Characterization of UHF RFID Sensor Tags with Electromagnetically Coupled Passive Sensors

Abstract:
The standard UHF RFID system can be used to convey additional sensor data by means of attaching a coupling loop with an embedded sensor on top of a tag antenna. The sensor is electromagnetically (EM) coupled to the UHF RFID tag in order to modulate the properties of the tag antenna. This paper presents an investigation of the key factors affecting the performance of the EM coupled RFID sensor tags. Equivalent circuit models for the EM coupled sensor tags with two typical types of antenna structures are also proposed. The results calculated from the models show a close match with the corresponding full-wave simulations. The presented models can thus be used for analyzing and predicting the behavior of electromagnetically coupled sensor tags.