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Does paint affect EMI ability of enclosure?

Plastic enclosure for small productCustom Enclosure Design?EMI filter for 1-wireWeather protected enclosureLight- and vapor-tight enclosure entryEMI protection for unused pinsWill EMI strongly affect my sensor readingMaking aluminium conductive for an RF shield enclosureCooling an outdoor electronics enclosureUse of internal PCB ground plane as ESD baseplate/EMC reference plane of product in plastic enclosure

7

$begingroup$

This could be a very stupid question, but when it comes to RF you never know.

Does painting (non-conductive) over the top of a grounded metal enclosure affect its ability to absorb/block RF interference? At the mechanical fixings, the enclosure is not painted and has a good ground connection.

I was wondering because I remembered that RF currents travel on the surface of conductors. Would they just travel "beneath" the paint?

Thanks.

emc enclosure

share|improve this question

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  What kind of paint?
  $endgroup$
  – Eugene Sh.
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Non-conductive paint
  $endgroup$
  – Jack the Lad
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  This is a qualified it depends. If you paint over a ground plane then no. If it's part on an enclosure and the the paint acts as an insulator between the lid and the base, both conductive then yes. This is not a detailed explanation of why but I will leave that for a proper answer.
  $endgroup$
  – Warren Hill
  7 hours ago
  

  
  
  
  

add a comment | 

7

$begingroup$

This could be a very stupid question, but when it comes to RF you never know.

Does painting (non-conductive) over the top of a grounded metal enclosure affect its ability to absorb/block RF interference? At the mechanical fixings, the enclosure is not painted and has a good ground connection.

I was wondering because I remembered that RF currents travel on the surface of conductors. Would they just travel "beneath" the paint?

Thanks.

emc enclosure

share|improve this question

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  What kind of paint?
  $endgroup$
  – Eugene Sh.
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Non-conductive paint
  $endgroup$
  – Jack the Lad
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  This is a qualified it depends. If you paint over a ground plane then no. If it's part on an enclosure and the the paint acts as an insulator between the lid and the base, both conductive then yes. This is not a detailed explanation of why but I will leave that for a proper answer.
  $endgroup$
  – Warren Hill
  7 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

This could be a very stupid question, but when it comes to RF you never know.

Does painting (non-conductive) over the top of a grounded metal enclosure affect its ability to absorb/block RF interference? At the mechanical fixings, the enclosure is not painted and has a good ground connection.

I was wondering because I remembered that RF currents travel on the surface of conductors. Would they just travel "beneath" the paint?

Thanks.

emc enclosure

share|improve this question

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 7 mins ago

SamGibson

11.1k41737

edited 7 mins ago

SamGibson

11.1k41737

asked 8 hours ago

Jack the LadJack the Lad

434

New contributor

Jack the Lad is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 hours ago

Jack the LadJack the Lad

434

2 Answers
2

active

oldest

votes

10

$begingroup$

Does painting (non-conductive) over the top of a grounded metal
enclosure affect its ability to absorb/block RF interference?

No, the idea of an EMI enclosure is to create a faraday shield around something to block electromagnetic waves around whatever it is enclosing. The shield itself needs to be conductive to be effective and have adequate skin depth, on the inside of the shield the electric field is zero (assuming there are no radiators on the inside). (The skin depth needs to be larger for a faraday shield to be effective, but for most metals anything more than 5mm is effective against anything above 0.1Hz). And watch out for anodization also, which is an oxide layer on aluminum and not very conductive.

For a faraday cage to be effective, it needs to be conductive and continuous as possible (slots and apertures can provide inlets for electric fields to bleed in). This also means that conductivity needs to be maintained at the seams of the enclosure by not painting junctions, using conductive gaskets and flanges that cover seams. (and any shieldconductor interfacing to the enclosure also needs good conductivity and no paint)

As long as the surface of the enclosure is conductive and continuous, it will have the same blocking power even with materials of different conductivity on the outside. If anything the paint will attenuate high frequencies or change the reflection (because any two materials that have a boundary have reflection and transmission coefficients).

In short, adding paint to the surface of a metal enclosure will not change the conductivity of the metal underneath (unless there is some kind of severe chemical reaction, which is unlikely). And at the end of the day it is the conductivity of the metal enclosure that matters most.

share|improve this answer

edited 1 hour ago

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  It's probably worth explicitly adding that you need to be sure there is NOT paint in the seams between parts of the enclosure.
  $endgroup$
  – The Photon
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I didn't because the OP mentioned it, but a good idea nonetheless
  $endgroup$
  – laptop2d
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Can't have paint between any wire/connector used to ground the cage and the cage, either.
  $endgroup$
  – Scott Seidman
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ScottSeidman also mention in the post above
  $endgroup$
  – laptop2d
  3 hours ago
  

  
  
  
  

add a comment | 

4

$begingroup$

Well, although laptop2d answer is correct, if you interpret the word "ability" in a somewhat different sense, some kind of paints could actually improve the overall shielding provided by the underlying metal enclosure.

