Johnwasser: could I create some kind of iteration to check multiple antenas, for example? Or the time needed to create the current on the coil, needed to create the magnetical field allowing to power up the card's rfid chip would be so long it wouldn't really work?
Chagrin: not really sure if I understood what kind of contacts you mean. The different resistance per piece idea is interesting, but maybe since its something that people are supposed to handle that will have an interference on it?