Building Faraday room

[Steve Larson]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass? Are there any
more cost-effective materials?

2. How much does grounding influence the degree of shielding? I would
assume grounding is more effective for lower frequencies where
reflection is not as much of a factor. Can anyone quantify this effect
in Hz?

3. Now-a-days most aluminium screen is anodized. Does the insulation
this adds between each strand diminish its overall effectiveness in
grounded applications?

Thank you for any advice along these lines.

Steve

 

[Mike Harrison]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass? Are there any
more cost-effective materials?

I suspect the main problem with ali is getting a low-impedance join due to the oxide layer.
You really need a solid seam join, which typically means welding/soldering/brazing, which is hard to
do with ali

 

[Rene Tschaggelar]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass? Are there any
more cost-effective materials?

2. How much does grounding influence the degree of shielding? I would
assume grounding is more effective for lower frequencies where
reflection is not as much of a factor. Can anyone quantify this effect
in Hz?

3. Now-a-days most aluminium screen is anodized. Does the insulation
this adds between each strand diminish its overall effectiveness in
grounded applications?

If aluminum, take chromatized one. It has a conducting
surface. A good faraday has thw shield within each
other joined at just one point and at the same point
both shields are earthed. Iron is even better, by the
way. It is better for lower frequencies.

Rene

 

[MassiveProng]

I suspect the main problem with ali is getting a low-impedance join due to the oxide layer.
You really need a solid seam join, which typically means welding/soldering/brazing, which is hard to
do with ali

That's why brass is what the industry uses. The frame gets soldered
or brazed such that all screen thread elements are grounded to the
frame, and the frame is then attached to the rest of the shielded room
constructs.

 

[Paul Mathews]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass? Are there any
more cost-effective materials?

2. How much does grounding influence the degree of shielding? I would
assume grounding is more effective for lower frequencies where
reflection is not as much of a factor. Can anyone quantify this effect
in Hz?

3. Now-a-days most aluminium screen is anodized. Does the insulation
this adds between each strand diminish its overall effectiveness in
grounded applications?

Thank you for any advice along these lines.

Steve

There was a really good article in Compliance Engineering or one of
the ITEM publications a few years back comparing various low-cost
approaches to building screened rooms. Galvanized steel actually came
out the overall winner in the estimation of the authors, but some of
the really low-cost options considered were nearly as good at most
frequencies. The resistivity of the steel provides some benefits,
IIRC.
Paul Mathews

 

[MooseFET]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass? Are there any
more cost-effective materials?

The biggest problem is at the joints. You have to be able to make a
good joint all along where the sheets meet.

Copper based materials can be soldered and this saves a lot of labor.
Another option would be to put a screw every 1/2 inch but this would
take forever.

2. How much does grounding influence the degree of shielding? I would
assume grounding is more effective for lower frequencies where
reflection is not as much of a factor. Can anyone quantify this effect
in Hz?

Grounding is an issue of the common mode voltage. You want all of the
grounds of everything inside the shield to be at the same voltage. You
also want all the signals and power lines that come into the sheild to
pass through the same point and be bypassed there.

The main reason to ground the shield is because it has a large
capacitance to the earth. If the shield is at some AC voltage,
currents will flow through this capacitance.

If the shielded space is a small fraction (lets say 1%) of the
wavelength of a signal, the shield blocks the electrostatic component
of the radiation but less so the magnetic. For the magnetic
component, you can think of the shield as a turn of an inductor with
some resistance.

3. Now-a-days most aluminium screen is anodized. Does the insulation
this adds between each strand diminish its overall effectiveness in
grounded applications?

I would stay away for anodized screen for this reason. You can also
get material that is sometimes called "expanded". If you are working
below 100MHz, if you go with aluminum, I suggest you look at it.

Even that plastic "bubble wrap" like insulation that has a metalized
surface will block a lot of the electrostatic field from 60Hz mains.
If you imagine an 8 foot cube with that stuff stapled to the inside.
A box like that lowered the electrostatic part of the 60Hz down to
about 1mV.

In many cases more layers of less good shielding is better. You most
likely want at two layers that are connected to each other only at the
ground point. This is much easier to build than 3 layers and not much
harder than one. You need a frame to hold all this stuff up. This
frame can be nonconductive. Both the inside and outside surfaces can
be covered with conductive material. Dry wood works.

 

[Neimadre]

The biggest problem is at the joints. You have to be able to make a
good joint all along where the sheets meet.

Nothing like smoking a good joint before hitting the sheets. Rock on
dude.


Usenet lits score:
GIT-R-DONE!
#20 Usenet asshole
#6 Lits Slut
#11 Most posting trolls/hunters/flonkers 2007

 

[Henry Schmidt]

Nothing like smoking a good joint before hitting the sheets. Rock on
dude.

Oooh you even adopted a transmogrified form of his e-mail as yer return
address. Uh oh now he's really in yer crosshairs

 

[Neimadre]

Oooh you even adopted a transmogrified form of his e-mail as yer return
address. Uh oh now he's really in yer crosshairs

I own him and he will back down, I learned from a pro.


Usenet lits score:
GIT-R-DONE!
#20 Usenet asshole
#6 Lits Slut
#11 Most posting trolls/hunters/flonkers 2007

 

[As$Clown]

I own him and he will back down, I learned from a pro. ;-P


Usenet lits score:
GIT-R-DONE!
#20 Usenet asshole
#6 Lits Slut
#11 Most posting trolls/hunters/flonkers 2007

 

[Tim Williams]

Iron is even better, by the
way. It is better for lower frequencies.

