Computer-Aided Permittivity Measurements of Moistened and Pyrolized Materials in Strong RF Fields (Part I)

This paper presents the results of computer-aided permittivity measurements (CAPM) on moistened paper samples, exposed to strong RF fields inside a microwave cavity. Permittivity measurements, sample weight, and RF power absorbed by the sample are monitored in real time by a microcomputer. From the CAPM, the permittivity values and the moisture content of the material are calculated. The effects of paper pyrolization on the permittivity measurements are examined, and a reversal in the measured dielectric parameters is observed at the 0-percent moisture level. This CAPM method is useful to examine the dielectric properties of materials critically dependent on the moisture content, for example, in food products and in the telephone wire industry where the insulating material is obtained from dried paper pulp. In addition, this CAPM technique can be applied to study the effects of thermal and RF shocks in dielectric materials such as used in high-power microwave windows or in studying the biological effects of microwave radiation using both short and long exposure cycles.