Soil Effects on the Underground-to-Aboveground Communication Link in Ultrawideband Wireless Underground Sensor Networks

Wireless underground sensor networks (WUSNs) is an emerging area of research. They are used in many applications from intelligent irrigation to security and assisted navigation. WUSNs mainly use narrowband systems working in the frequency range below 1 GHz and, therefore, suffer from a poor localization capability and large-sized antennas. The use of impulse radio ultrawideband (UWB) technique allows alleviating these drawbacks. In this letter, the impact of soil on UWB underground-to-aboveground communication link is studied experimentally. More specifically, the effects of the orientation of the buried antenna and burial depth and soil moisture are investigated. The experimental results show that, at 7 GHz, additional attenuations of 10, 34, and 40 dB are noted for depointing the underground antenna by 90°, increasing the depth from 0 to 30 cm and raising the soil moisture from 0% to 20%, respectively. Burial depth lower than 30 cm or soil moisture lower than 20% allow getting acceptable received signal strength (superior to -100 dBm) for communication and localization, particularly in the UWB low band (3.1-5 GHz). The obtained results bring out the feasibility of UWB WUSN.