Near-Field Chipless-RFID System with High Data Capacity for Security and Authentication Applications

© 1963-2012 IEEE. A high data capacity chipless radio frequency identification (chipless-RFID) system, useful for security and authentication applications, is presented in this paper. Reading is based on the near-field coupling between the tag, a chain of identical split-ring resonators (SRRs) printed on a (typically flexible) dielectric substrate (e.g., liquid crystal polymer, plastic, and paper), and the reader. Encoding is achieved by the presence or absence of SRRs at predefined (equidistant) positions in the chain, and tag identification (ID) is based on sequential bit reading. Namely, the tag must be longitudinally displaced, at short distance, over the reader, a microstrip line loaded with an SRR and fed by a harmonic signal. By this means, the harmonic signal is amplitude modulated, and the (ID) code is contained in the envelope function, which can be obtained by means of an envelope detector. With this system, tag reading requires proximity with the reader, but this is not an issue in many applications within the domain of security and authentication (e.g., secure paper for corporate documents and certificates). Several circularly shaped 40-bit encoders (implemented in a commercial microwave substrate), and the corresponding reader, are designed and fabricated as proof-of-concept demonstrators. Strategies for programming the tags and a first proof-of-concept chipless-RFID tag fabricated on plastic substrate through inkjet printing are included in this paper.