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MIT study on aluminum foil hats

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  MIT study on aluminum foil hats Sam Wormley <swormley1@gmail.com> - 2015-11-15 14:59 -0600
    Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-15 21:05 +0000
      Re: MIT study on aluminum foil hats "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-15 13:24 -0800
        Re: MIT study on aluminum foil hats "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-15 13:26 -0800
        Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-15 21:58 +0000
    Re: MIT study on aluminum foil hats Fabian Russell <root@localhost.localdomain> - 2015-11-15 21:37 +0000
      Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-15 22:04 +0000
        Re: MIT study on aluminum foil hats Fabian Russell <root@localhost.localdomain> - 2015-11-15 23:00 +0000
          Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-15 23:05 +0000
    Re: MIT study on aluminum foil hats gilber34 <fafa@invalid.com> - 2015-11-15 16:06 -0600
      Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-15 22:57 +0000
        Re: MIT study on aluminum foil hats gilber34 <fafa@invalid.com> - 2015-11-15 19:51 -0600
          Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-16 02:33 +0000
            Re: MIT study on aluminum foil hats gilber34 <fafa@invalid.com> - 2015-11-16 10:12 -0600
              Re: MIT study on aluminum foil hats "nuny@bid.nes" <Alien8752@gmail.com> - 2015-11-16 09:28 -0800
              Re: MIT study on aluminum foil hats benj <none@gmail.com> - 2015-11-16 12:52 -0500
                Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-16 19:43 +0000
                  Re: MIT study on aluminum foil hats benj <none@gmail.com> - 2015-11-16 21:55 -0500
                  Re: MIT study on aluminum foil hats gilber34 <fafa@invalid.com> - 2015-11-16 23:04 -0600
              Re: MIT study on aluminum foil hats jimp@specsol.spam.sux.com - 2015-11-16 19:39 +0000
    Re: MIT study on aluminum foil hats HVAC <mr.hvac@gmail.com> - 2015-11-16 03:24 -0800
      Re: MIT study on aluminum foil hats HVAC <mr.hvac@gmail.com> - 2015-11-16 03:26 -0800
        Re: MIT study on aluminum foil hats benj <none@gmail.com> - 2015-11-16 12:42 -0500
      Re: MIT study on aluminum foil hats benj <none@gmail.com> - 2015-11-16 12:40 -0500

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#533352 — MIT study on aluminum foil hats

MIT study on aluminum foil hats
> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html


> Earlier this year, MIT engineers conducted an empirical study on the
> efficacy of aluminum foil helmets to block mind control rays. They've
> published the detailed results of their experiments online. From the
> abstract:

> Rahimi Helmet Ali2Among a fringe community of paranoids, aluminum
> helmets serve as the protective measure of choice against invasive
> radio signals. We investigate the efficacy of three aluminum helmet
> designs on a sample group of four individuals. Using a $250,000
> network analyser, we find that although on average all helmets
> attenuate invasive radio frequencies in either directions (either
> emanating from an outside source, or emanating from the cranium of
> the subject), certain frequencies are in fact greatly amplified.
> These amplified frequencies coincide with radio bands reserved for
> government use according to the Federal Communication Commission
> (FCC). Statistical evidence suggests the use of helmets may in fact
> enhance the government's invasive abilities. We theorize that the
> government may in fact have started the helmet craze for this
> reason.


-- 

sci.physics is an unmoderated newsgroup dedicated
to the discussion of physics, news from the physics
community, and physics-related social issues.

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#533364

Sam Wormley <swormley1@gmail.com> wrote:
> MIT study on aluminum foil hats
>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
> 
> 
>> Earlier this year, MIT engineers conducted an empirical study on the
>> efficacy of aluminum foil helmets to block mind control rays. They've
>> published the detailed results of their experiments online. From the
>> abstract:
> 
>> Rahimi Helmet Ali2Among a fringe community of paranoids, aluminum
>> helmets serve as the protective measure of choice against invasive
>> radio signals. We investigate the efficacy of three aluminum helmet
>> designs on a sample group of four individuals. Using a $250,000
>> network analyser, we find that although on average all helmets
>> attenuate invasive radio frequencies in either directions (either
>> emanating from an outside source, or emanating from the cranium of
>> the subject), certain frequencies are in fact greatly amplified.
>> These amplified frequencies coincide with radio bands reserved for
>> government use according to the Federal Communication Commission
>> (FCC). Statistical evidence suggests the use of helmets may in fact
>> enhance the government's invasive abilities. We theorize that the
>> government may in fact have started the helmet craze for this
>> reason.
 
