Ground Temperature Difference Driven Sensor for Environmental Monitoring

Abstract

In this paper, we present a novel approach to the realization of a battery-free soil profile probe that uses the temperature difference between the near-surface air and the underground soil as a power source. The temperature change in the underground soil is slower than that in the near-surface air, and thus a large temperature difference occurs between the near-surface air and the underground soil for most of the day. Hence, we developed a sensor prototype driven by a thermoelectric generator (TEG) that directly converts this temperature difference into electricity. The results of an experimental implementation of the prototype proved that when the difference in temperature between the near-surface air and the underground soil is only 3 °C, which is much lower than the average temperature difference in an actual field, the measured output power is about 80 μW. Because the typical sensing interval of a soil profile probe is 1 h, the average power consumption (e.g., for a Texas Instruments CC2650) is about 5 μW, which is much lower than the expected amount of harvested energy.