Performance Analysis of Antenna-Based Soil Sensing

This work deals with the soil moisture estimation based on received signal strength using low-power LoRa-based soil moisture sensing device. The proposed antenna design is a type of printed inverted F antenna and tuned with a capacitor in the loamy ground with varying properties. The electric field simulation results are given to depict its distribution above the ground with varying moisture content, and the measurements results give the comparison between the proposed printed antenna and the helical LoRA antenna. In the laboratory measurements, it is shown that a difference of approximately 13 dB between the dry and the highest moisture level (40 %) can be achieved in simulations, whereas in measurements, where the signal strength difference is measured from 10 % to 50 %, the difference is 6-7 dB. The proposed antenna tuned in an actual and very lossy soil, achieves very wide bandwidth and consequently less sensitivity to the soil moisture variation. Still it achieves somewhat better results of soil moisture estimation in relation to the conventional helical LoRa antenna. Generally, the results imply that this approach can be most effective in summer period, when smart irrigation is crucial due to droughts, sudden downfalls and the necessity of water consumption management.