Estudo de uma solução para monitoramento remoto da umidade de solo por meio da tecnologia FRID e sensores capacitivos

Abstract

Due to requirements in several contexts like precision agriculture and landslide risk mitigation, soil moisture analysis has been increasingly necessary. In this context, capacitive sensors combined with RFID can be an enforceable alternative to read soil moisture remotely. Hence, this work explores some functionalities aspects of this arrangement, focused on two main study objects, the reflections in RF propagation using RFID and the sensibility of the sensors for moisture considering the influence of two intrinsic soil variables: temperature and pH. Experiments with tags at different heights (1.4 and 1.7 meters) and distances (0.4 until 8 meters) show how transmitting signal propagation can be complex and how signal reflections can produce constructive and destructive results in signal power reception. In the same way, a comparison was presented with data collected by a spectrum analyzer with simulations using the Dieletryc Canyon model as a case of study to predict signal power loss as a function of the distance between transmit and receive antennas, considering environments with four reflections (two walls, top, and ground) and only one reflection (ground). In the case of the interdigital capacitive sensor, a high sensibility to temperature for moisture soils and low for dry soil was demonstrated in results, justified due to the temperature influence in electrical permissibility of water (a concept introduced in the fundamentals topic of this work). In the pH experiment, the capacitive sensor inserted in 4, 7, and 10 pH solutions for 60 minutes demonstrated insensibility for all of them. At moisture experiments, preliminary tests revealed more than 0.9 R² determination coefficients, and at external environment, experimentations with a duration of 10 and 30 days show the sensor sensibility to internal water fluxes in the soil. Finally, at the conclusion topic, results obtained in this work and related RFID aspects as maximum read distance, batteries lifetime, and the limits of the presented Dieletryc Canyon model are discussed, in the same way as some advantages and disadvantages on the use of interdigital capacitive sensors with the influence of temperature to measure soil moisture, and new possibly ramification works interdigital capacitive sensors considering temperature effects to measure soil moisture, and further possible ramification works.