Printed passive UHF RFID tags as wearable strain sensors

Strain measurements could be utilized in monitoring human bodily functions and movements. Cost effective and low maintenance wearable sensors are needed in this field. The goal of this paper was to produce wearable strain sensors based on UHF RFID technology and the behavior of the materials which were utilized in prototypes. Two tag geometries were compared. Polymer thick film silver ink was used as the conductive medium. The tags were fabricated by screen printing the ink on stretchable PVC and on fabric substrates. Performance of the tags and the effect of mechanical straining on tag functioning was examined. The prototypes tolerated large strain levels. The results showed that the behavior of the UHF RFID tag strain sensor is dependent on the material behavior under strain as well as the tag antenna geometry. These offer various possibilities in strain measuring.