Ignorant nonsense.

A hell of a lot of spectrum is reserved for "government use", i.e.
aircraft communications, GPS, radio navigation, emergency services
communication, etc.

 

-- 
Jim Pennino

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#533366

On Sunday, November 15, 2015 at 1:16:05 PM UTC-8, ji...@specsol.spam.sux.com wrote:
> Sam Wormley <swormley1@gmail.com> wrote:
> > MIT study on aluminum foil hats
> >> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
> > 
> > 
> >> Earlier this year, MIT engineers conducted an empirical study on the
> >> efficacy of aluminum foil helmets to block mind control rays. They've
> >> published the detailed results of their experiments online. From the
> >> abstract:
> > 
> >> Rahimi Helmet Ali2Among a fringe community of paranoids, aluminum
> >> helmets serve as the protective measure of choice against invasive
> >> radio signals. We investigate the efficacy of three aluminum helmet
> >> designs on a sample group of four individuals. Using a $250,000
> >> network analyser, we find that although on average all helmets
> >> attenuate invasive radio frequencies in either directions (either
> >> emanating from an outside source, or emanating from the cranium of
> >> the subject), certain frequencies are in fact greatly amplified.
> >> These amplified frequencies coincide with radio bands reserved for
> >> government use according to the Federal Communication Commission
> >> (FCC). Statistical evidence suggests the use of helmets may in fact
> >> enhance the government's invasive abilities. We theorize that the
> >> government may in fact have started the helmet craze for this
> >> reason.
>  
> Ignorant nonsense.
> 
> A hell of a lot of spectrum is reserved for "government use", i.e.
> aircraft communications, GPS, radio navigation, emergency services
> communication, etc.
> 
>  
> 
> -- 
> Jim Pennino


"Tin" is what you're looking for, 
not "aluminum" nor "aluminium" 
but "tin".  (Tin foil:  a lead alloy.)

"Lead paint" also greatly reduces radio 
frequency emissions through it.

This is for usual notions of Faraday 
cages and TEMPEST shielding as simply 
via construction materials.

If you're interested in the ambient radio 
frequency environment, you might find 
it of interest to get a Gauss meter and 
check it out.

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#533368

On Sunday, November 15, 2015 at 1:24:29 PM UTC-8, Ross A. Finlayson wrote:
> On Sunday, November 15, 2015 at 1:16:05 PM UTC-8, ji...@specsol.spam.sux.com wrote:
> > Sam Wormley <swormley1@gmail.com> wrote:
> > > MIT study on aluminum foil hats
> > >> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
> > > 
> > > 
> > >> Earlier this year, MIT engineers conducted an empirical study on the
> > >> efficacy of aluminum foil helmets to block mind control rays. They've
> > >> published the detailed results of their experiments online. From the
> > >> abstract:
> > > 
> > >> Rahimi Helmet Ali2Among a fringe community of paranoids, aluminum
> > >> helmets serve as the protective measure of choice against invasive
> > >> radio signals. We investigate the efficacy of three aluminum helmet
> > >> designs on a sample group of four individuals. Using a $250,000
> > >> network analyser, we find that although on average all helmets
> > >> attenuate invasive radio frequencies in either directions (either
> > >> emanating from an outside source, or emanating from the cranium of
> > >> the subject), certain frequencies are in fact greatly amplified.
> > >> These amplified frequencies coincide with radio bands reserved for
> > >> government use according to the Federal Communication Commission
> > >> (FCC). Statistical evidence suggests the use of helmets may in fact
> > >> enhance the government's invasive abilities. We theorize that the
> > >> government may in fact have started the helmet craze for this
> > >> reason.
> >  
> > Ignorant nonsense.
> > 
> > A hell of a lot of spectrum is reserved for "government use", i.e.
> > aircraft communications, GPS, radio navigation, emergency services
> > communication, etc.
> > 
> >  
> > 
> > -- 
> > Jim Pennino
> 
> 
> "Tin" is what you're looking for, 
> not "aluminum" nor "aluminium" 
> but "tin".  (Tin foil:  a lead alloy.)
> 
> "Lead paint" also greatly reduces radio 
> frequency emissions through it.
> 
> This is for usual notions of Faraday 
> cages and TEMPEST shielding as simply 
> via construction materials.
> 
> If you're interested in the ambient radio 
> frequency environment, you might find 
> it of interest to get a Gauss meter and 
> check it out.

