Soil-Monitoring Sensor Powered by Temperature Difference between Air and Shallow Underground Soil

Abstract

Energy harvesting (EH) technologies are useful for the semi-permanent operation of wireless sensor networks, especially, for agricultural monitoring as the networks need to be installed in large areas where power supply is unavailable. In this paper, we propose a battery-free soil-monitoring sensor for agriculture, which leverages the temperature difference between near-surface air and shallow underground soil using a thermoelectric generator (TEG). The performance of systems driven by the TEG mainly depends on the average temperature between the hot and cold sides of the TEG (T) and the temperature difference across the TEG (∆T). If T is low and ∆T is small, it is challenging to earn enough power to drive wireless microcontroller unit; however, with our dedicated electric circuit, and thermal designs including impedance matching of thermal circuit and suppression of heat loss, the sensor can harvest more than a hundred microwatt on average from the temperature difference between the air and underground soil at a depth of 30 cm. The performance of the energy harvester is evaluated both by numerical analysis using temperature data collected from various farm fields and by a prototype implementation. Moreover, the prototype was deployed to farm fields in Japan and India. Our field experiment results revealed that the prototype could harvest 100 µW-370 µW on average, and drive a wireless microcontroller unit to perform soil monitoring. CCS Concepts: • Hardware → Renewable energy; Sensor applications and deployments; • Human-centered computing → Ubiquitous and mobile computing systems and tools.

Battery-less zero-maintenance embedded sensing at the mithræum of circus maximus

“…Although these efforts communicate invaluable lessons on specific techniques, they provide no evidence of a complete system design. Similarly, only a few of them concretely fulfills the requirements of real end users [20,45], unlike what we do here.…”

“…Fewer examples exist replacing rechargeable batteries with environment-friendly super-capacitors [20,34,46,55,70] or regular capacitors [45,73,[75][76][77] to buffer energy and smoothen harvesting fluctuations. Again, only a fraction of these works consider energy sources other than solar [55,73,75,77], let alone real-world deployments [20,45]. The longest such deployment uses microbial fuel cells to power nodes for water quality monitoring for three months [20].…”

“…Real-world deployments. Besides systems that use solar radiation as energy source, few examples exist of long-term deployments demonstrating energy-harvesting zero-maintenance systems [20,21,45], as we discuss in Sec. 2.…”

FPGA-Embedded Smart Monitoring System for Irrigation Decisions Based on Soil Moisture and Temperature Sensors

“…Transport efficiency is generally defined as the ratio of water reaching a farm or field [28,29] and is defined as follows:…”

E-seed

“…As such, soil sensors that focus on low-cost capacitive sensing techniques were developed [22,31]. Such sensors were still bulky and inorganic; on the other hand, other researchers were working on a battery-free, wireless solution to soil-monitoring sensors that harvests the energy from temperature fluctuation [18]. Aside from sensing technology development, ListenTree is an example of creating or digitally augmenting interactive experiences with nature with an audio-haptic display embedded in trees [37].…”