What of RF?

Not really. Iron is pretty darn resistive, making it about useless for RFI,
and a mere screen isn't thick enough to block much EMI. (For that you need
sheer thickness. Hope you have 2x8's for rafters!)

Tim

 

[MassiveProng]

Nothing like smoking a good joint before hitting the sheets. Rock on
dude.

Damn. The KookTard actually said something funny.

 

[Homer J Simpson]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

Large dog cage?

 

[Meat Plow]

Damn. The KookTard actually said something funny.

Why is everyone to you (but not you) a:

Kootard
Retarded Twit
Idiot
Dipshit
Pathetic
Total Loser

Why is it that you think you are the only rational/viable entity while
exactly the opposite is glaringly evident?


--
#1 Offishul Ruiner of Usenet, March 2007
#1 Usenet Asshole, March 2007
#1 Bartlo Pset, March 13-24 2007
#10 Most hated Usenetizen of all time
Pierre Salinger Memorial Hook, Line & Sinker, June 2004
COOSN-266-06-25794

 

[[email protected]]

The biggest problem is at the joints. You have to be able to make a
good joint all along where the sheets meet.

Copper based materials can be soldered and this saves a lot of labor.
Another option would be to put a screw every 1/2 inch but this would
take forever.


Grounding is an issue of the common mode voltage. You want all of the
grounds of everything inside the shield to be at the same voltage. You
also want all the signals and power lines that come into the sheild to
pass through the same point and be bypassed there.

The main reason to ground the shield is because it has a large
capacitance to the earth. If the shield is at some AC voltage,
currents will flow through this capacitance.

If the shielded space is a small fraction (lets say 1%) of the
wavelength of a signal, the shield blocks the electrostatic component
of the radiation but less so the magnetic. For the magnetic
component, you can think of the shield as a turn of an inductor with
some resistance.


I would stay away for anodized screen for this reason. You can also
get material that is sometimes called "expanded". If you are working
below 100MHz, if you go with aluminum, I suggest you look at it.

Even that plastic "bubble wrap" like insulation that has a metalized
surface will block a lot of the electrostatic field from 60Hz mains.
If you imagine an 8 foot cube with that stuff stapled to the inside.
A box like that lowered the electrostatic part of the 60Hz down to
about 1mV.

In many cases more layers of less good shielding is better. You most
likely want at two layers that are connected to each other only at the
ground point. This is much easier to build than 3 layers and not much
harder than one. You need a frame to hold all this stuff up. This
frame can be nonconductive. Both the inside and outside surfaces can
be covered with conductive material. Dry wood works.

http://www.lessemf.com/mag-shld.html

This is a step up from the Al foil used in hats.

http://people.csail.mit.edu/rahimi/helmet/

 

[Neimadre]

Damn. The KookTard actually said something funny.

Still humping my posts obsesso?


Usenet lits score:
GIT-R-DONE!
#20 Usenet asshole
#6 Lits Slut
#11 Most posting trolls/hunters/flonkers 2007

 

[jasen]

I would like to build a faraday cage large enough to work in. Can
anyone please advise on the following points.

1. Will aluminium window screen work as well as brass?

if you can find a way to solder/weld the seams

Are there any
more cost-effective materials?

cooking foil ? sheet-steel ?

I'd be looking for a punched, expanded, or welded, mesh rather than a
woven one.

3. Now-a-days most aluminium screen is anodized. Does the insulation
this adds between each strand diminish its overall effectiveness in
grounded applications?

probably.


Bye.
Jasen

 

[Homer J Simpson]

3. Now-a-days most aluminium screen is anodized.

Don't assume that. It's more likely to be dyed and coated with lacquer. True
anodizing is expensive.

 

[Rene Tschaggelar]

What of RF?

Not really. Iron is pretty darn resistive, making it about useless for RFI,
and a mere screen isn't thick enough to block much EMI. (For that you need
sheer thickness. Hope you have 2x8's for rafters!)

Tim,
the RF is no problem at all. The poenetration depth
is inverse proportional to the conductivity, moreless.
So if the 100MHz penetrate 200um instaed of 20um, who
cares. And you're having two sheets of 1mm or so.
I'm have to look up the numbers.

Rene

 

[Phil Hobbs]

Tim,
the RF is no problem at all. The poenetration depth
is inverse proportional to the conductivity, moreless.
So if the 100MHz penetrate 200um instaed of 20um, who
cares. And you're having two sheets of 1mm or so.
I'm have to look up the numbers.

Rene

The skin depth is proportional to 1/sqrt(freq*mu*sigma), where sigma is
the conductivity. Iron's high permeability is a help at low frequency,
but not by as much as one would think from this calculation.

To think about shielding effectiveness, it's important to remember that
the concept of skin depth comes out of a perturbation theory problem.
The zero-order solution you start with is a perfectly conducting
boundary, i.e. E and H are zero at the metal surface. We often think of
RF shielding as a perturbation on the free-space problem, which leads
to underestimation of shielding effectiveness, because it assumes that
the fields on the metal surface are the same as the unperturbed free
space fields, which is far from true.

We also tend to get confused by analogies with light shields, which
makes us underestimate the importance of keeping the shield electrically
continuous. A truly continuous copper shield of any reasonable
thickness will eliminate all electromagnetic radiation from inside.

Iron is mostly important for quasistatic magnetic fields, e.g. from
power transformers.


Cheers,

Phil Hobbs