RF Energy Harvesting Hybrid RFID Based Sensors for Smart Agriculture Applications

Aiming to blend the advantages of passive and active RFID tags, this work presents the operation of a battery-free hybrid RFID tag possessing autonomous capability in temperature sensing for agricultural applications. Through the integration of a 915 MHz meander dipole antenna and a three-stage Dickson charge pump for energy harvesting with an onboard capacitor, sufficient power from reader interrogation can be rectified and stored to drive independent operations from an on-board microcontroller without continuous reader input. This opens the possibility for the inclusion of advanced features ranging from periodic sampling of sensor data to the possession of initiative to independently communicate data to nearby readers or humans by means of integrated oscillators or visual indicators when necessary. For a prototype demonstration, the batteryless hybrid tag of this paper includes a temperature sensor for periodic sampling and a seven-segment electrochromic e-paper digit display to visually indicate readings. In testing, the tag demonstrated a charge range up to 0.93 m from a Vivaldi antenna transmitting at 20 dBm and the maintenance of voltage from the onboard capacitor at a minimum of 2.5 V without further charging after reaching 2.8 V for a time range of 52.4 s to 420.9 s depending upon the actions required. Without the burden of limited device lifespan due to battery issues, the increased functionality of this hybrid RFID tag has the potential to widely expand the maximum limit of what RFID technology can offer the agricultural field in nearly all applications.