physical remarks (Was: Looking for thin, metal tape for shielding)

[Achim Hensel <achim.hensel@ruhr-uni-bochum.de>]

Hai, Folks..

>>> I had to take apart my SGI 1600SW flatscreen monitor to clean it out
>

This is a flatscreen; no huge voltages, no electrobeams. 

>> I would think that even if the adhesive isn't conductive, the
>> capacitive coupling to the grounded parts of the shielding that the
>> tape would partially cover should be enough to handle most EMI
>> concerns.
 
> I think the *opposite* is true because you would essentially form a
> huge metal-oxide-metal (MOM) transistor, i.e.:
 
This will work as a transistor, This is just a capacity. The
transistor would need an other/third contact to modify the electric
properties of the intermediate layer (I also do doubt if a 
metal-insulator-metal structure with that insulator matter and
thickness can fuction as a transistor). 

> The RF energy radiated from sweeping the electon beam would be pumped
> through the nonlinearity created by the tape "transistor" and
> re-radiated on multiple frequencies.  The effect is known as passive
> intermodulation or PIM.  Using non-conductive tape for EMI shielding
> is worse than leaving the hole.

Indeed a non-linear device (non-linear reaction to voltage) can
transduce a signal to different frequencies. But a capacity is, in this
regard, just a linear device. It might react different to various
frequencies, but it's reaction is proportional to the voltage (and
signal), so no other frequencies can be produced.
 
Tape with a conductive layer should seal the flatscreen to electronic
immissions and emissions. I really doubt, if high voltages are produced,
so that should be no problem.

If you really need connecting the metal tape layer to the metal base use
[well, I don't know the english word for it; in german it's
"Leitsilber". It's a conducting liquid which will dry and then form an
electric connection; maybe it's called "conduction silver paint" or "Colloidal
silver"]. 

	Cu,
		Achim