Excuse me, this is off-topic to a physics 
newgroup, eg high-energy physics, natural 
physics, experimental physics, theoretical 
physics, ....

But, those MIT students have quite an engaging 
sense of humor at some points, so let's not 
categorically discard all their efforts here 
as of the Rube Goldberg poke-the-socket set.

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#533375

Ross A. Finlayson <ross.finlayson@gmail.com> wrote:
> On Sunday, November 15, 2015 at 1:16:05 PM UTC-8, ji...@specsol.spam.sux.com wrote:
>> Sam Wormley <swormley1@gmail.com> wrote:
>> > MIT study on aluminum foil hats
>> >> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>> > 
>> > 
>> >> Earlier this year, MIT engineers conducted an empirical study on the
>> >> efficacy of aluminum foil helmets to block mind control rays. They've
>> >> published the detailed results of their experiments online. From the
>> >> abstract:
>> > 
>> >> Rahimi Helmet Ali2Among a fringe community of paranoids, aluminum
>> >> helmets serve as the protective measure of choice against invasive
>> >> radio signals. We investigate the efficacy of three aluminum helmet
>> >> designs on a sample group of four individuals. Using a $250,000
>> >> network analyser, we find that although on average all helmets
>> >> attenuate invasive radio frequencies in either directions (either
>> >> emanating from an outside source, or emanating from the cranium of
>> >> the subject), certain frequencies are in fact greatly amplified.
>> >> These amplified frequencies coincide with radio bands reserved for
>> >> government use according to the Federal Communication Commission
>> >> (FCC). Statistical evidence suggests the use of helmets may in fact
>> >> enhance the government's invasive abilities. We theorize that the
>> >> government may in fact have started the helmet craze for this
>> >> reason.
>>  
>> Ignorant nonsense.
>> 
>> A hell of a lot of spectrum is reserved for "government use", i.e.
>> aircraft communications, GPS, radio navigation, emergency services
>> communication, etc.
>> 
>>  
>> 
>> -- 
>> Jim Pennino
> 
> 
> "Tin" is what you're looking for, 
> not "aluminum" nor "aluminium" 
> but "tin".  (Tin foil:  a lead alloy.)

Nope, tin foil was nothing but thin tin and common before WWII.

It was replaced by aluminium foil as being cheaper, easier to work
with and without leaving a tin taste on food.


-- 
Jim Pennino

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#533369

On Sun, 15 Nov 2015 14:59:29 -0600, Sam Wormley wrote:

> MIT study on aluminum foil hats
>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
> 

Of course, the whole head cannot be covered without first cutting
it off (decapitation).

That certainly would solve the paranoia problem.

But it should be a straightforward matter to use Maxwell's equations
to determine the EM intensity inside of a metallic hemisphere (that
is open at the bottom).

What would those calculations show?  How much EM is present, at a given
wavelength, in the interior of a metallic hemisphere?

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#533378

Fabian Russell <root@localhost.localdomain> wrote:
> On Sun, 15 Nov 2015 14:59:29 -0600, Sam Wormley wrote:
> 
>> MIT study on aluminum foil hats
>>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>> 
> 
> Of course, the whole head cannot be covered without first cutting
> it off (decapitation).
> 
> That certainly would solve the paranoia problem.
> 
> But it should be a straightforward matter to use Maxwell's equations
> to determine the EM intensity inside of a metallic hemisphere (that
> is open at the bottom).

