Measurement of Complex Permittivity of Dry Rocks and Minerals with Perturbation Method at 9 370 MHz

Resonant cavity perturbation method, widely used as an easy and fast method for determining dielectric properties of materials at microwave frequencies, is very sensitive to the measurement of the materials with low ε′ and tanδ values. However, it is not suitable to measure a majority of rocks and minerals whose ε′ and tanδ values are beyond the measurement range using the perturbation method. This paper proposes the polythene dilution method, a new perturbation-based method, to measure complex dielectric permittivity of dry rocks and minerals over 9 370 MHz. At first, the dry rocks and minerals are ground into powder, and then they are mixed in a given proportion with polythene powder, both with relatively low ε′ and tanδ and with stable dielectric property, and then hot-pressed into fine granular specimens. The perturbation method is used to measure the complex dielectric permittivity of the rock and plastic mixture. The dielectric property of the two-phase mixed system and its relation to either of the two phases can be obtained with Lichtenecker mixture formulae. Since the complex dielectric permittivity of the polythene is known, the complex dielectric permittivity of the rock samples can be calculated from that of the rock and mineral samples. At 9 370 MHz, as shown by the measurement results, the measurement of the same testing sample produced the same result with either of the perturbation method of rectangular or round resonant cavities, or of the transmission reflectometry, and provided us with the complex dielectric permittivity data measured from part of the dry rocks and minerals.