I'd like to detect my cat at different locations, but I don't want the cat to walk through a tunnel like the sureflap products, which I have both the RFID-reading feeder and door.

If I make a say 30cm or larger coil and put it under a floormat, will it be able to read the cat walking over it?

  • \$\begingroup\$ Try it and see. \$\endgroup\$
    – Andy aka
    Commented Feb 8, 2018 at 11:10
  • 1
    \$\begingroup\$ Getting the equipment and winding a coil that big seems a waste of time and money if somebody can just say "Been there, done that, can't be done" \$\endgroup\$
    – Lenne
    Commented Feb 8, 2018 at 12:13
  • 1
    \$\begingroup\$ Well of course it can be done but there is no clue in the question about what you would consider to implement this or, are you looking for a website that is a free design service? \$\endgroup\$
    – Andy aka
    Commented Feb 8, 2018 at 12:19
  • \$\begingroup\$ Similar questions exist such as : electronics.stackexchange.com/questions/99135/… \$\endgroup\$
    – Solar Mike
    Commented Feb 8, 2018 at 12:57

1 Answer 1


Building up a NFC or RFID antenna is not that simple. But, for a rule of thumb, the diameter of the antenna is the average reading distance.

To understand the challenges of building an antenna you need to know how it works.

The antenna of the reader and the tag are a composition of coils which results in a complex RLC circuit. That circuits parameter depends on various of things like:

  • Shape of the antenna
  • number of windings
  • shape of windings
  • pcb
  • reader ic's parameters
  • etc...

The antenna then needs to be tuned to have it resonance on the carrier. For example: 13.56 Mhz. The quality of that RLC oscillating circuit must fit for the used modulation type. i.e. am or whatever is used.

I don't want to dive to deep into that, rather give you an idea of what is required for that rfid application.

Some reader-ic's are able to tune the antenna. If such a reader is used, it may help you with simple try-on-error approach.


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