Application of three self-developed ECT sensors for monitoring the moisture content in sand and mortar

Electrical capacitance tomography (ECT) is a novel non-destructive testing technology that can monitor the moisture content in cement-based materials with the application of a capacitive sensor. In this study, three types of ECT array capacitive sensors were developed, and a series of experiments was implemented using the designed sensors to investigate the influence of the relative humidity of a porous material on the capacitance. The experimental results indicate that the non-homogeneity of the sensitive field is improved within the measurement field by an external electrode sensor. Capacitive sensors with internal electrodes demonstrated more sensitivity to changes in moisture content under the same excitation conditions. In addition, the capacitance signals of sand and cement mortar increased exponentially as the relative humidity increased. Finally, a two-dimensional finite element method (FEM) was used to model the electromagnetic field distribution around capacitive sensors, and the numerical results agreed well with the experimental results, which indicated the feasibility of developing capacitive sensors. These findings may provide theoretical guidance for the engineering applications of capacitive sensors in the non-destructive testing of cement-based materials in the future. (C) 2020 Elsevier Ltd. All rights reserved.