Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
BCM
User Panel

Site Notices
Posted: 2/13/2013 8:58:16 AM EDT
I've beeen thinking about this for a while now and I'm getting nowhere, so I'm asking here where there should be more electronics saavy types than me.  A Faraday cage basically just a grounded metal box.

Here's where the questions start.

1. What metals would be good or bad for it to be built out of?

2. CAGE. could it be built out of wire mesh? If so what would be the largest acceptable size of the mesh?

3. Could there be windows/holes in the cage? Is a metal floor needed or is  the ground going to ground any EM coming from that direction?

4 Would a metal building be considered a Faraday cage? How about an old washer, dryer or refrigerator?
Link Posted: 2/13/2013 9:10:46 AM EDT
[#1]
Quoted:
I've beeen thinking about this for a while now and I'm getting nowhere, so I'm asking here where there should be more electronics saavy types than me.  A Faraday cage basically just a grounded metal box.

Here's where the questions start.

1. What metals would be good or bad for it to be built out of?

The better the conductor the more effective the cage.
Thickness matters also.
The magnetic field portion of any signal can be VERY hard to stop.


2. CAGE. could it be built out of wire mesh? If so what would be the largest acceptable size of the mesh?

Mesh creates limits on the RF frequencies the cage is effective at.

3. Could there be windows/holes in the cage? Is a metal floor needed or is  the ground going to ground any EM coming from that direction?

Only if you want signal to escape.  The size of the hole determines what wavelengths can escape. You need a floor unless you KNOW the ground is as good a conductor as the walls.
A signal can penetrate the ground, reflect, and then be radiated.


4 Would a metal building be considered a Faraday cage? How about an old washer, dryer or refrigerator?


A crude one unless it has electrically bonded panels.
Even fastener spacing matters for bonding though.

The gap between bonding fasteners creates a slot antenna that allows leakage of signals at a specific frequency.
If you repeat the same spacing over and over you create an array of slot antennas.

Link Posted: 2/13/2013 10:42:03 AM EDT
[#2]
I think the mesh has to be smaller than 0.1 wavelength of the highest frequency you want to block.

That is dredged up out of a very old memory bank.
Link Posted: 2/14/2013 9:28:17 AM EDT
[#3]
Quoted:
I think the mesh has to be smaller than 0.1 wavelength of the highest frequency you want to block.

That is dredged up out of a very old memory bank.


And thick enough for the holes to operate in cutoff mode.

Right near the cutoff frequency things get a little dicey and the conductance of the material becomes very important AT the frequency of interest (skin effect matters at high frequency).


Link Posted: 6/3/2013 12:41:47 PM EDT
[#4]
Th manufacturing plant where I used to work had a screened cage for aligning receivers in the 0.1-500 MHz range. It consisted of a wooden frame covered on both sides of each wall, the ceiling, and the floor with copper screen wire. The two doors were also of framed construction, covered both sides and with brass finger stock surrounding them that made contact with copper trim.

Link Posted: 6/5/2013 6:53:06 AM EDT
[#5]
Quoted:
Th manufacturing plant where I used to work had a screened cage for aligning receivers in the 0.1-500 MHz range. It consisted of a wooden frame covered on both sides of each wall, the ceiling, and the floor with copper screen wire. The two doors were also of framed construction, covered both sides and with brass finger stock surrounding them that made contact with copper trim.



Easy to shield range.

The wavelengths are all pretty large.

The biggest problem is keeping the cage solidly grounded at the larger wavelengths.

You have to be careful the whole thing does not 'pick up' and act as an antenna.

Lots of grounds using wide straps.

A piece of wire has such a high inductance over the upper end of your range it is not a suitable ground.

You need wide straps with few bends.


If you are tuning IFs the signals are also usually reasonably low power.
Link Posted: 11/4/2013 1:47:26 AM EDT
[#6]
Interesting, is it necessary to use folg for cage construction
Close Join Our Mail List to Stay Up To Date! Win a FREE Membership!

Sign up for the ARFCOM weekly newsletter and be entered to win a free ARFCOM membership. One new winner* is announced every week!

You will receive an email every Friday morning featuring the latest chatter from the hottest topics, breaking news surrounding legislation, as well as exclusive deals only available to ARFCOM email subscribers.


By signing up you agree to our User Agreement. *Must have a registered ARFCOM account to win.
Top Top