Two Solutions of Soil Moisture Sensing with RFID for Landslide Monitoring

Two solutions for UHF RFID tags for soil moisture sensing were designed and are described

in this paper. In the first, two conventional tags (standard transponders) are employed: one, placed

close to the soil surface, is the sensor tag, while the other, separated from the soil, is the reference for

system calibration. By transmission power ramps, the tag’s turn-on power levels are measured and

correlated with soil condition (dry or wet). In the second solution, the SL900A chip, which supports

up to two external sensors and an internal temperature sensor, is used. An interdigital capacitive

sensor was connected to the transponder chip and used for soil moisture measurement. In a novel

design for an UHF RFID tag the sensor is placed below the soil surface, while the transponder and

antenna are above the soil to improve communication. Both solutions are evaluated practically and

results show the presence of water in soil can be remotely detected allowing for their application in

landslide monitoring.