RADIO-FREQUENCY-IDENTIFICATION (RFID) SYSTEMS have long proven their worth in business and manufacturing for tracking and managing inventory. Typically, an RFID system consists of a reader or interrogator and a tag, the latter of which is often based on an integrated circuit. Of course, it is also possible to fabricate RFID tags without the integrated- circuit (IC) chip. Australian researchers Stevan Preradovic, Sushim M. Roy, and Memai C. Karmakar from Monash University in Victoria, describe a chipless RFID system using tags fabricated on 90-m TF290 laminate material with 35-m copper cladding from Taconic. The laminate has a dielectric constant of 2.45 in the z-direction at 10 GHz. The 23-b tag was designed on coplanar waveguide, making it a single-ended circuit. The design has the potential for as much as 60 b resolution.
The chipless tag consists of two cross-polarized ultrawideband (UWB) antennas and a multi-resonating zigzag circuit. Data encoding is performed in the multi-resonating circuit, which is comprised of multiple stop-band spiral resonators. The chipless tag encodes data into the spectral signature in both magnitude and phase, operating within the portion of the UWB frequency range from 5.0 to 10.7 GHz. By operating in the UWB frequency range, the power level of the reader is constrained to comply with the standard, to a maximum transmitted effective isotropic radiated power (EIRP) of -45 dBm outdoors and -55 dBm indoors. These low power levels do not hinder proper operation, however.
This design encodes data in both amplitude and phase and is not based on the variation of radar cross section (RCS) of the tag's antenna. The RFID tag retransmits the reader's interrogation signal with the encoded spectral identification code using the multi-resonator as the modulation device. See "RFID System Based on Fully Printable Chipless Tag for Paper-/Plastic-Item Tagging," IEEE Antennas and Propagation Magazine, Vol. 53, No. 5, October 2011, p. 15.