3D imaging of water ingress in wood using electrical capacitance volume tomography

Internal three-dimensional (3D) moisture distribution in wood was measured using electrical capacitance volume tomography (ECVT) to investigate the effect of growth ring and crack on the water ingress process. A bell-shaped ECVT sensor with 28 electrodes was developed to ensure high-precision imaging of the key location inside the sensor. The imaging performance of the designed ECVT system was confirmed through theoretical simulation and experimental analysis. Furthermore, the ECVT system for wood imaging was calibrated with homogeneously mixed particles to address the calibration problem caused by the nonuniformity of wood. An accurate relationship between the moisture content (MC) of the wood and the gray level of the images was established using a novel ECVT calibration method based on the principle of medium substitution. The ECVT system was used to detect the water ingress process of uncracked and cracked Chinese fir blocks, which enabled an exploration of the water ingress mechanisms of the wood. The wood that has sucked up water was then cut into pieces to measure its true 3D moisture distribution using the oven-drying method. The measured MC error between the ECVT and the oven-drying method was only ± 2.4 %. The proposed ECVT system for measuring 3D MC distribution provides a novel approach to investigating the durability and degradation mechanisms of the wood.