Proposed microwave technique for on-line measurement of moisture content in green lumber

The paper presents a proposal for a microwave technique for the measurement of high moisture content in green lumber. The technique is based on the fleld distribution in an inhomogeneous waveguide containing the moist wood. The transverse propagation coefficient (h) in the air region of the waveguide is found to be dependent essentially on the real part of the permittivity of the wood. From the industry point of view, three categories of moisture content (say, below 30%, about 70%, and above 100%) would be adequate for the purpose of economical drying. For these categories, the corresponding relative permittivities are substantially different from one another, allowing for good resolution to distinguish between these three categories. It is also found that the imaginary part of the permittivity, which is much smaller than the real part, is of little consequence in this study.