But far simpler and quicker to do empirical measurement with computer
controlled test equipment that would plot the data for you in a few
seconds.

As computer contolled test equipment did not become common and affordable
until the early 80's, it is no surprise you did not think of it.


-- 
Jim Pennino

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#533399

On Sun, 15 Nov 2015 22:04:07 +0000, jimp wrote:

> 
> But far simpler and quicker to do empirical measurement with computer
> controlled test equipment that would plot the data for you in a few
> seconds.
> 

But you'd have to get your hands dirty.  I wouldn't.

Furthermore, electronics workers, and especially RF workers, have a higher
incidence of brain cancer.  This is epidemiologically proven.

The best survival strategy is to stay out of the lab.

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#533404

Fabian Russell <root@localhost.localdomain> wrote:
> On Sun, 15 Nov 2015 22:04:07 +0000, jimp wrote:
> 
>> 
>> But far simpler and quicker to do empirical measurement with computer
>> controlled test equipment that would plot the data for you in a few
>> seconds.
>> 
> 
> But you'd have to get your hands dirty.  I wouldn't.

You would be fired for wasting time.

> Furthermore, electronics workers, and especially RF workers, have a higher
> incidence of brain cancer.  This is epidemiologically proven.

Nope, wrong again.

There was a case for accumlated lead from soldering many decades ago but
the regulations on fume emmisions solved that.


-- 
Jim Pennino

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#533377

On 11/15/2015 2:59 PM, Sam Wormley wrote:
> MIT study on aluminum foil hats
>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>
>
>> Earlier this year, MIT engineers conducted an empirical study on the
>> efficacy of aluminum foil helmets to block mind control rays. They've
>> published the detailed results of their experiments online. From the
>> abstract:
>

>


Aluminum does not stop low frequency waves, below 2Mhz, at all.  Nor Copper.

Need Iron content for that.

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#533397

gilber34 <fafa@invalid.com> wrote:
> On 11/15/2015 2:59 PM, Sam Wormley wrote:
>> MIT study on aluminum foil hats
>>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>>
>>
>>> Earlier this year, MIT engineers conducted an empirical study on the
>>> efficacy of aluminum foil helmets to block mind control rays. They've
>>> published the detailed results of their experiments online. From the
>>> abstract:
>>
> 
>>
> 
> 
> Aluminum does not stop low frequency waves, below 2Mhz, at all.  Nor Copper.
> 
> Need Iron content for that.
 
Not true; RF is RF.

Look up "skin effect" for why foil may not be the answer for low frequency.


-- 
Jim Pennino

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#533441

On 11/15/2015 4:57 PM, jimp@specsol.spam.sux.com wrote:
> gilber34 <fafa@invalid.com> wrote:
>> On 11/15/2015 2:59 PM, Sam Wormley wrote:
>>> MIT study on aluminum foil hats
>>>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>>>
>>>
>>>> Earlier this year, MIT engineers conducted an empirical study on the
>>>> efficacy of aluminum foil helmets to block mind control rays. They've
>>>> published the detailed results of their experiments online. From the
>>>> abstract:
>>>
>>
>>>
>>
>>
>> Aluminum does not stop low frequency waves, below 2Mhz, at all.  Nor Copper.
>>
>> Need Iron content for that.
>
> Not true; RF is RF.
>
> Look up "skin effect" for why foil may not be the answer for low frequency.
>
>

skin effect is only one part of the problem, re-radiation from the other 
side is another, a reason most shield rooms have two screens attached at 
a single point between them. and also lack of sufficient attenuation in 
material.  Gov switched from copper to galvanized steel sheet for many 
of their SCIFs, much cheaper, + better attenuation.  Need to knock it 
down by 90 to 150 Db



http://www.rfcafe.com/references/electrical/skin-depth.htm

note it depends upon permeability, of which Iron is far higher than Al.

