This paper describes a new method for permittivity measurement using microwave free-space technique. The general consideration is to measure the amplitudes of transmission and reflection coefficients and calculate the permittivity from the measurement values. Theoretical analysis shows that the permittivity of the sample can be calculated solely from the measurement values of the amplitudes of transmission and reflection coefficients when the sample is prepared with so large attenuation that the multiple reflections between the two surfaces of the sample can be neglected. Using this method, the permittivity measurement can be performed without reflection influence, and on-line measurement of the permittivity becomes possible because the permittivity can be measured instantaneously and without contact with the material.

An analysis is carried out about the reflection influence on the microwave attenuation measurement for moisture content determination. A new method taking into account the reflection influence is proposed and it is proved valid by the experiment results. Using this method, the density dependence of the attenuation is measured and the measured data can be fitted well by a straight line passing through the origin. Therefore, the attenuation per unit density and propagation distance is a function which depends only on the moisture content and the function is useful to the determination of the moisture content.