Application of metamaterial concepts to chipless-RFID

Chipless radiofrequency identification (chipless-RFID) has emerged as an alternative to RFID systems with tags equipped with chips. The main advantage of chipless-RFID over chipped-RFID is the lower cost of the tags, since the silicon integrated circuits (IC) of chipped tags are replaced with planar passive encoders in chipless tags. The main limitations of chipless-RFID tags are the data storage capability and tag size. In this paper, we propose an approach for the implementation of chipless-RFID systems, based on near-field coupling and sequential bit reading, which alleviates the previous limitations. The tags are implemented by chains of split ring resonators (SRRs) printed on a substrate (including plastic and paper substrates), and the logic state '1' or '0' is dictated by the presence or absence of these resonant elements at predefined positions (alternatively, programmable tags can be implemented by detuning certain resonant elements). Tag reading is achieved by means of a transmission line fed by a harmonic signal conveniently tuned, so that such signal is amplitude modulated by tag motion above the line (in proximity to it) due to inductive coupling. Such chipless-RFID system is especially suited for security and authentication applications, by directly printing the planar passive encoders on the items of interest (e.g., corporate and official documents, ballots, exams, etc.). It is demonstrated that the number of achievable bits is only limited by tag size; therefore, the proposed system is compatible with chipped-RFID system in terms of data capacity.