Re: Looking for thin, metal tape for shielding

["Michael Pender" <mpender@hotmail.com>]

Tony 'Nicoya' Mantler <nicoya@apia.dhs.org> wrote in message
nicoya-67D955.15253109072003@shawnews.wp.shawcable.net">news:nicoya-67D955.15253109072003@shawnews.wp.shawcable.net...
>
> 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.:

                    metal tape layer
---------------------------------------------
  capacitive coupling through adheisive layer
---------------------------------------------
                 metal shielding layer

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.

And of course there are also the safety issues created (read: huge electric
shock hazard) from using a high voltage electric field to capacitively
charge a piece of ungrounded metal...

- Mike