. If the coil's surface is made kind of paper (paper tape), the graphite paint will stick onto it better.

After the graphite is totally dried, take a piece of paper strip and polish gently the graphite surface of the coil. This process lowers the shielding resistance heavily. If you can't polish the graphite surface, you need either more glue in your paint or more graphite in your paint or other type of glue. Just try different things on a paper strip before you paint the coil. The graphite layer should be polishable without getting much damaged.

You can add more graphite layers with the same procedure above.

You can use the following water based glue's and binders:
- Kid's glue (dissolvable in water)
- Paste (dissolvable in water)
- Gum arabic (dissolvable in warm water, but not in alcohol)
- Rabbit-Skin glue (=Glutine glue, dissolvable in warm water)
- Shellac (dissolvable in alcohol and then dilutable in water)
- Acrylic binder (dilutable in water)

Note, some water based glues/binders can not be dissolved again when they get dry (like acrylic based binders). Shellac can still be dissolved in alcohol however.

There are other glue's and binders based on synthetic resin and they need other solvents, which might be hazardous for the people. So I can not recommend these types of glue's and binders.

Water based glue's and binders are much more flexable. Particularly, when your graphite paint gets dry and you can add some water to make it paintable again.

Note, the graphite shield needs a gap on the coil to avoid a "closed loop". And you also need a thin drain wire (silver coated) for the connection of the graphite layer to the shielding potential (ground). The drain wire may not form a "closed loop" again.

The final graphite shielding needs a protection of course. Just use a tape for this.

Cheers,
Aziz

[Aziz]

BTW,

the former proposed coil is not convenient for deep detecting. It might cause ground balancing problems with heavy mineralized soils and hot rocks (iron stone).

Just forget the coil design. It's not a gain for us.

Aziz

[WM6]

You can add more graphite layers with the same procedure above.

You can use the following water based glue's and binders:
- Kid's glue (dissolvable in water)
- Paste (dissolvable in water)
- Gum arabic (dissolvable in warm water, but not in alcohol)
- Rabbit-Skin glue (=Glutine glue, dissolvable in warm water)
- Shellac (dissolvable in alcohol and then dilutable in water)
- Acrylic binder (dilutable in water)

Note, some water based glues/binders can not be dissolved again when they get dry (like acrylic based binders). Shellac can still be dissolved in alcohol however.

Thank you Aziz for instructions.

We can use Alu powder (pigment) as well.

[Aziz]

Thank you Aziz for instructions.

We can use Alu powder (pigment) as well.

I would not recommend it. Maybe it will work. I don't know.

But when graphite shielding is polished (smearing of the graphite), it cures the bad conductive regions and hence it increases it's conductivity. I can produce with polished graphite layer a shielding layer of approx. 10-20 Ohm/cm. The drain wire additionally keeps the overall shielding resistance low.

The polishing of the graphite shielding layer is one of the most important aspects.

Aziz