Main Page | Report this Page
 
   
Science Forum Index  »  Physics - Electromagnetic Forum  »  Combining wavelengths within a Faraday cage
Page 1 of 1    
Author Message
Mac Lawson
Posted: Thu Oct 11, 2007 5:29 am
Guest
Ok, so If I construct a Faraday cage from a conductive material that should
block out a large portion of the electromagnetic spectrum, can I still
create such electromagnetic wavelengths within the Faraday cage by combining
other wavlengths at a focal point within it?
Wimpie
Posted: Thu Oct 11, 2007 7:15 am
Guest
On 11 oct, 12:29, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Quote:
Ok, so If I construct a Faraday cage from a conductive material that should
block out a large portion of the electromagnetic spectrum, can I still
create such electromagnetic wavelengths within the Faraday cage by combining
other wavlengths at a focal point within it?

Hello,

Yes, you can establish a EM field in closed cage.. When there are no
absorbing materials inside, you can create large field strength with
relative low RF input power.

You can see the cage as a large resonator (can be compared with
acoustic resonance). Internal reflections can interfere in a
constructive (more field) or destructive (less field) way. Closed
cavities are used frequently in the microwave industry (as part of a
filter or a frequency determining component).

In many cases, the reflections from the walls are a problem during
measurement of field parameters.

You did not mention your application. Maybe you can provide us some
additional info.

Best regards,

Wim
PA3DJS
www.tetech.nl
Mac Lawson
Posted: Thu Oct 11, 2007 9:20 am
Guest
Thanks. So is a 100% effective Faraday cage possible? That is one in which
no electromagnetic frequencies of any kind can exist?


"Wimpie" <wimtel@tetech.nl> wrote in message
news:1192104914.922074.65040@k79g2000hse.googlegroups.com...
Quote:
On 11 oct, 12:29, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Ok, so If I construct a Faraday cage from a conductive material that
should
block out a large portion of the electromagnetic spectrum, can I still
create such electromagnetic wavelengths within the Faraday cage by
combining
other wavlengths at a focal point within it?

Hello,

Yes, you can establish a EM field in closed cage.. When there are no
absorbing materials inside, you can create large field strength with
relative low RF input power.

You can see the cage as a large resonator (can be compared with
acoustic resonance). Internal reflections can interfere in a
constructive (more field) or destructive (less field) way. Closed
cavities are used frequently in the microwave industry (as part of a
filter or a frequency determining component).

In many cases, the reflections from the walls are a problem during
measurement of field parameters.

You did not mention your application. Maybe you can provide us some
additional info.

Best regards,

Wim
PA3DJS
www.tetech.nl
Wimpie
Posted: Thu Oct 11, 2007 12:12 pm
Guest
On 11 oct, 16:20, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Quote:
Thanks. So is a 100% effective Faraday cage possible? That is one in which
no electromagnetic frequencies of any kind can exist?

"Wimpie" <wim...@tetech.nl> wrote in message

news:1192104914.922074.65040@k79g2000hse.googlegroups.com...

On 11 oct, 12:29, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Ok, so If I construct a Faraday cage from a conductive material that
should
block out a large portion of the electromagnetic spectrum, can I still
create such electromagnetic wavelengths within the Faraday cage by
combining
other wavlengths at a focal point within it?

Hello,

Yes, you can establish a EM field in closed cage.. When there are no
absorbing materials inside, you can create large field strength with
relative low RF input power.

You can see the cage as a large resonator (can be compared with
acoustic resonance). Internal reflections can interfere in a
constructive (more field) or destructive (less field) way. Closed
cavities are used frequently in the microwave industry (as part of a
filter or a frequency determining component).

In many cases, the reflections from the walls are a problem during
measurement of field parameters.

You did not mention your application. Maybe you can provide us some
additional info.

Best regards,

Wim
PA3DJS
www.tetech.nl

Hello,

As room temperature conductivity is limited, there will be no cage
where the screening is infinite. For many practical uses, a cage can
be constructed with extremely low EM field levels inside. As soon as
you have to open the cage to feed cables in it, problems may arise.
Also when you have measuring equipment in the cage, EM level will
increase especially when the emitted frequency is close to a
resonance.

Maybe you can provide more information about your application.

Best regards,

Wim
PA3DJS
www.tetech.nl
Benj
Posted: Thu Oct 11, 2007 12:38 pm
Guest
Mac Lawson wrote:
Quote:
Thanks. So is a 100% effective Faraday cage possible? That is one in which
no electromagnetic frequencies of any kind can exist?

Sure, just build it out of superconductor!

