> 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
> > placed.
> >
> > My CRT monitor radiates hard with 91.1 kHz, but I found many other
> > frequencies.
> >
> > You may hold a world receiver in front of your laptop.
> >
> > Greetings,
> > Charles Claessens
> > member Verband Baubiologie
> > www.milieuziektes.nl
> > www.hetbitje.nl
> > checked by Norton Antivirus
> >
> >
> > ----- Original Message -----
> > From: "Beau" <netfarer2@y...>
> > To: <[hidden email]>
> > Sent: Monday, September 27, 2004 01:48
> > Subject: [eSens] Re: shielding Notebook
> >
> >
> > >
> > > Hi Glenn & Randolf,
> > >
> > > If we can take the computer's CPU clock speed as its highest
> 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
> > > transverse emissions in the above example.
> > >
> > > Beau
> > >
> > > --- In [hidden email], "Glenn Coleman" <glennhcoleman@h...>
> > > wrote:
> > > > Hello,
> > > >
> > > > I have thought of something similar, but to hook an external
> > > keyboard, and
> > > > use a wire-mesh fence between me and the notebook. I figure if
> 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
> > > monitor
> > > > better. I was going to start with some wire fencing with 1/4"
> > > holes to
> > > > begin with.
> > > >
> > > > Glenn
> > > >
> > > >
> > > > ----Original Message Follows----
> > > > From: "randolf_everywhere" <Thats@M...>
> > > > Reply-To: [hidden email]
> > > > To: [hidden email]
> > > > Subject: [eSens] shielding Notebook
> > > > Date: Sun, 26 Sep 2004 11:09:02 -0000
> > > >
> > > > Hello,
> > > >
> > > > I am thinking of shielding my Notebook. Maybe with paint or with
> > > > wallpaper on its outside. I tested and know shielding it will
> help.
> > > But I do
> > > > not know If there can occur problems when I do it.
> > > >
> > > >
> > > > Randolf Weinand
> > >
> > >
> > >
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>