--- In magnetometer@yahoogroups.com, "sae140" <SAE140@...> wrote:
>
> Just came across something which I've not heard anyone comment on before, so
thought I'd pass this along ....
>
> I'm currently working with some library tags as a source of permalloy, and it
was while trying to identify the cause of some sensor imbalance, that I
discovered that these library tags are not uniform along their length.
>
> The tags I'm working with are 166mm long, and have 6 small 'pads' of (what
appears to be) permalloy spaced every 18mm or so. The 'pads' are 5mm long and
the same width as the strip, and are almost invisible to the eye at a casual
glance.
> They can be spotted either by carefully examining the side of the strip with a
magnifying glass, or by holding the strip itself up to the light at an angle so
that light reflects from the plastic's surface, and the pads can just be
identified by being slightly raised.
>

Quick update - I eventually found a method of recovering the permalloy strip
without causing physical damage to it. What I found works well is to remove the
plastic from either side of the strip, then form the remainder into a ring and
soak it for half an hour in the bottom of a jam-jar under a centimetre of
cellulose (lacquer) thinners. The adhesive eventually turns to a mushy goo and
the permalloy strip easily separates when the thinners is swirled around.
I've posted a graphic in the /photo-album subdirectory, in the 'security tags'
album.