Development of a low cost printable chipless RFID humidity sensor

A novel low-cost chipless radio frequency identification tag sensor is presented. The tag sensor provides identification data as well as monitors relative humidity (RH) of tagged objects. The tag sensor is made of passive microwave circuit that uses humidity sensitive polymer material for RH sensing. The aim of this paper is to investigate RF sensing properties of moisture absorbing polymer polyvinyl alcohol at microwave frequency. In addition, frequency shifting technique is used to encode data bits for high data capacity. The overall size of the proposed tag sensor is 15 mm ×6.8 mm and has 6 bit data capacity for ID generation and single bit for humidity sensing. Results presented here show ∼607 MHz frequency deviation for 50% RH increase. The tag sensor has potential to be printed on flexible laminates such as plastic and paper for ultra-low cost item level tagging and ubiquitous sensing.