Measurement of Wood Moisture Content Using Microwaves

The moisture content of wood is an important parameter for wood technology. Material mechanical resistance, cracking and resistance to fungi attack are dependent on this quantity. In this article we present the development of a moisture content measuring system for wood samples. The system measures the microwave propagation at 35-45 GHz using a free space collimated beam. Measured quantities are the phase delay and attenuation constant for both polarizations, parallel and perpendicular to wood fibers. This features depends strongly on moisture content, density, and fibers growth direction. Based on laboratory measurements we have obtained a relation between the average humidity of a set of woods and the measured propagation constants data. The proposed setup shows a first approach for a fast, contactless and reliable moisture level meter, which could be operated remotely in industrial environments. In this work we present our preliminary results including the microwave system design, the theoretical analysis of microwave propagation in wood, and the first experimental measurements.