northwest Coil shielding
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils  |  Topic: Coil shielding 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Coil shielding  (Read 4294 times)
Jeddas
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« Reply #40 on: Tuesday January 2 2018 18:20:10 AEDT PM »

Is there any advantage in using conductive foam (as used in ic static protection) as a coil shield ? Maybe less capacitance or eddy currents.
Question... Why is the total area of a coil shielded ? (as in paper circle covered in graphite paint) Would shielding around only the coil windings, and not circle area be better ?
I ask because I don't have the answers.
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WM6
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« Reply #41 on: Tuesday January 2 2018 21:04:41 AEDT PM »

  

Would shielding around only the coil windings, and not circle area be better ?


Better is to assure biggest possible distance between coil windings and shielding layer.

Usually this can be achieved better with shielding layer near to coil housing and not near to coil windings.
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Aziz
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« Reply #42 on: Tuesday January 2 2018 21:51:03 AEDT PM »

Hi all,

there is a big myth about coil shielding purpose.

1. Every piece of wire is an antenna. It's length and geometric design specifies it's best operating frequency and efficiency.
2. A round mono loop coil is a loop antenna by design.
3. Propagating electro-magnetic waves consists of electric (E-field) and magnetic (H-field) fields (strength varies in time, E-field is perpendicular to H-field and is alternating between them).
4. A faraday cage (typically a shielding) is only shielding electric fields.

So our search coils are simply loop antennas by design and they can't shield EMI noise because they still will pick up magnetically coupled H-fields. The search coil placed directly on the ground will pick up be less EMI noise due to Fresnel zone effect. If you rise the search coil up, you will pick up more EMI noise.
Search coil cable is a relative long piece of wire too. It's a perfect rod antenna. But you can shield it against EMI noise better than a round coil by its design. A rod antenna is not efficient to pick up H-fields.

So what's the real purporse for coil shielding?
For electric fields nearby the ground and search coil.
Ground, soil, rocks, grass, bush, coil housing itself can be electrically charged up by wind, scrubbing the coil housing on the ground or other mentioned things can cause electric charge, which can cause abrupt discharge of the charge, which then causes false signals in the detector.

Electric fields can be (capacitively) coupled to our search coils, which would affect the damping behaviour of the coil too.
Aziz
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autitch
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« Reply #43 on: Tuesday February 20 2018 14:23:59 AEDT PM »

Just wondering if anyone has used the following shielding paint.  What are peoples thoughts.
Yshield Shielding Paint HSF54  or Shielding Paint NSF34
  
  
AuTitch
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Muntari
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« Reply #44 on: Tuesday February 20 2018 16:13:42 AEDT PM »

Hi Autitch,

I haven't tried it but it does look Ok, from memory someone over on another forum used a similar product.

Noticed it has a shelf life of about 12 months.

Cheers

Muntari
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autitch
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« Reply #45 on: Wednesday August 22 2018 10:31:14 AEST AM »

For those looking for graphite shielding paint.  I've tested out this shielding paint and three coats is giving 60 to 70 Ohms per inch.  It easily goes on XPS foam, wood or paper and it appears to be very similar to what is used on Coiltek Goldstalker range of coils.

Available at the following link and ships from the US in about 3 weeks.

  

AuTitch


* Shielding Paint.jpg (172.38 KB, 758x703 - viewed 45 times.)
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geof_junk
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« Reply #46 on: Wednesday August 22 2018 20:17:15 AEST PM »

About 1990 I used both nickel and carbon shielding paint they were both in a spray pack. Back then Coil knowledge was hard to get, but spraying the top cover was easy. 







    
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australian electronic gold prospecting forum.com  |  Detector Technology and Electronics and new detectors  |  Detector Coils  |  Topic: Coil shielding « previous next »
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