A Prototype RFID Humidity Sensor for Built Environment Monitoring

This paper presents a prototype RFID humidity sensor capable of passive wireless sensing through far-field backscatter coupling. A commercial UHF RFID tag is employed as a sensing platform to receive the power and to reflect the sensed data back to the RFID reader. A humidity sensitive polyimide film is incorporated onto the top surface of the RFID tag for humidity sensing. The prototype sensor demonstrated that power required to activate the sensor tag is a linear function of relative humidity and the maximum sensing distance between the reader antenna and the RFID humidity sensor tag reaches to about 1.5 m. Due to its unique features of low cost, battery-less wireless operation, maintenances-free, and disposable, the RFID humidity sensor can be integrated into wallpaper for humidity monitoring in a built environment.