Hi Peter:

The way I read the article the coin shown was one used for hiding micro 
dots and they were saying the tracking coin was similar.  The link to 
the U.S. coin web page is broken.

If the actual coin was physically large there would be less chance of it 
getting used in some machine.  And if it was a Canadian coin then it 
would be less likely to be spent in the U.S.

One approach would be some type of anti shoplifting tag.  That way the 
coin could be made from a non magnetic metal with the tag inside.  Just 
a guess.  The subject would need to pass through what amounts to a 
"gate" like at store exits, but this could be hidden in a door frame for 
this application rather than being out in the open in the case of 
discouraging people from shoplifting.   The operational parameters of 
the tag could be made different from the common tags so that it would 
mark the subject as a shoplifter when he was leaving a store.

Another approach might be some type of RFID tag.  These are powered by 
an external LF signal picked up in a coil.  The response is a UHF 
signal.  By splitting the coin into two or more electrically isolated 
parts it might act as an antenna for the UHF signal.  A coil could be 
placed just inside the diameter.

Have Fun,

Brooke Clarke

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