RFID transponder are available in varios form factors and sizes. Transponders that are used for animal identification and will be implanted under the animals skin can be as small as the diameter of reservoir. Transponders, that will be applied to trees have the shape of a srew. For an access control system a contacless smart card is used. The devices made of hard plastic fiber that we often find in departement stores for electronic article surveillance are RFID transponder as well.

Definition of a RFID transponder

Transponder ("tags") are in lowest topology of the RFID system. The word "transponder" is a newly created word and combines "transmitter" (device that is sending out a signal) and the word "responder" (the receiver). The word transponder is a collective term for a data carrier with antenna and memory, that is contactless readable and writable by an air interface.