Summary of USING LORA NODES AS SOIL MOISTURE SENSING ANTENNAS
This article describes a 2022 Sensors paper by Maja Škiljo et al. showing that buried LoRa nodes can act as soil moisture sensors by measuring radio-signal attenuation. An Arduino Pro Mini (ATmega328P) with an RFM95W (SX1276) LoRa module was buried ~14 cm deep; gateway-measured parameters like RSSI and SNR correlated with soil moisture. Experiments found a narrowband printed PCB antenna best for sensing. Powering deployed nodes long-term remains an open practical consideration.
Parts used in the LoRa soil moisture sensing project:
- Arduino Pro Mini (ATmega328P-based)
- RFM95W LoRa module (SX1276-based)
- Spring antenna (used initially)
- Narrowband printed PCB antenna (recommended)
- LoRa gateways to receive RSSI and SNR
- Battery (for node power)
- Burial enclosure or casing for underground deployment
Although we generally think of Internet of Things (IoT) and similar devices as things that are scattered around above ground, there are plenty of reasons to also have such devices underground. These so-called IoUT devices are extremely useful when it comes to monitoring underground structures, but communication via radiowaves is obviously impacted when soil is in the way. Although there are ways to get around this, a 2022 paper by Maja Škiljo and colleagues in Sensors covers an interesting way to make use of this signal attenuation property of changing moisture levels in soil.
By quantifying the exact attenuation of the signal received at the gateways, they were able to determine the soil moisture levels around the LoRa node which had been buried at a depth of approximately 14 centimeters. This LoRa node used off-the-shelf components consisting of an ATmega328P-based Arduino Pro Mini and SX1276-based RFM95W LoRa module with a spring antenna.
During experimentation in- and outdoors it was determined that a narrowband, printed (PCB) antenna was optimal for soil moisture sensing purposes. Other than the interesting question of how to keep soil moisture sensing nodes like this powered up over long periods of time (perhaps periodic retrieval to replenish the battery), this would seem to be a very interesting way to monitor the soil moisture levels in something like a field, where each node can provide its own ID and the received signal providing the relevant data in the form of the SNR and other parameters recorded by the gateway.
(Heading image: The measurement results of: (a) RSSI in dBm collected from gateway 2 and (b) soil moisture during the winter period. (Credit: Maja Škiljo et al., 2022) )
Source: USING LORA NODES AS SOIL MOISTURE SENSING ANTENNAS
- What components comprised the buried LoRa node?
The article states the node used an ATmega328P-based Arduino Pro Mini and an SX1276-based RFM95W LoRa module with a spring antenna. - At what depth was the LoRa node buried for the experiments?
The LoRa node was buried at approximately 14 centimeters depth. - How was soil moisture detected using the LoRa setup?
Soil moisture was inferred by quantifying attenuation of the signal received at gateways, using parameters like RSSI and SNR. - Which antenna type was found optimal for soil moisture sensing?
Experiments determined a narrowband printed PCB antenna was optimal for soil moisture sensing purposes. - Were experiments conducted in both indoor and outdoor settings?
Yes, experimentation was conducted in- and outdoors according to the article. - Does the article address long-term powering of buried nodes?
The article notes powering nodes long-term is an open practical consideration, suggesting periodic retrieval to replenish the battery as a possibility. - What gateway measurements provided the relevant data?
The gateways recorded received signal parameters such as RSSI and SNR which correlated with soil moisture.
