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RE: [Fwd: Re: Implications for wearables]

FYI - a Faraday cage gets its name from Michael Faraday, a British Physicist
who discovered the principle of magnetic induction in 1831. Five years later
he described the concept of the Faraday Cage (the copper screening
contraption you make reference to) in his diary.

A  Faraday box is only intended to deflect and insulate against E-fields at
very low levels.  I'm sure that all of the computers that the HERF gun was
demonstrated on in the ZDnet article were lined with Faraday cages. Some
sensitive avionics equipment on commercial aircraft cannot be outfitted with
these and still do what they were designed to do, and that's why you can't
operate some electronics equipment on aircraft during takeoff and landing.

To my knowledge, this device would not be an effective deterrent to
something as powerful as a an EMF/EMP at the levels described in the HERF
gun article (or worse yet, a nuclear bomb blast for that matter). A really
thick wall of lead and/or dense stone material would be the best shield
against something of that magnitude. There's a reason why NORAD is inside a
mountain, and even then, it's probably not impervious.

I can't see too many wearable users toting around enough lead or rock to
shield their devices though.

Tim

Tim M. King, Human Factors Engineer
Usability Engineering Services, A-3 02E30
Delta Technology - a Delta Air Lines subsidiary
voice: 404.773.8903     fax: 404.773.8865

-----Original Message-----
From: Robin Burgener [mailto:]
Sent: Monday, September 13, 1999 2:02 PM
To: wear hard
Subject: [Fwd: Re: Implications for wearables]

Claudius Li wrote:
> 
> On Mon, 13 Sep 1999, Thomas Geer wrote:
> 
> > Hmmn,
> > I remember, possibly incorrectly, that a f-cage will protect you from
> > standard EM interference, but not from an emp. The analogy was on the
> > order of stopping ordinary vs laser light source. I think
> > that lead and or stell shielding must be used to stop the pulse from
> > either a nuke or an emp gun. I guess it al depends on the strenght of
the
> > pulse.
> >
> I'm not sure either but I think an f-cage will work fine if it conducts
> well enough.
> 
> > I don't think you are allowed to protect your electronics from emp's.
The
> > standard FCC warning on all pocket electronics should make that clear.
YOu
> > know the one, reads something like this device must accept all
> > interference wether destructive or not. You can find it on all pocket
> > phones, calculators etc. I think that basically means that if the "fit
> > hits the shan" so to speak that FEMA or whomever will simple pulse our
> > sorry asses into pre pda bliss.
> >
> > #endrant
> > thom
> True, but I don't think there are any laws against shielding my house. If
> my electronics happen to be in that house...
> After all, elevators, tunnels, and some car bodies act as pretty good
> f-cages but it's not illegal for me to have my electronics while I'm in
> one of those.
> 

The FCC warning on electronics is informative only, you are still
allowed to add protection to electronics devices.  If milk had a warning
that it might spoil if left un-refrigerated, would you still put it in
the fridge?

As for Farraday cages (I don't know how to spell it either), you might
be better-off with copper screening.  The small holes don't matter and
you would still get natural light into your house.  The most important
thing about a f-cage is that it must completly enclose the protected
area.  Any hole or crack larger then a few millimeters will cause
leakage.  And grounding, although unnecessary, does help.  To protect
yourself from something as powerful as a EMP, all you need to do is use
better conductors, such as screen made from 14 gauge solid gold wire.

-- 
  Robin Burgener / Linux Kernel Group / COREL Corporation
  mailto:        
  web: http://207.236.3.210
  20Q: http://come.to/20q or http://207.236.3.210/avm.html

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