Prediction Moisture Content and Strength of Wood Using Free-Space Microwave Transmission Line NDT

Wood is a natural sustainable orthogonal material. It is a renewable construction material but measuring its strength properties is costly, time-consuming, may provide significant variations. Standard methods for measuring wood strength and moisture characteristics are destructive in nature. Therefore, the necessity to establish innovative nondestructive methods for wood application is critical. This paper presents the development and use of Free Space Microwave Transmission Line Nondestructive Testing (FSMTL-NDT) to evaluate moisture and strength properties of wood. The measured complex permittivity of wood using the proposed FSMTL-NDT was related to the moisture and strength properties of wood. Seventeenth Malaysian wood spices were collected and tested to determine its physical, mechanical and dielectric properties. Wood samples also tested at various moisture content and at different rain angles. The results indicate that wood moisture content and compressive strength could be predicted using the permittivity of wood. The results also show that, in the longitudinal direction, the dielectric constant and loss factor are observed to be higher compared to those in the radial and tangential directions. However, there isn't a substantial distinction between the dielectric properties in the radial and tangential directions. It's noted that dielectric constants decrease as the angle between the electric field direction and the timber grain direction increases. Leveraging the measured dielectric constants via microwave methods enables the determination of the angle between the electric field and timber grain direction.