Re: Mirror as ground plane

On 27/11/2024 16:41, Joe Gwinn wrote:

On Wed, 27 Nov 2024 14:24:20 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

legg <legg@nospam.magma.ca> wrote:

>
Anyone had experience using metalization on glass (mirror)
as a ground plane or shield?
>
Any data on conductivity etc?
>
RL
>

>
The best quality second-surface mirrors are coated with silver, followed by
copper plating and a coat of paint.  Those should be pretty good if you can
get wires on them.

 A classic way to connect to such things is conductive silver epoxy,
probably to silver-plated copper wire.  Not tin-plated for long-term
use.
 .<https://www.masterbond.com/properties/silver-filled-electrically-conductive-adhesives>
 As for shielding effectiveness, the key question is the resistance of
a square of the coating, connected only on opposite parallel sides.
 

Poorer ones have aluminum coatings around 2-3 nm thick and no plating.

 Probably won't work, between high square resistance and oxide layer
preventing reliable connection.
 Though people do use metallized Mylar film, with a long bare tinned
copper ground wire in direct contact with the aluminum side, and in a
cable this does work.
 Joe Gwinn

At high enough frequencies there is no need for direct connection.
Adhesive copper tape stuck to the varnish film on the back of an
ordinary mirror may provide enough capacitive coupling to make a
good connection.  It all depends on the proposed application, which
we don't know.
John