ABSTRACT Surface acoustic wave (SAW) radio-frequency identification (RFID) tags are encoded according to partial reflections of an interrogation signal by short metal reflectors. The standard encryption method involves time position encoding that uses time delays of response signals. However, the data capacity of a SAW RFID tag can be significantly enhanced by extracting additional phase information from the tag responses.
In this work, we have designed, using FEM-BEM simulations, and fabricated, on 128°-LiNbO3, inline 2.44-GHz SAW RFID tag samples that combine time position and phase encoding. Each reflective echo has 4 possible time positions and a phase of 0°, -90°, -180°, or -270°. This corresponds to 16 different states, i.e., 4 bits of data, per code reflector. In addition to the enhanced data capacity, our samples also exhibit a low loss level of -38 dB for code reflections.
Digital Object Identifier 10.1109/TUFFC.2008.867
© 2008, by The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.