Multiport UHF RFID-Tag Antenna for Enhanced Energy Harvesting of Self-Powered Wireless Sensors

This paper presents the design and experimental evaluation of a long-range solar powered sensor-enhanced radio frequency identification (RFID) tag. The tag antenna is a multiport microstrip patch with an overlay of thin-film solar cells for energy harvesting. A second port is allocated on the patch antenna for supplementary energy harvesting from the RF signal transmitted by the reader. An I^{2}C-RFID chip along with a microcontroller unit (MCU) and temperature and humidity sensor are incorporated into the tag design to implement a low-cost wireless sensor using a commercial RFID reader. The measurements of the fabricated RFID-tag sensor demonstrate that a maximum sensing/reading range of 27 m is achieved when all the circuits are powered using solar cells, while it is 7.48 m with only the secondary option of energy harvesting. The proposed sensor with dual energy harvesting achieves both a longer range and a lifetime compared with similar battery-powered sensor-enhanced RFID tags. The RFID sensor is also evaluated in a climate chamber and the sensor data (temperature/humidity) were remotely recorded with an excellent accuracy using a commercial ultra high frequency (UHF) RFID reader. In addition, the sensor can be programmed for the temperature/humidity surveillance of sensitive items, such as those found in various supply chain and transportation applications.