material Relative Permeability μ/μ0 - Skin depth (0.1Mhz)

AL               1                        259.0 um
Fe              500                       22.2 um

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#533449

gilber34 <fafa@invalid.com> wrote:
> On 11/15/2015 4:57 PM, jimp@specsol.spam.sux.com wrote:
>> gilber34 <fafa@invalid.com> wrote:
>>> On 11/15/2015 2:59 PM, Sam Wormley wrote:
>>>> MIT study on aluminum foil hats
>>>>> http://boingboing.net/2005/11/11/mit-study-on-aluminu.html
>>>>
>>>>
>>>>> Earlier this year, MIT engineers conducted an empirical study on the
>>>>> efficacy of aluminum foil helmets to block mind control rays. They've
>>>>> published the detailed results of their experiments online. From the
>>>>> abstract:
>>>>
>>>
>>>>
>>>
>>>
>>> Aluminum does not stop low frequency waves, below 2Mhz, at all.  Nor Copper.
>>>
>>> Need Iron content for that.
>>
>> Not true; RF is RF.
>>
>> Look up "skin effect" for why foil may not be the answer for low frequency.
>>
>>
> 
> skin effect is only one part of the problem, re-radiation from the other 
> side is another, a reason most shield rooms have two screens attached at 
> a single point between them. and also lack of sufficient attenuation in 
> material.  Gov switched from copper to galvanized steel sheet for many 
> of their SCIFs, much cheaper, + better attenuation.  Need to knock it 
> down by 90 to 150 Db

Re-radiation from the other side of a closed, solid conductor is impossible
for practical sheet metal of any kind.

Screens always have leakage, which is quite different than re-radiation.

> 
> http://www.rfcafe.com/references/electrical/skin-depth.htm
> 
> note it depends upon permeability, of which Iron is far higher than Al.

Note it actually depends on the resistivity, frequency, magnetic
permeability, and the permittivity.

> material Relative Permeability μ/μ0 - Skin depth (0.1Mhz)
> 
> AL               1                        259.0 um
> Fe              500                       22.2 um

If that is supposed to be skin depth, it is meaningless without frequency.

 
 

-- 
Jim Pennino

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#533480

On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:

>> skin effect is only one part of the problem, re-radiation from the other
>> side is another, a reason most shield rooms have two screens attached at
>> a single point between them. and also lack of sufficient attenuation in
>> material.  Gov switched from copper to galvanized steel sheet for many
>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>> down by 90 to 150 Db
>
> Re-radiation from the other side of a closed, solid conductor is impossible
> for practical sheet metal of any kind.


True, if the solid conductor is thicker than skin depth, and has some 
Iron content to attenuate down to 1KHz.   But the seams, doors can be a 
challange, etc.

It is a matter of how much attenuation you want, 20 Db or 150 Db
more material, more layers, more attenuation. (easier as you go up in 
frequency)

Try cutting off a DC magnetic field from a PMT tube

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#533515

On Monday, November 16, 2015 at 8:13:01 AM UTC-8, gilber34 wrote:
> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:
> 
> >> skin effect is only one part of the problem, re-radiation from the other
> >> side is another, a reason most shield rooms have two screens attached at
> >> a single point between them. and also lack of sufficient attenuation in
> >> material.  Gov switched from copper to galvanized steel sheet for many
> >> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
> >> down by 90 to 150 Db
> >
> > Re-radiation from the other side of a closed, solid conductor is impossible
> > for practical sheet metal of any kind.
> 
> True, if the solid conductor is thicker than skin depth, and has some 
> Iron content to attenuate down to 1KHz.   But the seams, doors can be a 
> challange, etc.

  I don't know why you're so fixated on iron.

> It is a matter of how much attenuation you want, 20 Db or 150 Db
> more material, more layers, more attenuation. (easier as you go up in 
> frequency)
> 
> Try cutting off a DC magnetic field from a PMT tube

  That's what superconductors are for.


