A novel carbon nanotube loaded passive UHF RFID sensor tag with built-in reference for wireless gas sensing

This paper presents a novel architecture of inkjet-printed passive UHF RFID based sensor tag for wireless gas (CO2) sensing. An RFID tag made with Silver (Ag) ink is loaded with carbon nanotube (CNT) ink for sensing purpose. A switch in its structure provides two modes of operation, sensor on (SON) mode and sensor off (SOFF) mode. In SON mode, the sensor tag modifies its backscatter properties in the presence of gas. In SOFF mode, the realized gain of the sensor tag remains constant, which provides a reference measurement. The difference in threshold power between SON mode and SOFF mode is used as the sensing parameter. Fabricated sensor tags, when exposed to CO2, show a threshold power variation of up to 2dB, with a read range of about 4m at 915MHz.