E and M fields in a faraday cage

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Discussion Overview

The discussion centers around the behavior of electric and magnetic fields in relation to Faraday cages, specifically addressing the penetration of static electric and magnetic fields, definitions of static fields, and the materials used for shielding against these fields. The scope includes conceptual clarifications and technical explanations related to electromagnetic theory.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that Faraday cages block static electric fields but not static magnetic fields, noting that their effectiveness varies with the frequency of changing magnetic fields.
  • Another participant questions whether static magnetic fields can penetrate a Faraday cage, suggesting that if a magnetic field is static, it does not move and thus should not pass through the cage.
  • A clarification is offered that "static" should be understood as constant in time, which some participants agree with.
  • There is a reference to a previous discussion that defines static electricity as charges that are not moving, leading to a similar interpretation for static magnetic fields.
  • One participant inquires about the use of mu metal at low frequencies, specifically asking if 60 Hz AC qualifies as low frequency.
  • A response clarifies that mu metal refers to a shielding material rather than an inductor core, and confirms that 60 Hz is typically considered low frequency.

Areas of Agreement / Disagreement

Participants express differing views on the penetration of static magnetic fields through Faraday cages, with some asserting that static magnetic fields can penetrate while others argue they cannot. The definitions of static fields also appear to be a point of contention, with no consensus reached.

Contextual Notes

Participants discuss the definitions of static fields and their implications, but there are unresolved assumptions regarding the behavior of magnetic fields in relation to Faraday cages and the specific conditions under which they may or may not penetrate.

Who May Find This Useful

This discussion may be useful for individuals interested in electromagnetic theory, materials science, and applications of Faraday cages in various contexts.

Robismyname
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I have a question regarding Faraday Cages...

Faraday Cages blocks static electrical fields

I read somewhere that static magnetic fields can penetrate the faraday cage when changed slowly. Faster changes in static magnetic fields cannot penetrate a faraday cage, is this true?

Also does Magnetostatic = static magnetic fields?

Does Electrostatic = static electric fields?
 
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Farady cages block static electric fields not static magnetic fields. Their effectiveness depends on the frequency of the changing magnetic field. Typically, one uses mu metal at low frequencies and cages at high frequencies and there is considerable overlap.
 
If the magnetic field is static then that means it does't move. So if it doesn't move that means that it can't pass through the cage correct? Or does static just mean slow moving?
 
You should understand static to mean constant in time.
 
Not to be a pain but I read a post from the Physics forum

( https://www.physicsforums.com/archive/index.php/t-12250.html) that suggest that

"Static electricity" can really only be defined one way: "charges that are not moving."

So I thought that Static Magnetic fields implied: "Magnetic fields that are not moving."

Thanks for the clarification...
 
Robismyname said:
Not to be a pain but I read a post from the Physics forum

( https://www.physicsforums.com/archive/index.php/t-12250.html) that suggest that

"Static electricity" can really only be defined one way: "charges that are not moving."

So I thought that Static Magnetic fields implied: "Magnetic fields that are not moving."

Thanks for the clarification...

"constant in time" means dB/dt = 0. Saying that they do not change with respect to time is, IMHO, a little better way to say it than "not moving"
 
When you say that "one uses mu metal at low frequencies" I assume you are talking about an inductor core made of mumetal powered by a low frequency power supply?

Would 60Hz Ac be considered a low frequency power supply?
 
No. I meant a mu metal shield. Google "mu metal shield" for lots of good info. 60 Hz is usually considered low frequency.
 

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