Author Topic: Effectiveness of partial Faraday Cage?  (Read 2898 times)

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Offline @rt

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Effectiveness of partial Faraday Cage?
« on: October 07, 2016, 09:14:02 am »
Hi Guys :)
I was wondering what if any effectiveness is provided by a partial Faraday cage shielding an analogue circuit from a digital circuit on the same PCB.
I imagine if you had an open side facing away from the radiator, that should be somewhat effective as an antenna ground plane or even a antenna or satellite dish would be, or am I way off here?
Cheers, Art.
 

Online bson

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Re: Effectiveness of partial Faraday Cage?
« Reply #1 on: October 09, 2016, 05:57:21 am »
If it's open on one side it's not a Faraday cage and it won't keep out signals along an aperture formed by the opening.  However, if you ground it it will still be effective as an EMI shield.  (A Faraday cage doesn't need to be grounded.)
 

Online Gyro

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Re: Effectiveness of partial Faraday Cage?
« Reply #2 on: October 09, 2016, 08:58:57 am »
Hi Art. Strictly speaking, you don't have a Faraday cage in the first place. A Faraday cage is, by definition, an uninterrupted conductive enclosure. As soon as you have signals going into and out of it, what you have is simply a screen, not a Faraday cage.

The lowest frequency 'airborne' (radiated) signal that can get in and out of a screened enclosure are defined by its wavelength in comparison with the longest dimension of any aperture in the screen. Conducted signals into the enclosure are dependent on how well they are filtered and decoupled to the screen.

The basic advice is to keep the apperture as small as possible.  If possible make multiple smaller apertures rather than one big one (tabs down to the ground plane). filter and decouple signals going in and out of the screen as well as possible.
Chris

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Online ChristofferB

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Re: Effectiveness of partial Faraday Cage?
« Reply #3 on: October 09, 2016, 10:42:33 am »
The tinfoil-hat dilemma. You can probably get some benefits from partial shielding- i believe it's seen both in rf cans, and especially copper-clad Manhattan construction, to use partial "walls" of either sheet metal or copper clad board, to separate filters, filter stages etc. I don't know HOW effective it is, though.
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