In fact the paint could reduce the incoming RF wave energy, dissipating it as heat. That's the principle behind what are called RAM (Radiation Absorbent Materials), which are used, for example, on stealth vehicles.

Such paints can also be non-conductive. For example, microscopic iron balls are coated in an insulating film and then deployed on the surface to coat embedded in an insulating epoxy matrix. So, overall, the coating is non-conductive.

share|improve this answer

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  They actually make a wide variety of conductive paints that can block RF in various frequencies (especially 2.4ghz) nowadays
  $endgroup$
  – laptop2d
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  yep, Hammond even makes ABS enclosures that are coated on the inside with that.
  $endgroup$
  – Tyler Stone
  5 hours ago
  

  
  
  
  

add a comment | 

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10

$begingroup$

Does painting (non-conductive) over the top of a grounded metal
enclosure affect its ability to absorb/block RF interference?

No, the idea of an EMI enclosure is to create a faraday shield around something to block electromagnetic waves around whatever it is enclosing. The shield itself needs to be conductive to be effective and have adequate skin depth, on the inside of the shield the electric field is zero (assuming there are no radiators on the inside). (The skin depth needs to be larger for a faraday shield to be effective, but for most metals anything more than 5mm is effective against anything above 0.1Hz). And watch out for anodization also, which is an oxide layer on aluminum and not very conductive.

For a faraday cage to be effective, it needs to be conductive and continuous as possible (slots and apertures can provide inlets for electric fields to bleed in). This also means that conductivity needs to be maintained at the seams of the enclosure by not painting junctions, using conductive gaskets and flanges that cover seams. (and any shieldconductor interfacing to the enclosure also needs good conductivity and no paint)

As long as the surface of the enclosure is conductive and continuous, it will have the same blocking power even with materials of different conductivity on the outside. If anything the paint will attenuate high frequencies or change the reflection (because any two materials that have a boundary have reflection and transmission coefficients).

In short, adding paint to the surface of a metal enclosure will not change the conductivity of the metal underneath (unless there is some kind of severe chemical reaction, which is unlikely). And at the end of the day it is the conductivity of the metal enclosure that matters most.

share|improve this answer

edited 1 hour ago

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  It's probably worth explicitly adding that you need to be sure there is NOT paint in the seams between parts of the enclosure.
  $endgroup$
  – The Photon
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I didn't because the OP mentioned it, but a good idea nonetheless
  $endgroup$
  – laptop2d
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Can't have paint between any wire/connector used to ground the cage and the cage, either.
  $endgroup$
  – Scott Seidman
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ScottSeidman also mention in the post above
  $endgroup$
  – laptop2d
  3 hours ago
  

  
  
  
  

add a comment | 

10

$begingroup$

Does painting (non-conductive) over the top of a grounded metal
enclosure affect its ability to absorb/block RF interference?

No, the idea of an EMI enclosure is to create a faraday shield around something to block electromagnetic waves around whatever it is enclosing. The shield itself needs to be conductive to be effective and have adequate skin depth, on the inside of the shield the electric field is zero (assuming there are no radiators on the inside). (The skin depth needs to be larger for a faraday shield to be effective, but for most metals anything more than 5mm is effective against anything above 0.1Hz). And watch out for anodization also, which is an oxide layer on aluminum and not very conductive.

For a faraday cage to be effective, it needs to be conductive and continuous as possible (slots and apertures can provide inlets for electric fields to bleed in). This also means that conductivity needs to be maintained at the seams of the enclosure by not painting junctions, using conductive gaskets and flanges that cover seams. (and any shieldconductor interfacing to the enclosure also needs good conductivity and no paint)

As long as the surface of the enclosure is conductive and continuous, it will have the same blocking power even with materials of different conductivity on the outside. If anything the paint will attenuate high frequencies or change the reflection (because any two materials that have a boundary have reflection and transmission coefficients).

