Desenvolvimento de sensor de umidade de solo baseado em antena patch de microfita com capacitor interdigital

Abstract

Soil water content and water availability are critically important for terrestrial activities, especially those involving agriculture, forestry, hydrology, and engineering. For this reason, many researchers have dedicated efforts to proposing practical and simple methods to obtain this information using diverse measurement techniques. Among existing techniques, those based on dielectric properties, such as time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR), stand out as the most widely used for in situ soil moisture measurements. However, the high cost of such sensors limits their large-scale use. Thus, planar microwave sensors have gained significant attention as an alternative for soil moisture sensing in the field, due to their inherent characteristics, such as low production cost, ease of handling, lightweight design, compact size, and fast measurement speed, making them highly suitable for applications requiring continuous and distributed sensing in situ. In this context, this work presents the design of a low-cost planar microwave sensor for soil moisture monitoring, integrating an interdigital capacitor (IDC) with a rectangular microstrip patch antenna. The device was developed using an FR-4 dielectric substrate (εr = 4.4 and tan(δ) = 0.02) and operates at 1.5 GHz when unloaded. For experimental validation, the sensor was tested on Oxisol soil samples with moisture levels ranging from 0% to 14%, demonstrating a mean error of 3.56%, sensitivity of 1.10%, and frequency resolution of 15.17 MHz, parameters comparable to those reported in the literature for sensors of the same class. This shows that the proposed sensor is viable for applications requiring continuous and distributed monitoring, such as precision agriculture and water resource management.