RF Coils Characterization in Soil for Wireless Soil Sensing Applications

This paper presents the characterization results of RF coils in loamy soil with a goal to develop low-cost, long-life, wireless, in-situ sensing technologies for monitoring soil health to ensure future sustainable agriculture. Two types of RF coil exhibiting 6 cm-Φ / 9-turn and 12 cm-Φ / 9-turn are employed for the study. The characterization results reveal that coils maximum quality factor takes place around 1 MHz limited by the loamy soil loss. A small gap on the order of 1-2 cm between a coil and surrounding soil can help improve the quality factor significantly. Wireless power transfer efficiency estimation reveals that a sufficient amount of power can be transferred across a soil depth of 30 cm to energize an underground wireless soil sensing network. Further optimized designs are expected to achieve an enhanced performance and extended power transfer distance underground.