A Microwave System for measuring Relative Humidity of hollow concrete blocks: a new proposal and a sensitivity analysis
Structural health monitoring, Frequency selective surfaces, Relative humidity sensors, Sensitivity analysis.
This work aims to develop a non-destructive system for measuring humidity using electromagnetic waves in concrete blocks used in masonry. This system applies the Structural Health Monitoring (SHM) technique to the blocks analyzed. Changes were proposed in a microwave system for measuring relative humidity of hollow concrete blocks presented in the literature, aiming to improve the sensitivity of the system. The operating frequency range was changed from 2.5 GHz to 5.8 GHz. This reduced the dimensions of the antenna arrays used in the system. Five block samples were used in this work. The frequency selective surface (FSS) used as a sensor was modified from a double circular ring to a square loop, which presents a single-band frequency response. The results obtained in this work showed a high correlation between the frequency variation and the relative humidity level. First, second and third order functions were compared to see which one would best relate the resonance frequency to the relative humidity. The second order function presented the best results, considering the Mean Absolute Percentage Error (MAPE), the Root Mean Square Error (RMS) and the coefficient of determination. A sensitivity analysis of the sensor was performed showing that the new proposed system is more sensitive than others presented in the literature.