Setup-Independent Phase-Based Sensing by UHF RFID

By processing the phase of the backscattered field from an RFID-UHF tag antenna, physical information can be derived about the change of the materials and boundary conditions around a sensor-less tag. The phase-based sensing however is strongly dependent on the specific set-up arrangement and huge artifacts would arise in successive independent measurements involving temporary (hand-held) readers at different distances. The paper introduces a multi-port tag arrangement suitable to achieve distance-independent measurements. The method exploits the use of sensitive and reference tags. Their phase responses are combined within a Double Phase Difference metric suitable for robust data-inversion. The method is demonstrated through an experiment with a displacement-sensing system.