A Compact UHF RFID Tag Antenna for Sub-soil Temperature Sensing in Precision Agriculture

This paper presents a unique compact passive UHF RFID tag that is capable of hosting a temperature sensor for wireless sub-soil measurements. In particular, a newly developed dipole antenna is matched to the complex conjugate of the temperature sensing passive RFID AMS SL900A IC at 900 MHz. A prototype tag is then buried 7.62 cm in the top soil of a field used for agricultural purposes and the read range is measured. It is shown that the sensor has a maximum measured read range of 0.5 m in the field and has a 50% reduction in overall size when compared to previously reported designs. Moreover, it was demonstrated that the prototype can transmit accurate temperature data of the soil. These measurements of the tag in the field demonstrate that the proposed low-profile UHF RFID tag can be used in other sub-soil applications to support precision agriculture.