In this paper, a miniaturized Ultra High Frequency Radio Frequency Identification (UHF-RFID) tag-based sensor antenna using a magneto- dielectric substrate (MDS) for wireless identification and sensor applications is presented. Two models of RFID tag-based sensors are designed, fabricated and measured. The first model uses two RFID tags; both of the tags are incorporated with two RFID chips. A passive sensor is also integrated in one of the proposed tags to serve as a sensor node, while the other tag is used as a reference node. Based on the difference in the minimum power required to activate the reference and sensor nodes, the sensed data (temperature or humidity) can be determined. The magneto-dielectric substrate layer is placed underneath the patch antenna to reduce the size of the proposed sensor by about 75% compared to a conventional RFID tag-based sensor. The magneto-dielectric layer is thin enough to embed in the planer circuit. To reduce the size of the proposed sensor, a multi-port tag for including the reference and sensor node in one antenna is also presented. The proposed RFID tag-based sensors have several features such as small size, they are completely capable for two objectives at the same time and easy to integrate with a planer circuit.
A planar wideband microstrip patch antenna for UHF RFID tag