Meaning
Signal loss phenomenon that reduces the effective range of radio waves when they travel through soil, rock, clay and moisture instead of open air. Successful implementation of water meters or ground sensors requires accounting for subterranean rf attenuation when planning a wireless connection. The density and composition of the earth significantly reduce the signal strength available for a gateway receiver.
Soil Conductivity
High salt or mineral content in the ground increases the absorption of radio energy. Because subterranean rf attenuation depends on the electrical properties of the medium, a sensor buried in wet clay will have a much shorter range than one in dry sand. Moisture levels are the most volatile factor, as rain can suddenly degrade a previously stable link.
Antenna Tuning
Proximity to the earth changes the resonant frequency of the radiating element. To combat subterranean rf attenuation, the antenna must be specifically tuned for the dielectric constant of the surrounding material. A standard antenna designed for free space will perform poorly when placed underground due to impedance mismatch.
Range Limitation
Depth is the most critical variable in determining the success of a wireless transmission. As the distance between the device and the surface increases, subterranean rf attenuation rises exponentially. Most systems operating at sub-ghz frequencies are limited to a few meters of depth before the signal becomes unrecoverable.
Specialized low frequency protocols or high power transmitters are required for deeper applications. The placement of the surface receiver is also adjusted to minimize the total path through the soil. Strategic positioning can often recover several decibels of signal strength that would otherwise be lost to the earth.
