Design and implementation of high data capacity RFID tag using eight-phase encoding

Abstract

Enhancing the data capacity of surface acoustic wave (SAW) radio frequency identification (RFID) tags using the combination of time position and phase encoding with fewer number of reflectors is investigated in this work. Simulation and fabrication of SAW RFID tags are performed using COMSOL Multiphysics and standard photolithography process. Lithium Tantalite (LiTaO3) is used as a substrate and Aluminium metal electrodes are used to realise the interdigital transducer (IDT) electrodes. The data capacity enhancement is tested using a SAW RFID tag consisting of a single-phase unidirectional transducer (SPUDT) transducer and four code reflectors. By designing the width of SPUDT electrodes and floating electrodes and proper positioning of reflectors, eight phases (i.e. 0°, −45°, −90°, −135°, −180°, −225°, −270° and −315°) are detected which correspond to 3 bits of data per reflector. These eight phases would result to have one more data bit per reflector. Therefore, eight phase states along with four time positions lead to 32 different states (i.e. 5 bits of data per reflector). To facilitate the realisation of our idea, the fabrication process has been performed at 250 MHz; however, it can easily be implemented at higher frequencies (i.e. GHz range).