  Mark L. Fergerson

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#533525

On 11/16/2015 11:12 AM, gilber34 wrote:
> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:
>
>>> skin effect is only one part of the problem, re-radiation from the other
>>> side is another, a reason most shield rooms have two screens attached at
>>> a single point between them. and also lack of sufficient attenuation in
>>> material.  Gov switched from copper to galvanized steel sheet for many
>>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>>> down by 90 to 150 Db
>>
>> Re-radiation from the other side of a closed, solid conductor is
>> impossible
>> for practical sheet metal of any kind.
>
>
> True, if the solid conductor is thicker than skin depth, and has some
> Iron content to attenuate down to 1KHz.   But the seams, doors can be a
> challange, etc.
>
> It is a matter of how much attenuation you want, 20 Db or 150 Db
> more material, more layers, more attenuation. (easier as you go up in
> frequency)
>
> Try cutting off a DC magnetic field from a PMT tube

Simple. Just need lower resistance.


-- 

       ___           ___           ___            ___
      /\  \         /\  \         /\__\          /\  \
     /::\  \       /::\  \       /::|  |         \:\  \
    /:/\:\  \     /:/\:\  \     /:|:|  |     ___ /::\__\
   /::\~\:\__\   /::\~\:\  \   /:/|:|  |__  /\  /:/\/__/
  /:/\:\ \:|__| /:/\:\ \:\__\ /:/ |:| /\__\ \:\/:/  /
  \:\~\:\/:/  / \:\~\:\ \/__/ \/__|:|/:/  /  \::/  /
   \:\ \::/  /   \:\ \:\__\       |:/:/  /    \/__/
    \:\/:/  /     \:\ \/__/       |::/  /
     \::/__/       \:\__\         /:/  /
      ~~            \/__/         \/__/

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#533577

benj <none@gmail.com> wrote:
> On 11/16/2015 11:12 AM, gilber34 wrote:
>> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:
>>
>>>> skin effect is only one part of the problem, re-radiation from the other
>>>> side is another, a reason most shield rooms have two screens attached at
>>>> a single point between them. and also lack of sufficient attenuation in
>>>> material.  Gov switched from copper to galvanized steel sheet for many
>>>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>>>> down by 90 to 150 Db
>>>
>>> Re-radiation from the other side of a closed, solid conductor is
>>> impossible
>>> for practical sheet metal of any kind.
>>
>>
>> True, if the solid conductor is thicker than skin depth, and has some
>> Iron content to attenuate down to 1KHz.   But the seams, doors can be a
>> challange, etc.
>>
>> It is a matter of how much attenuation you want, 20 Db or 150 Db
>> more material, more layers, more attenuation. (easier as you go up in
>> frequency)
>>
>> Try cutting off a DC magnetic field from a PMT tube
> 
> Simple. Just need lower resistance.
 
Mu metal.

Been there, done that for a chamber that had to exclude RF as well
as magnetic fields.
 

-- 
Jim Pennino

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#533697

On 11/16/2015 02:43 PM, jimp@specsol.spam.sux.com wrote:
> benj <none@gmail.com> wrote:
>> On 11/16/2015 11:12 AM, gilber34 wrote:
>>> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:
>>>
>>>>> skin effect is only one part of the problem, re-radiation from the other
>>>>> side is another, a reason most shield rooms have two screens attached at
>>>>> a single point between them. and also lack of sufficient attenuation in
>>>>> material.  Gov switched from copper to galvanized steel sheet for many
>>>>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>>>>> down by 90 to 150 Db
>>>>
>>>> Re-radiation from the other side of a closed, solid conductor is
>>>> impossible
>>>> for practical sheet metal of any kind.
>>>
>>>
>>> True, if the solid conductor is thicker than skin depth, and has some
>>> Iron content to attenuate down to 1KHz.   But the seams, doors can be a
>>> challange, etc.
>>>
>>> It is a matter of how much attenuation you want, 20 Db or 150 Db
>>> more material, more layers, more attenuation. (easier as you go up in
>>> frequency)
>>>
>>> Try cutting off a DC magnetic field from a PMT tube
>>
>> Simple. Just need lower resistance.
>
> Mu metal.
>
> Been there, done that for a chamber that had to exclude RF as well
> as magnetic fields.

