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Currently, researchers at the University of New Mexico (UNM) are developing a ZigBee-based wireless RFID sensing system to help scientists better understand the natural environment of caves and lava caves and potential changes in the earth’s climate. Researchers believe that this technology can be used not only in natural caves, but also in mines, and may even be used on other planets, such as Mars.
Environmental factors outside the cave can affect the condition of the underground. Changes in air pressure caused by weather fluctuations can form a breathing effect in the cave, because warm and cold air circulates. Scientists say that according to some underground conditions, many things on the earth have been understood by people, but currently those deep or inaccessible caves have hardly been monitored and explored. Monitoring instruments like this cave must not cause interference to the cave environment.
The research team initially considered using sensors in caves for ground research, including a fluctuation sensor (thermocouple to measure rapid fluctuations in temperature). In 2009, the research team (led by Anders Jorgensen, Associate Professor of Electronic Engineering at the University of New Mexico) began planning a system for use in the cave, in which a network of sensors can track fluctuations, temperature, air pressure, and humidity, and then report to The back-end system transmits data, and the information in it can be saved and analyzed.
In the second half of 2009, researchers developed a wireless system using 2.4 GHz RFID sensors to collect data about the state of the cave. The system built by the research team includes temperature, air pressure, humidity, and fluctuation sensors, but the air pressure information does not work, Jorgensen said, because the measuring instrument is not sensitive enough to the pressure changes the research team wants to measure. Each sensor is connected to an on-board processor with a battery-powered ZigBee transceiver from Freescale Semiconductor.
In the deployment in 2009, the graduate students in the team placed six sensors on the natural flat ground near the walls of Junction Cave, which is located at the El Malpais National Monument in New Mexico (located west of Albuquerque, away from Albuquerque. 90 minutes away). Some sensors are also placed at higher altitudes in the cave because the top of the cave is higher. Other sensors are placed in the middle or near the top of the cave. Researchers placed sensors in the first few hundred feet of the 1,000-foot-long cave, with a spacing of 30 feet to maintain an effective reading range.
The size of each sensor device (including the ZigBee transceiver) is approximately 2 inches by 3 inches. The deployed RFID technology solution includes the MC1321X evaluation kit from Freescale Semiconductor purchased by the University of New Mexico. Each sensor forms a ZigBee mesh network. In the network, the data is transmitted to the next sensor until the transmission reaches the center (a small computer running on the Linux system). This center is located 45 meters in the cave, at the sensor’s The center is equipped with RFID software developed by the research team to receive, compile and manage data. These sensors measure humidity, temperature and fluctuations, and transmit these measurement information and the unique ID number of the sensor device. The center’s software collects data, compiles the measurement results, and connects these results to the sensors in the cave and the location of the sensors.
After 24 hours, the data collected by the research team showed what happened in the first few hundred feet (the length of the system installation) in the cave. It rained heavily outside the night when the system was installed, but the inside of the cave was dry. The data showed that during the heavy rain, there was no change in the cave, but there were strong air fluctuations near the top of the cave on that rainy night, which seemed to be consistent with the time of rain. Jorgensen said that one surprising result is that the presence of people seems to affect the readings. For example, when there are researchers or visitors in the cave, the temperature will rise and fluctuate more. This type of data is important to scientists because the presence of people in caves may affect the ecosystem.
The research was conducted for 24 hours. Based on the research, the researchers found that the wireless sensor system can reliably collect and transmit data in the cave. The group also discussed the establishment of a system with a cellular connection so that data can be sent from the center to the back-end server in real time.
Jorgensen said that after this, the team developed a smaller and more effective system, using Texas Instruments’ eZ430-RF2480 starter kit, which may make ZigBee-based RFID tags smaller. The students found that the new system consumes less power than the previous system, and the cost per sensor node is only $25. The nodes have not been installed in any caves, because such a project will require additional investment. Researchers have discovered that the new, smaller nodes have a transmission distance of up to 150 feet. The running time of the new system is expected to exceed 80 days, collecting samples from 4 sensors every minute. The realization of the power-saving function benefits from the microcontroller’s ability to collect and transmit data from the sensor, and then enter the sleep mode, until the next acquisition is activated.
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