A new soil environment monitoring system based on RFID sensors and LoRa technology

RFID sensors and LoRa technology

Modern agriculture faces the significant challenge of increasing productivity against the backdrop of a continuously growing global population. However, existing agricultural technologies still lack efficiency and struggle to meet this demand. Real-time monitoring of the soil environment is considered a key factor in enhancing agricultural productivity, but the widely used Wireless Sensor Networks (WSN) have many limitations in the agricultural field. For example, sensors are often exposed on the ground, making them susceptible to external environmental interference, and most of these sensors rely on battery power, which becomes difficult to replace once buried in the soil. Additionally, discarded batteries may pollute the soil environment.

To address these issues, researchers have shown a strong interest in soil monitoring systems based on LoRa communication technology in recent years. Compared to traditional wireless communication technologies (such as ZigBee), LoRa technology offers a longer communication distance, longer node lifespan, and stronger anti-interference capabilities. However, the wireless transmitters of these LoRa sensors are still exposed to the air, which can hinder agricultural activities and be affected by environmental factors. In response to these challenges, this paper proposes a new soil environment monitoring system based on RFID sensors and LoRa technology. This system aims to overcome the shortcomings of existing technologies through low-cost, long-term precise monitoring, providing a more effective and sustainable solution for the agricultural field.

RFID sensors and LoRa technology

Methods

The core of the system consists of several parts, including RFID sensors embedded in the soil, patrol cars equipped with RFID reading and LoRa communication functions, a farm monitoring center, and a cloud platform (Figure 1). The RFID sensors are designed as high-precision environmental monitoring devices that can be buried in the soil to monitor key parameters such as soil temperature, humidity, and chloride ion concentration in real-time. Patrol cars play the role of data collection in the system. They provide energy to the sensors through built-in RFID transmitters and use receivers to obtain data signals sent by the sensors. The patrol car then transmits this data to the monitoring center through the LoRa module, achieving long-distance data communication.

RFID sensors and LoRa technology

To improve the efficiency of data transmission and reduce the system’s power consumption, the authors propose an innovative communication mechanism that no longer relies on traditional non-volatile memory (NVM) to store data but instead directly encodes the data measured by the sensors into the ID of the RFID tags (Figure 2).

This method significantly shortens the data reading time and reduces power consumption, making the system more suitable for long-term, large-scale monitoring tasks. In addition, since the number of RFID sensor tags in the system is relatively small, the authors introduced the Q algorithm based on the EPC Gen2 protocol in the design, combined with the Reader Collision Avoidance Arrangement (RCCAA) method, to effectively handle potential multi-tag communication collisions. Through these designs, the system successfully achieved low-power, high-precision, long-distance soil environment monitoring, with high practicality and application prospects.

The circuit design of the RFID sensor consists of energy management, communication, and digital parts (Figure 3). The energy management part collects energy through the antenna and uses a new type of boost rectifier to convert the collected RF energy into DC power to provide stable voltage for other parts of the sensor. The communication part uses antennas and RFID chips for wireless transmission and reception of signals. To optimize antenna design, the authors chose a smaller but higher-performance monopole antenna and used a microstrip impedance transformer for matching, thereby ensuring good communication performance while reducing antenna size.

Results

The authors verified the performance of the designed RFID sensor and its application in the soil environment monitoring system through a series of experiments. Figure 4 shows the field test environment. In the laboratory communication performance test, the results showed that the designed RFID sensor could communicate stably at a distance of 2 meters with a transmission power of 4 watts.

Compared to traditional data storage methods, the new method proposed by the authors significantly reduced data transmission time and power consumption. In field applications, the authors tested the maximum communication distance of the RFID sensor and its performance at different soil burial depths. The results showed that when the soil moisture was 5% and the sensor burial depth was 60 centimeters, the maximum communication distance could reach 1.3 meters; however, beyond this burial depth, the signal strength significantly decreased, and the communication error rate also increased.

In addition, the experiment also evaluated the impact of soil moisture on the communication performance of the RFID sensor. As soil moisture increased, signal strength gradually weakened, and the error rate also rose accordingly, especially when the moisture exceeded 30%, the sensor’s communication performance significantly declined (Figure 5).

To improve this issue, the authors proposed a multi-sensor layout scheme, effectively reducing the error rate by arranging two “T”-shaped RFID sensors at the same measurement point (Figure 6). Finally, the experiment explored the impact of patrol car speed on the communication success rate and coverage area of the RFID sensor. The results showed that when the patrol car speed was maintained at 33 kilometers per hour, the communication success rate could exceed 90%, and the coverage area reached 10 square kilometers, which is the optimal working state of the system.

Conclusion

The system, based on RFID sensors and LoRa technology, can achieve long-term, low-power monitoring of soil temperature, humidity, and chloride ion concentration. Experimental results show that the designed RFID sensor has an effective communication distance of 1.3 meters under the conditions of a burial depth of 60 centimeters and soil moisture less than 30%, with temperature and humidity measurement errors of 1.5% and 1.0%, respectively. The best effect is achieved when the patrol car speed is 33 kilometers per hour.