Impact of frequency on Faraday cages

[stanley]

I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0.
Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able to hear him talking through the speakers, he said that's because the speakers were in a much higher frequency.
My questions are:

• Why the fact that the eletric charge inside the condutor being 0 blocks electromagnetic fields?
• Why aren't faraday cages effective for high frequency waves?
• Why aren't they effective for very low frequencies?
• Are there better ways to block low frequency waves than with a faraday cage?

 

[berkeman]

Summary:: Faraday cages and low/high frequencies

I've been reading about faraday cages. The way I see, it works because the condutor will separate the charges so that the eletric charge inside is 0.
Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able to hear him talking through the speakers, he said that's because the speakers were in a much higher frequency.
My questions are:

• Why the fact that the eletric charge inside the condutor being 0 blocks electromagnetic fields?
• Why aren't faraday cages effective for high frequency waves?
• Why aren't they effective for very low frequencies?
• Are there better ways to block low frequency waves than with a faraday cage?

Welcome to the PF.

In one part of your question, you are asking about DC electric fields. In the next part of your post, you are asking about RF radio transmission fields.

Can you post a link to what you have been reading, and say what your end goal is in understanding this? What are you wanting to shield from what?

Thanks.

 

[stanley]

Welcome to the PF.

In one part of your question, you are asking about DC electric fields. In the next part of your post, you are asking about RF radio transmission fields.

Can you post a link to what you have been reading, and say what your end goal is in understanding this? What are you wanting to shield from what?

Thanks.

Mostly here and here.

As for what I'm wanting to shield from, I just want to know when and WHY a faraday cage might not be able to completely block EM signals(i.e when the frequency is either too high or too low)

 

[berkeman]

Mostly here

The title of that article is nonsense, so I didn't bother reading any farther. Quiz Question for you -- why is that nonsense to try to talk about a Faraday cage shielding magnetic fields? Lordy.
Does a Faraday cage block all magnetic field frequencies lower than x?

and here.

Sorry, I don't usually bother with YouTube videos as scientific references. There are exceptions of course, but on basic stuff that you want to learn about, it's usually okay to start at Wikipedia:

https://en.wikipedia.org/wiki/Faraday_cage

Also, if you want to learn more about the shielding of RF EM fields, it's good to go to a website of a manufacturer of shielded enclosures:

http://www.ets-lindgren.com/solutions

The main issue for RF shielding is how seamless the metal shield is, especially for feed-throughs that need to go through the enclosure walls (like for power and communication wiring, HVAC, etc.), and for doors for access into the room. There are different ways to do the RF gasketing that is needed for such entry doors...

 

[davenn]

Summary:: Faraday cages and low/high frequencies

Then I saw a lecture in which the professor was carrying a radio and the signal stopped as soon as he entered the cage however we were still able to hear him talking through the speakers, he said that's because the speakers were in a much higher frequency.

This really doesn't make sense as written and need for you to clarify

Did he have speaker(s) inside the cage playing music or something ?
If so, then the cage ISNT going to stop sound waves from coming out

Sound from speakers is MUCH lower than the radio frequency he would have been using
and Faraday Cages ONLY work on radio signals

Why aren't faraday cages effective for high frequency waves?

They are very effective at high, very high and right up to microwave frequencies when designed for the required frequency

eg. the grid shield on your microwave oven door very effectively stops 2.4GHz microwave radio signals from escaping

Why aren't they effective for very low frequencies?

as long as they are radio frequencies, they are effective

Are there better ways to block low frequency waves than with a faraday cage?

Again, Faraday Shields ( cages) are effective as long as it is for radio ( electromagnetic) signalsYou seem to have some misunderstandings around low and high frequencies and if they are electromagnetic or sound.
And that is what is causing your confusionDave