Cross-polarized RCS Based Chipless RFID Tag for Wound Monitoring Through pH Sensing

This paper proposes a chipless RFID pH sensor tag for wound monitoring. The sensor tag is designed to operate in the industrial, scientific, and medical (ISM) frequency band. The working principle of the device is based on the resonance frequency shift in cross-polarized RCS. The tag consists of a thin metal patch layer with a slotted double-split ring in the middle which is placed on an FR4 substrate. The slotted ring was rotated 45 degrees to create the asymmetry to produce cross-polarized RCS. Chitosan is used as the pH sensing material in the proposed model. The design has shown good performance when placed on the stacked simulation model of skin, fat, and muscle layer. A frequency shift of 180 MHz was detected over the pH range of 4 to 7 with a sensitivity of 60 MHz per unit pH change. The size of the model is fairly small (28×28 mm
²
) for the ISM band. The proposed chipless model shows a great prospect in the field of wound monitoring as it can be easily manufactured and implemented.