Passive RFID couplets as wireless interface for sensor applications

RFID tags are renowned for their versatility and low cost. In recent years, applications making use of them are growing in number and maturity level, but still lack in combining both communication and sensing optimal performance. The present work shows how to use a two-port RFID grid (e.g. a couplet of electromagnetically coupled RFID tags) as a general transducer of sensor information, able to transform a variation of the impedance of a load to which it is connected into a remotely-readable phase variation: in such a way, the tags are effectively turned into a wireless interface for the variable load sensor and are moreover able to provide constant antenna matching and hence stable read range.