Why Can’t Chipless RFID Tags Convey a Serial Number?

A chipless RFID tag can convey a serial number, though it does not usually use conductive inks or polymers. Instead, such tags use RF-resonant materials in the inks. So, for instance, if you have 20 types of resonant materials, and you label each one with a number from 1 to 20, you can create serial numbers. If a reader emits RF energy and gets a signal back from materials 1,3, 5, 7 and 9, you can use software to convert that to serial number 13579.

The limitation is the number of resonant materials that can accurately be detected. If there is only a limited number than you can detect, and I'm told there is, then you can only create a small number of unique IDs. With a 256-bit number stored on a microchip, however, you can create a sufficient number of unique IDs to have one for every manufactured item on the planet.