Good luck on your project.
Mac Lawson
Posted: Fri Oct 12, 2007 8:48 am
Guest
Wouldn't high-frequency X rays penertrate a superconductor, they can
penertrate steel?


"Benj" <bjacoby@iwaynet.net> wrote in message
news:1192124295.240557.35560@22g2000hsm.googlegroups.com...
Quote:

Mac Lawson wrote:
Thanks. So is a 100% effective Faraday cage possible? That is one in
which
no electromagnetic frequencies of any kind can exist?

Sure, just build it out of superconductor!

Good luck on your project.
Mac Lawson
Posted: Fri Oct 12, 2007 9:17 am
Guest
"Wimpie" <wimtel@tetech.nl> wrote in message
news:1192122749.947458.68070@50g2000hsm.googlegroups.com...
Quote:
On 11 oct, 16:20, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Thanks. So is a 100% effective Faraday cage possible? That is one in
which
no electromagnetic frequencies of any kind can exist?

"Wimpie" <wim...@tetech.nl> wrote in message

news:1192104914.922074.65040@k79g2000hse.googlegroups.com...

On 11 oct, 12:29, "Mac Lawson" <newthreat2...@yahoo.com> wrote:
Ok, so If I construct a Faraday cage from a conductive material that
should
block out a large portion of the electromagnetic spectrum, can I
still
create such electromagnetic wavelengths within the Faraday cage by
combining
other wavlengths at a focal point within it?

Hello,

Yes, you can establish a EM field in closed cage.. When there are no
absorbing materials inside, you can create large field strength with
relative low RF input power.

You can see the cage as a large resonator (can be compared with
acoustic resonance). Internal reflections can interfere in a
constructive (more field) or destructive (less field) way. Closed
cavities are used frequently in the microwave industry (as part of a
filter or a frequency determining component).

In many cases, the reflections from the walls are a problem during
measurement of field parameters.

You did not mention your application. Maybe you can provide us some
additional info.

Best regards,

Wim
PA3DJS
www.tetech.nl

Hello,

As room temperature conductivity is limited, there will be no cage
where the screening is infinite. For many practical uses, a cage can
be constructed with extremely low EM field levels inside. As soon as
you have to open the cage to feed cables in it, problems may arise.
Also when you have measuring equipment in the cage, EM level will
increase especially when the emitted frequency is close to a
resonance.

Maybe you can provide more information about your application.

Best regards,

Wim
PA3DJS
www.tetech.nl


The application is purely theoretical at the moment. Let's say that I want
to communicate with a device that operates at a certain frequency and is
contained in a Faraday cage designed to specifically block out that
frequency. Is it still possible to communicate with the device? Can I use
two electromagnetic waves with frequencies that can penetrate the cage,
combine these within the cage to produce the correct frequency and, thus,
the device can receive such communication? Can the device communicate back
through the Faraday cage by combining it's communication frequency with
another electromagnetic wave, one that is also transmitted into the cage
when required, to produce a frequency that can then pass back out of the
cage? Once the electromagnetic wave is received can it then be decoded back
into the original communication frequency?

So, essentially my question is, is it possible to communicate with a device
within a Faraday cage and one that uses the frequency that the cage is
designed to block out by combining electromagnetic waves within the cage?
Benj
Posted: Fri Oct 12, 2007 4:05 pm
Guest
Mac Lawson wrote:
Quote:
Wouldn't high-frequency X rays penetrate a superconductor, they can
penetrate steel?

WHOA! That is an EXCELLENT question! I have no idea. I'd have to go
ask some low temperature physicists about it! Such an experiment
seems to suggest interesting theoretical implications!

Benj
Benj
Posted: Fri Oct 12, 2007 4:14 pm
Guest
Mac Lawson wrote:

Quote:
So, essentially my question is, is it possible to communicate with a device
within a Faraday cage and one that uses the frequency that the cage is
designed to block out by combining electromagnetic waves within the cage?

Ah! I see what you are getting at! The answer is that IF the
shielding is of limited frequency capability, then YES, you can insert
two frequencies OUTSIDE the band of effective shielding. But the
question of if can you communicate with the device inside the shield
depends upon the device itself. The missing fact is that if you want
two different frequencies to create a third, you are required to have
some kind of non-linear interaction to do it. In your device this
would pretty much imply the input portion of the receiving device in
question. IF that device exhibited enough input non-linearity without
overloading or other undesirable traits, then yes, you are correct you
could communicate right through the shield. But only in the inward
direction. The device could not communicate out of the shield unless
it also was designed to do so.

Benj
 
Page 1 of 1       All times are GMT - 5 Hours
The time now is Fri Oct 10, 2008 11:09 pm