Measure your finger or ring that fits well to determine what size to go for-- then seek out RFID tags with a coil close to this same diameter.
You can also take a bigger tag like the business card-size one pictured above, and dissolve away the plastic with acetone (cover with plastic and a rubber band and keep in a well-ventilated space until the antenna and chip can be easily removed).
Test your tag periodically to be sure it still scans (here we're using the NFC Tools app).
If using a larger tag, you will need to rewind the antenna coil to fit your finger. Be careful not to scratch or break the thin enameled antenna wire!
We modeled up two 3D printable rings with channels for the antenna coil, should you have a 3D printer handy. Adjust the size to match your finger and tuck the wire and chip into the interior groove on the ring. Test that it still scans! We broke a few tags before we got one to work.
Last updated on 2015-05-04 at 04.27.44 PM
Published on 2014-05-14 at 05.59.59 PM
The most straightforward way to make an NFC ring is to glue a tag to an adjustable ring base (with E6000 craft adhesive, of course). The black tag pictured came out of our MiFare bracelet (we just cut it open and removed the tag disc).