IDX pro concentric coil with copper foil shield

[ifrenide]

KT317, support your criticism with evedance or reasonable explanation, don't try to speak on me , be objective please . you said in your first reply that I have to remove it , and as you can see there are some people said I have just to make a gap , there are different suggestions here , and not just one to be taken as a must.We all know that copper foil is used in EMI shielding , if you have a reason why we shouldn't use it in metal detector's coil , go ahead and explain it to us from a scientific perspective or leave me with my problem , there are a lot of nice people here will help me as you see in the previous replies , don't tell me anything about myself

[ifrenide]

KT317 as far as I know you , you're subjective, you are trying to criticize persons rather than ideas, give us some explanations from a scientific perspective or leave me with these nice people trying to help me, you said remove the foil, and now we are discussing making a gap. there are different opinions here to choose from, and you are telling me " you don't listen suggestion" are you blind or what!!!? be logic little bit.

[ArchibaldSTM]

When the sensor is heated in the sun, the foil will also heat up and change its properties, which will affect the operation of the sensor. Then. Is the foil laid in separate sectors, without soldering? Then, when poured with epoxy, it isolates the parts from each other. And the last. Sooner or later, but the foil will oxidize and this is also bad. P.S. It's also extra weight.

[Carl-NC]

If you do it right then foil will work fine. Before wrapping the coil in foil you want to first add a spacer to minimize capacitance. Then, the foil should wrap around the wire bundle in a uniform way. The magnetic field generated by the coil is parallel to the foil shield and does not cut through the surface to create eddy currents. However, it does so through the thickness of the foil so it is important to use thin foil. And, as mentioned before, it is critically important not to wrap the entire circumference of the coil, but to leave a gap of 1mm or so.

[ifrenide]

Hello everyone, hello Mr Carl. My coil is Concentric one , you can see pictures I uploaded them top of page 1, I have no graphite spray, I'm trying to make a copper foil shield, as I saw it in many electronic devices , so I already shield it but I don't want to wast copper wire and I want to know if it will work with this setup and discussing the science behind EMI shielding to understand what I'm doing in any future occasion, I want to know the working principle to know if it will work or not based on physical principle. the way you showed me to shield a concentric coil will be very hard when dealing with bucking coil , and maintaining the null point . I'm learning through this discussion , maybe someone will not repeat my mistake

[Carl-NC]

What you are doing is this:

By stretching the shield across the face of the coil you now have the magnetic field cutting through the shield and generating surface eddy currents. Even if you leave a gap in the shield this will reduce sensitivity, although it should still work. If you don't leave a gap it will severely reduce sensitivity. You can add radial breaks in the foil to further reduce the eddy losses, like this:

Note the complete break in the bottom radial. And it might take a lot more radial breaks than this to do the job.

This is why manufactured coils use spray shielding; it is a higher resistance and the eddy losses are minimal.

[ifrenide]

Thank you Mr Carl for your clear explanation, I really appreciate your help and all of the members here , now I will decide what to do . Now I learned that shielding a coil is different than shielding other electronic devices like electric guitars ,... since the coil is an active electromagnetic source and not "only" passive part to be shielded . And one more thing Eddy currents distrubution in 3D , I can now imagine it , and why graphite spray is a preference when shieling a concentric coil . I'm convinced now 100% Thank you again

[Ssoufian]

https://youtu.be/_4dNd3SJ-bo
Idx pro conentric coil 22cm

[ifrenide]

Sofian this is same enclosure as mine

[ifrenide]

I will remove copper foil and order a graphite foil instead, maybe someone here give me an advice

[Altra]

Not sure what country you are in? But search ebay or Alliexpress for " guitar shielding paint" a small bottle will do a few coils.

https://www.ebay.com/sch/i.html?_fro...paint&_sacat=0

[ifrenide]

Thank you Altra for your advice

[sinclairuser]

Not sure what country you are in? But search ebay or Alliexpress for " guitar shielding paint" a small bottle will do a few coils.

https://www.ebay.com/sch/i.html?_fro...paint&_sacat=0

its also sometimes called electrostatic doping compound, in old days i had a huge sack of it in powder form, we used to mix it with solvent to paint it on.
i bet it doesn't come in sacks at a reasonable price these days, though a small amount will do a few coils.
if i still had that sack i could mix it put it in small glass bottles and sell it on ebay.
never mind i dont miss working on those huge old systems anyway.

[Altra]

its also sometimes called electrostatic doping compound, in old days i had a huge sack of it in powder form, we used to mix it with solvent to paint it on.
i bet it doesn't come in sacks at a reasonable price these days, though a small amount will do a few coils.
if i still had that sack i could mix it put it in small glass bottles and sell it on ebay.
never mind i dont miss working on those huge old systems anyway.

When I first started using it. They called it "Electrodag".It was used for coating CRT tubes mostly.Then LCD's replaced crt's and electrodag became obscure.

[Qiaozhi]

I remember it as "Aquadag" (Aqueous Deflocculated Acheson Graphite).