Atenuador dielétrico do solo baseado em cera de carnaúba e RFID para aplicação como sensor de umidade

Abstract

Advances in Internet of Things (IoT) applications have provided the development of new paradigms in this area, such as the Internet of Underground Things (IoUT). An important component in the architecture of IoUT is Underground Things (UT) responsible for sensing soil parameters, such as temperature and moisture. In view of this, the Radio Frequency Identification (RFID) technology has been shown promising for the development of UTs, mostly due to the ability of RFID tags to operate as sensors. However, the adaptation of wireless communication in IoUT systems for application in underground conditions represents a challenger yet. In this context, the proposal of the work is to develop a UT based on RFID technology for sensing soil moisture. The UT proposed is formed by a rectangular patch microstrip antenna designed to operate at Ultra High Frequency (UHF), connected to a passive UHF RFID tag chip. The RFID tag in buried in the soil and functions as a moisture sensor. To reduce the effects of soil moisture on the RFID tag, the microstrip antenna designed in the systems was encapsulated in a Dielectric Soil Attenuator (DSA). The DSA is formed by multilayers made of natural carnauba wax and applied over the antenna. The development of this proposal involved three studies. In the first study, the dielectric properties of three types of collected soil were measured and analyzed in different moisture levels. Using the modified Friis model, an attenuation in the order of 10 to 20 dB of the signal was found to a depth of 5 cm from the soil. In the second study, it was found that the use of multilayers in the soil reduces the variation in the coefficient of reflection of the buried microstrip antenna caused by soil moisture. In the third study, some statistical analyzes of the Received Signal Strength Indicator (RSSI) measures showed that the proposed UT can be used as a soil moisture sensor.