Modeling and Applications of a Chemical-Loaded UHF RFID Sensing Antenna With Tuning Capability

A key-issue of the wireless gas sensing by radio frequency identification is the capability to control the sensor's response while minimizing the amount of chemical interactive materials (CIM) required to dope the tag antenna. An open-circuit shielded slot-line layout is proposed as a general purpose tunable radio frequency identification (RFID) radiator, suitable to host small amounts of CIM. It operates both as a very efficient passive sensor and as a tool to estimate the electromagnetic equivalent parameters of the CIM during the gas exposure. A hybrid distributed-lumped model permits to separate the CIM's contribution from the antenna's response and, in addition, it provides a simple tool to shape the calibration curve relating RFID power signals to the physical changes of the environment. The tag layout and the method are applied to the UHF characterization of the conductive polymer Pedot:PSS and to the optimization of high-performance humidity sensor capable of a three-times higher sensitivity than those achieved by the current state of the art RFID devices.