A low-cost passive wireless capacitive sensing tag based on split-ring resonator

Wireless sensors technology have provided industry with an efficient tool for precise monitoring and automation control of any particular quantity. In situations in which many sensors need to be deployed, a low-cost solution plays a decisive role. Passive chipless sensing tags have been recently proposed in order to reduce the cost of the sensors significantly in comparison with traditional RFID tags. In this paper we propose a wireless capacitive sensing tag that works on the UHF RFID band based on a small antenna loaded with a metamaterial in a single-layer design. The proof-of-concept was shown with two implemented prototypes, one on FR4 and the other on paper substrates. Both prototypes were easily adapted to work as humidity sensors. Simulations and measurements results showed the suitability of the tags for low-cost sensing applications.