Flexible Graphene Textile Temperature Sensing RFID Coils Based on Spray Printing

Radio frequency identification (RFID) is a well-established technology utilized in inventory management, security, logistics, product marketing as well as next generation smart flexible sensor platforms. This work reports the development of printed, wearable graphene temperature sensor on flexible textile substrates with structural configuration of RFID coil. Patterning of graphene in the form of sensing RFID coils on textile surfaces was achieved with cost-effective and scalable spray printing of graphene oxide and sequential reduction to reduced graphene oxide. Graphene RFID coil operating at 13.56 MHz with temperature sensing capability, are printed on flexible, ordinary fabrics to enable wearable and flexible electronics applications. The demonstration of reduced graphene oxide on textile as temperature sensitive layer is the distinct feature of this work. Good sensitivity of 0.0125 degrees C-1 is achieved with linear response in the range of 25 degrees C to 45 degrees C and similar to 12 % decrease in resistance was observed over the measured temperature span. Induced voltage of 100 mV peak-to-peak at an area of 30.25 cm(-2) is measured. RFID performance of the sensor coil under different bending radii starting from fully flat (0 degrees) to complete bending (90 degrees) was also studied, showing that sensor coil performs well during flat operation (100 mV) and stays above noise floor even under fully bended condition (12 mV). Finally, flexible temperature sensing RFID antenna attached to human body to investigate performance for wearable applications, indicating that the sensor can effectively monitor temperatures in the range of 25 degrees C to 45 degrees C.