Is aluminum foil an effective protection against cell phone radiation?

Everyone knows the typical noise that a cell phone makes in electrical amplifiers.

Does a closed cage (in a wooden housing) made of thin aluminum foil help? If so, does thickness play a role?

What other effective countermeasures are known? Ferrite beads? Sheath current filter?

Cheers

PS: shielding is for a tube driven spring reverb

rock soderstrom said:

Everyone knows the typical noise that a cell phone makes in electrical amplifiers.

Does a closed cage (in a wooden housing) made of thin aluminum foil help?

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Yes.

If so, does thickness play a role?

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It does, but doubling the thickness does not double the efficiency. Multi-layer is much more efficient. Sandwiching layers of AL between layers of insulating material.

What other effective countermeasures are known? Ferrite beads? Sheath current filter?

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Indeed, Faraday shielding is useless if the inpurs/uotputs are not properly protected. It's easy for the drive coil, adding 1nF caps usually does the trick. For the pick-up coil, adding capacitors may shring the frequency response.
Often, the electronics have a capacitor across the p/u coil; it must be moved at the input connector, with a solid connection to the chassis.

abbey road d enfer said:

Yes.
It does, but doubling the thickness does not double the efficiency. Multi-layer is much more efficient. Sandwiching layers of AL between layers of insulating material.
Indeed, Faraday shielding is useless if the inpurs/uotputs are not properly protected. It's easy for the drive coil, adding 1nF caps usually does the trick. For the pick-up coil, adding capacitors may shring the frequency response.
Often, the electronics have a capacitor across the p/u coil; it must be moved at the input connector, with a solid connection to the chassis.

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Thanks Abbey for the valuable info!
Basically you can say that each input or output must be protected, besides the actual shielding of the housing. For the signal inputs and outputs I will use the capacitor solution you mentioned. What about the power supply/powercord? Do I have to take additional measures here? If so, would a ferrite filter, see attachment, be effective?

rock soderstrom said:

Thanks Abbey for the valuable info!
Basically you can say that each input or output must be protected, besides the actual shielding of the housing. For the signal inputs and outputs I will use the capacitor solution you mentioned. What about the power supply/powercord? Do I have to take additional measures here? If so, would a ferrite filter, see attachment, be effective?

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Power supply should be protected with at least 3 caps. One X (across) capacitor between Line and Neutral, and two Y capacitors, one between Line and Earth, the other between Neutral and Earth.
Google XY capacitor for more info.
Ferrite filters are effective for filtering RF and particularly emissions from smps.
You may want to use a ready-made mains filter, which has the XY caps and common-mode inductors.

abbey road d enfer said:

Power supply should be protected with at least 3 caps. One X (across) capacitor between Line and Neutral, and two Y capacitors, one between Line and Earth, the other between Neutral and Earth.
Google XY capacitor for more info.
Ferrite filters are effective for filtering RF and particularly emissions from smps.
You may want to use a ready-made mains filter, which has the XY caps and common-mode inductors.

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Thanks again for the refresher! It's been a while since I've dealt with this and some regulations/implementations have changed since then. Ready-made mains filters are the way to go.

You can also get mains filters with integrated fuses and power switch depending on your needs. Just something to consider as it simplifies the wiring.

john12ax7 said:

You can also get mains filters with integrated fuses and power switch depending on your needs. Just something to consider as it simplifies the wiring.

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I just saw this while doing some research. This is exactly what I need.

abbey road d enfer said:

Yes.
It does, but doubling the thickness does not double the efficiency. Multi-layer is much more efficient. Sandwiching layers of AL between layers of insulating material.

Click to expand...

Indeed - it's very much a law of diminishing returns. My main EMC Test House mate reckons it's worth picking up some of the slightly thicker 'Turkey Foil' that is available around christmas (UK - USA may vary rather than the standard kitchen foil but after that it's marginal...

Newmarket said:

Indeed - it's very much a law of diminishing returns. My main EMC Test House mate reckons it's worth picking up some of the slightly thicker 'Turkey Foil' that is available around christmas (UK - USA may vary rather than the standard kitchen foil but after that it's marginal...

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Thanks for your input. I also used thicker aluminum foil, unfortunately I could not find the extra thick one. Another advantage is that you can process and cut the thick foil better.

One last (probably stupid) question, should I connect the Faraday cage to the PE ground? Necessary or counterproductive?

Here's a neat article...
Magazine is pretty cool too..
Registration seems painless after the couple of free articles...

https://www.assemblymag.com/articles/94891-shielding-tips-and-tricks

scott2000 said:

Here's a neat article...
Magazine is pretty cool too..
Registration seems painless after the couple of free articles...

https://www.assemblymag.com/articles/94891-shielding-tips-and-tricks

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Wow, this is a good source of information. I have read it briefly, there are many relevant points in it. I will take a closer look tonight. Thanks a lot!

rock soderstrom said:

One last (probably stupid) question, should I connect the Faraday cage to the PE ground? Necessary or counterproductive?

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I would say it's recommended in most cases. Only in a few cases it will make no diference.

rock soderstrom said:

One last (probably stupid) question, should I connect the Faraday cage to the PE ground? Necessary or counterproductive?

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Well the Faraday Cage should be connected to a reference potential - and that is usually your 0V reference.
With 'earthed' equipment this is almost always connected to chassis/PE at some point so the Faraday Cage is connected to 'Earth'.

It's worthwhile / interesting to note that the there is nothing special about the 'Earth' wrt 'grounding' - it's just a big ball of mass!
This does/has been the cause of a lot of misconceptions. One well known EMC consultant/author has, I believe, half jokingly 'banned' the use of the term 'Ground' in favour of referring to reference potential(s)

Ok, thank you very much for the confirmation. I always connect my "dirty" grounds (cable shields, all conductive housing parts, etc. ) to the central PE ground point. It's true, the grounds of the amplifier circuits and other circuit parts like digital and auxiliary circuits are also mostly connected directly there. Nevertheless, I consider these structurally as different instances.

rock soderstrom said:

Ok, thank you very much for the confirmation. I always connect my "dirty" grounds (cable shields, all conductive housing parts, etc. ) to the central PE ground point. It's true, the grounds of the amplifier circuits and other circuit parts like digital and auxiliary circuits are also mostly connected directly there. Nevertheless, I consider these structurally as different instances.

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Well 'ideally' cable screens etc go to (metal) chassis asap and '360 degree' connection to keep interference currents on the outside. The PE connection is there for electrical safety / regulations.
It's always worth thinking about an in flight aircraft - obviously* not earthed ! but lots of rfi issues to take care of.
* - although there is - apparently - an rf impedance of free space value of approx 377 Ohm.
https://en.wikipedia.org/wiki/Impedance_of_free_space