New density-independent moisture measurement using microwave phase shifts at two frequencies

A new method for density-independent moisture measurement using the microwave free-space technique is proposed. The method is based on the measurement of two microwave phase shifts at two different frequencies. The principle is demonstrated experimentally in the moisture measurement of three wood species, Douglas fir, spruce and cedar. The result shows that the reliable density-independent moisture measurement can be made for timbers. In the moisture range from 2% to 30% on a dry basis, the mean value of the measurement error is 1.4%, and the maximum error is 4.4%.