Posted by Glenn Coleman on
URL: https://www.es-forum.com/Re-shielding-Notebook-Quantum-Byte-tp1536920.html

Thanks Beau,

I really appreciate your analysis of this application of wire mesh. Knowing
it may have a good chance to help is enough to try it.

I am curious if you have looked at the Quantum Byte software, and how it
works. I have been quite critical if this software could really accomplish
anything since I thought software would only be limited to the logic gates
of a computer, which do only what they are programmed, and usually only
trigger other logic gates and hardward. But after reading your concept of
CPU frequencies getting into the equation, I start to wonder if the Byte
software is simply exercising the logic gates in computer in a more uniform
rythym (perhaps triggering some logic gates just to exercise CPU and not
accomplish any functional result) so the cpu is operating in a more uniform
pattern?

I am curious if any other people had positive results with Quantum Byte
software?

Best wishes,

Glenn


----Original Message Follows----
From: "Beau" <[hidden email]>
Reply-To: [hidden email]
To: [hidden email]
Subject: [eSens] Re: shielding Notebook
Date: Mon, 27 Sep 2004 18:11:27 -0000

Hi Charles,

I respectfully disagree with you concerning the equation. Please note
that I conditioned the equation's application by an a priori knowledge
of frequencies by saying "*If we can take* the computer's CPU clock
speed as its highest frequency component...". Of course, I do agree
that we can't know all the frequencies without measuring them first.
However, if we assume a maximum for the frequencies a body is emitting
we have concurrently placed a minimum on the emitted wavelengths.
Meshes with spacing smaller than this minimum wavelength begin to
appear as continuous surfaces without holes for transverse EM.

Also, I want to emphasize that I am not saying a mesh provides *total*
shielding of the transverse EM from a notebook computer. Everyone,
please pardon me if I inadvertently gave that impression by saying
near the end of my previous message "...should readily shield the
transverse emissions in the above example."

Let me be more complete. Given a mesh with spacing much smaller than
the minimum radiated wavelength, the level of shielding is dependent
on the characteristics of the mesh material -- its depth, its
permeability, its conductivity -- as well as the geometry and
frequency of the radiated field encountering it.

If we have an aluminum mesh enclosure fitting our spacing criteria
with wire thickness of 0.25 mm, a 1 GHz transverse EM plane wave
encountering it will be approximately attenuated to around
1/(2.718)^(100) its original amplitude after penetrating the mesh. A
100 MHz transverse EM plane wave will suffer attenuation to around
1/(2.718)^(33) its original amplitude. In near-field conditions, such
as a mesh around a notebook computer, the level of shielding is more
complex to calculate, but it will exist to some extent for these
frequencies for both the electric and magnetic field components.

Unfortunately, low-frequency transverse EM won't be hampered by this
mesh even though it 'looks' like a smooth surface to it. For a 100 Hz
transverse EM plane wave would require the mesh's depth to be 36x
thicker (around 8.5 mm) just to attenuate it down to 1/3 its original
amplitude.

Beau

--- In [hidden email], "Charles" <charles@c...> wrote:
> Hello,
>
> this equeation does not work.
>
> You can't know what ferquencies are radiating from this thing.
>
> The damaging part are the magnetic fields emanating.
> And we know that they can be heavy.
> Especially above the keyboard, whereunder the hard disk and
motherboard are frequency
> > component then the aperture/mesh size below which shielding for
the
> > computer will begin is:
> >
> > (0.3 m)/(CPU speed in GHz) or
> > (300 m)/(CPU speed in MHz)
> >
> > Smaller aperture sizes than this work much better. For typical
square
> > mesh, divide by the square root of 2 to account for the diagonal
of
> > the mesh being its largest aperture width.
> >
> > For example, if we had a 1 GHz CPU, then square mesh below (30
> > cm)/(sqrt 2) ~ (21 cm) will begin to confine the transverse EM
> > radiation. A 1/4" square mesh has as its largest aperture width
> > (0.25") * (1.414) ~ (0.35") ~ (0.89 cm) which should readily
shield the wire
> > mesh
> > > works on microwaves it may work here too. I may even make a
whole
> > box
> > > around my notebook with notebook sitting in cage.
> > >
> > > If it does work, then I can find a finer quality mesh so I can
see help.