Actually multiple layers works best, but superconductor works better.



-- 

       ___           ___           ___            ___
      /\  \         /\  \         /\__\          /\  \
     /::\  \       /::\  \       /::|  |         \:\  \
    /:/\:\  \     /:/\:\  \     /:|:|  |     ___ /::\__\
   /::\~\:\__\   /::\~\:\  \   /:/|:|  |__  /\  /:/\/__/
  /:/\:\ \:|__| /:/\:\ \:\__\ /:/ |:| /\__\ \:\/:/  /
  \:\~\:\/:/  / \:\~\:\ \/__/ \/__|:|/:/  /  \::/  /
   \:\ \::/  /   \:\ \:\__\       |:/:/  /    \/__/
    \:\/:/  /     \:\ \/__/       |::/  /
     \::/__/       \:\__\         /:/  /
      ~~            \/__/         \/__/

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#533716

On 11/16/2015 1:43 PM, jimp@specsol.spam.sux.com wrote:
> benj <none@gmail.com> wrote:
>> On 11/16/2015 11:12 AM, gilber34 wrote:
>>> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:

>>>>> skin effect is only one part of the problem, re-radiation from the other
>>>>> side is another, a reason most shield rooms have two screens attached at
>>>>> a single point between them. and also lack of sufficient attenuation in
>>>>> material.  Gov switched from copper to galvanized steel sheet for many
>>>>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>>>>> down by 90 to 150 Db

>>>> Re-radiation from the other side of a closed, solid conductor is
>>>> impossible
>>>> for practical sheet metal of any kind.
>>>
>>>
>>> True, if the solid conductor is thicker than skin depth, and has some
>>> Iron content to attenuate down to 1KHz.   But the seams, doors can be a
>>> challange, etc.

>>> It is a matter of how much attenuation you want, 20 Db or 150 Db
>>> more material, more layers, more attenuation. (easier as you go up in
>>> frequency)
>>>
>>> Try cutting off a DC magnetic field from a PMT tube

>> Simple. Just need lower resistance.
>
> Mu metal.
>
> Been there, done that for a chamber that had to exclude RF as well
> as magnetic fields.
>
>

Been there, done that too, built a small chamber worked well down to 
about 1 MHz, got a measured 149 Db isolation at 400-500 Mhz, .

and the PMT was a hemispherical 8 inch looking up, had lots of room used 
galvenized sheet metal box, and mu metal wire in a grid across the top. 
the mu metal sheet foil very pricy. slight loss if field tilts beam 
path, can turn tube 90 degrees, for less effect too.

anyhow the OP was about MIT and their Al Foil Deflecter Beniees
apperently the Chinese have patented it this year.

see this site for the latest;
http://zapatopi.net/afdb/

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#533576

gilber34 <fafa@invalid.com> wrote:
> On 11/15/2015 8:33 PM, jimp@specsol.spam.sux.com wrote:
> 
>>> skin effect is only one part of the problem, re-radiation from the other
>>> side is another, a reason most shield rooms have two screens attached at
>>> a single point between them. and also lack of sufficient attenuation in
>>> material.  Gov switched from copper to galvanized steel sheet for many
>>> of their SCIFs, much cheaper, + better attenuation.  Need to knock it
>>> down by 90 to 150 Db
>>
>> Re-radiation from the other side of a closed, solid conductor is impossible
>> for practical sheet metal of any kind.
> 
> 
> True, if the solid conductor is thicker than skin depth, and has some 
> Iron content to attenuate down to 1KHz.   But the seams, doors can be a 
> challange, etc.

No, it does not have to have iron content.

> It is a matter of how much attenuation you want, 20 Db or 150 Db
> more material, more layers, more attenuation. (easier as you go up in 
> frequency)

Layers are needed because of leaks in screen and things like door seals.

It is far cheaper to use multilayer screens than it would be to use
solid sheet metal.

> Try cutting off a DC magnetic field from a PMT tube

DC is not RF and a totally separate issue.


-- 
Jim Pennino

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