New Concentric Co-planar Coil with Strong MF.

[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.

[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

[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

[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

[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?

[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!

[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

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

[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

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