Magnetic Tattle Tape Security Strips? 1

[Hyteck]

Hi,

Does anyone have any info on Tattle tape security Strips and how they can be magnetized and demagnetized and in particular how one can "sense" whether one and more than one strip is placed within a specfic area?

The 3M tattle strips seem to have 5 sections which are magnetised - any particular reason for this? - what is the principle involved in their detection?

What sort of magnetic field intensity is requied to magnetize these strips?

thanks

 

[melone]

Forgive me for stating the obvious, but talk to 3M. They manufacture these devices, they should have a resonable understanding of the final application.

 

[Hyteck]

Melone, No technical info from 3m (a standard 3m practice) - they want you to buy their machines at enormous costs which is fair enough. The technology has been around for some 40 years or so but I can find no info! I dont want their machines but their tattle tapes are cheap and can be applied to other applications (they sell to library)

 

[melone]

They won't point you in the right direction to find this info????

 

[nbucska]

You can find a BUNCH of info at the Patent Office at
<

http://www.uspto.gov>

<nbucska@pcperipherals.com>

 

[itsmeRICK]

...and what would you use this information for?

 

[Hyteck]

To make a detector offcourse and go into competition with 3m! ... and maybe also to satisfy our curiosity???

 

[IRstuff]

You could try to find a cooperative business that will allow you to disassemble their equipment and/or take measurements.

TTFN

 

[Hyteck]

The magnetizing & de-magnetizing aspects are relatively straight-forward using standard techniques as I have tested this to some extent, but a &quot;reliable&quot; method for detecting the presence of the strips (in their demagnetized state) is a problem? I want to be able to detect the strips within a certain area very &quot;reliably&quot; and also need to detect if one and if more than one are within the same area? The magnetic material used seems to 'saturate very easily&quot; unlike most other magnetic materials I have tested!
thanks anyway!

 

[lytec]

lytec

hi,
thanks for the idea, we have the same study with 3M tattle tapes and its detection process

 

[Skogsgurra]

A system that I worked on more than ten years ago had a 1000 Hz exciter that made the soft magnetic strip (Vacon, not 3M) saturate.

When doing so, it emitted a weak magnetic field with lots of odd harmonics - which were picked up by a sense coil and analyzed to verify that frequency contents and phasing was right. If so, an alarm was sounded.

There were also lots of even harmonics and no one could understand why. A soft strip should only produce odd frequencies like 3000, 5000, 7000 and so on. Until we found out that the eart's magnetic field pushed the B of the strip away from zero so that even hermonics were produced.

The strip was deactivated by magnetizing a hard magnetic backing material. Doing so forced the soft strip into the saturated mode and the 1000 Hz field had no influence on it.

That is the general principle for that kind of EM labels. And it is knowledge in public domain. See also

http://electronics.howstuffworks.com/anti-shoplifting-device4.htm

for some pictures.

Gunnar Englund

http://www.gke.org

 

[Hyteck]

Thanks Gunnar,

Yes I can detect the tattle tapes OK, but my problem relates to the detection of whether there is onl;y one strip or multiple strips in the same area and at close proximity?

Any ideas ?
I was thinking of somehow detecting the interference pattern from multiple strips but since the emitted frequencies are identical and most likely in phase they would be difficult to detect ?