In short, adding paint to the surface of a metal enclosure will not change the conductivity of the metal underneath (unless there is some kind of severe chemical reaction, which is unlikely). And at the end of the day it is the conductivity of the metal enclosure that matters most.

share|improve this answer

edited 1 hour ago

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  It's probably worth explicitly adding that you need to be sure there is NOT paint in the seams between parts of the enclosure.
  $endgroup$
  – The Photon
  5 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I didn't because the OP mentioned it, but a good idea nonetheless
  $endgroup$
  – laptop2d
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Can't have paint between any wire/connector used to ground the cage and the cage, either.
  $endgroup$
  – Scott Seidman
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  @ScottSeidman also mention in the post above
  $endgroup$
  – laptop2d
  3 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

Does painting (non-conductive) over the top of a grounded metal
enclosure affect its ability to absorb/block RF interference?

No, the idea of an EMI enclosure is to create a faraday shield around something to block electromagnetic waves around whatever it is enclosing. The shield itself needs to be conductive to be effective and have adequate skin depth, on the inside of the shield the electric field is zero (assuming there are no radiators on the inside). (The skin depth needs to be larger for a faraday shield to be effective, but for most metals anything more than 5mm is effective against anything above 0.1Hz). And watch out for anodization also, which is an oxide layer on aluminum and not very conductive.

For a faraday cage to be effective, it needs to be conductive and continuous as possible (slots and apertures can provide inlets for electric fields to bleed in). This also means that conductivity needs to be maintained at the seams of the enclosure by not painting junctions, using conductive gaskets and flanges that cover seams. (and any shieldconductor interfacing to the enclosure also needs good conductivity and no paint)

As long as the surface of the enclosure is conductive and continuous, it will have the same blocking power even with materials of different conductivity on the outside. If anything the paint will attenuate high frequencies or change the reflection (because any two materials that have a boundary have reflection and transmission coefficients).

In short, adding paint to the surface of a metal enclosure will not change the conductivity of the metal underneath (unless there is some kind of severe chemical reaction, which is unlikely). And at the end of the day it is the conductivity of the metal enclosure that matters most.

share|improve this answer

edited 1 hour ago

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

$endgroup$

share|improve this answer

edited 1 hour ago

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

answered 7 hours ago

laptop2dlaptop2d

25.7k123380

4

$begingroup$

Well, although laptop2d answer is correct, if you interpret the word "ability" in a somewhat different sense, some kind of paints could actually improve the overall shielding provided by the underlying metal enclosure.

In fact the paint could reduce the incoming RF wave energy, dissipating it as heat. That's the principle behind what are called RAM (Radiation Absorbent Materials), which are used, for example, on stealth vehicles.

Such paints can also be non-conductive. For example, microscopic iron balls are coated in an insulating film and then deployed on the surface to coat embedded in an insulating epoxy matrix. So, overall, the coating is non-conductive.

share|improve this answer

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  They actually make a wide variety of conductive paints that can block RF in various frequencies (especially 2.4ghz) nowadays
  $endgroup$
  – laptop2d
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  yep, Hammond even makes ABS enclosures that are coated on the inside with that.
  $endgroup$
  – Tyler Stone
  5 hours ago
  

  
  
  
  

add a comment | 

4

$begingroup$

Well, although laptop2d answer is correct, if you interpret the word "ability" in a somewhat different sense, some kind of paints could actually improve the overall shielding provided by the underlying metal enclosure.

In fact the paint could reduce the incoming RF wave energy, dissipating it as heat. That's the principle behind what are called RAM (Radiation Absorbent Materials), which are used, for example, on stealth vehicles.

Such paints can also be non-conductive. For example, microscopic iron balls are coated in an insulating film and then deployed on the surface to coat embedded in an insulating epoxy matrix. So, overall, the coating is non-conductive.

share|improve this answer

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

$endgroup$

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  $begingroup$
  They actually make a wide variety of conductive paints that can block RF in various frequencies (especially 2.4ghz) nowadays
  $endgroup$
  – laptop2d
  6 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  yep, Hammond even makes ABS enclosures that are coated on the inside with that.
  $endgroup$
  – Tyler Stone
  5 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

Well, although laptop2d answer is correct, if you interpret the word "ability" in a somewhat different sense, some kind of paints could actually improve the overall shielding provided by the underlying metal enclosure.

In fact the paint could reduce the incoming RF wave energy, dissipating it as heat. That's the principle behind what are called RAM (Radiation Absorbent Materials), which are used, for example, on stealth vehicles.

Such paints can also be non-conductive. For example, microscopic iron balls are coated in an insulating film and then deployed on the surface to coat embedded in an insulating epoxy matrix. So, overall, the coating is non-conductive.

share|improve this answer

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

$endgroup$

share|improve this answer

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476

answered 7 hours ago

Lorenzo DonatiLorenzo Donati

16.9k44476