Microwave measurement of wood in principal directions

This paper reports a new method for broadband microwave wood measurement using a focused beam antenna system that allows the determination of propagation factors along the principal directions of the sample. The concept was used previously for wood measurement with modulated scattering technique, but is applied here to a focused beam system. The expressions for two propagation factors are revisited using S parameters representation, allowing the use of free space calibration procedure. The microwave propagation factor obtained by this method can be used to separate the contributions that grain angle, moisture content and density have in the measured signal. In addition, the grain angle, a significant wood quality indicator that is highly correlated to the strength and stiffness of the sample, can be determined.