THEORY OF ZERO-POWER RFID SENSORS BASED ON HARMONIC GENERATION AND ORTHOGONALLY POLARIZED ANTENNAS

In this paper a novel approach is proposed to solve the issue of the absolute accuracy required by the most of passive chip-less RFID sensors. To this purpose the sensor information is encoded as the phase difference between two signals, one of the two acting as the reference signal for the other one. First the tag receives a carrier at frequency f0, then two equal signals at frequency 2 f0 are generated by means of a diode-based frequency doubler and a power divider. At this point one of the two signals is phase-shifted using a passive sensing element. Finally the 2 f0 signals are re-irradiated by exploiting two orthogonally polarized antennas. With this approach the sensor information can be extracted by a suitable reader equipped with two complex (I/Q) receivers. The idea will be first developed from a theoretical basis and then verified with several particular cases. The novel tag concept is compatible with paper substrate and ink-jet printing technology since antennas diodes and passive sensing elements, i.e. all the main tag components, are going to be developed on paper materials.